Ocean Circulation and El Nino: New Research [1 ed.] 9781608768738, 9781606920848

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Copyright © 2009. Nova Science Publishers, Incorporated. All rights reserved.

Copyright © 2009. Nova Science Publishers, Incorporated. All rights reserved.

OCEAN CIRCULATION AND EL NIÑO: NEW RESEARCH

Copyright © 2009. Nova Science Publishers, Incorporated. All rights reserved.

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OCEAN CIRCULATION AND EL NIÑO: NEW RESEARCH

JOHN A. LONG AND

DAVID S. WELLS

Copyright © 2009. Nova Science Publishers, Incorporated. All rights reserved.

EDITORS

Nova Science Publishers, Inc. New York

Copyright © 2009 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS.

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LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Long, John A. Ocean circulation and El Nino: new research / John A. Long and David S. Wells. p. cm. Includes index. ISBN 978-1-60876-873-8 (E-Book) 1. El Niño Current--Research. 2. Ocean currents--Pacific Ocean--Research. 3. Ocean circulation--Pacific Ocean--Research. 4. Meridional overturning circulation--Research. I. Wells, David S. II. Title. GC296.8.E4L66 2009 551.46'2--dc22 2009003617

Published by Nova Science Publishers, Inc.    New York

CONTENTS Preface

vii

Research and Review Studies Chapter 1

Chapter 2

Chapter 3

Chapter 4

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Chapter 5

Chapter 6

Seasonal Cycle Variations on the Supercontinent of Pangaea: Implications for the Early Jurassic Palaeoceanography of the European Epicontinental Sea Carmen Arias Modal Decomposition for Oceanic Circulation: Applications for a High- Resolution Model and Lagrangian Data L. M. Ivanov and C. A. Collins

1

31

Ocean Circulation from Altimetry: Progresses and Challenges Yongsheng Xu, Jianke Li and Shenfu Dong

71

Ocean Circulation: An Overview and Current Trends in Research Bernd J. Haupt

99

Temporal Variability of the Florida Current Transport at 27oN G. Peng, Z. Garraffo, G. R. Halliwell, O. M. Smedstad, C. S. Meinen, V. Kourafalou and P. Hogan Global Climate Change and Biotic-Abiotic Interactions in the Northern Chilean Semiarid Zone: Potential Long-Term Consequences of Increased El Niños Peter L. Meserve, Julio R. Gutiérrez, Douglas A. Kelt, M. Andrea Previtali, Andrew Engilis, Jr. and W. Bryan Milstead

119

139

vi

Contents

Chapter 7

Managing Climate Variability in Agricultural Analysis Víctor E. Cabrera, Daniel Solís, Guillermo A. Baigorria and David Letson

Chapter 8

ENSO Impacts on European Winter Rainfalls and Their Modulation by Leading Euro-Atlantic Teleconnections D. Zanchettin, P. Traverso and M. Tomasino

181

Effects of El Niño Southern Oscillation (ENSO) on Marine Fish and Shellfish Populations and Their Habitats in North America Paulinus Chigbu, Joseph W. Love and Joshua J. Newhard

207

Chapter 9

Chapter 10

Coral Color — Reflection and Absorption Noga Stambler

163

241

Short Communications A

B

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Index

Interannual and Intraseasonal Variability in the Boreal Summer Asian Monsoon before and after Climate Regime Shift of Mid 1970s as Revealed in the NCEP/NCAR Reanalysis Igor I. Zveryaev El –Niño and Coral Reefs M. James C. Crabbe, Emma L. L. Walker and David B. Stephenson

253 265

275

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PREFACE Progress toward better understanding of ocean variability is closely linked to the development of signal processing tools for multi-scale analysis of ocean flows. This book includes a review of recent progress in physical oceanography, such as results on studying ocean circulation and mesoscale ocean dynamics derived from satellite altimetry. Ocean currents are driven by wind as well as by thermal differences. This book examines the basic functions of the global three dimensional thermohaline circulation and its influence on climate. The impacts of the El Nino/Southern Oscillation(ENSO) on tropical climates are well-established. Research is presented to provide a relationship to the European climates. In the semiarid zones of western South America, for example, implications of increased rainfall during ENSO warm phases are multiple and complex. An investigation of the interannual and intraseasonal variability in the summer wind fields in the Asian monsoon system is presented. The book also includes information from the scientific community on the state-of-art studies related to climate risk in agriculture and helps to identify priorities for ongoing and future research. Chapter 1 - A new conceptual palaeoceanographic model for the Early Jurassic European Epicontinental Sea is outline in this chapter. The present palaeoceanographic reconstruction is primarily based on physical oceanographic principles that govern the global ocean circulation system. The European Epicontinental Sea was located along the present European continent at the beginning of the Early Jurassic. The ocean circulation of the European Epicontinental Sea derived from climate models shows a clear monsoonal nature. During the summer, highpressure cell is sited over southern Gondwana and low-pressure cell over the pre-Central Atlantic Ocean, the polar ocean and western Laurasia would generate easterlies winds along the Epicontinental Sea. In winter, land cools and the warm pressure low-pressure cells are replaced by high-pressure cells over the north-eastern coast of Gondwana and central Laurasia landmasses. At high latitudes the low-pressure cells are replaced by high-pressures. The strongest winds are the easterly surface winds. The resulting equatorial, western boundary, prevailing easterlies, and eastern boundary currents combine to create a circular flow, a clockwise subtropical gyre, within the European Epicontinental Sea. These results were integrated in a new multilayered deep ocean circulation proposal based on the spatial distribution of several Early Jurassic invertebrate groups, temperature, salinity and lithological data. Taking into account the combined faunal and lithological data and the EES and Tethyan salinity and temperature distribution derived from climate models, an integrated three-fold classification of water masses has been proposed. In this model, it proposes a new

