The Kuroshio: A Symposium on the Japan Current 9780824885830

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The Kuroshio

The Kuroshio A Symposium on the Japan Current Edited by John C. Marr

East-West Center Press Honolulu

This volume was published w i t h the assistance of a grant from the United Nations Educational,

Scientific,

and Cultural Organization.

Copyright

©

1970 by East-West Center Press

University of Hawaii All rights reserved International Standard Book Number:

0-8248-0090-7

Library of Congress Catalog Card Number: Printed in the United States of America First edition

70-104044

Contents

GEOPHYSICS.

YASUI, Masashi, Seiya Uyeda, Sadanori Marauchi, and Nozomu Den.

Current

aspects of geophysical studies in the Kuroshio and its adjacent seas BOTTOM TOPOGRAPHY GILG, Joseph G.

3 19

Bathymetry of the South China Sea.

PHYSICAL OCEANOGRAPHY

21 29

BARKLEY, Richard A. vortices.

The Kuroshio-Oyashio front:

A system of near-stationary

31

HIKOSAKA, Shigeo, Shozo Yoshida, and Jun Okumoto. Observations at CSK reference stations—variability of the water temperature and salinity in the subsurface and deep waters.

37

HUSBY, David M. Seasonal variation of oceanographic conditions from Ocean Station Victor to the coast of Japan along lat. 34° N.

k3

ISHINO, M. , and K. Otsuka. On the coastal "Kyucho," a catastrophic influx of offshore water from the Kuroshio.

61

LaFOND, E. C., and E. L. Smith. Kuroshio.

69

LEE, Chang Ki.

Temperature and current in and near the

Drift bottle experiments in the eastern Yellow Sea, 1962-66.

79

McALISTER, W. B., F. Favorite, and W. J. Ingraham, Jr. Influence of the Komandorskie Ridge on surface and deep circulation in the western North Pacific Ocean.

85

MUROMTSEV, Alexey M. Some results of investigations of dynamics and thermal structure of the Kuroshio and adjacent regions.

97

NITANI, Hideo, and Daitaro Shoji. Kuroshio

On the variability of the velocity of the 107

R0G0TSKY, A. A. Some results of the CSK investigations carried out by the research vessels of the U.S.S.R. Hydrographic Service

117

SHOJI, Daitaro, and Kinji Iwasa. Continuous measurement of subsurface temperature by submarine cable: A preliminary report

121

Yl, Sok-U. Variations of oceanic condition and mean sea level in the Korean Stra it

125

CHAN, Kwan Ming. The seasonal variation of hydrological properties in the northern South China Sea

143

CHU, Tsu-You. Report on the variation of velocity and volume transport of the Kuroshio LaVIOLETTE, Paul E.

Monthly extremes of temperatures

163

in the surface waters

south of Japan.

175

TAFT, Bruce A.

Path and transport of the Kuroshio south of Japan

YOSHIDA, Kozo. CSK data

Subtropical countercurrents:

Band structures revealed from

185 197

CANNON, Glenn A. Characteristics of waters east of Mindanao, Philippine Islands, August 1965

205

NI TAN I, Hideo. Oceanographic conditions in the sea east of the Philippines and Luzon Strait in summers of 1965 and 1966.

213

CHEMICAL OCEANOGRAPHY

233

SUGIURA, Yoshio. Significance of AOU of the surface water in the Kuroshio and the Oyashio regions: A slower rate of gas exchange between air and sea. M0T0DA, Sigeru, Teruyoshi Kawamura, and Satoshi Nishizawa. Biological structure of the sea at long. 142° E. in the North Pacific with particular reference to the interrelation between living and nonliving organic matter Z00PLANKT0N

—235

2^1 2^9

M0T0DA, Sigeru, Haruhiko Irie, and Isamu Yamazi. Report on the preliminary processing of zooplankton standard samples in Japanese CSK studies, 1965-66

251

YAMAZI, Isamu. Regional distribution of major systematic groups of zooplankton in the Kuroshio region based on material taken by Japanese ships, 1965-67

259

KUN, M. S., G. N. Gladkikh, E. P. Karedin, W. P. Pavlychev, W. I. Rachkov, and E. G. Starodubtsev. Hydrological conditions and biological characteristics of the Kuroshio waters in area lat. 20°-43° N. and long. I38°-I49° E

279

HONG, Sung Yun.

291

The euphausiid crustaceans of Korean waters.

PARK, Joo Suck. The distribution of chaetognaths in Korean waters, particularly in the southern waters, and their relation to the character of water masses in the summer of 1967

301

LI AW, Wen-Kuang. On the chaetognaths collected from the waters surrounding Taiwan during CSK cruises

313

TAN, Tien-hsi.

323

On the distribution of copepods in waters surrounding Taiwan

TSENG, Wen-young. On the distribution of plankton settling volumes in the neighboring seas of Taiwan, summer 1965.

333

TSENG, Wen-young. A preliminary report on cypridinids (Ostracoda) from Taiwan Strait

339

YU, C. P., and C. W. Lee. The effect of environmental factors on the macrozooplankton community around Taiwan.

3^7

MAGNUSSON, Jakob, Elvira 0. Tan, and Rizalina M. Legasto. Zooplankton distribution and abundance in Lamon Bay and its approaches.

353

THAM, Ah Kow, Hong Woo Khoo, and Thia Eng Chua. A study of the plankton in Singapore waters in relation to the environment.

361

vi

BIOLOGY OF FISHES

377

SUZUKI, Akimi. Detection of the erythrocyte antigens of tuna with radioactive antibodies.

379

FUJINO, Kazuo. Skipjack tuna subpopulation identified by genetic characteristics in the western Pacific.

385

UEYANAGI, Shoji. Distribution and relative abundance of larval skipjack tuna (Katsuwonus pel amis) in the western Pacific Ocean.

395

HATTORI, Shigemasa. Preliminary note on the structure of the Kuroshio from the biological point of view, with special reference to pelagic fish larvae

399

HIRANO, Toshiyuki, and Minoru Fujimoto. Preliminary results of investigation of the Kuroshio functioning as a means of transportation and diffusion of fish eggs and larvae.

405

EGGLESTON, David. Biology of Nemipterus vi rgatus in the northern part of the South China Sea.

417

NAKAMURA, Eugene L. Stolephorus

425

Synopsis of biological data on Hawaiian species of

HONGSKUL, Veravat. On the study of Formalin preservative and the shrinkage of the Indo-Pacific mackerel, RastrelI iger neqlectus (van Kampen).

447

ISARANKURA, Andhi P. Synopsis of biological data on threadfin bream, Nemipterus hexodon (Quoy and Gaimard) 1824.

455

KUHLMORGAN-HILLE, Georg. A contribution to the knowledge of the growth of Saurida undosquamis Richardson in the Gulf of Thailand

467

SUCONDHAMARN, Prakorp, Chujit Tantisawetrat, and Usa Sriruangcheep. Estimation of age and growth of chub mackerel, RastrelIiger neqlectus (van Kampen), in the western Gulf of Thailand.

471

TAN, Elvira 0. Notes on the biology of chub mackerel, RastrelIiger brachysoma (Bleeker), in Manila Bay.

479

THAM, Ah Kow. Synopsis of biological data on the Malayan anchovy, Stolephorus pseudoheteroIobus Hardenberg 1933.

481

FISHERIES

491

CH00, Wo 11.

A summary report on yellow croaker in Korea

493

TUNG, Ih-hsiu. Studies on the fishery biology of the grey mullet, Mu.q i I cepha I us Linnaeus, in Taiwan.

497

KIM, Yong Mun, and Yong Sool Kim. Geographical distribution of the bottom fishes in the southwestern waters of Korea. CHOMJURAI, W., and R. Bunnag.

505

Preliminary tagging studies of demersal fish

in the Gulf of Thailand MENASVETA, Deb.

517

Potential demersal fish resources of the Sunda Shelf

TONGYAI, M. L. Prachaksilp.

525

Plah in-see, Scomberomorus spp., of Thailand,

1967 OTSU, Tamio.

557 Tagging of skipjack tuna, Katsuwonus pelamis, in Palau

UCHIDA, Richard N.

565

The skipjack tuna fishery in Palau

569

vi i

FISHERY-OCEANOGRAPHY HAN, Hi Soo, and Yeong Gong.

583 Relation between oceanographicaI

catch of saury in the eastern Sea of Korea.

conditions and

UDA, Michitaka. Fishery oceanographic studies of frontal eddies and transport associated with the Kuroshio system including the "Subtropical Cou ntercur rent. '!

585

593

AUTHORS AND PARTICIPANTS

605

PAPERS PUBLISHED ELSEWHERE OR WITHDRAWN

613

vi i i

Foreword

The papers presented in this collec-

need to attempt to provide a summary of the

tion were prepared for a CSK (Cooperative

Symposium results here.

Study of the Kuroshio) Symposium held April

like to comment on one of the less obvious

29-May 2, 1968 at the East-West Center,

benefits of the CSK, but one which, in the

University of Hawaii, Honolulu.

long run, may prove to be of greater value

The Sym-

I should, however,

posium was organized jointly by (1) the

than the increased understanding of the

Intergovernmental Oceanographic Commission,

western Pacific Ocean and its fishery re-

United Nations Educational, Scientific and

sources.

Cultural Organization, (2) the Fisheries

tions, in the broad sense of the word,

Department, Food and Agriculture Organiza-

among the CSK countries.

tion of the United Nations, and (3) the

the impediments to communications were

Office of Programs and Conferences, East-

manifold.

West Center, with assistance from the Bio-

tongue of very few of the participants, is

logical Laboratory, Honolulu, of the U.S.

the official language of the meetings of

Bureau of Commercial Fisheries.

the International Coordinating Group.

Forty-

I refer to improved communicaAt the outset,

English, which is the original

seven individuals from nine countries

interests in the sea, and the problems

participated.

connected therewith, for countries such

Brief accounts of the Symposium have

The

as, say, Korea and Thailand, are quite

already appeared in Science, Transactions,

different.

American Geophysical Union, and an FAO Fish-

dividuals representing the CSK countries

eries Report.1

had not known each other personally prior

There is, therefore, no

Many, if not most, of the in-

to the start of the CSK.

Finally, atti-

tudes were influenced initially by recent 'Marr, John C., 1968, Kuroshio, Science (Wash.) 161(3841): 603-604; 1968, Cooperative Study of the Kuroshio and Adjacent Regions, Trans. Amer. Geophys. Union 49: 559-560; 1968, Report of the Symposium on the Cooperative Study of the Kuroshio and Adjacent Regions (CSK), organized through the joint efforts of UNESCO, FAO, and East-West Center, Honolulu, Hawaii, USA, 29 April-2 May 1968, report and abstracts of papers, FAO Fish. Rep. 63, 57 pp.

(historically speaking) experiences between countries.

It has been interesting,

and gratifying, to see this communication problem ameliorate over the course of successive meetings.

Personal contacts have

been made, lines of communication, both

formal and informal, have been established,

I greatly appreciate the services of

and experience has been gained in the con-

the following colleagues on the staff of

duct of international cooperative effort.

the Biological Laboratory, Honolulu:

These will be constructive forces in the

Richard A. Barkley, Eugene L. Nakamura,

future.

and Tamio Otsu, who served as scientific

I should like to use this occasion to

editors of the papers; Thomas A. Manar, who

express my pleasure for the opportunity of

acted as copy editor and saw the papers

being associated with Dr. Kiyoo Wadati,

through the many stages of preparation;

CSK International Coordinator, and to

Robert Bonifacio and Tamotsu Nakata, who

express my appreciation to my colleagues in

prepared many of the illustrations; Louise

the International Coordinating Group for

F. Lembeck, Irene H. Toyomura, and Eliza-

the opportunity afforded me by them to

beth F. Y. Young, who typed the papers and

serve as the Assistant International

checked the numerous literature citations.

Coordinator for Fisheries. J. C. M.

x

Current Aspects of Geophysical Studies in the Kuroshio and Its Adjacent Seas MASASHI YASUI, SEIYA UYEDA, SADANORI MURAUCHI, and NOZOMU DEN Maizu.ru Marine Observatory, Maizuru University of Tokyo} Tokyo National Science Museum3 Tokyo Hokkaido University} Hakodate

ABSTRACT

Results of geophysical studies in the Kuroshio and its adjacent seas are reviewed. Heat-flow measurements show that the marginal seas, such as the Sea of Japan and the Okhotsk Sea, are geothermally hot, while heat flow in the seas east of Japan is uniformly subnormal. The geomagnetic anomaly lineations in the seas east of Japan, including the Okhotsk Sea, run in the east northeast-west southwest direction. The lineation trends in the Sea of Japan are less distinct and run along the longitudinal axis of the sea. Seismic refraction measurements show that the crustal structures in the northwestern part of the Pacific Basin and the Philippine Basin are quite oceanic with the exception of the second layer with a little slower wave velocity. In the Sea of Japan and Okhotsk Sea, oceanic or suboceanic crust is found beneath the deep basins. The deep-sea terrace is clearly found at the depths of 1,000 to 2,000 m. on the continental slopes around the Japan Arc. The rate of the sedimentation varies from 0.05 to 1.5 cm./I,000 yr. in the seas east of Japan, while it is about 1.5 cm./I,000 yr. in the Sea of Japan.

INTRODUCTION

In 1951, British scientists (Gaskell, Hill, and Swallow, 1958) aboard H.M.S.

Marine geophysical studies have not always been active in the Kuroshio and its 1

adjacent seas.

Most of the present knowl-

Challenger made seismic refraction measurements of the crustal structure in the CSK region by means of their newly developed

edge has been acquired since World War II.

sonobuoy method as a part of their round-

A notable exception is the marine gravity

the-world expedition.

survey off Japan made by Matsuyama (1936),

exploration has been performed by Russian

which followed the pioneering work of Vening

groups since 1956 in the marginal seas of

Meinesz (1948) in the seas around Indonesia.

the region, such as the Sea of Japan

The same sort of

(Andreyeva and Udintsev, 1958) and the 1

In the following, the Kuroshio and its adjacent seas are referred to as the CSK region for simplicity.

Okhotsk Sea (e.g., Kosminskaya, Zverev, Veitsman, Tulina, and Krakshina, 1963).

American and Japanese groups started their

tory (Langseth, private communication), the

joint program of seismic exploration in the

Academy of Sciences, U.S.S.R. (Popova, pri-

region in 1962.

vate communication) and the Earthquake Re-

Aside from three component

measurements of the earth's magnetic field

search Institute, University of Tokyo (Wata-

by a special ship, geomagnetic studies in

nabe, private communication) made more than

these seas using the towed magnetometer

100 measurements, though they are yet unpub-

system have been carried out since 1958

lished.

(Oguchi and Kakinuma, 1959).

on land of the Japanese Islands (Uyeda and

At almost the

Taking account of 42 measurements

same time, gravimetric work at sea was re-

Horai, 1964), this area can be considered

sumed with a ship-borne gravity meter devel-

as one of the most densely surveyed in the

oped by Tomoda and Kanamori (1961).

world.

In 1960,

Nevertheless, the number of measure-

the Tokyo University-type thermograd meter

ments is still few in the East China Sea and

was developed by Uyeda, Tomoda, Horai, Kana-

none in the South China Sea and the

mori, and Futi (1961) and since then, terres-

Australian-Asian Mediterranean Sea.

The

trial heat-flow measurements have been active- published data are summarized in figure 1 by symbols.

ly made in these areas. Thus geophysical studies in the CSK region have been gradually activated.

How-

Tentative contours are drawn at

every 0.5 ]ical./cm.s sec.taking the unpublished data into consideration.

ever , knowledge accumulated mainly in the seas around Japan, and other parts of the region have not yet been well surveyed. The aim of this paper is to summarize existing knowledge in geophysics of this region. TERRESTRIAL HEAT FLOW Since 1961, terrestrial heat flow has been intensively studied in this area by several agencies.

Uyeda, Horai, Yasui, and

Akamatsu (1962), Uyeda, Yasui, Sato, Akamatsu, and Kawada (1964), Yasui, Horai, Uyeda, and Akamatsu (1963), Yasui, Kishii, Watanabe, and Uyeda (1968), Yasui, Kishii, and Sudo (1967), Yasui, Kishii, Nagasaka, and Halunen (1968), Yasui, Kishii, Nagasaka, and Anma (1969) , and Vacquier, Uyeda, Yasui, Sclater, Corry, and Watanabe (1967) have published data measured at 327 stations. Besides these the Lamont Geological Observa-

k

Figure 1. Summary of heat-flow distribution in the CSK region. The contours are influenced by unpublished data by M. Langseth and T. Watanabe.

From the

figure, the heat flow in this

Japanese islands have been separated from

area is characterized by the following three

the Asian-Continent, the Sea of Japan being

major features:

a developed rift with high heat flow. Yasui,

a uniformly subnormal area

east of the Kuril-Japan-Izu-Bonin Island

Kishii, Watanabe, and Uyeda (1968) inferred

Arcs; a high heat flow area along the mar-

that the excess heat was transported by up-

ginal seas, the Sea of Japan,and the Okhotsk

ward intrusion of magma beneath the bottom.

Sea; and although the area has not been sur-

Watanabe (1966) considered that a tectonic

veyed well, what preliminary data indicate

deformation of the crust in the past re-

is a complicated distribution in the area

sulted in the anomaly of heat flow at pres-

west of the Izu-Bonin-Mariana Ridge.

ent.

In the first area, data from areas

Menard (1967) pointed out that the mar-

ginal seas which have an oceanic or semi-

with major topographic relief, such as the

oceanic crust may be the transient state

Emperor Seamounts and Shattsky Rise, are

from the ocean to the continent.

also subnormal.

disturbances during this process could af-

This fact shows that the

If so,

features in the Northwest Pacific are in a

fect the heat flow at the surface for a

sharp contrast to those in the east Pacific,

fairly long period.

including the East Pacific Rise (Von Herzen

(1968) pointed out the possible correlation

and Uyeda, 1963, Vacquier, Sclater, and

between deep focus earthquakes and high heat

Corry, 1968).

flow.

The complicated distribution

Uyeda and Vacquier

McKenzie and Sclater (1968) estimated

in the Philippine Basin may be related to

the effect of various heat sources which

its equally complicated physiographic struc-

could be the origin of high heat flow in

ture.

marginal seas and concluded that none of

The basin is not only situated behind

the Izu-Mariana Arc but also has another

them could be large enough to explain the

island arc system at its western margin, i.e.

excess heat in the area.

the Ryukyu Arc.

It must be noted that the

To clarify the origin and the areal ex-

heat flow is high above the Kyushu-Palau

tent of this

Ridge which supposedly ceased tectonic ac-

measurements in the other marginal seas,

tivity long ago (Watanabe, private communica-

such as the South China Sea, Celebes Sea,

tion) .

Sulu Sea, Banda Sea, and so on, should be

The high heat flow in the marginal seas behind the island arcs presents interesting problems.

carried out.

high heat flow zone, heat flow

Further measurements in the

Philippine Sea also have to be made.

Seismic refraction studies

show that the crustal structure beneath the

GEOMAGNETISM

Japan Basin and Kuril Basin, where the heat flow is extremely high, is semioceanic or oceanic.

This means that heat from radio-

Marine geomagnetic measurements in the CSK region by Japanese groups, which were

active substances in the crust cannot be

started by the Japanese Antarctic Research

the source of the high heat flow.

Expedition in 1958, were accelerated by im-

Murauchi

(1966) presented the hypothesis that the

proved instruments (Uyeda, Tomoda, Yabu, and 5

Utashiro, 1964).

Series of studies by Uyeda,

other hand, Hayes and Heirtzler (1968) sug-

Sato, Yasui, Yabu, Watanabe, Kawada, and

gest that the lineations in this area would

Hagiwara (1964), Uyeda, Vacquier, Yasui,

not be continuous with those in the eastern

Sclater, Sato, Lawson, Watanabe, Dixon,

Pacific and that the lineations off Japan

Silver, Fukao, Sudo, Nishikawa, and Tanaka

would be older than those off California.

(1967), Yasui, Hashimoto, and Uyeda (1967a,

Palaeomagnetic studies of the seamounts

1967b), Yasui, Hashimoto, Nagasaka, and Anma

in this area support the northerly movement

(1968), Segawa, Ozawa, and Tomoda (1967),

of the ocean floor (see the next section).

Tomoda and Segawa (1967), and Tomoda (1967)

However, the chronological study of pieces

were compiled into the isodynamic total

of rocks dredged on the seamounts could not

force and its anomaly charts as shown in fig-

verify this tendency (Ozima, Ozima, and

ures 2 and 3.

Kaneoka, 1968).

In these figures, measurements

The aeromagnetic survey in

by the Lamont Geological Observatory and

the Kuril-Kamchatka region conducted by the

the Scripps Institution of Oceanography were

Russian group (Solov'yev and Gainanov, 1963)

taken into consideration.

clearly shows the anomaly pattern parallel

The U.S. Hydro-

graphic Office Chart No. 1703 for 1965

to the Kuril Islands in the sea south of the

was adopted for the general trend chart.

islands.

Although this chart was found to represent

to send their ships to the area between long.

the general trend in this region poorly,

160° E. and 180° in 1968.

figure 3 seems to delineate some of the

are aiming to trace anomaly trends and to

characteristic features of the anomaly; that

learn whether the anomaly trends east and

is, it shows a series of elongated narrow

west of the above mentioned area are

bands of anomaly almost parallel to the Kuril

continuous.

Arc, though these lineations are less dis-

Several institutions are planning Presumably they

It is not yet known whether there is

tinct in both amplitude and length than

any lineation pattern in the southern part

those in the eastern Pacific.

of the Kuroshio area.

Uyeda,

Intensive study is

Vacquier, Yasui, Sclater, Sato, Lawson,

required in the East and South China Sea and

Watanabe, Dixon, Silver, Fukao, Sudo, Nishi-

the Australian-Asian Mediterranean Sea.

kawa, and Tanaka (1967) and Uyeda and Vacquier (1968) mentioned hesitantly the

PALAEOMAGNETISM

possibility of their being correlated with those off California, which make a sharp

It is possible to compute the direction

bend in the northeastern Pacific (Peter,

and intensity of magnetization of seamounts

1966).

from their topographical and geomagnetic to-

If so, the North Pacific would be

bordered by circum-Pacific anomaly trends, and if the hypothesis presented by Vine and Matthews (1963) is valid, the ocean floor would have to creep centripetally from the marginal part of the North Pacific . On the 6

tal force data at the sea surface.

Vacquier

(1963) presented a practical method for the computation of palaeomagnetism of seamounts. The palaeomagnetic direction and intensity of seamounts in the CSK region was obtained

172 E

Figure 3.

8

Geomagnetic total force anomaly distribution in the CSK region.

with this method by Uyeda and Richards (1966), Vacquier and Uyeda (1967) and Yasui Hashimoto, and Uyeda (1967a).

The location

of seamounts and the palaeomagnetic polepositions which were estimated from the direction of magnetization of seamounts are summarized in figure 4 and the results of computation are tabulated in table 1.

These

results show that the inclination of magnetization is generally shallower than that of the present geomagnetic field at the location of seamounts.

If the conventional

palaeomagnetic assumptions are accepted, this fact would mean that the seamounts in

Figure 4A. Location of palaeomagnetically veyed seamounts.

the CSK region were originally formed at

sur-

.0

localities nearer to the geomagnetic equator than the present locations.

It is consist-

ent with the hypothesis of northward drift of ocean floor.

Apparently the seamounts

in the Okhotsk Sea seem to have come into the Okhotsk Sea through the Kuril Island Arc from the south. Since this is unlikely, it may be that the Japan and Kuril Basins were separated from the Pacific by the extrusive formation of the Kuril-Japan Arc (Udintsev, 1966).

The magnetization of seamounts in

the Sea of Japan so far investigated has not shown systematic evidence of the northerly creep (Uyeda et al., private communication). The depositional remanent magnetization in sediment is useful in the study of palaeomagnetism at sea.

However, this type of

Figure 4B. Palaeomagnetic pole positions determined from the magnetization of seamounts in the CSK region.

work in Japan has just been started in the marginal seas by Yasui and in the Northwest

Lamont cores taken in the sea west of the

Pacific by Kobayashi (private communication)

date line zone, 24 were chosen for prelim-

and no major result has been reported yet.

inary analys is and 12 cores were supposed to

The only report on this type of work in the

have penetrated the sediment deposited dur-

CSK region is by Ninkovich, Opdyke, Heezen,

ing the epoch of the last geomagnetic rever-

and Foster (1966).

sal.

From the large number of

However, only four of them, three from 9

Table 1.

Palaeomagnetic pole positions of seamounts in the CSK area

Seamount

Lat. N.

41 40 40 38 37 36 28 28 27 28 27 29 30 47 45

A S B R 3-1 3-2 4-1 4-2 4-3 4-4 4-5 4-6 4-7 OTK-1 0TK-2 1

3° 9° 6° 0° 1° 6° 8° 4° 1° 0° 7° 6° 2° 1° 5°

Declination GeoGeomagne tic graphic

Long. E.

146.0° 144.9° 146.9° 146.0° 163.8° 163.9° 148.4° 148.2° 148.7° 147.6° 140.4° 137.1° 136.7° 150.5° 147.5°

0° 348° 360° 349° 267° 276° 315° 9° 17° 12° 7° 3° 3° 13° 35°

Inclination

-7° 341° 353° 344° 268° 278° 313° 28° 16° 11° 5° -1° -1° 5° 27°

Intens ity (emu./cc. x 10

2° 22° -4° 3° 38° 44° -35° 5° -13° -1° 39° 31° 7° 38° 31°

1.56 1.04 0.39 0.60 0.34 0.72 0.23 0.42 0.64 0.30 0.32 0.51 0.12 0.10 0.16

2

)

Palaeomagnetic pole position Lat. Long. N. E. 49° 56° 47° 51° 11° 21° 24° 53° 53° 60° 82° 77° 63° 64° 53°

337° 359° 337° 352° 92° 91° 17° 278° 302° 306° 382° 320° 319° 320° 280°

Age determination from dredged rock1

72 x 10® yr. 25

72 92 18

After Ozima, Ozima, and Kaneoka (1968).

stations along the date line zone in lat.

taken within 1,000 km. of the Japan-Kuril

43° to 48° N. and from the flank of the

Arc, mainly along long. 156° E., failed to

Emperor

pass through the thickness of the sediment

Seamounts, were found to have

actually reached strata deeper than that of

of the present normal epoch in spite of the

the last reversal.

fact that their length exceeded 10 m.

The results are sum-

marized in figure 5.

The other eight cores

Studies of magnetic inclination in these cores did not show any significant evidence of ocean floor spreading or geomagnetic pole wondering in the last 3 million years. However, it is notable that the occurrence of reversals in the geomagnetic field proposed from terrestrial palaeomagnetism studies was ascertained by work on ocean sediments.

In particular, it was suggested

that each complete reversal of geomagnetic polarity occurred in less than 1,000 years. Figure 5. Distribution of palaeomagnetically and chronologically studied cores: Open circle: Palaeomagnetically studied core. The letter in the circle shows the earliest palaeomagnetic epoch or event penetrated (B, Brunhes; 0, Olduvai; M, Matsuyama; G, Gauss). Solid circle: Cores dated by means of Io/Th ratio. Number attached shows the deposition rate in unit of cm./I,000 yr.

10

The epoch of the last reversal of the earth's magnetic field (called the Matsuyama Epoch) is reportedly 700 thousand to 2.4 million years ago (e.g., Cox and Dalrymple, 1967).

Dividing the core length from the

surface to the uppermost part of the sediment of the Matsuyama Epoch, the mean rate

of sedimentation was obtained—0.7 cm./I,000

EXPLOSION SEISMOLOGY

yr. in the date line zone and more than 1.5 cm./I,000 yr. in the long. 156° E. zone.

A Japanese group conducted its first seismic refraction work in the sea south of

The sedimentation rate in the CSK region was studied by measuring the y-ray

the central part of Honshu in 1962, in co-

intensity ratio of ionium to thorium (Miyake

operation with an American group (Murauchi,

and Sugimura, 1961, 1965, 1968; Sugimura and

Den, Asano, Hotta, Chujo, Asanuma, Ichikawa,

Miyake, 1968).

and Noguchi, 1964).

The results are also summa-

The same groups ex-

In the Pacific, the

tended their project to the sea east of the

value obtained by them ranges from 0.05

northern part of the Honshu (Ludwig, Ewing,

cm./I,000 yr. to 0.25 cm./I,000 yr. with the

Ewing, Murauchi, Den, Asano, Hotta, Hayakawa,

exception of a little larger value of 0.63

Asanuma, Ichikawa, and Noguchi, 1966), the

cm./I,000 yr. from the east flank of the

Sea of Japan (Murauchi, Den, Asano, Hotta,

Japan Trench.

Asanuma, Yoshii, Hagiwara, Ichikawa, Iizuka,

rized in figure 5.

These rates are about one-

tenth of the above-mentioned values from the

Sato, and Yasui, Crustal structure of the

magnetic stratigraphy.

Japan Sea derived from the deep-sea seismic

The problem whether

the difference between these results is

observations, unpublished), the sea off

geologically meaningful or is merely due to

Shikoku (Den, Murauchi, Hotta, Asanuma, and

differences in method is important.

Hagiwara, A seismic refraction exploration

In the

Northeast Pacific, Harrison (1966) calcu-

of Tosa deep-sea terrace off Shikoku, unpub-

lated a sedimentation rate of 0.03 cm./I,000

lished), the Philippine Sea to the East

yr. from palaeomagnetic stratigraphy.

China Sea (Murauchi, Den, Asano, Hotta,

This

is in the same order of magnitude as those

Yoshii, Asanuma, Hagiwara, Ichikawa, Sato,

obtained by the Io/Th ratio method in the

Ludwig, Ewing, Edgar, and Hautz, Crustal

western Pacific.

structure of the Philippine Sea, unpub-

The palaeocurrent struc-

ture might determine the distribution of the

lished) . The locations of the refraction

sedimentation rate in this region.

profiles are summarized in figure 6.

There-

In

fore, the palaeomagnetic study of sediment

figures 7, 8, and 9, cross sections of the

in the seas just east of the Japan Trench

crustal structure along the lines indicated

has a good possibility of reaching the

in figure 6 are presented.

Matsuyama and further the Gauss Epochs even with rather short cores.

Ocean Basins

A higher rate of sedimentation has been

The Northwest Pacific Basin and the

found in the marginal seas, though the num-

Philippine Basin resemble each other in the

ber of measurements is very small.

thickness of the second layer, based on the

This

higher rate will be convenient for palaeo-

mean structure in the western North Pacific

magnetic study of the

(Raitt, 1963).

microscopic stratig-

raphy of the recent era.

It must be noted that the

depth of the upper surface of the second layer in the Parece Vela Basin is almost 1 1

6CTN 160°

E.

55*N

5CTN

I

I

OKHOTSK

SEA

45"N

I

BASIN -

KURILE ISLANDS-TRENCH

A'

Sedimentary

40 Km

Figure 7. Cross section along AA' (after Kosminskaya et al., 1963).

the crust is quite oceanic on the ocean side of the trenches and is continental on the continental side.

As a matter of course,

their detailed characteristics are different. Beneath the Kuril Trench, down-warpings of the Moho discontinuity between the trench and the island arc are remarkable.

In the

Japan Trench, a succession of grabens and step faults was observed along the seaward slope. Figure 6. Distribution of refraction profiles in the CSK region. Solid line: United States-Japan cooperative group. Dashed line: Russian group. Open circle: H.M.S. Challenger. Number attached: crustal thickness in km. Lines AA', BB', and CcC' show the positions of cross sections demonstrated.

The Mariana Trench has a little different structure from those of other trenches; the structure of the ridge west of the trench is not continental but rather oceanic. Ridges The Kuril, Japan, and Nanseishoto Arcs

constant at about 6 km. from the sea surface

have a typical continental crust.

and the sea bottom configuration in the area

granitic layer exists between the sedimentary

is mainly formed by variation in the thick-

and the third layers, and the Moho disconti-

ness of the first layer.

nuity is depressed a few tens of kilometers.

The Shikoku Basin

A thick

also can be considered as having oceanic

Beneath the Oki-Daito, Kyushu-Palau, and

structure.

Mariana Ridges, an increase in thickness of the 3.5 km./sec. layer and an appearance of

Trenches The series of Kuril-Japan-Nanseishoto Trenches have a similar structure; that is, 12

the 6.0 km./sec. layer also result in the crustal thickening, though the thickness of the basaltic layer is rather uniform.

PRIMORYE

JAPAN JAPAN

BASIN

SEA

HONSHU

JAPAN TRENCH

OKI-DAI TO RIDGE

O

I3N

I

PI5

I

I6S ITS

I I I9NI

PACIFIC O C E A N

YAMATO B A N K

KYUSHU -PALAU RIDGE

ISLAND CHAIN

P20

I P1

NWPACIFIC

HONSHU-MARIANA {BONIN ) TRENCH

HONSHU -MARIANA RIDGE P7 n

P6 1

2 67

231

^474,-

v AM TO!

686

6-93

;

Figure 9.

c

P5 1

672 8 11

Cross section along CcC' (after Murauchl et al., 1968).

M a r g i n a l Seas

Iizuka, Sato, and Yasui, Crustal structure

It must first be noted that the struc-

of the Japan Sea derived from the

deep-sea

ture of the Japan Basin, Yamato Basin, and

seismic observations, unpublished) observed

Kuril Basin is semioceanic or oceanic.

three layers (2.1, 3.0, and 4.8 km./sec.)

the Japan Basin, Russian scientists

In

(Kovylin

with 4.5 km. thickness above the basaltic

and Neprochnov, 1965; Kovylin, 1966) found a

layer.

2.0 km. thick sedimentary layer directly

the structure beneath the Kuril Basin, where

overlying the basaltic layer.

the basaltic layer is directly beneath the

This struc-

This structure is almost the same as

ture can be conceived as being typically

3.5 to 4.0 km. thick sedimentary layer.

oceanic.

Yamato Basin has a structure almost similar

The Japanese group (Murauchi, Den,

Asano, Hotta, Asanuma, Hagiwara, Ichikawa,

to those in the above described basins

13

The

though the wave velocity of the second layer

tween the terrace depths along the Pacific

is as great as 5.5 km./sec.

and the Sea of Japan is unexplained.

On the other

Though results have yet to be published,

hand, beneath the Nanseishoto Trough the layer with the wave velocity of 6.0 km./sec.

the United States-Japan cooperative group

presumably a granitic layer, is as thick as

has made some refraction profiles in the

10 km. between the 3 km. thick sedimentary

Sulu Sea, East and West Caroline Basin,

layer and the 7.2 km./sec. layer.

Solomon Sea, Bering Sea, the sea just west

It is

very interesting that the basins in the mar-

of Luzon Island, and over the Shattsky Rise.

ginal seas show equally high heat flow,

Still, major parts of the CSK region, such

though their crustal structures are different

as the main part of the South China Sea, the

from each other.

Yellow Sea, remain unsurveyed.

Except for the Kuril Basin, the Okhotsk Sea has a three layer structure, sedimentary,

These areas

are important in clarifying the structure of the island arcs.

granitic, and basaltic, as thick as 20 to 30 km.

Gravity Surveys and Other Studies

Thus about 80 percent of the Okhotsk

Sea consists of continental crust.

Gravity surveys at sea have been made

The Yamato Rise, one of the major banks

mainly by Tomoda (1967), Tomoda and Segawa

around Japan, also seems to have a granitic

(1967),and Segawa, Ozawa, and Tomoda (1967).

layer and a thick basaltic layer.

Hagiwara (1967), compiling the existing

However,

further exploration is necessary for a more

data, provided a terrain-corrected Bouguer

definite interpretation because of the com-

anomaly map of Japan and its environs.

plicated topography.

Though the free-air anomaly map would be

Studies of sedimentary layers by the

more desirable for the ocean area, this map

reflection technique have revealed a number

suggests that the Japan Trench region is not

of interesting features in the CSK region.

in isostatic equilibrium.

According to Murauchi, on the continental

and thorough compilation of gravity measure-

slope on the Pacific side of the circum-

ments in the whole CSK region is desirable

Pacific arc in the western Pacific, the

for better interpretation of results ob-

upper surface of the 2.5 km./sec. layer

tained in other disciplines.

almost always shows a flat terrace at a fairly great depth.

An attempt is being made to microscop-

This must be the deep-

sea terrace reported by Hoshino (1962).

A detailed survey

The

ically study the seismicity underneath the ocean bottom by the use of an ocean bottom

depth of the deep-sea terrace ranges from

seismograph.

2,000 to some 3,000 m. though it sinks down

sawa (1965) have repeatedly made instru-

to nearly 4,000 m. along the Aleutian Trench

mental tests and now intend

and the Lombok Strait.

earthquakes on the summit of some of the

Along the Japanese

Nagumo, Kobayashi, and Koreto record

coast facing the Sea of Japan, the deep-sea

Emperor Seamounts.

terrace can also be recognized at depths of

a unique experiment in the Kuril Trench

only 1,000 m. and so.

area with ocean bottom seismographs

] k

The difference be-

An American group made

(McDermott, Labhart, and Marshall, 1967). Sixteen seismographs whose relative locations are checked by calibration detonations were scattered in a rather small area and recorded 176 events or pulsations in the sea bottom for about 7 weeks.

Since studies of

oceanic seismicity have so far been made only from the land stations, the use of ocean bottom seismographs will contribute to the rapid progress of this field. Ozima, Ozima, and Kaneoka (1968) examined some of the physical and chemical properties of rocks dredged from the ocean bottom.

Further accumulation of these data

will also be helpful. Finally, it should be noted that the CSK region is one of the most tectonically active areas in the world, so that it is expected that promotion of geophysical studies in this area will accelerate studies of the origin and development of the ocean floor and of island arcs.

ACKNOWLEDGMENTS The authors wish to express their hearty thanks to M. Langseth and J. Heirtzler of the Lamont Geological Observatory, and T. Watanabe of the Earthquake Research Institute, for their unpublished data which were taken into account in summarizing the existing data. They are also grateful to C. Tsuboi and T. Rikitake for their constant interest. This work was partially supported by a grant from the Japan Society for Promotion of Science as part of the U.S.-Japan Cooperative Science Program (G-33).

LITERATURE CITED Andreyeva, I. B., and G. B. Udintsev. 1958. Bottom structure of the Sea of Japan from the "Vityaz" expedition data. Izv. Akad. Nauk, S.S.S.R., Geol. Ser. 10: 3-20. [In Russian.]

Cox, Allan, and G. Brent Dalrymple. 1967. Statistical analysis of geomagnetic reversal data and the precision of potassium-argon dating. J. Geophys. Res. 72: 2603-2614. Gaskell, T. G., M. N. Hill, and J. C. Swallow. 1958. Seismic measurements made by H.M.S. Challenger in the Atlantic, Pacific and Indian Oceans and in the Mediterranean Sea, 1950-53. Phil. Trans. Roy. Soc. London, Ser. A 988, 251: 23-83. Hagiwara, A. 1967. Analyses of gravity values in Japan. Thesis, Univ. Tokyo. Harrison, C. G. A. 1966. The palaeomagnetism of deep sea sediments. J. Geophys. Res. 71: 3033-3043. Hayes, Dennis E., and James R. Heirtzler. 1968. Magnetic anomalies and their relation to the Aleutian Island Arc. [Abstract.] Presented at the 49th Annual Meeting, Amer. Geophys. Union, pp. 207-208. Hoshino, M. 1962. The Pacific Ocean. Geosci. Ser., Ass. Geol. Collab. Jap. 18: 1-136. [In Japanese. ] Hotta, H. 1967. The structure of sedimentary layer in the Japan Sea. Geophys. Bull. Hokkaido Univ. 18: 111-131. [In Japanese with English abstract.] Kosminskaya, I. P., S. M. Zverev, P. S. Veitsman, Yu. V. Tulina, and R. M. Krakshina. 1963. Basic features of the crustal structure of the Sea of Okhotsk and the KurilKamchatka zone of the Pacific Ocean from deep seismic sounding data. Izv. Acad. Nauk, S.S.S.R., Geophys. Ser. 1: 20-41. [In Russian.] Kovylin, V. M. 1966. Results of seismic research in the south-western part of the abyssal basin of the Japan Sea. Oceanology 6: 294-305. [In Russian.] Kovylin, V. M., and Yu. P. Neprochnov. 1965. Crustal structure and sedimentary layer in the central part of the Japan Sea derived from seismic data. Izv. Acad. Nauk, S.S.S.R., Geol. Ser. 4: 1026. [In Russian.] Ludwig, W. J., J. I. Ewing, M. Ewing, S. Murauchi, N. Den, S. Asano, H. Hotta, M. Hayakawa, T. Asanuma, K. Ichikawa, and I. Noguchi. 1966. Sediments and structure of the Japan Trench. J. Geophys. Res. 71: 2121-2137. Matsuyama, M. 1936. Distribution of gravity over Nippon Trench and related area. Proc. Imp. Acad. Jap. 12: 93-95. McDermott, J. G., R. J. Labhart, and V. 0. Marshall. 1967. Ocean-bottom seismographic experiment. Preliminary Bull. Kurile Islands Experiment. Sci. Serv. Div., Texas Instr. Inc. Dallas. 15

M c K e n z i e , D o n P . , and J o h n G. Sclater. 1968. H e a t flow Inside the island arcs of the n o r t h w e s t e r n Pacific. J . Geophys. R e s . 73: 3173-3179. Menard, H. W. 1967. T r a n s i t i o n a l types of crust under small o c e a n b a s i n s . J. Geophys. Res. 72: 30613073. M i y a k e , Y a s u o , and Yukio Sugimura. 1961. I o n i u m - t h o r i u m chronology of deep-sea sediments o f the w e s t e r n N o r t h P a c i f i c O c e a n . Science 133: 1823-1824. 1965. A study o n the rate of deep sea deposition in the w e s t e r n N o r t h P a c i f i c b y means of ionium-thorium m e t h o d . J. Geogr., T o k y o 74: 95-99. [In J a p a n e s e w i t h E n g l i s h abstract.] M i y a k e , Yasuo, Yukio Sugimura, and Eigi M a t s u tnoto. 1968. I o n i u m - t h o r i u m chronology of the J a p a n Sea cores. R e c . Oceanogr. Works Jap. 9: 189-195. M u r a u c h i , S. 1966. The UMP seismic r e f r a c t i o n m e a s u r e m e n t in and around Japan. P r e s e n t e d at the 11th Pac. Sci. Congr., Tokyo, A u g u s t 1966. M u r a u c h i , S., N . Den, S. A s a n o , H . H o t t a , J. C h u j o , T . A s a n u m a , T . Ichikawa, and I. N o g u c h i . 1964. A seismic refraction e x p l o r a t i o n of K u m a n o N a d a (Kumano Sea), J a p a n . Proc. J a p . A c a d . 4 0 : 111-115. M u r a u c h i , S., N . Den, S. A s a n o , H. H o t t a , T . Y o s h i i , T . A s a n u m a , K . Hagiwara, K . Ichikawa, T . S a t o , W . Ludwig, J . I. Ewing, N . T. Edger, and E[. E . H o u t z . 1968. Crustal structure of the Philippine Sea. J . Geophys. Res. 73: 3143-3171. N a g u m o , Shozaburo, Heihachiro K o b a y a s h i , and Sadayuki K o r e s a w a . 1965. C o n s t r u c t i o n of ocean b o t t o m seismograph. B u l l . Earthq. Res. Inst. 4 3 : 671-683. N i n k o v i c h , Dragoslav, Neil Opdyke, Bruce C. H e e z e n , and J o h n H . Foster. 1966. P a l a e o m a g n e t i c stratigraphy, rates of d e p o s i t i o n and tephrachronology in N o r t h P a c i f i c d e e p - s e a sediments. E a r t h Planet. Sci. Lett. 1(6): 476-492. O g u c h i , T . , and S. K a k i n u m a . 1959. P r e l i m i n a r y report of geomagnetic surv e y d u r i n g J A R E the second. Antarctic Rec. 7: 17-25. O z i m a , M i n o r u , M i t u k o Ozima, and Ichiro K a n e o k a . 1968. P o t a s s i u m - a r g o n ages and m a g n e t i c p r o p e r t i e s of some dredged submarine b a s a l t s and their geophysical implications. J. Geophys. Res. 73: 711-723. P e t e r , George. 1966. M a g n e t i c anomalies and fracture p a t t e r n in the n o r t h e a s t Pacific O c e a n . J. Geophys. Res. 71: 5365-5374.

16

R a i t t , R. W . 1963. The crustal rocks. In M . N. H i l l (editor), T h e sea, ideas and observations on progress in the study of the seas. Xnterscience P u b l i s h e r s , N e w York 3: 85102. Segawa, J., K . O z a w a , and Y . Tomoda. 1967. Local m a g n e t i c anomalies in the N o r t h Pacific O c e a n . La Mer 5: 8-20. Solov'yev, 0 . N . , and A. G. Gainanov. 1963. Features of deep geological structure in the zone of transition from the Asiatic Continent to the Pacific O c e a n in the region of the K u r i l e - K a m c h a t k a island arc. Sov. Geol. 3: 113-123. S u g i m u r a , H . , and Y. M i y a k e . 1968. I o n i u m - t h o r i u m geochronology of the Lamont Core-V-20-130 of the w e s t e r n N o r t h P a c i f i c . Bull. Nat. Sci. M u s . 11: 327-332. Tomoda, Y. 1967. Continuous m e a s u r e m e n t of gravity and m a g n e t i c force in the 4th southern sea expedition of the Umitaka-Maru. La Mer 5: 175-205. T o m o d a , Y . , and H. K a n a m o r i . 1961. Tokyo surface ship gravity m e t e r - 1. J . Geod. Soc. Jap. 7: 116-145. Tomoda, Y . , and J. Segawa. 1967. M e a s u r e m e n t s of gravity and total m a g n e t i c force in the sea near and around J a p a n . J. Geod. Soc. Jap. 12: 157-164. U d i n t s e v , G. 1966. T e c t o n i c d i v i s i o n of the Pacific. Presented at the 11th Pac. Sci. Congr., T o k y o , September 1966. U y e d a , S., and K. H o r a i . 1964. T e r r e s t r i a l h e a t flow in J a p a n . J. Geophys. Res. 69: 2121-2141. Uyeda, S., K . H o r a i , M . Yasui, and H . A k a m a t s u . 1962. H e a t - f l o w m e a s u r e m e n t s over the Japan T r e n c h . J . Geophys. Res. 67: 1186-1188. U y e d a , S . , and M . R i c h a r d s . 1966. M a g n e t i z a t i o n of four Pacific seamounts n e a r the J a p a n e s e Islands. Bull. Earthq. Res. Inst. 4 4 : 179-213. Uyeda, Seiya, Takahiro Sato, M a s a s h i Y a s u i , Takeo Yabu, Teruhiko W a t a n a b e , K a o r u K a w a d a , and Yukio Hagiwara. 1964. Report o n geomagnetic survey in the n o r t h w e s t e r n Pacific d u r i n g JEDS-VI, J E D S - V I I , and JEDS-VIII cruises. Bull. Earthq. Res. Inst. 4 2 : 555-570. Uyeda, Seiya, Yoshibumi Tomoda, Ki-iti H o r a i , H i r o o K a n a m o r i , a n d H i d e t a k a Futi. 1961. Studies of the thermal state of the earth. T h e seventh paper: A sea b o t t o m thermogradmeter. Bull. Earthq. Res. Inst. 39: 115-131.

Uyeda, Seiya, Yoshibumi Tomoda, Takeo Yabu, and Shinkichii Utashiro. 1964. Improvement of sea-going proton magnetometer. Bull. Earthq. Res. Inst. 42: 383-395. Uyeda, Seiya, Masashi Yasui, Takahiro Sato, Hideo Akamatsu, and Kaoru Kawada. 1964. Heat flow measurements during the JEDS-6 and JEDS-7 cruises in 1963. Oceanogr. Mag. 16: 7-10. Uyeda, S., and V. Vacquier. 1968. Geothermal and geomagnetic data in and around the island arc of Japan. Crust and upper mantle of the Pacific area. Geophys. Mongr. Ser. 12, Amer. Geophys. Union, pp. 349-366. Uyeda, S., V. Vacquier, M. Yasui, J. Sclater, T. Sato, J. Lawson, T. Watanabe, F. Dixon, E. Silver, Y. Fukao, K. Sudo, M. Nishikawa, and T. Tanaka. 1967. Results of geomagnetic survey during the cruise of R/V Argo in western Pacific in 1966 and the compilation of magnetic charts of the same area. Bull. Earthq. Res. Inst. 45: 799-814. Vacquier, V. 1962. A machine method for computing and the magnetization of a uniformly magnetized body from its shape and a magnetic survey. Proc. Benedum Earth Magnet. Symp., Pittsburgh, pp. 123-137. Vacquier, Victor, John Sclater, and Charles Corry. 1967. Studies of the thermal state of the earth. The 21st paper: Heat-flow, eastern Pacific. Bull. Earthq. Res. Inst. 45: 375-393. Vacquier, Victor, and Seiya Uyeda. 1967. Palaeomagnetism of nine seamounts in the western Pacific and of three volcanoes in Japan. Bull. Earthq. Res. Inst. 45: 815-848. Vacquier, Victor, Seiya Uyeda, Masashi Yasui, John Sclater, Charles Corry, and Teruhiko Watanabe. 1966. Studies of the thermal state of the earth. The 19th paper: Heat-flow measurements in the northwestern Pacific. Bull. Earthq. Res. Inst. 44: 1519-1935.