Copyright © 2009. Nova Science Publishers, Incorporated. All rights reserved.

viii

John A. Long and David S. Wells

deep-water circulation model (estuarine type), with Tethyan warm water flowing northwards at depth to the EES and Boreal superficial cold and freshening water flowing out from the EES to the Tethys Ocean. Furthermore, results from both methodologies provide an important test for the theoretical predictions which coming from the numerical ocean models for the Early Jurassic. Chapter 2 - The classical Fourier polynomials are generalized for non-rectangular basins: partially open, simply and multiply connected, and are used as basis functions (modes) for the spectral representations of ocean velocity, temperature and tracer concentrations. Calculation of the modes accounts for basin geometry and bottom topography only but neither dynamical forcing nor dissipation processes. Therefore these basis functions are unlike empirical orthogonal functions (EOFs) and cannot mix effects of different spatial scales on a particular spatial circulation pattern. Circulation velocity or any scalar field can be represented as a weighted sum of modes (a modal decomposition) with weights (spectral coefficients) determined in the least squares sense from the orthogonal feature of modes. Using different combinations of modes, a 3D circulation is decomposed as a hierarchy of “elementary” currents of different scales and/or with different kinematic properties. These can be used to select the spatial energy-dominant scales and coherent circulation structures in complex oceanic flows. The dominant time scales of the flow can be extracted from the spectral coefficients using wavelet analysis. It is always possible to select the wavelet coefficients with respect to a specified time scale, and reconstruct a filtered version of the flow from them, selecting only energy-dominating scales (ridges on scalogram). To perform such decomposition, an objective threshold is defined in terms of the wavelet coefficients. Using modal decomposition and a highly efficient filtering technique (which determines the optimal number of modes in the modal decomposition) ocean currents are reconstructed from irregularly spaced and noisy data, filling spatial gaps in inhomogeneous observational coverage. The estimates are robust for a given observational sampling and tend to the “true” solutions as the variance of random measurement error vanishes. The capability of the developed modal decomposition is illustrated by a number of oceanographic examples. First, energy-dominant currents including coherent mesoscale eddies and Rossby waves were detected in high-resolution ROMS (UCLA) output fields off Central California. Second, the mid-depth large-scale currents in the North Atlantic were reconstructed from Argo float data. Third, the FGGE data were used to reconstruct the nearsurface large-scale circulation in the Southern Ocean. These examples show that the modal decomposition seems to be a highly efficient diagnostic technique for ocean circulation from large scales to submesoscales. Chapter 3 - The chapter provides a review of recent progresses in physical oceanography, such as results on studying ocean circulation and mesoscale ocean dynamics derived from satellite altimetry. Since 1992, satellite altimetry has provided an unprecedented 16 years monitoring of sea level and ocean circulation variations. Continuous measurements from satellites like TOPEX/Poseidon and Jason-1 help us understand and foresee the effects of the changes in ocean circulation on climate and on extreme climate events such as El Niño and La Niña. Altimeter measurements have improved our understanding of both the dynamics and thermodynamics of western boundary currents by providing a synoptic view of the current systems and their interannual variations, and allowed scientists to quantify eddy-induced salt and heat transport, and seasonal and interannual variations in eddy kinetic energy. Altimeter