Vening Meinesz, F. A. 1948. Gravity expeditions at sea. Delft. Netherlands Geod. Comm. 4. Vine, F. J., and D. H. Matthews. 1963. Magnetic anomalies over oceanic ridges. Nature 199: 947-949. Von Herzen, R. P., and S. Uyeda. 1963. Heat flow through the eastern Pacific Ocean floor. J. Geophys. Res. 68: 42194250. Watanabe, T. 1966. Heat flow in the Japan Sea. Thesis, Univ. Tokyo. Yasui, M., Y. Hashimoto, K. Nagasaka, and K. Anma. 1968. Bathymetric and geomagnetic studies of the Okhotsk Sea (2). Oceanogr. Mag. 20: 65-72. Yasui, M., T. Hashimoto, and S. Uyeda. 1967a. Geomagnetic and bathymetric study of the Okhotsk Sea. Oceanogr. Mag. 19: 7385. 1967b. Geomagnetic studies of the Japan Sea (1); the anomaly pattern in the Japan Sea. Oceanogr. Mag. 19: 221-231. Yasui, Masashi, Ki-iti Horai, Seiya Uyeda, and Hideo Akamatsu. 1963. Heat flow measurement in the western Pacific during the JEDS-5 and other cruises in 1962 aboard M/S Ryofu-Maru. Oceanogr. Mag. 14: 147-156. Yasui, M., T. Kishii, K. Nagasaka, and K. Anma. 1969. Heat flow over the Tatar Plateau in the Japan Sea. Oceanogr. Mag. 22. Yasui, M., T. Kishii, K. Nagasaka, and A. J. Halunen. 1968. Terrestrial heat flow in the Okhotsk Sea (2). Oceanogr. Mag. 20: 73-86. Yasui, M., T. Kishii, and K. Sudo. 1967. Terrestrial heat flow in the Okhotsk Sea (1). Oceanogr. Mag. 19: 87-94. Yasui, M., T. Kishii, T. Watanabe, and S. Uyeda. 1968. Terrestrial heat flow in the Japan Sea. Crust and upper mantle of the Pacific area. Geophys. Mongr. Ser. 12, Amer. Geophys. Union, pp. 3-16.

17

Bathymetry of the South China Sea JOSEPH G. GILG

U.S. Naval Océanographie Office} Washington} D.C.

ABSTRACT

The South China Sea can be divided into five bathymetric provinces: (1) the shelf areas; (2) the submerged continental margin of Asia; (3) the submerged island margins of Taiwan, Luzon, Palawan, and Borneo; (4) the plateau of the "dangerous grounds" area; and (5) the central basin. The shelf areas are broad on the west and south, and narrow along the islands on the east. Coral reefs are common on nearly all shelves. Water exchange takes place across the shelves with the Indian Ocean and the East China Sea at sill depths of 30 and 70 m., respectively (17 and 38 fathoms). Channels through the shelves connect the South China Sea with the Sulu Sea and Pacific Ocean at depths of 450 and 100 m., respectively (246 and 55 fathoms). The submerged continental and island margins include a number of terraces, coral reefs, and valleys. The coral reefs occur primarily on the terraces. Since the terraces extend to depths of 1,800 m. (1,000 fathoms), the presence of coral reefs upon them is unusual. It is thought that the terraces represent subsiding blocks, and the coral growth has kept pace with the subsidence. The "dangerous grounds" area includes a large plateau upon which numerous coral reefs have developed, and into which a number of valleys have been cut. Since the irregular plateau surface lies at depths between, 1,500 and 2,000 m. (800 and 1,100 fathoms) the presence of coral reefs indicates subsidence of this block also. The central basin is primarily a plain which slopes generally southward from 3,400 to 4,200 m. depth (1,850 to 2,300 fathoms). A number of seamounts are present near the center of the basin. These are thought to be volcanic in origin, and most do not reach sea level. The bathymetry of the South China Sea is portrayed on a bathymetric features chart, a recent development at the Naval Oceanographic Office. This chart shows features and provinces in outline form rather than in the full contour development of bathymetric charts. The outlining contour is not limited to a fixed contour interval, and important slope changes and small relief features can be shown.

INTRODUCTION

the Philippines, and Borneo on the east; and by the mainland on the west.

The South China Sea is one of several

The south-

ern border is the Gulf of Thailand and the

bathymetrically related bodies of water

Malay Peninsula.

located along the eastern margin of the

considered as a line from the northern tip

Asian mainland.

of Taiwan to the Asian coast.

It is bordered by Taiwan,

The northern border is

The bathymetry and oceanography of the

métrie features chart uses only those con-

South China Sea have been described by a

tours and soundings needed to outline the

number of individuals.

features.

LaFond (1966) sum-

marizes much of the previous material.

He

For example, one contour line

is required to outline the Continental

includes a general bathymétrie chart by

Shelf and give the shelf edge depth on the

Udintsev.

bathymetric features chart.

Several large scale nautical and

One addition-

bathymétrie charts, covering portions of

al contour line is required to outline the

the South China Sea, have been published by

continental slope.

the Naval Oceanographic Office in the H.O.

terrace within this slope.

and H.O./B.C. chart series.

trough are each defined by one contour and

Although the chart to be presented

one sounding.

Two contours outline a A seamount and

Bottom irregularities that

here includes no significant amount of new

are too small or too irregular to show by

data, it does employ a new approach in

contour are defined by using profiles and

charting; bathymétrie features and prov-

by outlining the area of irregularity.

inces are shown by a contour outline,

Color (or Zip-A-Tone) patterns are

rather than by the full contour development

used on the bathymetric features charts as

of conventional bathymétrie charts.

an aid in identifying the outlined features

This

chart, the bathymétrie features chart, was

and provinces.

developed in the Bathymetry Division of the

used to indicate flat to gently sloping

Naval Oceanographic Office in June 1967.

bottoms; dark green is used for moderate

It is hoped that the bathymétrie features

to steep slopes; and light green is used

chart can become a standard product of the

for depressions.

Oceanographic Office, since it is capable

used in conjunction with color on depres-

of portraying information concerning bottom

sions to indicate their axes.

topography that cannot be shown on bathy-

with arrows are used to indicate direction

métrie charts.

of slope of depressions.

A prototype chart including

a bathymétrie text has been printed recently for the Sea of Japan.

This chart is

available from the Bathymetry Division of

Yellow, orange, and red are

Dotted lines are also

Dotted lines

There are two main reasons for using the simple portrayal method of the bathymetric features chart.

First, if one is

the Naval Oceanographic Office on request.

THE BATHYMETRIC FEATURES CHART Figure 1 shows the bathymétrie chart method (A), and the bathymétrie features chart method (B), of representing topography.

Note that the bathymétrie chart

requires a full contour development to show bathymétrie features, while the bathy-

22

(A)

(B)

Figure 1. Comparison of (A) conventional bathymetric chart, and (B) bathymetric features chart.

familiar with the form of common bathymetric

the South China Sea.

features, the full contour development is

submerged continental margin of the Asian

often unnecessary.

mainland.

Second, the data which

Province A is the

Province B is the submerged is-

identify a feature are often insufficient

land margins of Taiwan, Luzon, Palawan, and

to justify a full contour development.

Borneo and includes the adjacent trenches

The advantages of the features chart,

and troughs.

Province C is a large sub-

in addition to the simple portrayal, in-

merged plateau, dotted with coral reefs, fre-

clude:

quently referred to as "dangerous grounds."

slope or gradient changes between

the usual contour interval can be shown;

Province D is the central basin area, or

relief of less than the usual contour inter-

deep-water portion of the South China Sea.

val can be shown; and the topographic provinces and geologic structure of the ocean bottom can be more easily visualized.

BATHYMETRIC FEATURES CHART OF THE SOUTH CHINA SEA

Bathymetric features charts can be constructed at any scale and will show more

Figure 3 is a bathymetric features

about the topography than a bathymetric

chart of the South China Sea.

chart based on the same amount of sounding

this chart is H.O. chart 5595 and many of

data.

the data from H.O. 5595 have been retained on the features chart.

MAJOR TOPOGRAPHIC PROVINCES AT THE SOUTH CHINA SEA

The base for

The contours out-

lining provinces and features are based on soundings on H.O. 5595 and on additional large scale H.O. or H.O./B.C. charts of the

Figure 2 shows the shelf areas and the four other major topographic provinces of

area.

When shown in color, the color scheme

used is the one previously described.

The

features chart is in uncorrected fathoms but in the following discussion depths will be given in meters.

THE SHELF AREAS The shelves of the South China Sea extend to depths of 90 to 165 m. (50-90 fathoms).

The largest shelf areas are

those between Malaya and Borneo and in the embayments along the Asian mainland. shelf

average widths of the shelf are:

The

90 nauti-

cal miles along mainland China; 6 miles off Figure 2. Shelf area and four other major topographic provinces of the South China Sea.

Taiwan; 10 miles off Luzon; 30 miles off Palawan; and 50 miles off Borneo.

23

116-

117"

118'

119"

120'

12P

122'

123'

IASED ON I.O. 5 5 9 5 d e p t h s in f a t h o m s .

• E I. H H F. S

isb.

Figure 3. Ik

Bathymétrie f e a t u r e s of the South China Sea.

S K .

Host of the shelf areas of the South

is probably an additional factor, filling

China Sea are dotted with coral reefs.

in depressions formed in or by the sub-

Since these reefs are best studied on the

siding blocks.

larger scale nautical charts, they are not shown in detail or described here.

Several

Most of the coral reefs occur on or within the terraces.

The largest of these

channels cross the shelf areas and connect

are Pratas Reef, Helen Shoal, and Paracel

the South China Sea with adjacent waters.

Islands.

On the north, there is a connection with

tionally large reef which is not related

the East China Sea through Taiwan Strait.

to a terrace.

The sill depth here is reported to be 70 m.

ridges to the south, which do not reach

(38 fathoms).

sea level, appear to extend with steep

On the south, there is a

Macclesfield Bank is an excepThis bank, and several large

connection with the Java Sea through Kari-

slopes to the basin floor on the east.

mata and Gaspar Straits.

submerged ridges may also be coral reefs.

Both straits are

The

scoured locally to depths in excess of 40 m.

Since corals do not grow at the depths to

(22 fathoms) but 40 m. would appear to be

which some of these features extend, it

near the sill depth.

seems likely that upward reef development

On the west, there is

a connection with the Indian Ocean through

has kept pace with subsidence of the con-

the Strait of Malacca at a sill depth of 30

tinental blocks.

m. (17 fathoms).

Several deep channels

The continental slopes extend from

connect the South China Sea to the Sulu and

the margin of the terraces and ridges to

Philippine Seas but these will be discussed

the central basin floor at depths of 3,500

with the bathymetry of the island margins.

and 4,200 m. (1,900 and 2,300 fathoms). The continental slope is broken into num-

ASIAN CONTINENTAL MARGIN - PROVINCE A

erous segments, generally separated from one another by valleys.

The Asian continental margin, Prov-

Many segments are

offset from adjacent segments, indicating

ince A, includes a series of large, step-

a structural control of the topography.

like terraces, a continental slope, numer-

number of minor ridges and depressions are

ous coral reefs, and several valleys.

present within, and parallel to, the slopes.

The

terraces have many shapes and sizes and

These are not indicated because of their

occur at varying depths down to about 1,800

small size and difficulty of outlining

m. (1,000 fathoms).

their extent.

Most terraces include

A

An exceptionally large

additional smaller terraces within them,

arcuate valley is seen to the north and

but data are inadequate to outline these.

west of the Paracels.

The terrace east of Pratas lies between

slope is split here, and one segment con-

2,400 and 2,950 m. (1,300 and 1,600 fath-

tinues along the north side of this valley.

oms) and is exceptionally deep.

These

The continental

Despite the complexity of the struc-

terraces probably represent continental

ture and the large number of individual

blocks that have subsided.

features of various types in this province,

Sediment fill

25

there are comparatively large areas of

studded Balabac Strait serves as a less

simple, low relief topography.

important connection south of Palawan and

For example,

the terrace northwest of Helen Shoal increased in depth 370 m. (200 fathoms) over

has a sill depth of 100 m. (55 fathoms). The slopes of the island margins are

a distance of 30 miles, or a gradient of

narrow and steep.

only 1:200.

than 40 nautical miles wide and extend to

The total area of the terrace

Most slopes are less

at this gradient approaches 5,000 square

depths ranging from 2,900 to 5,200 m .

miles.

to 2,800 fathoms), or the average depths of the bordering trenches or troughs.

ISLAND MARGIN - PROVINCE B

(1,600

There

are numerous terraces on these slopes.

The

largest occurs between 2,400 and 2,550 m. The islands of the island margin,

(1,300 and 1,400 fathoms) along the coast

Province B, have in common a relatively

of Luzon near Manila Bay.

narrow Continental Shelf, an island slope,

smaller terraces are present along the

and a depression at the base of the slope

island slope of Palawan and Borneo b u t the

in the form of a trench or trough.

sounding data are inadequate to properly

An

A number of

additional depression in the form of a

outline them.

deep channel extends northeastward across

off Borneo may represent small valleys

the submarine ridge between Taiwan and

extending down the slope.

Luzon.

are not shown because of lack of data.

This channel is 3,100 to 3,650 m.

(1,700 to 2,000 fathoms) deep

throughout

Irregular topography noted

These valleys

A m a x i m u m depth of 4,425 m.

(2,420

its length, except for sills of 1,830 and

fathoms) is shown at the southern end of

2,380 m. (1,000 and 1,300 fathoms) off the

the trough between western Taiwan and

tip of Taiwan.

Stewart Bank.

Numerous small channels

Two sills occur in this

and valleys connect this deep channel with

depression in the next 100 miles south of

the Pacific Basin across the submerged

Stewart Bank, followed by a deepening of

ridge n o r t h of Luzon.

the depression to 5,245 m . (2,868 fathoms)

One of these chan-

nels, northwest of Y'Ami Island, has a

west of Mindoro.

sill depth of 2,600 m . (1,420 fathoms) and

eastward toward Mindoro Strait and does not

is probably the m a i n water

appear to connect to the Palawan trough.

interchange

associated w i t h the Bashi Channel.

The

This depression swings

The Palawan trough reaches a m a x i m u m depth

other channels across this ridge have sill

of about 2,925 m. (1,600 fathoms) off

depths of 730 to 1,300 m. (400 to 700 fath-

Borneo, but decreases rapidly to about

oms) .

1,550 m. (850 fathoms) near Seahorse shoal. The South China Sea connects to the

The Palawan trough appears to connect with

S u l u Sea at the northern end of Palawan

the central b a s i n b y way of a valley on the

through the Mindoro Strait with a sill

northeast side of Reed Bank.

d e p t h of 4 5 0 m. (246 fathoms).

26

The coral-

DANGEROUS GROUNDS-PROVINCE C

to be volcanic in origin.

Most of the sea-

mounts do not reach sea level.

There is a

large sediment-filled trough or valley

The dangerous grounds, Province C, includes a large, elongate plateau upon

north of the Prince of Wales Bank.

w h i c h numerous coral reefs have been built

small northeast trending ridges occur with-

and into which a number of large valleys

in this trough but are not outlined.

have b e e n cut.

lar small ridges occur along the western

The plateau surface is

Several

Simi-

irregular but generally lies between 1,470

m a r g i n of the central basin n o r t h of here.

and 2,010 m. (800 and 1,100 fathoms).

These ridges m a y indicate the presence of

The

coral reefs are variable in size.

Most are

additional continental margin structure

elongated in a northeast-southwest

direc-

beneath this trough and along the w e s t e r n

tion.

A study of the elongation of reefs

edge of the central b a s i n floor.

in the nearby Celebes Sea led to the suggestion that the elongation reflects the direction of currents.

ORIGIN OF SOUTH CHINA SEA STRUCTURES

The reefs are un-

doubtedly more numerous than indicated.

The South China Sea is in the shape of

The presence of reefs in deep water sug-

a rhomb w i t h one set of north-south sides

gests that, here too, coral growth has

and one set of northeast-southwest

kept pace w i t h the subsidence of a large

Similar rhomb shapes are seen for the Sea

crustal block.

of Japan, Sea of Okhotsk, and the P h i l i p -

Valleys are prominent along the western margins of the plateau.

The valleys

pine Sea.

sides.

These shapes are related to

crustal structures and represent a similar-

m a y represent the western and deeper end

ity of geologic processes over a large area.

of depressions extending completely across

These structures have b e e n interpreted to

the plateau.

indicate that the A s i a n Continent has swung

A n apron of sediments is

present at the south end of the "dangerous

away from the Pacific Basin at some time in

grounds" and coral reefs appear less numer-

the past.

ous here.

tinental margin was stretched, breaking it

During this movement, the c o n -

into blocks, some of w h i c h then subsided to moderate depths.

THE CENTRAL BASIN-PROVINCE D

Some of the blocks have

separated to the extent that new ocean The central basin, Province D, includes a plain w h i c h slopes from 3,400 m.

(1,850

floor may have b e e n created between them. In the South China Sea the submerged

fathoms) at the n o r t h end, to 4,200 m .

continental and island margins represent

(2,300 fathoms) at the south end.

the subsided blocks.

Depths

The terraces repre-

b e l o w 4,400 m. (2,400 fathoms) are noted

sent individual blocks, the coral reefs

in several places in the south half of the

represent continuous growth on these struc-

basin.

tures during subsidence.

There are a number of seamounts in

the center of the basin which are thought

The central b a s i n

is probably an area of n e w ocean floor,

27

although a thick sediment cover now obscures

south.

this fact.

in bathymétrie interpretation in areas

Nearly every elongate b a t h y -

métrie feature or province in this sea

This consistency of trend iâ an aid

where data are sparse.

follows the trend of one or more sides of the rhomb.

In general, a specific type of

topography within a major province consistently follows the same trend.

For example,

LITERATURE CITED

all of the terraces along the submerged m a r g i n of A s i a are elongated northeastsouthwest; the majority of valleys on the "dangerous grounds" plateau align n o r t h -

28

LaFond, E . C. 1966. South China Sea. In Rhodes W. Fairbridge (editor), The E n c y c l o p e d i a of O c e a n o g r a p h y , Reinhold Publishing Corporation, pp. 829-837.

T h e Kuroshio- Oyasliio Front: A S y s t e m of Near-Stationary Vortices RICHARD A. BARKLEY

Bureau, of Commercial Fisheries Biological Laboratory,

ABSTRACT

Honolulu

The author's kinematic model of the Kuroshio-Oyashio front, consisting of a pair of von Karman vortex streets arranged side by side (or four parallel rows of Rankine vortices), accounted for m a n y major features of that important region of the Pacific Ocean. However, the model did not include coriolis force; as a result, the model predicts an eastward displacement of the vortex system of about 50 cm. sec. - 1 , whereas observations suggest that the vortices are more or less stationary. Recent theoretical work b y Warren shows that, on a b e t a plane, circular currents of the type proposed in the vortex street model should be displaced westward at a rate w h i c h would, in large part, cancel the eastward velocity induced by other nearby vortices in the author's model w i t h o u t the b e t a plane effect. T a k e n together, these two theoretical analyses complement each other, providing a model w h i c h is complete and accounts for all major observed features of the Kuroshio-Oyashio front, at least to the degree w h i c h can be expected from first-order theory applied to the existing fund of published data. Some predictions based on the model are presented as a basis for field work designed to test the validity of the theoretical model.

INTRODUCTION

density, and sea surface currents.

This

simple concept fails in one particular, In a paper entitled "The Kuroshio-

however:

It predicts that each vortex

Oyashio front as a compound vortex street"

w i l l be moved eastward b y the effects of

(Barkley, 1968), it was shown that all

neighboring vortices, so that the entire

major features of the front east of Japan,

array should m o v e eastward at about 50 cm.

where the Kuroshio and Oyashio come togeth-

s e c . - 1 ; the evidence available for the

er, can be accounted for in a near-quanti-

1955-64 decade indicates that the array is

tative manner by a relatively simple kine-

quasi-stationary, instead.

matic model (fig. 1).

ing of the m o d e l was attributed to the

The compound vortex

This

shortcom-

street, w h i c h consists of four parallel

fact that coriolis force was not taken

rows of vortices or eddies that rotate in

into account.

alternate directions, accounts in large part for the distributions of temperature,

It is shown in this paper that the effects of coriolis force in the compound

o

o

o

Quarterly charts of the isotherms at the sea surface, 100 and 200 m., and of the sea surface currents (Japanese Hydrographic

o

o

Division, undated) contain unmistakable evidence for the presence of an array of vortices, similar to that shown in figure 1,

a

-ha

for almost all of the 1955-64 decade.

The

subsurface isotherms in nature are very

o-

-o

h-

-H

a

nearly parallel to the streamlines of the model.

The topography of isopycnal sur-

faces also resembles the streamlines of figure 1.

Unique features of the model's

field of flow, such as the westward countercurrents at the centerline of the array, appear in nature where the model implies they should occur.

Further, velocities at

points A, B, and C (fig. 1) are in the mathematical model in the proportions -0.46:0.57:1 and average sea surface current velocities at corresponding points in the Kuroshio-Oyashio front are in the proportions -0.4:0.5:1 (the negative sign refers to westward flow). Figure 1. Compound vortex street. Upper panel coordinate system and notation; lower panel streamlines showing theoretical pattern of flow.

Finally, the transport of water in the two-dimensional model, extended to three dimensions by the use of any of several reasonable assumptions, agrees well with

vortex street model are, in theory, essen-

values in the prototype.

tially equal and opposite to the kinematic

fore has geometric similarity to the

effects which the vortices have upon each

Kuroshio-Oyashio front, predicts velocities

other.

of the proper magnitude and direction, and

As a result, the array should re-

The model there-

main nearly stationary, as the Kuroshio-

accounts for most of the transport within

Oyashio front appears to do.

the region. Theoretical analysis shows, neverthe-

COMPOUND VORTEX STREET MODEL

less, that an array like that in figure 1 should move toward the east as a unit; each

Evidence supporting the vortex street

eddy should be moved in this direction by

model of the Kuroshio-Oyashio front (Bark-

its neighbors at a speed of about 56 cm.

ley, 1968) can be summarized as follows:

sec.

32

which value does not agree with the

quasi-stationary nature of the frontal

of which should respond to the effects of

system itself.

the earth's rotation by moving westward,

This one discrepancy in an

otherwise accurate model was tentatively

in approximate accord with equation (1).

attributed to the fact that coriolis force

Since all eddies in each row of the array

was not considered in the simple kinematic

are assumed to be identical, and to lie at

model.

the same latitude, each row should respond to the beta effect as a unit.

EFFECTS OF CORIOLIS FORCE

The simple mathematical model assumes that each vortex has zero radial velocity,

According to Warren's (1967) first-

and tangential velocity given by the equation :

order theoretical analysis, meridional variation in the coriolis force, the socalled beta effect, should cause a circular

V

to 34.1°/ot) between

a nearly uniform oxygen content; a layer

600 and 800 m. with a temperature of less

of gradients, the thermocline and halo-

than 8° C.

cline; the Subarctic Intermediate Water; and the deep water.

OCEANOGRAPHIC CONDITIONS

The winter mixed

layer varied in depth from 300 to 100 m.,

ALONG THE LINE The line along lat. 34° N. lies south

JJL

i- \

\

of the "normal path of the Kuroshio extension," but it is placed so that it should include the meanders of the current.

Uda

•Lp-^f

a

(1964) said that the troughs (or southward

L}J[f]

projections) almost always occur at long. 146°-148° E. and long. 152°-155° E.

He

also stated that the amplitude of these meanders is from 80 to 240 nautical miles

/

/

ISO*

:

H.

T7

• V X 35-

So^sfir

135"

140°

145*

ISO*

E.

Figure 2. The meandering pattern of the current axis of the Kuroshio during the years 1959-63. (After Uda, 1964.)