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Preface

ix

measurements have also been used to map eddies, quantify their amplitudes and diameters, track their trajectories, and examine their eddy dynamics and roles in the ocean processes and climate variability. Recent advances in satellite altimetry, in synergy with other remote sensing techniques, constrain the uncertainty of mechanic energy driving meridional overturning circulation which regulates climate change. Moreover, altimetry has discovered a surprising sea level anomaly propagation speed which challenges the existing linear Rossby wave theory, and revealed the presence of elusive zonal fronts and jets in the ocean. However, challenges still exist in monitoring the ocean variability from satellite altimetry. Satellite altimeters are not able to measure the time-mean geostrophic currents due to the large uncertainty in geoid. This poses challenges for deriving the absolute geostrophyic flow in regions where bottom velocities are non-zero since hydrographic estimates of absolute dynamic topography are unable to capture the effects of the bottom. The uncertainties of satellite altimetry measurements have a high geographic variability. The existence of high frequency energetic barotropic motions in the ocean can lead to a large aliasing error in satellite altimetric observations. New evidences show that the combined aliasing from several neighboring and crossing tracks could produce unreal mesoscale signals in altimeter mapped product. Although satellite altimetry has improved our understanding of the climate system dramatically, it is important to keep in mind that problems still remain and new challenges will arise. Chapter 4 - Ocean circulation is the large-scale movement of water masses within and among ocean basins. Ocean currents are driven by wind as well as by thermal differences and are modified by ocean topography and the rotation of the Earth. Surface ocean water warms in equatorial and low-latitudinal regions. The surface circulation carries the warmer surface water to higher latitudes where it disburses heat from the water into the atmosphere. This cooling water becomes denser and eventually sinks into the deep ocean. The major areas for this so-called deepwater formation are the northern North Atlantic, where North Atlantic Deep Water and Labrador Sea Water forms, and the waters around Antarctica, where the coldest and densest deep ocean water, the Antarctic Bottom Water, is formed. In this chapter, we will examine the basic functions of the global three dimensional thermohaline circulation and its influence on climate. Included will be examples of research from three dimensional numerical climate models as well as results of data analyses that link changes in climate with changes in the freshwater balance of the ocean which result from alterations in the cryosphere and subsequent changes in the glob al ocean circulations system that transports heat and matter worldwide. Chapter 5 - The variability of annual cycle of the Florida Current transport and its relationship to variability of large-scale atmospheric forcing is examined using time series of daily Florida Current transport based on submarine cable voltage measurements from 1982 to 2005. To investigate the impact of large-scale atmospheric forcing variations represented by the North Atlantic Oscillation (NAO), two NAO regimes, strong positive and strong negative, are defined in order to isolate basic characteristics of the annual cycles of the Florida Current transport associated with those two regimes. The strong positive (negative) NAO regime is defined as being when the NAO index is greater (less) than 0.8 (-0.8). A minimum of 30.46 Sv in the Florida Current transport is found in January and a maximum of 33.71 in July with a mean of 32.12 Sv based on daily composites of all cable data, which is consistent with previous studies. A distinct difference between those two opposing NAO regimes occurs in

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John A. Long and David S. Wells

late winter, with a minimum (maximum) for the strong positive (negative) NAOs in March. As for the summer peak, it occurs in May for the strong positive NAOs and in July for the strong negative NAOs, as in the normal year. There is a 5% fluctuation in the mean Florida Current transport values between those two strong NAO regimes. Using daily transport time series for the Florida Current calculated from various model experiments for the year 2004, along with the Florida Current transport derived from cable and in-situ measurements from research cruises, we have shown that the Florida Current transport is not sensitive to the resolution of local atmospheric forcing or to the model vertical resolution. However, the major influence on fluctuations on time scales of a few days to several weeks is found to be linked to basin-scale variability in the North Atlantic Ocean. The decadal variability of the Florida Current transport is examined using a 54-year time series of Florida Current transport anomaly from a 1/3o North Atlantic model simulation. The model Florida Current transport anomaly is found to be loosely correlated with the NAO anomaly. The time series of the sea surface height difference (sshdif) between the subtropical gyre and subpolar gyre, however, is strongly correlated with the NAO anomaly, with NAO leading by about 2.5 years. The results also show that the sshdif is well correlated with the model Florida Current transport anomaly, with sshdif leading by about 3.5 years. This suggests that the decadal variability of the Florida Current transport is largely controlled by the variability of the internal ocean dynamics forced by the NAO variability rather than by the NAO variability itself. Chapter 6 - Global climate change (GCC) has become a major focus in ecology as ramifications of environmental alteration grow increasingly evident. Although dispute remains about linkages, increased frequency, duration, and magnitude of El Niño events are a predicted consequence of GCC. In western South America, increased rainfall tends to occur during El Niño Southern Oscillation (ENSO) warm phases especially in semiarid zones of northwest Peru and north-central Chile; conversely, low rainfall occurs in other arid regions such as Australia and southern Africa. The implications of such changes for semiarid regions are multiple and complex. For example, increased rainfall leads to dramatic changes in ephemeral plant cover; however, in multiyear El Niño/high rainfall events, ephemeral cover often decreases in subsequent years, suggesting nutrient depletion. Many other organismal groups increase dramatically following El Niños, including small mammals, their predators, birds, and other components. The responses appear due to cascading-upwards effects of rainfall on productivity in regions which historically have been arid. A similar pattern holds for plant and animal groups elsewhere when unusually high rainfall occurs during El Niño years (e.g., North America). During ENSO cool (dry) phases (i.e., La Niña events), rainfall declines dramatically in the same regions with consequential negative effects on ephemeral plants and animals. In 1989, the authors initiated a large-scale manipulation in a national park in the northcentral Chilean semiarid zone. Based on earlier work, we focused our attention on the role of biotic interactions in the community, specifically vertebrate predation, small mammal herbivory, and interspecific competition among members of the small mammal assemblage. Although they have documented some transitory effects of excluding vertebrate predators and small mammal herbivores from fenced, replicated live-trapping grids on small mammals and plants, respectively (e.g., “top-down” control), their responses to increased precipitation have been overwhelming, strongly implicating overall “bottom-up” control. In the last 19 years, five El Niño/ high rainfall events, differing in duration and intensity, have generated variable

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Preface

xi

responses by plants, small mammals, birds, and insects. Potential consequences of increased duration and frequency of El Niños in the Chilean semiarid zone include changes in community dynamics, and greater impacts of introduced species as well as disease vectors and reservoirs. Chapter 7 - This chapter offers some analytical insights for a comprehensive theoretical understanding of how to develop reliable ENSO-based crop yield forecasts and how to incorporate this information into an ENSO-sensitive farm-plan. A discussion on the usefulness of climate information for policy analysis is also presented. An improved basic understanding on the impact of seasonal climate variability (i.e., ENSO) on agriculture involves a more in-depth discussion of the value of the information as well as a broader knowledge of actual (or created) distinctions between adaptation, mitigation and response to climate risks. This chapter intends to inform the scientific community of the state-of-art on studies related to climate risk in agriculture and to help identify priorities for ongoing and future research. Chapter 8 - While the impacts of the El Niño/Southern Oscillation (ENSO) on tropical climates are well established, the way warm and cold phases of ENSO may influence the European climates is still debated controversially. This research contribution aims to provide further arguments to the discussion by highlighting some remarkable symmetries between ENSO and European winter rainfalls, in particular demonstrating that the propagation of ENSO signals onto Europe is likely to also depend on the concurrent state of two leading Euro-Atlantic teleconnections, namely the North Atlantic Oscillation (NAO) and the East Atlantic/Western Russia (EAWR). Chapter 10 - Corals absorb, reflect, scatter, and fluoresce light. Light absorption per unit of coral surface area decreases with increase in colony size, with a clear effect of different coral morphologies. In branched colonies, shading among branches reduces the absorbed light per unit area and per zooxanthella. Corals often have different colors. Color is variable, even among colonies of the same species growing together. While the colors blue, pink, and green are due to the protein pigments in the host tissue, the brown color is due to the absorption of the zooxanthellae pigments. Coral colors change as a result of acclimation and adaptation to environmental conditions. Dark brown colors, representing higher absorption, are due to low light intensities or exposure to high-nutrient concentration, while light colors are due to low-pigment concentrations, in some cases due to natural conditions while others indicate stress conditions. These variations can be monitored at a reef level; however, corals can exhibit different colors in the same colony. In some cases, the spectral variation between color morphs of the hermatypic corals is higher than between species. Therefore, species recognition based on reflectance spectra is only possible in certain cases. The absorption range of the corals and their symbiotic zooxanthellae, and their ability to change their color by photo-acclimation and photoadaptation, enable the coral to grow and survive. Short Communication A - Interannual and intraseasonal variability in the summer wind fields in the Asian monsoon system is investigated using 850 hPa zonal wind data obtained from the National Centers for Environmental Prediction - National Center for Atmospheric Research (NCEP/NCAR) Reanalysis. In the boreal summer Asian monsoon the first EOF modes in interannual variability of both mean zonal wind and intensity of intraseasonal

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John A. Long and David S. Wells

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oscillations (ISO; i.e., oscillations with dominant time scale 30-60 days, characterized by predominantly northward propagation) demonstrate significant interdecadal changes. Both before and after climate regime shift interannual variability of ISO was not linked to that of the mean zonal wind, and was associated with very different sea surface temperature and convection patterns. After climate regime shift links between interannual variability of zonal wind and SST variations became stronger in the Pacific and weaker in the central Indian Ocean. For ISO significant links to SST variations in the eastern Indian and southwestern Pacific Oceans were found before climate regime shift, but no such links were detected during later period. Analysis of correlations between ISO and convection suggests that, in contrast to earlier period, alterations in Walker circulation could affect interannual variability of ISO during 1979-1999. Some similarity between spatial patterns of the first EOF modes of the mean zonal wind and ISO has been revealed. However, in general present results do not suggest that there is common leading mode in interannual and intraseasonal variability in the boreal summer Asian monsoon. Short Communication B - Sea surface temperatures (SSTs) in all regions have been increasing over the past 20 years. This increase has brought corals up to their upper thermal limit of survival, and as a result bleaching occurs when there are higher than normal sea temperatures such as during an El Niño-Southern Oscillation (ENSO) event. Corals can die as a result of bleaching, though they may partially or fully recover from bleaching events. Bleaching causes a decrease in the growth rate of corals, and the time taken for a coral to recover from a bleaching event may take several years or decades. If the frequency of bleaching increases then the capacity for coral reefs to recover is diminished. Bleaching events mostly occur when the southern oscillation index is less than -5. Warm season sea surface temperature anomalies associated with mass bleaching events in the Indian Ocean, Southeast Asia and parts of the Pacific Ocean are more likely to occur during an ENSO event. Negative correlations between atmospheric CO2 and coral growth have been measured. The combined affect of increased CO2 levels and temperatures are predicted to reduce the potential habit for corals on a global scale.