45

west to east, with a temperature of 17.0°-

thermocline layer, indicating a flow to

19.0° C. and a salinity of 34.7°/ co to

the south.

34.8°/ 0 0 .

bottom of the thermocline had shoaled to

The thermocline (6°-16° C.)

East of long. 153°-154° E. the

and halocline (34.2°/ 00 to 34.6°/ 0 0 )

about 600 m. in depth.

regions showed a great deal of variation

cline was the intermediate water charac-

in depth, indicating the presence of

terized by a salinity minimum of about

meanders across the line.

34.0°/ oo to 34.1°/ 0 o and having a temper-

Between long.

Beneath the thermo-

143° and 152° E. the thermocline was

ature of 4.0°-6.0° C.

located between about 300 and 800 m. in

between 500 and 700 m.

depth, but between long. 152° and 154° E.

below the intermediate water was charac-

there was an abrupt rising to the east of

terized by an oxygen minimum of 0.9 to

all the isopleths and a compression of the

1.1 ml./t. between 1,200 and 1,500 m.

STATION NUMBER 6 5

4

It was located The deep water

OCEIH STAT I OH VICTOR

142" 14? 144" «5« 146" 147" 148" 1491 tW° 151" 152' 153° 154" 155° 156" 157" 156" 158" 160" 161' 162" 163" 164* LONGITUDE Figure 3. Vertical section of temperature (° C.) from Ocean Station Victor, lat. 34° N., long. 164° E., to lat. 34° N., long. 141°47' E., CSK 1, USCGC Chautauqua. January 1966.

46

Vertical displacements of the isopleths

was a shallow mixed layer at 25-50 m. in

were evident even at the 2,000-m. level,

depth w i t h a temperature of 24.0°-25.0° C.

indicating that the water movement was

A seasonal thermocline and halocline were

affecting the deep water.

established between 50 and 150 m.

Unfortunately,

The

the winter data are incomplete for Janu-

thermocline had a gradient from 24.0° to

ary 1967, because adverse weather condi-

about 19.0° C. and the halocline

tions prevented oceanographic operations

3 4 . 5 ° / 0 0 to 3 4 . 8 ° / 0 0 .

between long. 147° and 154° E.

sonal clines was a relatively large layer

During the summer the basic stratif-

from

B e n e a t h the sea-

of homogeneous w a t e r w i t h a temperature

ication was modified b y the addition of

of 17°-19° C. and salinity of 3 4 . 7 ° / 0 0

heat to the surface layer and the advec-

to 3 4 . 8 ° / 0 0

tion of warmer water into the area.

m. The oxygen content of this water was

13

12

11

10

There

located b e t w e e n 150 and 300

STATION NUMBER

9

5

OCEAN STATION VICTOR

|_I

IO N. HI.

J 142"

I

I

I

I

I

I

L

143"

144°

145"

146'

147"

148°

149°

150°

J

I

151°

IS*

I

I

I

I

I

L

153°

154p

155°

156"

157°

158°

159°

160°

161°

162°

163°

164°

LOHBITUDE

Figure 4. Vertical section of salinity ( ° / 0 c ) from Ocean Station Victor, lat. 34° N., long. 164° E., to lat. 34° N., long. 141°47' E., CSK 1, USCGC Chautauqua. January 1966.

kl

from 4.0 to 4.5 ml./^.

and the presence of the cold water intru-

The main thermo-

cline was in the same position as in

sions from the mixed water zone between

winter, but its variations in depth were

the Kuroshio front and the Oyashio front.

much more pronounced in the region east of

Beneath these cold water masses the salin-

long. 153° E.

ity minimum layer had shoaled to the 300-

The abrupt rising of the

isopleths at long. 153° E. amounted to

400 m. level.

about a 400-m. displacement in July 1966 and to 200 m. in October 1967.

The abrupt rising to the east of the

A more

isopleths of all properties between long.

intensified southward flow was indicated

152° and 154° E. was observed on all four

in the summer of 1966.

cruises and a relatively permanent trough

Southerly meanders

of the Kuroshio were indicated by the

of the Kuroshio might be found here.

vertical shrinking of the 16°-18° C. water

January and July of 1966, two warm (17°-

STATION 15

1 4

1 3

1 2

1 1

1 0

9

9

7

In

NUMBER

6

5

4

3

2

1

«CEIN

S T U I O «

IICTO«

LONGITUDE

Figure 5. Vertical section of oxygen (ml./l.) from Ocean Station Victor, lat. 34° N., long. 164° E., to lat. 34° N., long. 141°47' E., CSK 1, USCGC Chautauqua. January 1966.

48

19° C . ) , high s a l i n i t y

(34.6°/ 0 0

Kuroshio was f a r t h e r north.

to

October was probably too l a t e in the sum-

3 4 . 8 ° / 0 0 ) cores were observed in the region to the east of long. 153° E.

However,

mer to observe peak summer f l o w .

The

The p r o f i l e s of density

oxygen content in these cores was about

(sigma-t)

5.5 ml./

«y

/ '" h

1

30 Ml - H 1

. 12°

TOW DIRECTION

308° ^ r v V

•,/AA*

Figure 4. Example of the recorded analog data section from section A of figure 3. The two isotherms 24° and 19° C. used for depth analyses are indicated.

72

;

«

the thermocline and one just below in the weaker part of the thermocline.

The depth

of encounter of the two isotherms was determined for every half-minute interval. From the depth difference per unit horizontal distance, the slopes were calculated. At a speed of 6 knots, the ship traveled 304 feet in each half-minute interval; therefore, dividing the depth differences by 304 feet gave the slope of the isothermal surface in the direction of the ship's motion.

The slope can also be expressed by

the arc tangent. The five sections selected for isotherm depth analyses were continuous for 8 hours. A total of 960 isotherm depth readings was taken from each sample section.

The distri-

bution of adjacent depth changes and slopes for each selected isotherm on each section was diagrammed.

Figure 5 shows the cumula-

tive frequency curve of depth changes for individual sections and isotherms.

The S-

shaped cumulative frequency curve shows that the isotherm variations are nearly symmetrical about zero slope. The graphs show that a half-minute isotherm depth change as large as 25 feet in one section was observed over a horizontal distance of 304 feet, which corresponds to a slope angle of 4°43'.

Figure 5. Cumulative percentage distribution of differences in depth between half-minute, or 304-foot-spaced, readings of the shallow and deep isotherms of the five sections (fig. 3). The 25th and 75th percentiles delineate the central 50 percent of data; the 15th and 85th percentiles delineate the central 70 percent. The vertical changes of isotherms per 304 feet, corresponding to these percentiles, are indicated.

However, 26 percent

of the adjacent half-minute readings showed

0°59'.

little or no change for all isotherms.

of the 50th and 70th percentiles for each of

The 50th percentile of depth changes for the 10 accumulative curves (fig. 5) range

Table 1 gives the individual values

the five sections. From these results it is apparent that

from 0.7 to 2.6 feet for the shallow iso-

some parts of the Kuroshio contain steeper

therm.

thermoclines than others by a factor of

This corresponds to 0°8' and 0°29',

respectively.

The 50th percentile of depth

nearly four.

The average slope of both iso-

changes for the deep isotherm was steeper,

therms of the five sections (9,600 values)

ranging from 1.1 to 3.5 feet or 0°18' to

is 0°161 for the 50th percentile. 73

Table 1.

Slope of

Power Spectrum of Depth Values

isotherms

Kuroshio a r e a

The power spectrum is the energy con-

Percentile 50th

tributed by each frequency band to the total 70th

(minutes of angle)

(minutes of angle)

Shallow Deep

17' 20'

31' 38*

2

Shallow Deep

9' 12*

19' 24'

3

Shallow Deep

29' 35'

54' 59'

4

Shallow Deep

8' 16'

18' 32'

5

Shallow Deep

8' 11*

18' 25*

K u r o s h i o a r e a average

16'

32'

Section

Isotherm

1

O t h e r areas San Diego to H o n o l u l u

16'

30'

Off B a j a C a l i f o r n i a 1

25'

51'

California front

12'

26'

1

L a F o n d , E . C.

(1963).

variance of the vertical oscillations of isotherms (Tukey, 1949; Mode, 1951). By using the same half-minute isothermdepth data, power spectra (fig. 6) were computed for each selected isotherm and section. The figures show several small peaks ranging in frequency from less than 0.1 to 1.0 cycle per minute, which correspond to wavelengths greater than 1 . 0 _ t o respectively.

The distribution of these

small peaks is not consistent from section to section.

The spectra show few signifi-

cant peaks.

This result is not consistent

with other spectral analyses for the North Pacific which show preferred wavelengths of about 0.7 nautical mile (Smith, 1967). Therefore from the present results it is

Figure 6. Power spectra from successive half-minute readings of the depth of the deep and shallow isotherms of the five sections (see fig. 3).

Ih

0.1 nautical mile,

concluded that the g r e a t e s t energy l i e s

t h r e e and f i v e a r e n e a r e r the c o r e and a r e

in

the low f r e q u e n c i e s and the o s c i l l a t i o n s

are

n o r t h e r l y w i t h 1.4 knots a t p o s i t i o n

five.

composed of a wide frequency spectrum w i t h -

Although p o s i t i o n s i x i s i n the b e g i n n i n g of

out s i g n i f i c a n t peaks.

the Kuroshio e x t e n s i o n ,

Hence, i t i s

prob-

a b l e t h a t the isotherm depth v a r i a t i o n s due t o

are

flow.

T h i s may be caused by meandering as a

JAPAN|

( s

Current d e t e r m i n a t i o n tow p a t t e r n s were conducted at s i x p o s i t i o n s .

The l o c a t i o n

the b o x - p a t t e r n tows as w e l l as the current v a l u e s

is

of

g i v e n i n t a b l e 2.

c u r r e n t s a r e those near the s u r f a c e .

Figure

(13-m.) f l o w ,

t i v e t o 240 m., f o r the s i x

A

> 3

1

The these

7 shows the n e a r - s u r f a c e

/

relative

most s i g n i f i c a n t and the s t r o n g e s t of

N1 > K

rela-

1

positions.

The r e l a t i v e c u r r e n t s at p o s i t i o n s one and two a r e s o u t h e r l y and a r e i n d i c a t i v e the Kuroshio c o u n t e r c u r r e n t .

Station

shows a n o r t h e r l y

turbulence.

CURRENT

Table 2.

it

of

Positions

Figure 7. Relative current at 13 m., referenced to 240 m., as determined from box-tow patterns. Length of arrow indicates speed. Position 5 i s 1.4 knots.

Current r e l a t i v e to 240 m. determined from box-pattern tows Position Lat.

(N.)

Long.

(E.)

Date 1966

Time (135° E.)

Depth (m.)

Current Speed (Knots)

Direction

1

32°18.8'

142°14.2'

July 30

0230

13 83 162

0.6 0.4 0.3

151° 187° 153°

2

33°44.0'

140°22.1*

July 31

1645

13 83 162

1.2 0.8 1.0

175° 180° 135°

3

35°00.21

141°20.1'

Aug. 1

1000

13 83 162

0.7 0.5 0.7

21° 6° 45°

4

33°52.2'

142°51.1'

Aug. 2

0900

13 83 162

0.3 0.1 0.0

99° 153°

5

35°10.0'

141°47.9'

Sept. 21

0100

13 83 162

1.4 0.6 0.4

322° 325° 320°

6

35°46.1'

146°06.0'

Sept. 22

1510

13 83 162

0.7 0.5 0.2

352° 41° 0°

-

75

result of Oyashio intrusions.

The relative

OYASHIO SECTION

currents at three depths for each of the six positions are shown in figures 8A through 8F. The speed of water with respect to the

On the second leg at lat. 35°20' N., long. 144°24' E., we encountered a strong

chain at four levels was recorded throughout

horizontal temperature gradient (3° C. per

the towing tracks and hourly values have

7.5 km.), characteristic of an internal front

been reported (LaFond, 1968).

(fig. 9).

The relative

flow was as great as 3.9 knots in some areas.

This cold subsurface tongue con-

tinued for 18 miles and is believed to be an intrusion of the Oyashio.

The total temper-

ature decrease at 170 m. was over 7° C. in

RELATIVE CURRENT AT POSITION I

RELATIVE CURRENT AT POSITION 7

RELATIVE CURRENT AT POSITION 3

L0"FST METfR

Figure 8. Relative currents at three distances above lowest meter at the six box-tow positions. Current speed and direction are relative to the flow at 240 m. The values are also included in table 2.

76

18.5 km. (10 miles) of tow from the warm

the center, spiraling to east and west at a

Kuroshio into the cold Oyashio.

speed of about 0.7 knot.

A similar

This is typical of

but weaker increase was traversed on the

convective processes associated with vertical

eastern boundary.

eddy circulation.

There was only a 2° C.

change in surface temperature; the colder surface water was directly above the Oyashio water.

The main thermocline strength over

CONCLUSIONS

the cold tongue (10° C. per 14 m.) remained at about the same depth but increased in strength over the colder subsurface water. The current section through the cold

Detailed temperature and current sections east of Japan show larger vertical oscillations than in any other place in the

tongue provided information on the circula-

North Pacific Ocean; however, the slopes of

tion processes.

small segments along the isotherms are only

Westward of the first in-

ternal front the relative current at depth

average.

was about 0.3 knot to the east compared with

isotherms indicated that the oscillations

the sea surface.

are made up of a wide spectrum of wavelengths.

Just beyond the front, the

relative flow became westward with a speed of 0.7 knot.

The westward flow decreased

The power spectrum of the depth of

A significant feature in the thermal structure was a cold subsurface tongue of

across the tongue of cold water and turned

the Oyashio.

to an eastward flow on the eastern side of

section consisted of convective circulation

the cold tongue.

with a speed of 0.7 knot.

Passing out of the cold

The current in the west-east In other parts of

water and across the second front, the

the Kuroshio where relative current vectors

eastward flow decreased markedly.

were determined, horizontal current differ-

From

these changes in flow it is concluded that

ences in the upper 240 m. were as high as

within the tongue there was upward motion in

1.4 knots.

Figure 9. Vertical temperature section through a cold tongue of the Oyashio (fig. 3). Horizontal arrows show the relative current speed between the surface and the indicated depths. The larger arrows show the general circulation as interpreted from the data.

77

ACKNOWLEDGMENTS

The authors are grateful to Owen S. Lee for helpful suggestions for preparation of the manuscript and to Mrs. Karen G. Carter for data processing and analysis.

LITERATURE CITED

LaFond, E. C. 1963. Detailed temperature structures of the sea off lower California. Limnol. Oceanogr. 8: 417-426. 1964. Three-dimensional measurements of sea temperature structure, ^n Studies on oceanography dedicated to Professor Hidaka in commemoration of his sixtiety birthday, Tokyo (Univ. Tokyo), pp. 314320.

78

1968.

Oceanographic data report for Cooperative Study of the Kuroshio and Adjacent Regions (CSK) No. 1. Naval Undersea Center, 22 pp. LaFond, Eugene C., and Katherine G. LaFond. 1967a. Internal temperature structures in the ocean. J. Hydronautics 1(1): 48-53. 1967b. Temperature structure in the upper 240 meters of the sea. J^n Marine Technology Society, The New Thrust Seaward; Transactions of the Third Annual MTS Conference & Exhibit, 5-7 June 1967, San Diego, Calif., pp. 23-45. Mode, E. B. 1951. Elements of statistics. 2d ed. Prentice-Hall, Inc., New York, pp. 246, 329. Smith, E. L. 1967. A predictive horizontal-temperaturegradient model of the upper 750 feet of the ocean. U.S. Navy Electron. Lab. Rep. 1445, 36 pp. Tukey, J. W. 1949. The sampling theory of power spectrum estimates. _In Woods Hole Oceanographic Institution, Symposium on Applications of Autocorrelation Analysis to Physical Problems, pp. 47-67.

Drift Bottle Experiments in the Eastern Yellow Sea, 1962-66 CHANG KI LEE Fisheries Resources Divisioni Fisheries Research and Development Agency3 Pusan

ABSTRACT

Surface currents in the eastern Yellow Sea were investigated by six drift bottle experiments during 1962-66. A total of 4,374 bottles was released and 488 (11.2 percent) were recovered. The results were: 1. The recovery rate was higher during the time of the northerly warm coastal current (summer) and lower during the southerly cold coastal current (winter). 2. The greatest number of recoveries was generally in the area between Chejudo and Junra-namdo regardless of month of release. 3. The period of northward flow of the warm current was from April to August. 4. The period of southward flow of the cold current was from September to March. 5. Easterly flow in the Chejudo-Junra-namdo area was observed through the whole season; in April-May it was composed of both the warm current that had passed to the west of Chejudo and the coastal southward current; during August-September it was the warm current; and during October-March it was composed of both the southward coastal cold current and the circulating current system of the Yellow Sea.

INTRODUCTION Nishida (1932) reported on drift bottle

PROCEDURE Bottles of 250 cc. capacity were

experiments and a few current measurements

ballasted with dry sand so as to float

made in the period from 1928 to 1931 in the

nearly awash; a loop of wire was attached

eastern Yellow Sea area by the Fisheries

to make it easy to pick up the bottle if

Experiment Station, Pusan, Korea. Uda

it was found at sea.

(1934, 1936) discussed the summer and

card with messages in Korean and in English

winter current patterns of the Yellow Sea

requesting recovery data was enclosed in

on the basis of synoptic observations.

each bottle.

This report deals with six drift bottle

releases, which were made in conjunction

experiments conducted south and east of

with lines of hydrographic stations.

Korea from 1962 through 1966.

A self-addressed post-

Figure 1 shows the pattern of

returns resulted from releases during winter, when cold southward flow prevails.

In

March 1966 the drift bottles drifted south with the cold current for about 3 weeks, and then were carried back toward the north when the flow reversed in response to the change in monsoon winds. Table 2 shows the relationship between releases (identified by number of hydrographic line, see fig. 1) and the coastal areas where bottles were found (identified by capital letter, see fig. 1).

Area C,

which includes the estuary of the Keum Kang River, showed the lowest rates of return, which suggests that river outflow kept bottles from landing on the nearby coastline.

Figure 1. Hydrographie lines on which bottles were released and areas of return (capital letters).

Similarly, runoff in the south-

ern part of area A could account for the relatively low rates of return from that area during all of the experiments subsequent to that conducted in April of 1962.

RETURNS

Releases from hydrographic station line No. 311, where upwelling normally is present

Table 1 presents the overall results of the drift bottle experiments.

from May through October, produced fewest

In general

the highest percentage of returns was ob-

returns, presumably because upwelling

tained from April through August, the period

carried the drift bottles offshore.

of warm northerly flow.

Table 1.

Lower percentage

Summary of results

Dates

Experiment

Number of stations

Number of bottles released

Number of bottles recovered

Recovery rate Percent

April 17-26, 1962 October 2-19, 1962 April 25-May 7, 1963 September 1-15, 1963 August 14-27, 1965 March 17-31, 1966 Total

80

1 2 3 4 5 6

27 25 43 43 26 20

1,089 1,013 860 858 354 200

251 34 84 55 35 29

23.1 3.4 9.8 6.4 9.9 14.5

184

4,374

488

11.2

Table 2.

Total number of returns from specified areas Area returned

Hydrographie line of release

jT apan

K A

B

C

D

E

F

G

Number returned

Number released

H Percent

(March 1966) 306 307 308 309 310 311 312 313 314 Total Percent

1

2 1

1 1 2

1

2 3 1 3

5 17.2

4 13.8

2 6.9

7 24.2

1 2 1 1 4 13.8

1 2 1 5 17.2

Recovery rate

5 1 4 4 1 5 6 3 0

30 20 30 30 30 20 30 10 0

16.7 5.0 13.3 13.3 3.3 25.0 20.0 30.0 0

2 6.9

29 100

200

14.5

228 80 198 80 209 50 224

37.3 27.5 7.1 0 22.0 12.0 32.4

1

1

(April 1962) 308 309 310 311 312 313 314 Total Percent

19 3 8

64 18 3

1 1

1

7

11 4 49

6 1 5

16 1 17

85 22 14 0 45 6 79

19 7.6

64 25.5

12 4.8

34 13.5

251 100

1,089

23.1

1

7 19 4 3 9 23 29

120 120 100 80 120 120 120

5.8 7.5 4.0 3.8 7.5 19.2 24.2

84 100

860

9.8

2 4 7 3 2 7 7 3

30 59 58 45 44 60 28 30

6.7 6.8 12.1 6.7 4.5 11.7 25.0 10.0

35 100

354

9.9

3

4

8

1 35 13.9

85 33.9

2 0.8

(April-May 1963) 308 309 310 311 312 313 314 Total Percent

5 3

3

2 2 2 1 15 17.9

1

3 3 3.6

4 4.8

2

1

1 5 12 16

2 3 6

36 42.9

12 14.3

1

3

3 6 10 11.9

1 1.2

3 3.6

(August 1965) 307 308 309 310 311 312 313 314 Total Percent

3 4 1

8 22.8

1 3 1 1 6 4 1 17 48.7

2 2 1 1 2

1

1

8 22.8

1 2.9

1 2.9

81

Table 2.

Total number of returns from specified areas—Continued

Hydrographie line of release

Area returned Korea A

B

C

D

Japan E

F

G

H

Number returned

Number released

Percent

(September 1963) 307 308 309 310 311 312 313 314 Total Percent

1 1 1 3

5

5 9.1

4 2

14 6 1

8 2

27 49.1

16 29.1

Recovery rate

80 120 120 100 80 118 120 120

6.3 6.7 0.8 3.0 1.3 14.4 13.3 3.3

1 1

1 2 1 1

5 8 1 3 1 17 16 4

2 3.6

5 9.1

55 100

858

6.4

13 5 0 10 0 6

229 200 79 206 50 249

5.9 2.5 0 4.9 0 2.4

34 100

1,013

3.4

(October 1962) 308 310 311 312 313 314 Total Percent

4

4 1

5 2

3

4

1 4 11.8

9 26.5

2 1

1

1 2.9

3 8.8

2

3 14 41.2

Figure 2. Approximate paths of drift bottles (spring). days at sea. Letters identify the release points.

82

1

3 8.8

Number in parentheses shows the number of

Figure 3. Approximate paths of drift bottles (fall). at sea. Letters identify the release points.

DIRECTION OF SURFACE CURRENT

Number in parentheses shows the number of days

Considering in addition the usual speeds of southward drift (table 3), one can conclude

Figures 2 and 3 show the approximate

that the bottles must have been transported

paths of the bottles which were recovered

toward the south for about 20 days before

during these experiments.

turning north.

Bottles which

These results agree with the

took an unusually long time to reach their

conclusions reached by Nishida (1932) and

destination were not included.

Uda (1934).

Bottles

which were recovered on the coast of Japan were also not shown.

The lower case letters

identify release points, and numbers in parentheses give the days at sea.

Period of release

It is

assumed that motion was due to currents only, since the bottles were ballasted to minimize windage.

Table 3 . — D r i f t speed of fastest-moving bottles

The results are discussed by

season, regardless of year.

April 1962 April-May 1963 August 1965 September 1963 October 1962 March 1966

South

North

Knot

Knot

0.17 0.14

0.1 0.13 0.4

0.16 0.22 0.4

March 1966 The southward flow present early in the month reversed as the Yellow Sea branch of

April 1962 The general drift toward the south, at

the Kuroshio began its period of northward

the beginning of the experiment, reversed

flow.

offshore as warm water began to flow north.

The time required for bottles

released west of long. 125° E. to arrive at

The southerly drift along the coast nar-

the coast exceeded the usual time required

rowed as a result.

for northward drift by a month or more.

north drifted toward the south then turned

Bottles released in the

83

toward the coast and most were carried northward thereafter.

Bottles released in

October 1962 Flow toward the south, with an off-

the south were carried toward the east with

shore component (presumably due to offshore

the Tsushima Current, except for those

Ekman transport) was present everywhere

released farthest offshore, which entered

except in the southernmost line of stations,

the warm current and were carried north.

where easterly flow prevailed.

Thus April 1962 represented a period of development of the warm current. April-May 1963

SPEED OF SURFACE CURRENT The results for the fastest-moving

Most bottles were carried north, landing in area A, with only one bottle moving south in the coastal flow.

Thus during

drift bottles are shown in table 3. During periods of northward flow, April to August, the speed increased from

this period the warm current was fully de-

low values in April to a maximum of 0.4

veloped and the eastern drift in area D,

knot in August.

along Korea's south coast, had weakened.

of southward flow, September to March, the

Similarly, during periods

highest speeds, 0.4 knot, were encountered August 1965

toward the end of the period.