In: Ocean Circulation and El Nino: New Research Editors: J. A. Long, D. S. Wells, pp. 1-30

ISBN: 978-1-60692-084-8 © 2009 Nova Science Publishers, Inc.

Chapter 1

SEASONAL CYCLE VARIATIONS ON THE SUPERCONTINENT OF PANGAEA: IMPLICATIONS FOR THE EARLY JURASSIC PALAEOCEANOGRAPHY OF THE EUROPEAN EPICONTINENTAL SEA Carmen Arias Departamento de Paleontología e Instituto de Geología Económica (CSIC-UCM). Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, Spain

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ABSTRACT A new conceptual palaeoceanographic model for the Early Jurassic European Epicontinental Sea is outline in this chapter. The present palaeoceanographic reconstruction is primarily based on physical oceanographic principles that govern the global ocean circulation system. The European Epicontinental Sea was located along the present European continent at the beginning of the Early Jurassic. The ocean circulation of the European Epicontinental Sea derived from climate models shows a clear monsoonal nature. During the summer, high-pressure cell is sited over southern Gondwana and low-pressure cell over the pre-Central Atlantic Ocean, the polar ocean and western Laurasia would generate easterlies winds along the Epicontinental Sea. In winter, land cools and the warm pressure low-pressure cells are replaced by high-pressure cells over the north-eastern coast of Gondwana and central Laurasia landmasses. At high latitudes the low-pressure cells are replaced by high-pressures. The strongest winds are the easterly surface winds. The resulting equatorial, western boundary, prevailing easterlies, and eastern boundary currents combine to create a circular flow, a clockwise subtropical gyre, within the European Epicontinental Sea. These results were integrated in a new multilayered deep ocean circulation proposal based on the spatial distribution of several Early Jurassic invertebrate groups, temperature, salinity and lithological data. Taking into account the combined faunal and lithological data and the EES and Tethyan salinity and temperature distribution derived from climate models, an integrated threefold classification of water masses has been proposed. In this model, it proposes a new deep-water circulation model (estuarine type), with Tethyan warm water flowing

2

Carmen Arias northwards at depth to the EES and Boreal superficial cold and freshening water flowing out from the EES to the Tethys Ocean. Furthermore, results from both methodologies provide an important test for the theoretical predictions which coming from the numerical ocean models for the Early Jurassic.

Keywords: Palaeoceanography, atmospheric circulation; ocean circulation models; ocean currents; Early Jurassic; European Epicontinental Sea; climate model.

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INTRODUCTION Our understanding of the stability and variability of the ocean and atmospheric global circulations has greatly advanced during the past decade through progress in numerical climate model simulations. Climate models are high-quality at simulating some aspects of the climate system and less fine at others. The value of any particular climate model is generally tested by how well its output conforms to a given set of known situations. Climate models are expected to reasonably reproduce present day conditions, but comparisons to past data, particularly those in which the boundary conditions are different than today are evidently a difficult question. Comparing models with each other may be informative, but it cannot be an absolute guide to their accuracy since different models, generally, rely on similar approximations and work in similar ways. Thus, the reliability of these models can be only estimated by comparing model-climates with reconstructions of past climates based on the information proportionate from other sources, e.g. information from the geological and fossil records. Therefore, evidence from the spatial and temporal distribution of several Early Jurassic marine fossil groups in the Jurassic European Epicontinental Sea can be used to test independently the ocean circulation pattern derived from climate models. An excellent example of the results of such comparison is the discrepancy between geological and paleontological data on the Early Jurassic and the predictions of the Numerical Climate Models as was pointed out by Chandler and colleagues (Chandler et al., 1992 and Chandler, 1994). Global climate is produced through a variety of processes and interactions that operate on a wide range of scales, including regional, continental and global. Changes in climate occur from physical interactions that take place on any or all of these scales. Unfortunately, the computers and programs that run the climate models are limited to gross representations of the geographic, geologic and atmospheric details that they use to run climate simulations. Then, many small scale features, such as the Early Jurassic European Epicontinental Sea (EES) cannot be represented, even though they may significantly impact the global climate. We can solve this problem through a comparison of geological and paleontological climate proxy data with climate model results. The Jurassic is a period of special interest in the earth’s climate history because was a time of one of the unclear global climate change in the geological record, one of the less-well known episodes of temperate to global warming transition, as the present time seems to be. Furthermore, the Jurassic was a time very well-studied because Jurassic fossiliferous rocks are exceptionally widely distributed, a time of very well studied fossil record, allowing for a detailed understanding of the global palaeogeography and faunal distribution, which is essential to palaeoclimatic and palaeoceanographic interpretations.

Seasonal Cycle Variations on the Supercontinent of Pangaea

3

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The geographical distribution of land and sea is of crucial importance to both regional and global oceanic circulation. Just as today, the oceanic circulation patter is dominant by the present disposition of the continents; past circulation patter would be influenced by the continental-ocean configuration that existed during the Early Jurassic. Therefore, an acute and comprehensible palaeogeography is a previous requisite for any analysis of the atmospheric and the oceanic pattern circulation. The palaeogeography of the Early Jurassic Earth shows all continents assembled in a large land-mass centred over the Equator, the Pangaea, surrounded by a world-wide ocean, the Panthalassa Ocean and with a wedge sea into the eastern margin called the Tethys Ocean (Dewey et al., 1973; Smith et al., 1973; Biju-Duval, et al, 1977; Owen, 1983; Dercourt et al., 1985; Ziegler, 1988, 1992; Ziegler et al, 2001). The rifting of this supercontinent ended in the division of the Pangaea into two large landmasses: the Laurasia (North America and the majority of Eurasian) and the Gondwana (South America, India, Australia and Antarctica) (Figure 1), and in-between them, an Epicontinental Sea was formed (between 10º and 60º North latitude), named the European Epicontinental Sea (EES) (Figure 1). The development of the Early Jurassic EES was influenced by the evolution of the Central Atlantic area and by sea-level variations. This coupled action allowed the development of new seaways and barriers among the different basins through the EES and between the EES and the Tethys and Panthalassa oceans (Vail et al., 1977; Hallam, 1978; Ziegler, 1988, 1990, 1992; Kutzbach, et al., 1990; Bassoullet et al., 1992; Meister and Stampfly, 2000; Ziegler et al., 2001; Scotese, 2003; Veevers, 2004).

Figure 1. The Early Jurassic Palaeogeography. Emergent areas: AM: Armonican Massif; BM: Bohemian Massif; CSH. Corsica- Sardinia High; FC: Flemish Cap; FM: Fünen High; GB: Grand Bank; GH: Grampian High; IBM: Iberian Meseta; IM: Irish Massif; LBM: London-Brabant Massif; MC: Massive Central; PB: Porcupine Bank; RHB: Rookall-Hatton Bank; RM: Rhenish Massif ;SP: Shetland Platform; VH: Vindelecian High; WH: Welsh Massif (after Ziegler, 1988, 1992; Bassoullet et al.,1992; Ziegler et al., 2001; Scotese, 2002).

There has been general consensus for many years that the climate of the Early Jurassic was more equable and warm than today to the extend that were no polar icecaps and cold

4

Carmen Arias

intolerant organisms apparently, extended over a wider range of latitude (Briden and Irving, 1964; Frakes, 1979; Hallam, 1975, 1994; Frakes and Francis, 1988, Frakes et al., 1992). But this equable climate condition has been recently called in question because a large supercontinent such as Pangaea is probably to have experienced a considerable seasonal range of temperature (Hay et al., 1982; Parrish, 1982; Parrish and Curtis, 1982; Parrish et al., 1982; Crowley, 1983; Brandt, 1986; Crowley et al., 1989; Crowley and North, 1991). Climate simulations indicate the large seasonal temperature fluctuations could occur over mid and high latitude continental interior might refuting equable conditions (Kutzbach, 1985; Kutzbach and Gallimore, 1989; Kutzbach et al., 1990; Wilson et al., 1994; Fawcett et al., 1994; Barron and Fawcett, 1995). General Circulation Model (GCM) simulations of the Early Jurassic climate reveals an Earth 5.2ºC warm and a latitudinal temperature gradient dominated by high-latitude warming (+20ºC) and a little tropical change (+1ºC) (Chandler et al., 1992; Chandler, 1994).