Bottles released offshore in the north apparently entered the Yellow Sea gyre,

LITERATURE CITED

landing on the coast of Korea after 3 to 4 months at sea.

Flow farther south was

toward the northeast.

The southerly coastal

flow seemed to be entirely absent. September 1963 Southward flow had replaced the summer warm current at the northern lines of stations, but releases made in the south continued to drift north and east with the warm current.

84

Nishida, K. 1932. Results of the drift bottle experiments in adjacent sea of Korea. Annu. Rep. Hydrogr. Observ. 7, Fish. Exp. Sta. Pusan, Korea. Uda, M. 1934. The results of simultaneous oceanographical investigations in the Japan Sea and its adjacent waters in May and June, 1932. J. Imp. Fish. Exp. Sta. 5: 186-235. 1936. Results of simultaneous oceanographical investigations in the Japan Sea and its adjacent waters during October and November, 1933. J. Imp. Fish. Exp. Sta. 7: 150-179.

Influence of the Komandorskie Ridge on S u r f a c e and Deep Circulation in the Western North Pacific Ocean W. B. McALISTER, F. FAVORITE, and W. J. INGRAHAM, Jr. Bureau, of Commercial

ABSTRACT

Fisheries

Biological

Laboratory,

Seattle

Data are presented from a series of hydrographie stations taken by the R/V George JB. Kelez in February and March 1966. Observations from 18 of the 34 stations extended below 4,000 m. Stations were taken during eight crossings of the Komandorskie Ridge (northern extent of Emperor Seamount Chain) between lat. 45° and 53° N. The data were compared with those of previous deep stations in this region and with a model of the general circulation in the North Pacific Ocean. The Komandorskie Ridge extends southward from the Komandorskie Islands; it lies almost normal to the North Pacific currents: the westward flow of the Alaskan Stream, and the eastward flow which results from the confluence of the Kuroshio and Oyashio. The Komandorskie Ridge marks the westernmost extent of the Alaskan Stream as a well-defined feature, the Alaskan Stream being deflected mainly to the north at the ridge. The Kuroshio-Oyashio flow shows little disturbance, but the presence of the ridge appears to inhibit any deep circulation in this region. Previous summer observations in this region showed similar flow; the observed distributions and transports are consistent with a generalized model circulation in the North Pacific Ocean.

INTRODUCTION

Near long. 165° E., the eastward flowing Kuroshio and Oyashio cross the Emperor

The circulation in the North Pacific

Seamount Chain.

At its northern extent

Ocean north of lat. 30° N. consists of a

the Seamount Chain becomes an extensive

general eastward flow.

undersea ridge rather than separated sea-

The flow is not uni-

form and can be divided into several dis-

mounts.

We have called this part of the

tinct currents and water masses which have

Emperor Seamount Chain the Komandorskie

their origin in the Kuroshio and Oyashio.

Ridge because it is located almost south of

The only well-defined return current in the

the Komandorskie Islands.

North Pacific is the Alaskan Stream, a rel-

almost normal to the eastward flow of the

atively narrow band of westward flowing

Kuroshio and the Oyashio and to the west-

water south of the Aleutian Islands.

ward flow of the Alaskan Stream.

The ridge is

The

Kuroshio-Oyashio flow at the surface shows

Favorite (1967), Kitano (1965, 1967),

relatively little disturbance by the sub-

and Ohtani (1965) have described summer

marine ridge, but its presence appears to

hydrographic conditions and the ocean cir-

restrict the deep circulation.

culation in the North Pacific Ocean near

The ridge

marks the westernmost extent of the Alaskan

the terminus of the Alaskan Stream and the

Stream as a well-defined oceanographic

Komandorskie Ridge.

feature.

and Hirano (1963) included this area in a

Oceanographic observations have been

Dodimead, Favorite,

review of the general oceanography of the

made in the subarctic region for several

North Pacific Ocean.

centuries, and general charts of surface

sidered the problem of the formation of

currents and surface temperatures are avail-

and relations between water masses through-

able.

out the Pacific Ocean.

Yet, our knowledge of specific

oceanographic features has been fragmentary until the last decade.

In 1955, the inter-

Reid (1965) has con-

Bathymetric charts show that peaks along the Komandorskie Ridge rise to within

national cooperative study of the North

1,000 m. of the surface; that the effective

Pacific (Norpac)

depth of the ridge is between 2,000 and

provided the first knowl-

edge of large scale continuity of flow and

3,000 m.; and that there are two deep,

distribution of properties during northern

narrow passes at 5,000 m. and several other

summers.

shallower passes.

Cooperative oceanographic studies

The ridge is not contin-

by members of the International North

uous on the north but is separated from the

Pacific Fisheries Commission, which began

Aleutian Island Arc and the Kuril Islands

in 1954 and are still in progress, have

by the Kamchatka and Aleutian Trenches.

added greatly to our knowledge of condi-

Figure 1 is a schematic representation

tions and processes in the subarctic

of the current systems and the dynamic

region.

topography as calculated from observations

Studies undertaken as part of the

Cooperative Study of the Kuroshio will con-

made during February and March 1966.

tribute further to our understanding of

positions of the Alaskan Stream and the

the subarctic Pacific Ocean.

Subarctic Current and West Wind Drift are

The first extensive winter observa-

The

also shown on the figure.

tions in this area of the Pacific Ocean were made in the winter of 1966 by the R/V

SURFACE A N D DEEP CIRCULATION

George 1$. Kelez of the Bureau of Commercial Fisheries and the R/V Argo of the Scripps Institution of Oceanography.

Additional

Surface Currents Taguchi (1959) released drift floats

investigations in the central and western

to provide direct measurement of surface

Aleutian region were conducted in the

currents and standard oceanographic data.

winter of 1968, also by the R/V George B.

He attached hooks to the floats, which were

Kelez.

recovered in gill nets (mostly during May

86

and June 1959) by the Japanese fishing fleet.

Attu Island.

A comparison of his release and recovery

kan Stream continued westward to about long.

points suggested that westward surface flow

165° E. in 1964, with little deflection to

in this area stopped near long. 165° E.,

north or south but with irregularities in

and that surface flow near Attu Island was

the width and strength of the flow.

northward into the Bering Sea.

flow through the Aleutian passes between

Ohtani

Kitano (1967) found the Alas-

The

(1965) examined some of the extensive data

Adak and the Komandorskie Island was pre-

collected by Japanese fishery research

dominantly to the north; east of the Koman-

vessels between 1957 and 1963 and concluded

dorskie Ridge, Kitano also observed a north-

that the Alaskan Stream normally extends

ward intrusion of modified subtropical water.

westward to about long. 170° E., where it branches in three directions:

northward

into the Bering Sea, southward to join the

Deep Flow Geostrophic current calculations pro-

Subarctic Current, and westward across the

vide a reasonable estimate of surface and

Komandorskie Ridge and toward Kamchatka.

near-surface currents.

Favorite (1967), who examined hydrographic

Pacific Ocean, velocity typically decreases

data obtained by research vessels of the

with depth just below the surface mixed

Bureau of Commercial Fisheries, also con-

layer; the direction of the subsurface flow

cluded that the Alaskan Stream ends between

to 2,000 m. is generally, if not always, the

long. 165° and 170° E. where it separates

same as at the surface.

into southerly and northerly flows, the

particularly below 3,000 m., velocities are

latter flowing into the Bering Sea near

much less than at the surface, but the flow

60®N.

I40°E.

I 50° E.

160° E.

I 70° E.

180°

In the northern

Below 2,000 m., and

170°W

50* N.

,c CUPBENT

40*N.

40*N. Figure 1.

Schematic surface circulation for the Subarctic Pacific region during winter.

87

may be in different directions.

In the ab-

follows a clockwise trajectory in the North

sence of a reference surface of known veloc-

Pacific Ocean.

ity, dynamic heights provide estimates of

wells into intermediate depths in the north-

relative currents only.

ern North Pacific Ocean.

Few direct observa-

The deep, bottom water upWe reviewed the

tions of deep currents are available for the

available deep station data for an indica-

northwestern Pacific Ocean, and absolute

tion of the effect of submarine topography

currents cannot be inferred from the dynamic

on deep flow in the Northwest Pacific.

topography alone.

Figure 2 shows temperatures and data points

A knowledge of absolute

water movement at depth must still be in-

at 4,000 m.

ferred from isentropic analysis and the dis-^

of potential temperature at lat. 48° N.

tribution of water properties.

These charts include present data and prior

The deep circulation and distribution

Figure 3 is a vertical section

available deep station data from 1935 to

of properties in the Pacific Ocean at 5,000

1965.

m. were summarized by Wooster and .Volkmann

3,000 m.) are slightly lower in water east

(1960) and by Knauss (1962), who primarily

of the Komandorskie Ridge, a fact which is

used the distribution of temperature and

consistent with stronger deep flow to the

oxygen.

north on the east of the ridge than on the

They reported a general abyssal

Temperatures in the deep water (below

circulation which enters the Pacific in the

west of the ridge.

Although the data were

Antarctic Circumpolar region, flows north-

limited, they were consistent and provided

ward on the west side of the Pacific, and

a reasonable hypothesis on deep circulation.

Figure 2. Composite of historical temperatures (° C.) at 4,000 m. Dots indicate locations of available data taken between 1935 and 1966. 88

DATA OBSERVATIONS, WINTER 1966

cal Laboratory, Seattle conducted observations in the western North Pacific Ocean.

Station Plan Between January 29 and March 29, 1966,

A total of 251 stations was taken, of which 30 were deep stations that extended to or

the R/V Argo of the Scripps Institution of

near the bottom—5 of 194 stations from the

Oceanography and the R/V George B_. Kelez of

Argo and 25 of 57 stations from the Kelez.

the Bureau of Commercial Fisheries Biologi-

Cruise tracks and station positions are shown in figure 4.

Hydrographie observa-

tions by the Kelez were Nansen bottle casts; those by the Argo included STD and Nansen bottle casts.

At the Kelez deep stations,

additional samples were taken with a large Bodman bottle, for trace metal analysis. Both vessels took standard zooplankton tows and measurements of primary productivity and phytoplankton. Distribution of Properties The dynamic topography is shown relaFigure 3. Vertical section of historical potential temperature (° C.) along lat. 48° N.

tive to a 1,500 in figure 5.

decibar reference surface

Although transport may be sig-

Figure 4. Location of oceanographic stations, R/V Argo and R/V George B.. Kelez. January 29 to March 29, 1966. 89

nificant below 1,500 decibars, geostrophic

station spacing, these currents may have

velocities at 1,500 decibars are much less

been more concentrated than shown.

than the surface velocities, and the dynamic

across the Komandorskie Ridge was irregular.

topography provides a good representation of

This irregularity does not appear to be a

surface flow.

simple type of deflection due to topography;

Bennett (1959), for example,

Flow

increased transport by a factor of 2.3 when

it is complex and suggests that flow across

he changed from a 1,000 to a 2,000 decibar

the ridge produces large eddies in the

reference surface; his surface velocities

surface circulation.

increased by about 50 percent.

The Alaskan

The circulation inferred from the

Stream flowed west, immediately south of the

dynamic topography was compared with the

Aleutian Islands, and terminated at the

surface salinity (fig. 6) and surface tem-

Komandorskie Ridge in 1966.

perature (fig. 7).

The East Kam-

The Subarctic-Subtropic

chatka Current was a narrow band that flowed

boundary (oceanic polar front) was near lat.

south along Kamchatka.

40° N. at the 34.0°/oo surface isohaline.

The northern edge of

the Kuroshio appeared off the coast of

The dilute surface water south of the Aleu-

northern Japan.

tian Islands, which extended west to the

These flows combined to

form the Western Subarctic Gyre.

Throughout

Komandorskie Ridge and north into the Bering

the rest of the western North Pacific Ocean,

Sea, characterized the Alaskan Stream

a general eastward flow was made up of the

highest surface salinities in the Subarctic

Subarctic Current and the extension of the

region were in the central Aleutian Islands

Kuroshio (West Wind Drift).

in an area of extensive vertical mixing,

Because of

60»N.

O 1500

/sec.)

50»N.

Figure 5. Geopotential topography (AD) °/l,500 db, winter 1966. 90

' 200* ¿^^sool 0^-4000!

The

generated by strong tidal motion and turbulence in the Aleutian passes.

The low salin-

an extension of Alaskan Stream water. The strong temperature gradient near

ity water (

K u s h i m o t o , if c h a n g e s o c c u r o n l y at one side of the K u r o s h i o . 135

T h e v a l u e of 7.6 cm. or 7.6 d y n a m i c

10

20

25

30

cm. i n c l u d e s a c o r r e c t i o n a p p l i e d to G E K observations, which underestimates

KUSHIMOTO (Ç cm.)

Figure 5. Average values of northerly component of velocity; total surface transport (V^L); and dynamic height anomalies at stations a' and b.

veloc-

ity b y 5 p e r c e n t as s t a t e d in N i t a n i Shojl

and

(1966).

ANOMALOUS CURRENT VECTOR kt.

OCTOBER 9-12,1965 0.4

OCTOBER 12-14,1965

OCTOBER 16-18, 1965

0.2

0 -0.2

-0.4

-0.4

-0.2

0.2

0.4 kt. - 0 . 4

-0.2

0.2

0.4

-0.4

-0.2

0.2

0.4

Figure 6. Hodographs of velocity residuals, obtained by subtracting long-term trends from the northerly and easterly components of surface currents.

Ill

1

1

1——1—I

1

1

SEA LEVEL AT KUSHIMOTO ( ? )

DYNAMIC HEIGHT ANOMALY AT STATION b(ADb)

ADb- Ç

(A)

(B)

(C)

> /C LATTER HALF / 8.8 dyn.cm./IOM.K.^'

LATTER HALF 'x " 6 2c m /IOM K-LATTER HALF ^ • 6.0 dyn. cm./IOM.K>V/

/

FIRST HALF 5.6 dyn. cm./IOM.K.

30

220

7

230

- ~ FIRST HALF 9.2dyn.cm./IOM.K. 240

_L

210

220

230

ADb~ï(dyn. cm.)

Ob (dyn. cm.)

Figure 7. Relationships between surface transport and: (A) sea level at Kushimoto; (B) dynamic height anomaly at station b; (C) the difference between these two values. Solid d o t s — d a t a from October 9-11. Open circles—data from October 12-14. X ' s — d a t a from October 16-18.

According to figure 7, sea level at

of the Kuroshio becomes larger (smaller),

Kushimoto, Q, changes with the surface

the sea surface falls (rises) at the coast

transport at rates of -5.0 cm./10 mile-

and rises (falls) at the outside of the

knot and -6.0 cm./lO mile-knot in the

Kuroshio like a seesaw.

first and second periods, respectively; dynamic height anomaly at station b, AD, , b changes at rates of 5.3 dynamic cm./10 mile-knot and 10.0 dynamic cm./lO mile-

Relation Between Sea Level and Surface Transport for Long-and Short-Period Variation As can be seen in figures 4 and 5,

knot in the first and second halves; and

semidiurnal and long-period variations are

the difference between dynamic height

present in the changes of surface trans-

anomaly at station b and sea level at

port and sea level.

Kushimoto, AD^-C, changes at rates of 9.5

examine separately the geostrophic rela-

cm./lO mile-knot and 8.8 cm./lO mile-knot

tions for the short-and long-period

(in the first and second halves), respec-

components to understand the mechanisms

tively.

of these variations.

The observed gradient of the sea

It is necessary to

Figure 8 shows the

surface is therefore larger than the value

relation between the surface transport

calculated on the assumption of geostrophic

averaged over time intervals of about 1

balance by about 20 percent.

day and the average sea level at Kushimoto;

Apparently

the geostrophic relation is satisfied,

average dynamic height anomaly at station

approximately.

b; and the difference in sea level across

112

When the surface transport

-U-I-, AVERAGE S E A L E V E L AT KUSHIMOTO ( t A )

1

1

1 ÛObA-ÏA

AVERAGE DYNAMIC HEIGHT ANOMALY AT STATION b ( A D b A )

(A)

(B)

(C)

LATTER HALF 13.6 dyn.cm./IOM.K.

LATTER HALF -11.0 cm./IOM.K.

LATTER HALF 18.0 dyn. cm./IOM.K.

4r.

FIRST HALF 10.0 dyn. cm./IOMK.

FIRST HALF -6.7 cm./IOMK.

10

—I—i^—I—

20

30

230

220

FIRST HALF 15.0 dyn. cm./IOM.K.

200

240

A D j , a (dyn. cm.)

Ç A (cm.)

210

220

ADbA-ÇA(dyn.cm.)

Figure 8. Relationships between surface transport averaged over 1-day intervals and: (A) average sea level at Kushimoto; (B) average dynamic height anomaly at station b; (C) the differences between these two variables. Solid d o t s — d a t a from October 9-11. Open circles—data from October 12-14. X ' s — d a t a from October 16-18.

the K u r o s h i o , r e s p e c t i v e l y . therefore, concerned with

F i g u r e 8 is,

long-period

a b o u t o n e - t h i r d to o n e - h a l f that e x p e c t e d f r o m the g e o s t r o p h i c

(several days) c h a n g e s of sea level and surface

F o r the r e s i d u a l c h a n g e , w h i c h is

transport.

mainly semidiurnal,

the a b o v e - m e n t i o n e d

r a t i o s are 4.5 c m . / l O m i l e - k n o t a t K u s h i -

T h e c h a n g e s in s e a level b e t w e e n K u s h i m o t o a n d s t a t i o n b are larger

balance.

m o t o in the f i r s t h a l f , and 1.7 d y n a m i c

than

e x p e c t e d f r o m the g e o s t r o p h i c b a l a n c e .

c m . / 1 0 m i l e - k n o t to 0.0 cm./10

T h e changes in e l e v a t i o n of the sea sur-

c m . / 1 0 m i l e - k n o t at s t a t i o n b i n the

face on e i t h e r side of the K u r o s h i o a r e

a n d second h a l v e s

e n o u g h to b a l a n c e the o b s e r v e d c h a n g e s velocity.

in

The ratio of d i f f e r e n c e s in sea

(fig. 9).

dynamic first

The ratio

c o r r e s p o n d i n g to the d i f f e r e n c e in sea level across the K u r o s h i o is 4.2

cm./lO

level across the K u r o s h i o to the s u r f a c e

mile-knot.

t r a n s p o r t b e c o m e s 15 c m . / 1 0 m i l e - k n o t

in slope c o r r e s p o n d i n g to s e m i d i u r n a l

and

T h e c o n t r i b u t i o n to c h a n g e s

18 c m . / 1 0 m i l e - k n o t in the first and

c h a n g e s in v e l o c i t y is larger on the

second periods, respectively.

s i d e than o n the r i g h t side of the K u r o -

This m e a n s

that the s e a s u r f a c e s l o p e a s s o c i a t e d w i t h

shio.

l o n g - p e r i o d changes is a b o u t two times

c i a t e d w i t h c h a n g e s i n s l o p e across

larger than expected f r o m the

face t r a n s p o r t are smaller than those

balance.

geostrophic

In other w o r d s , the v e l o c i t y

associated with long-period changes

is

T h e c h a n g e s in the K u r o s h i o

left

expected from geostrophic balance.

assosur-

In

other w o r d s , the v e l o c i t y a s s o c i a t e d w i t h

113

40

g

(A)

A D b o " ?o

(C)

LATTER HALF 0.0 dyn.cm./IOM.K.

U

wm Ss >

^

1 1 1 1 1 1

DEVIATED SEA L E V E L AT 30 KUSHIMOTO ( Ï D )

ce

0— -10 - 2 0 -

-30

L

FIRST HALF - 4 . 5 cm./IO M.K.

J_ I - 6 - 4 -2 ç0

I 0

I 2

I 4

FIRST AND LATTER HALF 4.2 dyn. cm./IOM.K.

FIRST HALF 1.7 dyn.cm./IOM.K.

L 6

J

-2

(cm.)

L

0 2

J

I

L

-2 0 2

,

AD bo (dyn. cm.)

I I I I I

- 4 -2

0

2

4

ADbo~ Sotdy"-cm-)

Figure 9. Relationships between residuals of surface transport and: (A) residuals of sea level at Kushimoto; (B) residuals of dynamic height anomaly at station b; (C) differences between these two sets of residuals. Solid dots—data from October 9-11. Open circles— data from October 12-14. X's—data from October 16-18.

semidiurnal changes i s larger than that expected from the geostrophic balance. In the present set of observations,

y =

the v a r i a t i o n of v e l o c i t y appears to be

p ys J

nearly geostrophic ( f i g . 7 ) , but i t may not be.

1» ys ! uydy yi

yl

udy

More detailed observations are where u i s the v e l o c i t y of the current, y

needed to resolve this question.

is the distance perpendicular

(although

Relationship Between Surface Transport and

this is not e s s e n t i a l ) to the current and

the Location of the Center of the Kuroshio

yi and ys are the coordinates of both

The current axis or the north and

boundaries.

This d e f i n i t i o n i s analogous

south boundaries of the Kuroshio w i l l s h i f t

to that of a center of g r a v i t y ; i t makes

north or south.

possible precise studies of movements of

The term "main axis of the

Kuroshio" i s commonly used.

I t means the

place where the v e l o c i t y reaches a maximum.

the Kuroshio. Figure 10 shows the northern boundary

Detailed v e l o c i t y sections across the Kuro-

of the Kuroshio where i t s v e l o c i t i e s

shio show that the actual v e l o c i t y

0.5 and 1.0 knot, the center of the Kuro-

distri-

are

bution i s very complicated with respect to

shio, and surface transport.

space and time, so i t is d i f f i c u l t to

movement of the northern boundary i s 13

determine the main axis p r e c i s e l y .

miles at most, while the mean range of

The

The range of

authors propose a new term, "the center of

movement associated with semidiurnal

the Kuroshio," defined as:

changes i s 4 miles.

114

The movements of the

Figure 10. Positions of the northern boundary of the Kuroshio, as defined by 0.5 knot and 1.0 knot velocities, the position of the center of the Kuroshio, and the surface transport.

Table 1.

The relation between the velocity and center of the Kuroshio

Period of change Long (several days) period change

Short (semidiurnal) period change

Time

Type

1964

First half Second half

E E

1965

First half Second half

(E) E

1964

First half Second half

E E,W

1965

First half Second half

W W

Remarks

Diurnal Diurnal and semidiurnal Semidiurnal Semidiurnal

center of the Kuroshio parallel those of

increases in surface transport (or mean

the northern boundary, but they are only

velocity) of the Kuroshio; the opposite

about half as large.

response is defined as type W.

The relation between the position of the center of the Kuroshio and the sur-

DISCUSSION

face transport (or mean velocity) is shown in table 1, which includes the 1964 results.

A progressive wave having the charac-

Type E refers to southward motion of the

ter of a Kelvin wave, for which changes of

center of the Kuroshio which coincides with

velocity and sea level are larger on the

115

right-hand side than on the left-hand side,

1/2tt of the magnitude of the second term for

would account for the occurrence of types

diurnal change, and 1/tt for the semidiurnal

E and W.

change.

When this wave progresses

towards

In these cases the time-dependent

the east, the change becomes type E and

term is not negligible, and one cannot ex-

w h e n it progresses towards the w e s t the

pect a complete geostrophic balance, espe-

change becomes type W.

cially for the semidiurnal variation.

But the existence

of such a wave is questionable owing to the semiopen character of the sea in this region.

ACKNOWLEDGMENTS

To examine this hypothesis it

will be necessary to look for progressive waves within the Kuroshio and to determine their direction of motion. The equation of motion for the variations, neglecting the inertia and friction

The authors are grateful to members of the scientific party, officers and crew aboard the Takuyo, M e i y o . and Kaiyo. Hydrographie O f f i c e of Japan, for their cooperation. They are indebted to M r . S. K u r a s h i n a and m a n y other members of Oceanographic Section, Hydrographie Office of Japan for assistance in the preparation of this manuscript.

terms, becomes 3Av , S T

+

8A? f A u

= "g

97"

'

LITERATURE CITED

where Au and Av are the variations of velocity parallel to and across the current, respectively.

If Au = Av, as figure 6 sug-

gests, the magnitude of the first term is

116

Shoji, D., and H . Nitani. 1966. O n the variability of the velocity of the Kuroshio - I. J. Oceanogr. Soc. Jap. 22(5): 192-196.