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THEORETICAL ATMOSPHERIC AND OCEAN CIRCULATION PATTERN Because the aim of this chapter is to revise the palaeoceanography of the Early Jurassic oceans and adjacent seas, an analysis of the global atmospheric circulation need to be previously considered. The ultimate cause for the general oceanic circulation is the solar radiation that acts on the physical processes at the boundary between the water and the air (exchange of heat, water vapour, gases, and momentum). The general atmospheric circulation, in particular the wind system, is responsible for the major ocean currents pattern in the upper part of the water masses and constitutes the "wind-driven circulation". Into the deep, a second kind of circulation called thermohaline dominates. This deep ocean circulation, partially influenced by the first one, is caused by surface density changes due to the change of salinity and temperature (Hill, 1962; Dietrich and Kalle, 1963; Neumann and Pierson, 1966; Pickard and Emery, 1990). In this chapter we will consider the wind-driven and the deep ocean circulation. The oceanic surface circulation is coupled with the atmosphere through the surface winds (under the control of the gravity, the pressure gradient, and the Coriolis force), surface energy budget and the moisture balance. The movement of the winds over the surface of the ocean puts the water column in motion through function at a right angle to the wind as a consequence of the Coriolis force that results from the imbalance between the gravitational force and centrifugal force. This deflection occurs to the right in the Northern Hemisphere and to the left in the Southern Hemisphere (Neumann and Pierson, 1966; Pickard and Emery, 1990). Initially, this deflation is small but with depth increases. In addition, the speed of the water associated with the wind stress decreases because each layer dissipates energy for internal friction. The result of the increase of deflection and the decrease of the motion form a spiral named the Ekman spiral. The sum of their motion vectors gives a mean direction for the water motion, which is to the right wind direction. For this reason, the surface current does not follow its theoretical orientation relative to the wind and is deflected. For example, the low latitude northeastern trade winds produce westerly ocean currents (Dietrich and Kalle, 1963; Neumann and Pierson, 1966; Pickard and Emery, 1990).

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In attempt to describe the atmospheric circulation during the Early Jurassic, it has been considered two approaches, one proposal would be based on analogies with the present general atmospheric circulation pattern and another would derive from climate simulations.

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Models Based on Analogies with the Present Atmospheric Circulation The underlying cause of the general circulation is the unequal heating of the earth's surface, since the tropics experience a net gain, while polar region a net loss. To balance, the atmosphere transport warm air poleward and cool air equatorward. This "thermally direct cell" is the result of the horizontal pressure gradient originated between the broad equatorial region of low pressure and the polar high pressure area since low-pressure is associated with the convergence and ascending air and high pressure with descent air and surface divergence. Such a simple cellular as this does not actually exist because rotation of the earth breaks this simple convection system into a series of three cells. Surface-based observations allowed to develop this new model, the "three cell model" (Polar, Ferrel and Hadley cells) that is bases on the occurrence of low pressure belts around the equator and at 60º latitude and high pressure at the poles and around 30º latitude. This general model is modified by the action of another force, the Coriolis force. The Coriolis force deflects the rising air from the equator to the poles, towards the right in the Northern Hemisphere (Figures 2 a,b) When we study the present world, in the northern Hemisphere, we obtain an average distinction of sea-level pressure and winds and we can see, as there are regions where pressure system appear to persist all year round and referred to as semi-permanent highs and lows. Semi permanent subtropical anticyclones (they are referred the Bermuda and the Pacific Highs) develop in response to the convergence of air aloft near an upper level jet stream. In the Northern Hemisphere, the air moves poleward from the tropics and is constantly cools by radiation. At the middle latitudes (30 º N), this airflow starts to converge what causes the formation of a belt of High pressure called Subtropical Highs, Horse latitudes or Anticyclones. They are well developed in the Southern Hemisphere where there is relatively less landmasses and so that, less contrast between land and water masses. In addition, there are Semi permanent subpolar lows. In these latitudes, the temperate air can move poleward, but encounters cold polar air, which moves equatorward. Masses did not mix; instead of they are separated by the polar front and a zone of low pressure in high latitude the Subpolar low is formed in this area, because the air rises and diverges. In the modern world, these lows are located at both sides of North American continent (Icelandic and Aleutian Lows), meanwhile in the Southern Hemisphere forms a continuous through that completely encircle the globe. In winter, there are others pressure cells, one not semi-permanent over Asia (the Siberian High), and another one less intense over northwestern North America (the Canadian High). Both of them are due to the intense cooling of the both landmasses. As summer begin, the land warms and the cold shallow highs disappear replaced by low-pressure cells (e.g. the warm thermal low sited over the desert that covered the southwester part of the States and over the plateau of Iran). In the Southern Hemisphere, low belts show a little intensity during the winter (Figure . 2a,b)

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Figure 2. (A) General circulation of the atmosphere and wind belt of the world (Left) precipitation versus evaporation (B) Wind-driven ocean surface pattern. Grey arrows represent wind patterns and black arrows represent ocean currents.