Some Results of the CSK Investigations Carried Out by the Research Vessels of the U.S.S.R. Hydrographie Service A. A. ROGOTSKY Hydrographie Service} Vladivostok

ABSTRACT

Investigations of the Kuroshio by the Hydrographie Service of the Soviet Navy were begun by the R/V Ulyana Gromova in the summer of 1965. Twenty-eight complete (to the bottom) hydrologie stations and 34 suspended (to lesser depths) hydrologie stations were taken. In summer and in winter, 1966, the oceanographic research vessel Nevelskov continued the investigations. Forty-two complete hydrologic stations and 79 suspended hydrologie stations were taken. In 1967 the investigations were carried out by the Ulyana Gromova at the beginning of the year and by the Nevelskoy at the end of the year. In 3 years of investigations, 245 hydrologie stations were taken in the area of the Kuroshio by the research vessels of the Soviet Navy. As a result of these investigations, information was obtained on the characteristics of the areal structure of subpolar front, the main stream of the Kuroshio, and the temporal changeability of the main hydrologie elements. However, the problem of the establishment of the regularities of the areal-temporal changeability of vertical and horizontal structure of the Kuroshio and the influence of frontal processes on the formation and changeability of the vertical and horizontal structure of the Kuroshio are still not worked out. Thus it is necessary to continue the investigations in the area from lat. 20° N. to the Equator, between long. 130° and 155° E. and in the area of the southern Kuril Islands between lat. 34° and 46° N.

The program of oceanographic investi-

In accordance with the plan adopted

gations by the research vessels of the

by the First Meeting of the International

Hydrographie Service of the Soviet Navy in

Coordinating Group for CSK, the research

the area of the Kuroshio is part of the

vessel Ulyana Gromova began investigations

Coordinated International Program of the

in the area of the Kuroshio in the first

CSK (Cooperative Study of the Kuroshio)

half of July 1965.

affirmed by the Fifth Meeting of the Intergovernmental Oceanographic Commission in June 1964.

Stations in the sections were spaced as follows: a)

In the area of the subpolar front

(section No. 3) b e t w e e n lat. 43° and 35° N.,

up now.

20 miles apart.

carried out by the research vessels of the

b)

In sections across the Kuroshio,

Hydrographic Service of the Soviet

Navy,

245 hydrologic stations were taken in the

30 miles apart. c)

For 3 years of investigations

In southern parts (sections Nos.

10 and 11), 60 miles apart.

Kuroshio area. Some results of these

During the cruise, 28 out of a total

investigations,

in the form of diagrams and charts

showing

of 62 hydrologic stations extended to the

temporal motion and vertical distributions

bottom.

of hydrologic elements, were submitted for

At all hydrologic stations,

hydrochem-

ical analyses of sea water were made in order to determine salinity, dissolved oxygen, and pH.

discussion by the delegates of the Eleventh Pacific Science Congress in Tokyo. As a result of the 3-year cycle of investigations in the Kuroshio area, satis-

In 1966 the oceanographic research

factory information on the characteristics

vessel Nevelskoy continued the investiga-

of the areal structure of the subpolar

tions of the Kuroshio.

front, the flow of the Kuroshio, and infor-

In winter (January-April) this vessel

mation about temporal changeability of the

took 62 hydrologic stations; 22 of them

m a i n hydrologic elements were accumulated.

reached the b o t t o m and 40 reached 1,500 m.

The results of the subpolar front investi-

Hydrochemical analyses of sea water were

gations showed considerable fluctuations of

made in order to determine salinity and dis-

water temperature in the surface strata in

solved oxygen.

summer and significant differences in water

In summer

(July-September)

the research oceanographic vessel Nevelskoy

temperature in different years of investi-

took 59 hydrologic stations in the same

gations .

sections, 20 of them to the bottom and 39 suspended.

Thus, for example, the temperature of water at the surface in July 1965

In 1967 the research vessels Ulyana

was 2°

to 6° lower than the mean of several years

Gromova and Nevelskoy took part in the

for this area, and in July 1966, it was 7°

investigations of the Kuroshio area.

to 8° lower.

In 1967 the research vessel Ulyana

In this area small horizontal gradients

Gromova took 62 hydrologic stations in

of temperature (0.5° to 0.7° per mile) in

February; 22 of them extended to the bottom;

the stratum from 0 to 250 m. were observed,

40 w e r e

w i t h maximum values in July 1965.

suspended.

Simultaneous w i t h the hydrologic investigations, meteorological investigations were made o n each of the cruises.

In July

1966, the gradients did not exceed 0.2° to 0.3° per mile.

A 3-year cycle

The character of temperature distribu-

of investigations in accordance w i t h the CSK

tion w i t h depth in the area of the subpolar

program was completed at the end of 1967.

front is changeable and is principally

Accumulated materials are b e i n g worked 118

determinated by the stratification of water.

Synchronous surveys carried out in the

The materials accumulated from the 3-

area of the subpolar front and in the Kuro-

year study of the Kuroshio provide quite

shio area

satisfactory information on characteristics

made it possible to prepare

charts of dynamic anomaly for each of the

of the areal structure of the subpolar

seasons of the year

front and the Kuroshio area.

and to single out the

They were

taken as a basis for study of temporal

main stream of the Kuroshio. Information about the Kuroshio based

changeability but, in our opinion, they

on the dynamic charts is being coordinated

did not resolve the main problem, that of

with the information about surface currents

determining regularities in the areal-

in hydrologie atlases.

temporal changeability of the vertical and

However, the investigations of 3 years

horizontal structure of the Kuroshio stream,

confirm the opinion that the main stream of

and the influence of frontal processes on

the Kuroshio undergoes considerable dis-

the formation and changeability of the

placements under the influence of seasonal

vertical and horizontal structure of the

wind conditions; the actual direction and

Kuroshio and its adjacent areas.

speed of the current may be very different

The complexity of the Kuroshio structure and its effect on frontal processes

from the currents given in atlases. The seasonal and annual variations of

demonstrates the necessity of going on with

the main stream of the Kuroshio are also

the investigations of the Kuroshio, in

confirmed.

order to establish the regularities between

For example, in winter the

Kuroshio weakens slightly and moves away

the areal-temporal changeability of the

from the coast of Japan.

horizontal and vertical structure of the

The opinion of Japanese scientists, that the limit of the Kuroshio is the 10° C.

Kuroshio and the frontal processes. In our opinion, it will be desirable

isotherm,is the most acceptable criterion

to continue investigations of the Kuroshio

for the determination of areal limits of

in 1969-70 in the area between lat. 20° N.

the main Kuroshio stream.

and the Equator, between long. 130° and

Though the research vessels of the Hydrographie Service of the Soviet

Navy

155° E., and in the area of the southern Kuril Islands between lat. 34° and 46° N.

did not carry out special biological obser-

These areas are adjacent to the research

vations, analyses of the results of tempera-

areas of 1965-68.

ture measurements and the oxygen content,in

The necessity for these investigations

conjunction with the information obtained

arises from the fact that prior cooperative

by the Japanese vessels in the area of sub-

efforts examined those areas in which the

polar front, make it possible to single out

strata of the warm current had been period-

the most probable areas of food-fish gather-

ically observed.

ing, and to establish some connections be-

enlarge the area of investigations to adja-

tween the variations of the main hydrologie

cent areas in order to reveal and study the

characteristics and migration of fish shoals.

conditions of formation of this current,

Now it is necessary to

119

w h i c h is very important for economics and

achieve standardization in methods of

science.

measurement and mutual calibration of

In addition, it is very important to explore the possible relation of the inten-

instruments. It is necessary to generalize the

sity of the Kuroshio to the conditions of

results of the investigations of the instru-

development and passage of the deep tropi-

ments and the methods of measurements,

cal cyclones, or typhoons.

seen by the CSK program and to inform the

It is very important for further investigations in the Kuroshio area to

120

fore-

countries participating in the CSK of the results.

Continuous Measurement of Subsurface Temperature by Submarine Cable: A Preliminary Report DAITARO SHOJI and KINJI IWASA Hydrographie Office

ABSTRACT

of Japan, Tokyo

It is now well known that the Kuroshio changes its position and strength very rapidly in the area south of Honshu. To monitor this rapid variation of the Kuroshio, the Hydrographic Office of Japan installed tide gages on the islands of Hachijo, Miyake, and Kozu. To supplement these sea level observations and to understand what is happening in the sea, submarine cables with thermistors were recently laid to measure the subsurface temperatures at Miyake and Hachijo and also at Shionomisaki, Honshu Island. The paper presents temperature records from Shionomisaki. It is expected that these continuous records will be very useful for the understanding of the Kuroshio.

INTRODUCTION

graphic stations should be employed in conjunction with observations by ships.

It is now well known that the Kuroshio

For this purpose, coastal surface

changes its position and strength very

temperature observations and mean sea level

rapidly in the area south of Japan (e.g.,

observations have been used by many ocean-

Yosida, 1961; Shoji and Nitani, 1966).

ographers.

Up to the present, observations by ships

enced strongly by meteorological factors

have been carried out no more than once or

and the interpretations are sometimes very

twice a month, except for the multiship

difficult.

surveys specially planned for more frequent

on the other hand, especially at the off-

observations.

shore islands, gives very useful informa-

However, the periods of the

Coastal temperature is influ-

The variation of mean sea level,

special surveys are usually quite limited.

tion on the variations in the Kuroshio.

It cannot be expected that the most inter-

There are several islands off the coast

esting phenomenon would always occur dur-

of Japan which are situated in the path

ing the brief periods of such special sur-

of the Kuroshio.

veys.

tide stations on these islands (fig. 1).

In order to monitor the variation

of the Kuroshio continuously, fixed oceano-

We have set up several

It is known that the mean sea level corre-

sponds c l o s e l y to the d y n a m i c h e i g h t of

is p r o p o r t i o n a l to its length, so that it

the n e i g h b o r i n g s e a (Shoji, 1954; Y o s i d a ,

is n o t n o w p r a c t i c a l to lay a v e r y

1961).

cable for s c i e n t i f i c

B e c a u s e the d y n a m i c h e i g h t of the

s e a surface is p r o p o r t i o n a l to the

long

purposes.

integral

of s p e c i f i c a n o m a l y of sea w a t e r , w h i c h is

LOCATION AND INSTRUMENTATION

a function of t e m p e r a t u r e and s a l i n i t y , the c o m p a r i s o n of s u b s u r f a c e

temperature

F i g u r e 1 shows the s o u t h coast of

and m e a n sea level is expected to g i v e

J a p a n a n d the K u r o s h i o .

m u c h i n f o r m a t i o n a b o u t the v a r i a t i o n in

cables w e r e laid at M i y a k e j i m a ,

oceanographic conditions.

jima, and S h i o n o m i s a k i .

It is k n o w n

The

The

submarine Hachijo-

submarine

that for the s e a s o u t h of J a p a n , the tem-

cable at S h i o n o m i s a k i w a s laid i n M a r c h

p e r a t u r e a t a d e p t h of a few h u n d r e d m e t e r s

1968.

is m o s t u s e f u l i n t h e c a l c u l a t i o n of dy-

Shionomisaki will be described briefly.

In this p a p e r , the o b s e r v a t i o n s

at

namic height. T o m e a s u r e the subsurface

temperature,

b u o y stations m i g h t b e the m o s t d e s i r a b l e instrumentation.

H o w e v e r , the p r e s e n t

stage of t e c h n o l o g y of b u o y

instrumenta-

tion in J a p a n is far from s u f f i c i e n t their i m p l e m e n t a t i o n .

Furthermore,

m a i n t e n a n c e of b u o y s is e x t r e m e l y

for the

costly.

W e h a v e t h e r e f o r e d e c i d e d to lay s u b m a r i n e cables w i t h t h e r m i s t o r s to m e a s u r e s u b s u r face t e m p e r a t u r e .

T h e m a i n d i s a d v a n t a g e of

the s u b m a r i n e c a b l e is in its cost w h i c h

Figure 1. Tide and temperature stations to study variations in the Kuroshio.

122

Figure 2. The location of the submarine cable, with thermistor, at Shionomisaki, Japan.

Figure 2 shows the position of the

trie resistance of the conductor is about

submarine cable at Shionomisaki, at the tip of Kii Peninsula.

17 ohms per kilometer at 20° C.

The Kuroshio usual-

The thermistors have a resistance of

ly flows near the cape, so that the people

about 30 k i l o - o h m at 0° C. and 9 k i l o - o h m

at the lighthouse can sometimes observe it

at 30° C.

directly.

electronic millivolt meter

The topography of the b o t t o m

The recorder is a six-point (Yokokawa ER-

is favorable since the b o t t o m slopes rath-

B6-10MLD12).

er sharply and the temperature of the deep

automatically into three ranges

layer can thus be measured w i t h a rela-

10°-25° C., and 20°-35° C.).

The records can be changed (0°-15°C.,

tively short cable. The laying of the cable in the area is shown schematically in figure 3.

RECORDS

A t Hachi-

jojima, a submerged buoy was used to obtain

Figures 4 and 5 show actual records.

data on the vertical distribution of tem-

It m u s t b e n o t e d that the surface thermis-

perature.

tor is situated in the shallow inlet b e -

Owing to the strong flow of the

Kuroshio in this area, the cable had failed in a very short time.

tween rocks.

However, the

system with a buoy is rather difficult and dangerous to install, especially in the deep sea.

points are noted: 1.

We have, therefore, resorted to

laying the thermistors on the bottom.

F r o m these figures the following

This

The shallowest record shows a

diurnal change of a few degrees. 2.

A t the 133-m. layer the tempera-

will probably cause some difficulties in

ture change is largest.

the interpretation of the results.

the temperature gradient is large in this

The cable used is of six cores

(four

cores for the middle part and two for the outer part), insulated b y polyethylene and armored w i t h 6 mm. steel wire.

The elec-

layer.

This is because

More precisely, this layer is at

the lower part of the seasonal 3.

thermocline.

The range of temperature change

in the two lower layers is nearly the same. 4.

The correlation in temperature

change b e t w e e n layers is generally poor. 5.

The lower two layers

sometimes

show coherent changes. 6.

Generally, drops in temperature

are sharper than their rise, w i t h the exception of the surface layer. 7.

There occasionally appears a

change over a period of 2 or 3 hours. 8. Figure 3. Schematic diagram of the location of the submarine cable at Shionomisaki, Japan.

In the deeper layer, diurnal or

semidiurnal variations are n o t conspicuous.

123

-0M. "1

1

1

133 M. 1 1

I

235 M. T

-298 M. t

v - ^ - ' Y ^ X """ APRIL 3 I I

I

1

I

I

I

I

I

I

I

I

L-

1

1

1

1

1

1

_l

1

L.

1

!

1

.......V5»4'* Ul cc

APRIL 4 _l

Ul o:

S

1

CE

Q. S ui L

S z y

is •

1

« J,1

^

•

y

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—

APRIL 5 i i

_ r,

v

i

i

i

i

^

i

^ - v i

Av'X",

i

i

~ >

v APRIL 6 6

8

10

12

14

16

18

20

22

24

0

2

4

6

TIME OF DAY F i g u r e 4. Records obtained w i t h the submarine cable at Shionomisaki, M a r c h 26-29, 1968.

8

10

12

14

16

_1 18

I 20

L. 22

24

TIME OF DAY F i g u r e 5. R e c o r d s o b t a i n e d w i t h the s u b m a r i n e cable at Shionomisaki, A p r i l 3-6, 1968.

A detailed analysis of the records is n o w underway.

For this, it is neces-

sary to compare these records w i t h tide records, ships' observations, meteorological data,and so on.

ACKNOWLEDGMENTS T h e a u t h o r s a r e m u c h i n d e b t e d to M r . T. S a k a m o t o o f the O c e a n C a b l e C o m p a n y , L t d . , for l a y i n g the c a b l e . A l s o the c o o p e r a t i o n o f the o f f i c e r s a n d c r e w of the R / V M e i y o ( C a p t a i n S . K a n e k o ) a n d the R / V K a i y o ( C a p t a i n H. O k a b e ) is m u c h a p p r e c i a t e d . T h i s w o r k h a s b e e n supp o r t e d b y t h e S p e c i a l I n v e s t i g a t i o n F u n d of the S c i e n c e and T e c h n o l o g y A g e n c y .

12k

LITERATURE CITED S h o j i , D. 1954. O n the v a r i a t i o n o f d a i l y m e a n s e a level a n d o c e a n o g r a p h i c c o n d i t i o n . Jap. S p e c . H y d r o g r . B u l l . 14: 1 7 - 2 5 . [In Japanese with English abstract.] S h o j i , D., a n d H . N i t a n i . 1966. O n the v a r i a b i l i t y of the v e l o c i t y of the K u r o s h i o - I. J. O c e a n o g r . S o c . Jap. 22(5): 192-196. Y o s i d a , S. 1961. O n t h e s h o r t p e r i o d v a r i a t i o n o f the K u r o s h i o i n the a d j a c e n t s e a o f I z u Islands. Jap. Hydrogr. Bull. 65: 1-18. [In J a p a n e s e w i t h E n g l i s h a b s t r a c t . ]

Variations of Oceanic Condition and Mean Sea Level in the Korea Strait SOK-U YI Korean Hydrographie Office, Seoul

ABSTRACT

Variations of oceanic condition in the Korea Strait are studied in connection with the variations of mean sea level using oceanographic and tidal data from 1962 to 1967. Variations of monthly mean sea level, reduced to standard atmospheric pressure, agree well with those of steric sea level or dynamic height. Sea-level observations at Pusan and Izuhara are useful to study variations of oceanic condition, especially current velocity through Korea Strait's western channel. The Izuhara-Pusan sea-level difference indicates that the average surface current in the western channel fluctuates seasonally with an annual change of about 1 knot, and irregularly, with periodicities of about 10-30 days, up to 1 knot during summer-autumn.

INTRODUCTION

condition or density causes rising and falling of sea level, which is recorded at

Variations of oceanic condition and

tide gages along the coast.

Sea-level ob-

mean sea level in the Korea Strait have

servations at suitable places are relative-

been studied by many oceanographers; the

ly easier to obtain than those taken by

former by Nishida (1927), Hidaka and Suzuki

ships.

(1950), Koizumi (1962), Yi (1966b), Nan-

In this paper, variations of oceanic

niti and Fujiki (1967), and the latter by

condition and mean sea level in the Korea

Miyazaki (1955), Lisitzin (1967), Yi (1967),

Strait are studied.

etc.

put on the variation of current in connec-

But no one has studied the variation

Special emphasis was

of oceanic condition related with the mean

tion with the variation of sea-level dif-

sea level in the strait.

ference between Pusan, Korea and Tsushima

Recently, the variations of sea levels in some areas were discussed in connection

Islands, Japan. The data used in this study are the

with internal structure of the sea by sev-

result of serial oceanographic observations

eral investigators; LaFond (1939), Mont-

across the section between Pusan and Mitsu-

gomery (1938), Stommel (1953), Shoji (1955),

shima, Tsushima Islands (BI-BVI), carried

Moriyasu (1958), etc.

out by the Fisheries Research and Develop-

The variation of sea

merit A g e n c y in P u s a n , K o r e a and the tidal

w a v e r o t a t e s c o u n t e r c l o c k w i s e a r o u n d an

r e c o r d s at P u s a n , U l s a n , and C h e j u a l o n g

a m p h i d r o m i c p o i n t a little w e s t of the

K o r e a coast c o n d u c t e d since 1962 b y the

m i d p o i n t of the n o r t h e a s t end of the

H y d r o g r a p h i c O f f i c e , K o r e a and I z u h a r a and

T h e spring r a n g e of tide is a b o u t 220 cm.

M o j i a l o n g the J a p a n e s e coast c o n d u c t e d b y

along the coasts of the Goto I s l a n d s ,

the H y d r o g r a p h i c D i v i s i o n , J a p a n .

330 cm. o n the c o a s t of K o r e a n e a r

Figure 1

strait.

about

the

shows the locations of the o c e a n o g r a p h i c

s o u t h w e s t e n d of the s t r a i t .

a n d tidal

g r a d u a l l y to the n o r t h e a s t a l o n g the shores

stations.

of the strait to a b o u t 20 cm. a n d 10 cm. at

T h e K o r e a S t r a i t is located b e t w e e n Korea and Japan.

the coasts of H o n s h u and K o r e a at the n o r t h -

It connects the S e a of

J a p a n w i t h the E a s t C h i n a Sea.

T h e strait

has a length of about 150 m i l e s

(280 km.),

a b r e a d t h of a b o u t 110 m i l e s

It d e c r e a s e s

east

end. A l o n g the T s u s h i m a Islands the flood

(200 k m . ) ,

c u r r e n t flows to the s o u t h , the ebb cur-

and d e p t h of 50 to 150 m . i n its g r e a t e s t

r e n t to the n o r t h .

part.

v e r s e at a b o u t the time of h i g h and

T h e strait is d i v i d e d into

two

c h a n n e l s b y the T s u s h i m a Islands.

The

waters.

Their directions

relow

In the e a s t e r n p a r t of the south

w e s t e r n c h a n n e l b e c o m e s n a r r o w e r to the

coast of K o r e a , the flood c u r r e n t goes to

n o r t h e a s t w a r d , d e e p e n i n g there to about

the s o u t h w e s t , the ebb c u r r e n t to the

200 m . ; the e a s t e r n channel w i d e n s

n o r t h e a s t off the coast, a n d r e v e r s e

north-

their

e a s t w a r d and h a s a constant d e p t h of about

d i r e c t i o n s a t a b o u t the time of h i g h a n d

100 m . o r m o r e .

low w a t e r s .

T h e tide i n the strait w a s by Ogura

(1933).

the

same coast, the current g e n e r a l l y sets to

discussed

T h e semidiurnal

I n the w e s t e r n half of

the east a n d w e s t i n the o f f i n g , the w e s t -

tidal

g o i n g c u r r e n t r u n n i n g from 2 - 3 hours

after

low w a t e r to 2 - 3 hours a f t e r h i g h w a t e r , w i t h m a x i m u m v e l o c i t y of 2 to 3 knots at

« OCEANOGRAPHIC STATIONS X TIDAL STATIONS

narrows.

SEA OF JAPAN

Nishida's

(1927) 24-hour c u r r e n t ob-

s e r v a t i o n s in the w e s t e r n channel show ^

~

CHANNEL

¿(TSUSHIMA I. ff

^SKAWAJIRI MISAKI

\

HONSHU

EASTERN CHANNEL/--J(M^)I^W^J

KYUSHU GOTOI.^

d

EAST CHINA SEA

126

0.7 k n o t in the upper layer,

respectively,

and the s t r e n g t h of tidal currents is

í^HÉjlu) 0pí> K , — f -33°

Figure 1. stations.

diurnal

tidal c u r r e n t a r e 0 . 7 - 1 . 3 knots and 0.4^

LHLJU_

127°

the c o m p o n e n t s o f s e m i d i u r n a l a n d

that

128° Oceanographic stations and tidal

e

a l m o s t the same from the surface to the bottom. The Tsushima Warm Current,

branching

from the K u r o s h i o s o u t h w e s t of K y u s h u , flows n o r t h e a s t w a r d t h r o u g h the K o r e a S t r a i t into the S e a of J a p a n w i t h a v e l o c -

ity of about 0.5-1.0 knot.

One noteworthy feature is a cold

In general,

the velocity of the ocean current in the

water intrusion in the bottom layer in the

strait, being influenced by the tidal cur-

western channel in summer-autumn.

rent, fluctuates twice a day, and the

curve of bottom temperature at station BIV

ocean current strength diminishes from the

shows a decreasing tendency from May to

surface downward.

September, contrary to the temperature

The

changes in the upper layers, which is a THE VARIATION OF OCEANIC CONDITION

general feature in the sea adjacent to the southeast coast of Korea.

Nishida (1927)

investigated the cold water of the Sea of

Water Temperature According to studies of the seasonal

Japan which reached the southwest end of

variation of surface water temperature in

the Tsushima Islands along the deep bottom

the strait by Koizumi (1962) and Yi (1966b),

on August 7, 1926; this phenomenon dis-

the range of the annual component of sur-

appeared in winter of 1926.

face water temperature in the strait ex-

the bottom temperatures at station BIV are

tends from 5° to 7° C.

Large values occur

along the south coast of Korea.

The range

i

of the semiannual component does not exceed 1.5° C.

In figure 3,

i

i

1

i

i

i

i

i

i i

25

STA.B I

The maximum surface water temper20

ature occurs at the end of August on the south of Korea and early in September at

15 -

sea.

„

50JTo o-

The average seasonal changes of sea water temperature for different depths at stations BI and BIV in the western channel are shown in figure 2.

The water tempera-

tures for different depths at BIV increase from winter-spring to summer-autumn, except below 150 m.

The annual range varies from

12° C. at the surface to 3° C. at 100 m., gradually decreasing downward.

The time of

Ui §

'

5


-

falls in winter-spring; its range is from 20 cm. at the southeast coast of Korea to

o Q

40 cm. at the Tsushima Islands and at the

LlJ >

northeast coast of Kyushu, Japan.

The

variation of monthly m e a n sea level is annual, having one maximum and one minimum, and mainly steric, i.e., caused by changes in sea water density and atmospheric pressure.

The steric effect is especially

predominant along the southeast coast of K o r e a and at the Tsushima Islands. The monthly m e a n sea levels reduced II

III

IV

V

VI

VII VIII

IX

X

XI

STATIONS Figure 6. The seasonal distribution of current velocity across the section Ulgi-Kawajirimisaki (I-XX).

130

to normal atmospheric pressure for the years 1962 to 1967 at Moji, Izuhara, Cheju, Ulsan, and Pusan are plotted in figure 7. A small annual range is present at Pusan

(about 15 cm.) and a large annual range at Izuhara and Moji

(about 20 cm.)»

The relations between monthly mean sea level reduced to the normal pressure

atmospheric

20

1

(AH ) and steric sea level or

dynamic height anomaly

1

1

1

1

PUSAN

(AH") at Pusan,

IX• // X/ •.Ovvili

10

Cheju, and Izuhara are shown in table 1 and figure 8.

9'

•VII

-10

1

1

1

1

0

10

20

CJ 2 o

"x
Ui
Ui -I
o

-10 Si

Ui

150

15

Figure 1. North-south temperature gradients at 200 m., winter of 1965-66. In the shaded areas temperature decreases northward, implying positive density gradients and eastward flow. The discontinuity appearing near long. 142° E. is not smoothed, considering some uncertainties in data taken at different times with possible topographic disturbances.

N. for almost all sections of different

picture resulted.

longitudes.

procedure, an extremely regular structure,

There seems to be little doubt

With this averaging

that the easterly current at these lati-

with bands separated by 3° latitudinal

tudes just to the north of lat. 20° N. is

intervals, is obvious.

a semipermanent feature, quite persistent

one is the one for reference levels of 2,000

and stable.

decibars (fig. 2).

The most beautiful

Easterly geostrophic

flow appears in bands, between lat. 21°

Easterly transport at somewhat higher latitudes is not so distinct as in this

and 22° N., between lat. 24° and 25° N.,

lowest belt, but may still indicate the

and between lat. 21° and 28° N., each

existence of a somewhat disturbed belt

reaching at least 1,500 m., with surface

around lat. 27° and 29° N., and an even

velocities of 10-20 cm. per second.

more confused belt is seen around lat. 24°

or less similar pictures are seen for

to 25° N.

dynamic sections with shallower reference

I attempted to average all

More

longitudes (sections), and obtained a mean

levels and for other seasons.

meridional distribution of east-west com-

figure 3, the bands are located at nearly

ponents of geostrophic flow.

the same places, but the easterly flow

A remarkable

As seen in

LATITUDES

1500 -j

til

mrnrn

Figure 2. Zonal average geostrophic currents (cm./sec.) relative to 2,000 decibars, from CSK cruises between long. 127° and 155° E., during winter 1965-66. Flow is toward the east in the shaded areas.

Figure 3. Zonal average geostrophic currents (cm./sec.) from CSK cruises between long. 127° and 155° E., during summer 1965 (panel A ) and winter 1965-66 (panel B). Flow is toward the east in the shaded areas.

199

between lat. 24° and 25° N. becomes much

Since the station intervals in this survey

shallower and weaker.

are 1.5°, a wider spacing than that for

Although these average distributions

the CSK stations, the apparent band intervals might not be significant.

do reveal distinct multiple eastward streams, individual distributions for the

Near the meridian of 180°, between

whole region are not so well separated

the CSK region and Hawaii, we have Vityaz

(fig. 4).

cruises during 1957-58.

H

t-t-

TJ 20, — 12 S

te c: Jm

135

H 140 145 LONGtTUDCS CEI

T1

H 1» , » 1 .q H p* >50 155 o Ofl/aSp tC4o to

Figure 4. East-west components of geostrophic flow, from CSK cruises during winter 1965-66.

Although the

station spacings are even wider, similar bands of eastward flow are also seen. Vityaz cruises extended to the southern oceans and indicate very clearly some symmetry between the Southern and Northern Hemispheres (figs. 6 and 7).

Subtropical

countercurrents appear to be present in both hemispheres.

Various other observa-

tions have also been examined.

Almost all

the data examined show the presence of eastward flow.

The positions and intervals of

those bands are not necessarily the same

OTHER DATA

as in the winter CSK data.

However, the

streams are very likely to vary with season, Using CSK data, we can only examine the eastward transport to the west of long. 155° E.

to meander, and may possibly break into large horizontal eddies.

The band inter-

A problem is whether there is any

substantial evidence of continuation or extension of it to the east of long. 160° E.

One of the best sets of data to offer

a look into this problem is that taken by the Trade Wind Zone Oceanography Pilot Study during 1964-65.

Eastward flow just

to the north of lat. 20° N. is evident, with time- and space-continuity.

Below 20°

N. somewhat continuous variations from month to month can be seen from this 17month survey.

On the average, however,

there seem to be two or three deep eastward undercurrents around lat. 12° and 18° N. (fig. 5).

The band intervals in these

lower latitudes appear somewhat wider.

200

Figure 5. Average geostrophic currents (cm./sec.) along long. 148° W. for the period February 1964 through June 1965.

31!

S.

35 37 3 SUP

2 X

ICL LlI o

0. Ld a

Figure 6. (a) Geostrophic current velocities (cm./sec.) in a section along long. 172° E. (b) Observed current velocities (cm./sec.) in a section along long. 172° E. (c) North-south components of currents along long. 174° W. (Burkov and Ovchinnikov, 1960.)

vais deduced from data may largely depend

One of the old current charts issued by

on spacing of stations.

the Japanese Hydrographie Office indicates

Therefore, it is

not yet possible to make more definite

very clearly the existence of subtropical

comments on the structure from existing

countercurrents and even their band struc-

data.

ture .

Future observations definitely are

needed to substantiate the hypothesis. 201

0 100 ZOO 300 uoo 500 600 7 00

800

X

ha lu Q

aoo 1000 uoo 1ZC0 1300 1U00 1500 1600 noo 1800-

35 STA. NO

30 N.

25

ZO

3780

15

3785

10 37.90

S 3735

0

10

3800

3805

15

30

25

3810 3812 3816 3820

30

38Z5

35

3830

S. UO UZ° 3835

0 100 zoo

S I IQ. Ld

300 uoo 500

Q

600

100 800

33° STA. NO

30

N. 3 780

25

ZO 3785

10 3790

3705

3800

3805

15 3810 38IZ

ZO 3816 3820

Z5 3825

30 3830

35

S.

àO 42"

3635

CL ÜJ

O

Figure 7. (a) Smoothed geoatroph±c current velocities (cm./sec.) in a section along long. 174° W. (b) Observed current velocities (cm./sec.) in a section along long. 174° W. (c) Geostrophic current velocities (cm./sec.) in a section along long. 174° W. (Burkov and Ovchinnikov, 1960.)

INTERPRETATION

held that the countercurrents were caused by wind-stress singularities near the

I have been puzzled by this new band

boundary between the trades and the west-

structure, since my own hypothesis for

erlies.

broader-scale subtropical countercurrents

required if the band structure of this

202

Further explanation would be

current is real.

I have not yet been able

to develop any convincing theories for

o

this but have only thought of various

O

possible explanations.

5

0

One possibility is regular convective patterns in the thermocline layer, what might be called stationary interval waves. Details of this model will not be shown

CO

6

layer is denoted as D, the wavelength of the bands will simply be given by

L = 2tt-

• X

TWZ 151* W OTHER SOURCES

X

I - 9, ( 9 Z 111 1 2 bJ 3 i 15

20

25

30

LATITUDES C*NJ

Figure 8. North-south wavelength of alternating bands of zonal flow as a function of latitude. Points represent observed values; the curve represents the theoretical relationship from equation (1).

of vital importance in connection with the source region of the Kuroshio.

where

WINTER

148* W SUMMER

5

tion of interest is the type of convection If the thickness of the thermocline

CSK

4

here, but I may add one thing--the convecdiscussed by Lineykin (1955).

•

A,A TWZ • CSK

If the

f = Coriolis frequency = 2a)sincj>

remarkable multiple structure of the cir-

g = gravity

culation in this region is real, the spacing of stations along meridional sections

— P

= vertical density contrast • per mean densxty 3

If we put D

500 m., ^ = 2 x 10~ , L P becomes about 4° around lat. 15° N., 3° around lat. 20° N., and 2° around lat. 35° N. (fig. 8).

separated by 1° latitude is definitely not sufficient to explore the current structure in this region.

The spacing of stations

should be no more than 0.5° of latitude. One might think that things are more complicated and irregular in reality.

The

detailed structures, and the instantaneous CONCLUSION

velocity field would probably be so.

Yet,

I suggest that there is a statistically There appears to be growing evidence

continuous eastward stream just to the

that eastward streams are present at lower

north of lat. 20° N., and that probably

subtropical latitudes.

several more easterly streams could be

Furthermore, these

streams, which might be called subtropical

present.

countercurrents, appear to have a banded

Hasunuma (personal communication) on the

structure.

distribution of salinity and other proper-

As this structure of multiple

More recent work by Tsuchiya and

eastward streams might be most pronounced

ties in this region seems to suggest that

in the western region, as first revealed

the eastward stream between lat. 20° and

from CSK data, this new feature could be

23° N. is likely to be continuous, at least 203

between long. 130° and 155° E.

It is not

LITERATURE CITED

yet known whether this may be continuous with eastward flow in the mid-Pacific, and even with flow in the eastern Pacific. Theoretically, it seems possible to anticipate that subtropical eastward streams cross entire oceans, not only the North Pacific, but also the South Pacific, Atlantic, and Indian Oceans.

I think we

are looking at something new which had not been known before.

The CSK program has

made this initial study possible, and it is hoped this will lead to future studies of this new feature of the world oceans, which I think is worth more attention.

20^

Burkov, V. A., and I. M. Ovchinnikov. 1960. Structure of zonal streams and meridional circulation in the central Pacific during the Northern Hemisphere winter. Tr. Inst. Okeanol. Akad. Nauk S.S.S.R. 40: 93-107. [In Russian.] Lineykin, P. S. 1955. On the determination of the thickness of the baroclinic layer in the sea. Dokl. Akad. Nauk S.S.S.R. 101: 461-464. Seckel, Gunter R. 1968. A time-sequence oceanographic investigation in the North Pacific trade-wind zone. Trans. Amer. Geophys. Union 49(1): 377-387. Voorhis, A. D., and J. B. Hersey. 1964. Oceanic thermal fronts in the Sargasso Sea. J. Geophys. Res. 69(18): 3809-3814. Yoshida, Kozo, and Toshiko Kidokoro. 1967a. A subtropical counter-current in the North Pacific --An eastward flow near the Subtropical Convergence. J. Oceanogr. Soc. Jap. 23(2): 88-91. 1967b. A subtropical countercurrent (II) --A prediction of eastward flows at lower subtropical latitudes. J. Oceanogr. Soc. Jap. 23(5): 231-246.

Characteristics of Waters East of Mindanao, Philippine Islands, August 1965 1 GLENN A. CANNON2

Department of Oceanography The Johns Hopkins Universitys Baltimore

ABSTRACT

Observations from two hydrographic sections made in August 1965 extending from Mindanao easterly to long. 130° E. show characteristics of the Mindanao Current and surrounding waters. The offshore limit of continuous strong currents is 70-80 km. Geostrophic surface currents and the ship's set are consistent near Mindanao. The transport and the depth of the current are different on the two sections, which are only about 100 miles apart. A double salinity maximum is observed within the thermocline at the eastern end of the southern section. In the present study the deeper maximum is observed at a thermosteric anomaly near 220 cl./ton and is associated with a thermostad near 15° C. The feature results from overlapping of waters of North and South Pacific origins because of seasonal changes in circulation.

INTRODUCTION

and its geostrophic transport.

No previous

data from this region had the required deTwo detailed hydrographic sections extending from Mindanao easterly to about

tail. The present paper describes some of

long. 130° E. were made in August 1965 by

the observations in the upper 1 km. and

the research vessel Atlantis II of the

some of the results.

Woods Hole Oceanographic Institution (fig.

tion is based on data obtained in July

1).

1965 by the Japanese research vessel Takuyo

These sections were about 100 miles

apart.

The main purpose of the study was

(fig. 1).

Part of the descrip-

Both the Atlantis II data and

to determine some details of the charac-

the Takuyo data are available in the "Data

teristics of the southerly flowing Mindanao

reports of the CSK" from the Japanese Ocean-

Current, particularly its easterly extent

ographic Data Center, Tokyo, Japan. The surface circulation of the western

' C o n t r i b u t i o n 120 of C h e s a p e a k e B a y I n s t i t u t e and Department of Oceanography, The Johns Hopkins U n i v e r s i t y , and C o n t r i b u t i o n 2103 of W o o d s H o l e Oceanographic Institution. Revised D e c e m b e r 1969. 2 N O W at D e p a r t m e n t of O c e a n o g r a p h y , U n i v e r s i t y of Washington, Seattle, Wash. 98105.

Pacific is complex because of seasonal winds.

Southwesterly winds blow over part

of the region from June to September and northwesterly winds from November to April.

lio-10 N

f

8

«

X

*

X

1

134°

,63

,35

+ C&

"•794 «52 • ATLANTIS I I x TAKUYO

M

+ »43

1

M

m4I

l

Figure 1. Location of Atlantis II stations and Takuyo stations.

Some of the currents in the region reverse direction with the winds, and some, including the Mindanao Current, do not.

The

100 km: 83 8485

H

86 87

TEMPERATURE 88

89

90

91

(°C.) 92

observations described in this paper were made in the season of southwesterly winds. DATA AND METHOD Temperature, depth, and salinity were measured at stations spaced 10-15 miles apart.

The maximum depth of observation

was alternately 1.5 and 4.5 km. (limited to 4.5 km. because of a broken strand on the hydrographic wire) or to the bottom where the depth was less than 4.5 km.

Because

almost all vertical changes in salinity associated with Tropical Water (Cannon, 1966) occurred within the thermocline, vertical spacing of samples (as close as 10 m.) at each station was based partly on BT observations.

The locations of the

samples are shown on the vertical sections (figs. 2 and 3). 206

Figure 2. Vertical sections of salinity (top) and temperature (bottom) for the southern section. Sample depths are shown by dots. The contour intervals are not uniform. A relative minimum in salinity is shown by the open circles. The vertical exaggeration is 400:1.

Dissolved oxygen was measured at all deep stations but is not discussed here. Continuous recordings were made of temperature and salinity versus depth at the

eastern end of each section (Stommel and Federov, 1967). Graphs were drawn of depth and salinity versus temperature, as suggested by Montgomery (1954), for the upper 1 km. for each station (e.g., fig. 4).

The

vertical temperature sections (figs. 2 and 3) were constructed by interpolating directly from the temperature-depth curves. The vertical salinity sections (figs. 2 and 3) were constructed by first reading the temperature corresponding to a chosen value of salinity

1« 810

100km. 9

8

TEMPERATURE 7

6

5

4

from the temperature-

(°C. ) 3

Figure 3. Vertical sections of salinity (top) and temperature (bottom) for the northern section.

Figure 4. Sample station curves for (A) a station near the coast of Mindanao (783) and for (B) a station near the eastern end of the southern section (792).

207

The map of salinity on the thermo-

salinity curve and then reading the depth from the temperature-depth curve.

steric anomaly surface of 220 cl./ton

Se-

lected values of thermosteric anomaly are

(fig. 6) was constructed by reading values

shown by arrows adjacent to the end sta-

directly from the station curves.

tions of each section.

smoothing was performed in contouring.

These values corre-

Some

spond to those used in studies by Reid VERTICAL SECTIONS

(1965), Cannon (1966), and Tsuchiya (1968) which include the region of the present study.

Both temperature sections near the

The geopotential profiles (fig. 5)

coast show relatively steeply sloping iso-

were constructed by integrating thermo-

therms (about 1:1,000) indicative of a

steric anomaly from 1,000 db to the sea

southerly current.

surface for each station.

comes sharper and shallower to the east.

This calculation

The thermocline be-

can be performed simply using the station

Station 792 (fig. 4) shows a change of 12°

curves.

C. between 50 and 100 m.

The geopotential difference re-

The distinctive

sulting from using thermosteric anomaly

difference between the two sections is the

instead of specific volume anomaly was

thermostad (Seitz, 1967) from 14° to 16° C.

about 1 dyn. cm. or less and produced no

at the eastern end of the southern section.

significant changes in the slopes.

A temperature minimum was observed at a

Because

the stations were very close, the transports

depth of about 3.5 km. on all deep stations.

were calculated only between the end stations of the nearshore region of large seasurface slope.

k -— 1 0 0

km.

8 ° 2 6 ' NCL

GEOPOTENTIAL

PROFILES

T10 dyn cm.

1

V / \

-

6'45'N.Q 7*37'NO -

— 0 t27*E.

128° !

6'02'N

129' 1

Figure 5. Geopotential profiles referred to 1,000 db for the northern (upper) and southern (lower) sections. The vertical scales are relative, and there is no significance to the separation between the profiles. 208

Figure 6. Distribution of salinity on the surface of constant thermosteric anomaly of 220 cl./t. The values (slanted numbers, Takuyo; vertical numbers, Atlantis II) are given as an excess over 34.00°/oo.

A salinity maximum, with some values

approximate location of this minimum is

in excess of 34.9°/ 00 , is observed along

shown on the salinity sections by a line

both sections between surfaces of thermo-

of open circles.

steric anomaly of 300 and 400 cl./ton.

less dense in the deeper water and may

The

Vertical sampling was

highest values are observed near the coast.

account for the minimum not being observed

This salinity maximum originates in the

at all stations.

tropical North Pacific and has been called

to Intermediate Water of Antarctic origin

Tropical Water (Cannon, 1966) and Subtrop-

(Reid, 1965).

ical Lower Water (Wyrtki, 1956).

salinity increases to almost 34.7°/ 00 near

It is

questionable whether the two regions of

This minimum corresponds

Below this minimum the

4,500 m.

salinity in excess of 34.8°/ 00 and 34.9°/ 00 on the northern section are really distinct.

CURRENT LIMITS AND TRANSPORT

A deeper maximum is observed at the eastern end of the southern section and sometimes it

Surface-current charts (e.g., Wyrtki,

exceeds the magnitude of the shallower

1961) show speeds of 1.5-2.0 knots for the

maximum.

Mindanao Current but cannot be used to

This deep maximum occurs at a

thermosteric anomaly of about 220 cl./ton

determine the offshore limit of the cur-

and coincides with the thermostad shown in

rent.

the temperature section.

present study show a nearshore region of

A salinity minimum is outlined by the 34.5°/ 00 contour on both sections. lowest values are near the coast.

The This

minimum corresponds to the Intermediate Water of North Pacific origin (Reid, 1965),

The geopotential profiles in the

large slope, followed by a region of relatively small and variable slope, and then a region of large, irregular slope farthest offshore. In the present study the eastern limit

but the minimum is located at a thermo-

of the Mindanao Current is assumed to be

steric anomaly greater than 125 cl./ton.

the limit of the large nearshore surface

The noticeable difference in the minimum

slope.

on the two sections is that the minimum

used by Masuzawa (1964) in studying the

is well defined across the entire northern

Pacific North Equatorial Current.

section but only extends about halfway

shore limit occurs at station 786 on the

across the southern section.

southern section and at station 807 on the

The minimum

This technique is similar to that The off-

is not observed beneath the region of the

northern section.

double salinity maximum on the southern

the current is about 70 and 80 km., re-

section.

spectively, for the southern and northern

Below the salinity minimum the water is remarkably uniform.

At most stations,

sections.

The resulting width of

The geostrophic surface current

and the geostrophic transport between the

however, a second salinity minimum is

two end stations (782-786 and 810-817) are

observed at values of thermosteric anomaly

1.3 m./sec. and 18 X 10s m. 3 /sec., re-

slightly greater than 80 cl./ton.

spectively, for the southern section and

The

209

1.1 m./sec. and 31 X 10 6 m . 3 / s e c . , respectively, for the northern section.

east to show whether this high-salinity At

water is still connected w i t h its source.

the northern section the current extends

The fact that this high-salinity water

d o w n to a d e p t h of about 800 m., b u t at

appears as a secondary m a x i m u m in conjunc-

the southern section it extends only to

tion w i t h the associated thermostad, there-

about 400 m.

fore, appears to be the result of the

These differences in the cur-

r e n t in only 100 miles seem large.

Both

Northern Tropical Water overlying the

salinity sections, however, showed that the

Southern Tropical Water.

North Pacific Tropical and the Intermediate

could easily come about because of the

waters were most pronounced within the

highly variable, especially seasonal, char-

Mindanao Current.

acteristics of the w i n d in the western

These features are shown

This overlapping

w e l l on the temperature-salinity curve for

equatorial Pacific.

station 783 (fig. 4).

supports an earlier study b y Wyrtki

The computed surface velocities may also seem large.

However, during the

The present study (1956),

who also concluded that the secondary maximum was due to overlapping of Northern

7-8 hours travel from Miangas to Mindanao,

and Southern "Subtropical Lower Water"

w i t h southerly winds, the ship's set indi-

(called Tropical Water in the present

cated a current of 2.0-2.5 knots to the

paper) . It is likely that the high-salinity

south.

water w h i c h is in the secondary maximum

SECONDARY SALINITY MAXIMUM

penetrates farthest north during the season of southwesterly winds

The station curves for station 792

(present case).

It is during this season that the South

(fig. 4) show a secondary salinity m a x i m u m

Equatorial Current penetrates

at a thermosteric anomaly of about 220

westward along New Guinea.

cl./ton and an associated thermostad at 15°

now raised is w h a t happens during the sea-

C.

son of northwesterly winds?

The map of salinity at 220 cl./ton

farthest

The question

Does this

(fig. 6) is presented here to aid in deter-

feature disappear?

mining the source of this water.

w i t h the Equatorial Countercurrent?

Because

Does it drift eastward If

the values of salinity in the secondary

it does, how far does it travel before its

maximum sometimes exceed those of the over-

identity is lost?

lying Tropical Water, the most probable

(Wyrtki, 1956) show high salinities at 220

explanation of the source of the high-

cl./ton along the islands of Halmahera and

salinity water in this maximum is that it

Talaud during May-June 1960.

is advected into the region.

from Vityaz cruise 25 in August-September

The map clear-

The Snellius data

However, data

ly shows that the feature is not of northern

1957 (Cannon, 1966) do not even show, at

origin.

220 cl./ton, salinities as high as 3 4 . 7 ° / 0 0

Thus, this high-salinity water must

come from the south.

Unfortunately, the

data do not extend far enough south and

210

near Halmahera.

Some discrepancies m a y b e

due to sampling at so-called

"standard

d e p t h s " w h i c h c o u l d m i s s the d e e p e r

maximum.

A s y s t e m a t i c f i e l d i n v e s t i g a t i o n of

the

r e g i o n s h o u l d b e p l a n n e d a n d c a r r i e d o u t to s t u d y the s e a s o n a l a s p e c t s of the c i r c u l a t i o n i n the w e s t e r n

Pacific.3

ACKNOWLEDGMENTS The author expresses his gratitude to Henry Stommel, chief scientist of the cruise, and to L. V. Worthington for providing the opportunity to conduct the field measurements. This study was supported in part by National Science Foundation grants GP 821 (to Woods Hole) and GP 2443 (to Johns Hopkins) and in part by Office of Naval Research contract NONR 4010 (11) (to Johns Hopkins).

Richard A. Barkley, Bureau of Commercial Fisheries Biological Laboratory, Honolulu, has kindly pointed out that secondary salinity maxima have been observed at a wide range of density levels across most of the northern equatorial Pacific. The maximum, when present, marks the upper boundary of Sverdrup's Equatorial Water Mass. At shallower levels the water consists of a mixture of high-salinity equatorial water and lower salinity North Pacific Central Water.

LITERATURE CITED Cannon, Glenn A. 1966. Tropical waters in the western Pacific Ocean, August-September 1957. Deep-Sea Res. 13: 1139-1148. Masuzawa, Jotaro. 1964. Flux and water characteristics of the Pacific North Equatorial Current. In Studies on oceanography dedicated to Prof. Hidaka. Univ. Washington Press, Seattle, pp. 121-128. Montgomery, R. B. 1954. Analysis of a Hugh M. Smith océanographie section from Honolulu southward across the Equator. J. Mar. Res. 13: 67-75. Reid, Joseph L., Jr. 1965. Intermediate waters of the Pacific Ocean. Johns Hopkins Oceanogr. Stud. 2, 85 pp. Seitz, R. C. 1967. Thermostad, the antonym of thermocline. J. Mar. Res. 25: 203. Stommel, Henry, and K . N. Fedorov. 1967. Small scale structure in temperature and salinity near Timor and Mindanao. Tellus 19: 306-325. Tsuchiya, Mizuki. 1968. Upper waters of the intertropical Pacific Ocean. Johns Hopkins Oceanogr. Stud. 4, 50 pp. Wyrtki, Klaus. 1956. The Subtropical Lower Water between the Philippines and Irian (New Guinea). Mar. Res. Indonesia 1: 21-52. 1961. Physical oceanography of the southeast Asian waters. Scientific results of marine investigations of the South China Sea and the Gulf of Thailand 1959-1961. In Naga Rep. Scripps Inst. Oceanogr. Univ. Calif. 2, 195 pp.

211

Océanographie Conditions in the Sea East of the Philippines and Luzon Strait in Summers of 1965 and 1966 HIDEO NITANI

Hydrographie Office of Japan3 Tokyo

ABSTRACT

The R/V Takuyo carried out oceanographic observations in the sea east of the Philippines and Luzon Strait in the summers of 1965 and 1966 as a part of the CSK synoptic survey. Results show: 1. The North Pacific Equatorial Current is clearly separated into two branches off Luzon at lat. 13°-14° N. The northward-moving branch is the Kuroshio and southward-moving one is the so-called Mindanao Current. The Kuroshio flows north along the coast of Luzon with a velocity of about 1.5-2.0 knots and enters Luzon Strait; then it turns to the northeast, and flows out into the Pacific. The water of the northern half of the North Pacific Equatorial Current forms the Kuroshio, and the current off Luzon is the origin of the Kuroshio. The transport of the Kuroshio here is about two-thirds to three-fourths that of the Mindanao Current. 2. There are two semipermanent eddies in these areas. One is a warm eddy on the east side of the Kuroshio in Luzon Strait, and the other one a cold eddy off Mindanao. 3. North Pacific Intermediate Water forms the lower part of the Kuroshio. 4. The transport of the Kuroshio off Luzon and in Luzon Strait is about 30-45 million tons/sec., which is smaller than that of the Kuroshio off the south coast of Japan.

INTRODUCTION

In these areas, several oceanographic studies have been made in past years, but

Investigations of the origin of the

broad systematic observations of the origin

Kuroshio were carried out as a part of the

of the Kuroshio that included the sea off

CSK (Cooperative Study of the Kuroshio) by

the east coast of the Philippines, Luzon

the R/V Takuyo in the summers of 1965 and

Strait, the South China Sea, and the sea

1966.

off Formosa at the same time, have not

The principal objectives were to

confirm the origin of the Kuroshio and to

been made.

investigate conditions in the sea east of

equatorial regions, piecemeal observations

the Philippines and in Luzon Strait.

were made on board the Snellius, Dana, and

In the western subtropical and

Albatross.

Before World War II, fairly

the North Pacific Equatorial Current, but

systematical, but not complete, observa-

detailed knowledge about its origin, speed,

tions were carried out using the R/V Manshu

volume transport, and many other charac-

(1925-28) and many other vessels operated

teristics was

by the Japanese Hydrographic Office.

After

still obscure.

In summer 1965, the R/V Takuyo

the war, only EQUAPAC (1956) and IGY (Inter-

covered the region between lat. 4° and 22°

national Geophysical Year) (1958) cruises

N., from long. 133° E. to the Philippine

were systematic, but the main areas exam-

coast, Luzon Strait, and the northeastern

ined by them were east of long. 130° E.

part of the South China Sea (fig. 1A).

Piecemeal observations extending to the

In summer 1966, the region of observa-

Philippine coast were carried out on board

tion in the Pacific extended from lat. 7°

the Spencer _F. Baird (1948-49) and Takuyo

to 24° N., and from long. 129° E. to the

(1959).

Philippine coast, and the region west of

From these data, it was learned

that the Kuroshio forms one part of the

Luzon Strait was nearly the same as that

North Pacific circulation continuing from

of 1965 (fig. IB).

Figure 1A. Chart showing stations occupied by the R/V Takuyo, June 25 to September 7, 1965.

Figure IB. Chart showing stations occupied by the R/V Takuyo, July 1 to September 13, 1966.

214

PATH OF THE KUROSHIO

as shown in table 1, which includes the results of past observations.

This point,

as a rule, lies to the north with increas-

The results of GEK (geomagnetic electrokinetograph) observations and the

ing depth.

dynamic depth anomaly of the sea surface

of the Takuyo in August 1966 show that this

referred to 1,200 db are shown in figures

neutral point is at lat. 12.5° N. at the

2 and 3.

sea surface and lat. 15° N. below 300 m.

The North Pacific Equatorial

Current flows westward and divides into

For example, the observations

The southward-moving current is called

southward-moving and northward-moving

the Mindanao Current.

currents off the coast of southern Luzon

along the coast of Mindanao and joins the

or Samar.

South Equatorial Current coming along the

The place where the current

It flows southward

divides was at lat. 14.5° and 12.5° N. off

north coast of New Guinea to form the

the coast of the Philippines in the summers

Equatorial Countercurrent.

of 1965 and 1966, respectively.

the geostrophic calculation, the Mindanao

The posi-

tion of this neutral point at the sea surface ranges from about lat. 11° to 15° N.

125°

According to

Current has velocities of about 1-2 knots. The northward-moving current flows

115° E.

^130°

30°

O 0~ 02 0.3-0-4 0.5-0.9 1.0-1.9 —» 2.0-2.9 3.0-3.9

o 0 — 0.2 Kt 0.3 -0.4 * 0 .5-0.9 1.0 -1.9 2.0-2.9 3.0-3.9

25° ,/

FORMÓSA

IT

r.

£

t 0

r^'hi* t / »

',

20°

LUZON

AAt 11

0

{ ( ru

LUZON

r

t

20°

v V -JTs '» >p ° o » o// ^

x

io n

1

" if tt

\*,A f "V^tg-

v'V^Av ^

'A

II

is/i ->w* I f V"

f

\4 \

T^I ^ i, --vMi 1 .

10

15°

M/J

MINDANAO CURRENT

Figure 2A. Current observation by GEK, June to September 1965.

Figure 2B. Current observation by GEK, July to September 1966. 215

Figure 3A. Geopotential topography of the sea surface in dynamic meters referred to the 1,200 db surface in the summer of 1965. Data sources: Takuyo, Chofu Maru. Kagoshlma Maru, Keiten Maru, Nagasaki Maru, Atlantis II, and Uliana Gromova.

Figure 3B. surface in db surface Takuyo and

Table 1.

velocity of about 3.0 knots.

Year

Variation of néutral point, 1934-66

Month

December December Augus t November June July August

11° 12.5° 12° 13° 12° 14.5° 12.5°

One branch

goes westward at lat. 20° N. and enters

Neutral point at the sea surface

Vessel

the South China Sea, where most of it circles a warm eddy and then returns to the

Lat. N. 1934 1935 1939 1942 1949 1965 1966

Geopotential topography of the sea dynamic meters referred to the 1,200 in the summer of 1966. Data sources: Chofu Maru.

Komahashi Katsuriki Takunan Maru No. 3 Toyama Maru Spencer F. Baird Takuyo Takuyo

main axis of the Kuroshio.

The Kuroshio in

Luzon Strait flows back into the Pacific and goes northward along the eastern coast of Formosa with maximum velocities of about 3.0 knots or more. There is a remarkable countercurrent having a velocity of 1.5-2.0 knots asso-

along the coast of Luzon with a maximum

ciated with the warm eddy located on the

velocity of 1.5-2.0 knots and enters Luzon

east side of the Kuroshio in Luzon Strait.

Strait, then turns northeast.

Shigematsu (1932) and Koenuma (1939) pointed

When it

reaches long. 121° E. it has a maximum 216

out the existence of this warm eddy from

results of the Manshu observations and N i -

strong off the eastern coast of Luzon and

tani (1961) showed this using data of the

in Luzon Strait.

R/V Takuyo in M a y 1959. The observations on

current from just north of the place where

board the Kaiyo No. JL (1942) and Spencer X .

the North Pacific Equatorial Current is

Baird (1949) show the existence of this eddy

separated into two branches at the eastern

associated w i t h the w a r m water.

shore of the Philippines to the east of

W h e n this

We conclude that the

eddy is strong, it is continuous from about

Japan where the current leaves land should

long. 130° E. farther east to the waters

be called the Kuroshio, in a broad sense.

offshore of eastern Formosa, along the right side of the Kuroshio, as a belt; w h e n this

DISTRIBUTION OF TEMPERATURE AND SALINITY

eddy is weak, it is isolated northeast of Luzon.

This eddy associated w i t h

warm

Temperature

water may exist semipermanently, though its

The horizontal temperature distribu-

scale and position w i l l vary from time to

tions at 200 and 500 m. in the summer of

time.

1965 are shown in figure 4.

It is difficult to say whether this

countercurrent corresponds to Munk's

(1950)

In this fig-

ure, as in the figures showing surface

in his theory of the wind-driven ocean cir-

dynamic depth anomaly, data obtained on

culation.

the ships Chofu Maru, Keiten Maru, Kago-

There are several other clockwise

eddies along the right side of the Kuroshio. Kishindo (1931) defined the Kuroshio as follows:

"The northward or eastward

shima Maru, and Uliana Gromova in the region north of lat. 20° N. were used.

The

pattern of distribution at 200 m. is simi-

current whose characteristic water is

lar to the dynamic depth anomaly at the

pelagic, from the eastern shore of Formosa

sea surface, but that at 500 m. is similar

to the Tohoku district of Japan is to be

only in the region

called the Kuroshio."

N.

Sverdrup, Johnson,

north of about lat. 10°

In the region south of lat. 10° N., the

and Fleming (1942) treated the Kuroshio as

temperature at 500 m. is nearly uniform,

a part of the Kuroshio system, and defined

corresponding to the shallowness of the

it as follows, "The current running north-

current in this region.

east from Formosa to Ryukyu and then close

At 200 m., a long w a r m belt of temper-

to the coast of Japan as far as lat. 35° N . "

ature greater than 22° C. is present on

O n the other hand Wyrtki

the right side of the Kuroshio in Luzon

(1961) called the

flow east of Formosa the Formosa Current in

Strait.

his paper.

east of Luzon and east of Formosa the hori-

Wust (1936) compared the Kuro-

In the Kuroshio north and north-

shio in the East China Sea and Tokara Strait

zontal temperature gradients are very large.

w i t h the flow in the Caribbean Sea and

In Luzon Strait, the intrusion of a cold

Straits of Florida, respectively.

eddy from the South China Sea and a w a r m

The separation into two parts off the

eddy from the Pacific are seen in the south-

eastern coast of the Philippines is clear

ern and northern parts of Luzon Strait,

and the northward-moving current grows

respectively, and the Kuroshio meanders in 217

association w i t h these cores.

The 16° C.

As Takahashi says, it represents Munk's

isotherm at 200 m. is an indicator of the

western boundary vortex between the N o r t h

western boundary of the Kuroshio at the sea

Pacific Equatorial Current and the Equa-

surface in Luzon Strait, and 18° C. is a n

torial Countercurrent.

indicator of the m a i n axis of the Kuroshio

Vertical sections of temperature at

at the sea surface in Luzon Strait and in

long. 133° E. across the North Pacific

the sea east of Formosa (the 15°-17° C. iso-

Equatorial Current, and at lat. 19°30' N.

therms are its counterpart in the sea south

across Luzon Strait in the summer of 1965,

of Japan).

are shown in figure 5.

There is a cold eddy associated with upwelling of deep water at lat. 7° N .

This

In the section at

long. 133° E., the thermocline is shallowest at lat. 7.5° N., and the vertical tem-

cold eddy is on the boundary between the

perature gradient is largest there, reaching

N o r t h Pacific Equatorial Current and the

to about 0.1° C./m.

Equatorial Countercurrent. Takahashi

19°30' N., the largest isotherm slope is

(1959),

In the section at lat.

Wyrtki (1961), and Reid (1961) mentioned

found between long. 121° and 123° E., and

the existence of this enclosed cold eddy.

the largest vertical temperature gradient

Figure 4A. Horizontal distribution of temperature (° C.) at a depth of 200 m., summer of 1965.

Figure 4B. Horizontal distribution of temperature (° C.) at a depth of 500 m., summer of 1965.

218

is found west of long. 120° E.; the latter

seen in the western subtropical region of

reaches a value of about 0.06° C./m.

the North Pacific (Masuzawa, 1965; Takahashi

The so-called "18° C. water" which is

and Chaen, 1967) and of the North Atlantic (Worthington, 1959) appears in the region north of lat. 20° N. at long. 133° E., and east of long. 123° E. at lat. 19°30' N., though it is not very obvious. In these two sections, below the 6° C. isotherm (which is at a depth of about 700 m.), there is no pronounced slope of isotherms in the region of the Kuroshio and the North Pacific Equatorial Current. Salinity

Figure 5A. Vertical section of temperature (° C.) at long. 133° E. across the North Equatorial Current, summer of 1965.

The horizontal distribution of salinity at 200 and 500 m. in the summer of 1965 is shown in figure 6.

The pattern of dis-

tribution at 200 m. is similar to the dynamic depth anomaly of the sea surface.

An

eddy, with low salinity water, is found at lat. 7.5° N. east of Mindanao.

High salin-

ity water from the South Pacific reaches to about lat. 6° N.

The salinity of the South

China Sea water near Luzon Strait is lower than that of the Pacific by about 0.3°/ oo . At 500 m., the main salinity minimum, which is lower than 34.3°/ OD , extends between lat. 15° and 20° N. Vertical sections of salinity along long. 133° E. across the North Pacific Equatorial Current and along lat. 19°30' N. across Luzon Strait in the summer of 1965 are shown in figure 7.

The northern maximum

(about 35.00°/„ 0 ) reaches to about lat. 6°7° N.

The northern minimum layer slopes

upward toward the south and extends to Figure 5B. Vertical section of temperature (° C.) at lat. 19°30' N. across Luzon Strait, summer of 1965.

about lat. 4° N. or beyond.

The layer of

high salinity having a maximum value of about 35.3°/ 00 extending from the south is 219

Figure 6A. Horizontal distribution of salinity C/oo) at 200 m., summer of 1965.

Figure 6B. Horizontal distribution of salinity C/..) at 500 m., summer of 1965.

clearly seen; it reaches to about lat. 5°-

extensively weakened because the Kuroshio

6° N.

acts as a barrier against the Pacific The salinity minimum extending from

waters.

the south is present but weak at about 700 m.

Having a minimum value of about

WATER MASS ANALYSIS

34.53°/oo> it reaches to about lat. 10° N. The existence of two minimum layers ex-

Sverdrup, Johnson, and Fleming (1942)

tending from north and south gives rise

showed three principal water masses in

to a secondary maximum, which has no sig-

upper layers of the western Pacific Ocean:

nificance from the viewpoint of water mass

the Western North Pacific Central Water,

analysis.

the Western South Pacific Central Water,

The vertical section along lat. 19°30'

and the Pacific Equatorial Water.

The main

N. shows the sudden rises of salinity maxi-

sources of these waters are the North and

mum and minimum layers to the west from

South Pacific High Salinity Waters and the

long. 123° E.

North and South Pacific Intermediate Waters.

These two layers reach to

the South China Sea, but their values are 220

According to Matsudaira (1964), Masu-

Figure 7A. V e r t i c a l section of s a l i n i t y (°/

s

\

*

4

/

> \

0

'

/

r

»

t

//

,

w ,

ir "

il

.

U

d é d

'Q

"I d Ss

od

Ir-!

f

t d

¿ ¿ i f l p r

1

°

t ?

i

,4

V

a

s

s

i

! . i f

^

Figure

274

1

55.

• M O*

li 0 *

Thaliacea ,

COLD WATER SEASON

Figure 56.

Figure 57.

Coelent erata , Si puncu Ioide a & other larvae WARM WATER SEASON

Figure 58.

Doliolidae

/

i

-

.4

Coelenterata.Sipunculoidea S other larvae COLD WATER SEASON

Figure 59.

275

Figure 60.

Figure 61.

Figure 62.

Figure 63.

276

277

Hydrological Conditions and Biological Characteristics of tlie Kuroshio Waters in Area Lat. 20°-43° N. and Long. 138°-149° E. M. S. KUN, G. N. GLADKIKH, E. P. KAREDIN, W. P. PAVLYCHEV, W. I. RACHKOV, and E. G. STARODUBTSEV Institute

ABSTRACT

of Marine

Fisheries

and Oceanographyj

Vladivostok

The report comprises the results of investigations during summer 1965 and winter 1965~66 in the area between lat. 20°-43° N. and long. 138°-149° E. Three main zones in the area under discussion are distinguished--namely, the subarctic zone, the zone of mixing, and the Kuroshio proper. Data are given on the determination of primary production by means of the radiocarbon method. The relations between distribution of plankton and hydrological conditions are defined. Great seasonal variation is noted. I n the area bounded b y lat. 32°-34° N. and long. 138°-149° E. biological spring begins in February April and summer lasts from July to October. The abundance of phytoplankton in the southern region in summer was 49 mg./m. 3 The general volume of mesoplankton was 210 mg./m. 3 during February-April and 613 mg./m. 3 during July-October. In the southern part of the northern region it was 230 mg./m. 3 in winter and 292 mg./m. 3 i n summer in the 0-150 m. layer. The total abundance of macroplankton in both seasons did not differ much. However, the abundance of certain groups differed considerably from the winter period to the summer. The main features of fish distribution during the summer and winter periods are described.

INTRODUCTION Zhemchug (summer 1965) and SRTR Orlik Research vessels of the U.S.S.R.

ter 1965-66).

Additionally, Orlik

(win-

(winter

carried out investigations for CSK (Coop-

1965-66) occupied a line running diagonally

erative Study of the Kuroshio) in summer

southeast from the coast of Japan from lat.

1965 and winter 1965-66 in the area bounded

36° to 34° N.

by lat. 20° and 43° N. and long. 138° and

sky of the Hydrometeorological

149° E., occupying lines from lat. 20° to

completed a number of biological investi-

43° N. along long. 149° E. and from lat.

gations in both summer and winter that

20° N. to the coast of Japan along long.

extended as far east as long. 155° E. and

138° (fig. 1).

from lat. 20° to 43° N .

The vessels were the SRT

A third vessel, the ShokalServices,

The data in the literature concerning

The importance of these investigations

the water regime of the area are as yet

is hardly to be argued, for this part of

fragmentary and do not present a full pic-

the ocean is a place of intensive commerce

ture of seasonal changes in the water

of many nations.

regime.

Nor do they reflect the causes of

As is evident from our data collected

long-term changes in the pulsation and

during the year of observation, the hydro-

direction of different currents of warm

logical regime is subject to seasonal

waters of the Kuroshio, although many in-

changes.

vestigations have dwelt on these problems

complicated and variable, according to the

(Suda, 1936; Masuzawa, 1957; Motoda and

analyses published in the CSK atlas, which

Marumo, 1965; Fujimori, 1964; Yoshida, 1961;

describes the results of investigations

and others).

during summer 1965.

Data on the hydrological regime collected during this expedition are now being examined, and further analyses as well as

The dynamics of this regime are

The most complicated

configuration of flow is observed east of Honshu. Frontal divisions between different

further observations will enable us to come

water structures depend directly upon the

to a final conclusion as to how the Kuroshio

hydrodynamics of the area investigated.

axis changes and to what this phenomenon is

These frontal divisions were defined by

due.

calculating horizontal temperature and salinity gradients.

we used the terminology of Suda (1936) and

140°

Kawai (1955).

f'- ! i v \ o j/ ^J~C* 1 /v-' zone of mixing (between lat. 37° and 41° N.) and zone of Kuroshio waters (south of lat. 37° N.).

In the zone of subarctic waters three

superposed water masses are distinguished with the surface temperature 3°-ll° C., the cold intermediate 0.9°-1.8° C., and the warm intermediate 2.0°-3.3° C.

The

salinities increase with depth from

LATITUDE

33.75°/00 at the surface to 34.25°/ 00 at

Figure 2. Water mass distribution during summer 1965 along long. 149° E.

1,000 m. (fig. 2).

Table 1. Horizontal temperature (° C. per nautical mile) and salinity (°/c gradients in the Oyashio and Kuroshio fronts, summer and winter

Winter

Summer Depth (m.)

Oyashi o front ° C.

Salinity

per nautical mile)

Kuroshio front ° C.

Salinity

C/..)

Oyashio front ° C.

Salinity

Kuroshio front ° C.

Salinity

0

0.08-0.10

0.035-0.056

0.06-0.10

0.008-0.010

0.20-0.28

0.029-0.032

0.08-0.15

0.005-0.006

50

0.31-0.41

0.039-0.063

0.12-0.27

0.008-0.010

0.21-0.28

0.026-0.035

0.09-0.18

0.006

100

0.19-0.33

0.022-0.043

0.14-0.24

0.010-0.020

0.21-0.29

0.023-0.040

0.10-0.21

0.010-0.011

200

0.09-0.24

0.022

0.18-0.24

0.011-0.026

0.08-0.19

0.012-0.016

0.14-0.37

0.012-0.026

400

0.04-0.08

0.004

0.15-0.24

0.015-0.018

0.04-0.08

0.001-0.004

0.18-0.35

0.012-0.030

281

intermediate waters usually shows how far

multistage structure of the subarctic front.

the subarctic waters penetrate to the south.

This is well demonstrated by the 10° iso-

Thus according to our data the Oyashio front

therm, which is considered by Japanese

is at lat. 41° N.

scientists as the lower boundary of Kuro-

In the zone of mixing,

higher temperatures were observed in the

shio waters.

surface layer; a general rise of tempera-

meandering of the axis of the Kuroshio

tures was seen from north to south—from

(fig. 3).

18° to 25° C.

In the Kuroshio region the

This phenomenon is due to

Thermal and saline regimes in the

surface waters had temperatures of 26° to

southern regions along both long. 138° and

21° C.

149° E.

differ from those of the northern

The vertical temperature gradient was 0.2°

region.

The influence of cold Oyashio

C. per meter, i.e., four times less than it

waters is seen at about lat. 33° N.

was in the northern part of the area under

weak form this effect is seen off the south-

investigation.

ern coast of Honshu at 200-400 m.

The thermocline was at 25-60 m.

In a Meander-

Frontal zones were noted in the region

ing of the Kuroshio in this region, together

of interaction of subarctic and subtropical

with cyclonic movement, results in formation

waters (between lat. 37° and 42° N.).

of a region of cold waters which rise from

These frontal zones are either associated

below.

with certain Kuroshio branches or belong to

this region is 10.5°-11° C., i.e., 5°-6°

the isolated eddies that are characteristic

less than in the subtropical waters of the

of this zone.

Kuroshio.

The temperature distribution

At 200 m. depth the temperature of

At the southern boundary of a

cyclonic eddy a frontal zone is formed which

in summer along long. 149° E. indicates the

i 0Ixl O H

(J)FLOW DIRECTED EASTWARD •

1,000 43« N.

FLOW DIRECTED WESTWARD

39°

37° LATITUDE

Figure 3.

282

Temperature distribution along long. 149° E. (summer 1965).

In contrast to the summer period, a

extends over great intervals of depth (50700 m.), protruding towards cold waters.

relatively homogeneous field of temperatures

The maximal horizontal temperature gradients

and salinities was observed along long. 149°

(0.17°-0.2° C. per mile) and those of salin-

E., except between 0 and 200 m. in the fron-

ity (0.008°/Oo to 0.009°/oo per mile) are

tal zones.

observed at 400-500 m. depth.

gradients are almost absent, since consid-

As a result

of summer heating there are no frontal zones

Vertical temperature-salinity

erable mixing takes place during winter.

in the surface layer.

In winter the cold intermediate layer

In the Kuroshio zone the temperature in the upper 50 m. layer is 25°-27° C.; 0

salinity is 34.25 /„ o to 34.50°/ oo .

In the

disappears as a result of vertical circulation.

The temperature of subarctic waters

to the north of the Oyashio front (0-200 m.

75-200 m. layer salinity at the maximum is

depth) ranges from 1.5° to 2.0° C.

34.75°/0