The atmospheric circulation is controlled by the presence and position of these pressure cells. From the belt of high-pressure, the horse latitudes (30º N) the air moves back toward the equator but due the Coriolis force is deflected toward the east in the Northern Hemisphere (between 0º-20º), creating the trade winds or easterlies. Near the equator, the northeaster trades winds (Northern Hemisphere) converge with the southeaster trades wind (Southern Hemisphere) along a boundary called the Intertropical Converge Zone (ITCZ) at the equator zone. On the polar side of the horse latitudes in either hemisphere, the atmospheric pressure diminishes toward low-pressure centres in middle and high latitudes. The winds set in motion poleward by these pressure systems are deflected toward the East by the earth's rotation. Because winds are known by the direction from which they blow, the winds in middle latitudes are known as the prevailing westerlies. Although has been speculated that a decrease in the equator-pole temperature gradient (Fischer and Arthue, 1977) might breakdown the zonal circulation pattern, the majority of the authors admit that should not be evidence of major differences between present and the Early Jurassic ocean circulation and so the wind pattern should be similar to the present day. Following this approach, Parrish and Curtis (1982) and Parrish et al. (1982) proposed a series of quantitative models based on the principles of atmospheric and oceanic circulation, although showing the differences due the Early Jurassic landmasses distribution. These authors considered the generally proposed Jurassic palaeobiogeography, and due to the absence of the Atlantic Ocean, they determine a change of the atmospheric pressure pattern. In winter, the subpolar low forms an only thermal cyclone and in summer, in high latitudes, the high-pressure cell would be replaced by a low-pressure cell over the polar ocean. The wind pattern proposed for the Early Jurassic served as the basis for preceding the locations most likely of upwelling zones (Parrish, 1982) and their results were later compared with the distribution of organic rich rocks, evaporites and coals as well as other climatically significant deposits such as bauxites, kaolinite bearing clay, etc. (Parrish et al., 1982). Another computer model was developed by Scotese and Summerhayes (1986). These authors mapping for the Pliensbachian the high and low –pressure cell distributions. Although the two sets of maps are basically similar, there are some important differences between the Parrish and Scotese and Summerhayes proposals. Parrish gives the oceanic high-pressure

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cells a more cellular character and indicates a polar high-pressure cell for the northern summer, where the computer model generates a low-pressure cell.

Simulations Proposed by Climate Models

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The second approach use dynamic models that simulate the physical processes of the atmosphere and the oceans using a methodology based on mathematics and fundamental physical laws (Crowley, 1983, 1988; Crowley et al, 1989; Kutzbach and Gallimore, 1989; Chandler et al, 1992; Chandler, 1994; Wilson et al., 1994; Barron and Fawcett, 1994; Fawcett et al., 1994). The Early Jurassic climatic models employ the Pangaea continental configuration with two major landmasses, Laurasia and Gondwana arranged in a symmetrical way across the Equator and drifted northward enough to situate the South Pole in open waters (Parrish, 1985). Most of these climatic simulations show that this configuration, with a maximum of continentally, would be characterized by the development of monsoon circulation conditions. During the summer monsoon, low-pressure would be centred poleward of the western Tethys Sea (between 10-30º N latitude) in the Northern Hemisphere. In winter, it would be over the southern part of the Gondwana and over the eastern part of the Southern Hemisphere Ocean, (Kutzbach, 1985; Crowley et al., 1989; Kutzbach and Gallimore, 1989; Chandler et al.,1992; Fawcett et al., 1994; Barron and Fawcett, 1995). In summer, the high-pressure subtropical would be sited through southern Gondwana continent and over the north-western part of the Northern Hemisphere Ocean. In winter, the subtropical high-pressure zone would cross the North Hemisphere up 30º latitude. The explanation of this change would be related to the fact that the low temperatures simulated (colder than 30º C) over the Laurentian continental landmass, may have stabilise the continental air masses and generate high-pressure cells. Meanwhile, the high sea surface temperature over the Tethys area does not allow the development of high-pressure in this last area (Crowley et al., 1989, Kutzbach and Gallimore, 1989; Kutzbach et al., 1990; Chandler et al., 1992). One concept that must be considered is that winter monsoon (high-pressure) would be more pronounced than central pressure of the summer monsoon (low-pressure), and thus winter monsoon conditions could have dominate the Global Atmospheric Circulation pattern.

MESOZOIC OCEAN CIRCULATION IN THE EUROPEAN EPICONTINENTAL SEA We started this chapter considering whether the past global atmospheric circulation may be considered similar to the present or not. Most of researcher recognises the applicability of the assumption that the past pattern should not have suffered many changes. For this study, we have assumed the existence of a past global atmospheric circulation similar to those is present in the today world, although adapted to the palaeogeography of the Early Jurassic reconstruction (Figure 1). For this model, it has been outlined a scenario that follows the atmospheric circulation pattern tentative postulated by Parrish and Curtis (1982); Parrish et al.(1982); Scotese and

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Summerhayes (1986) and the simulations of models by Crowley et al. (1989), Kutzbach and Gallimore (1989) Kutzbach et al. (1990) and Chandler et al. (1992). The results of this proposed paleocirculation pattern will be compared with evidence from the fossil record. Following these former assumptions, we have formulated a description about how might have been the atmospheric circulation during the Early Jurassic. The European Epicontinental Sea was located between 10º and 60º North latitude along the present European continent at the beginning of the Early Jurassic, when successive transgressions flooded the area previously occupied by evaporites during the late Triassic. The atmospheric circulation pattern over the European Epicontinental Sea should show a clear character monsoonal (Figures 3 A,B), where the surface winds display cyclonic and anticyclonic flows around the monsoonal low-pressure and high-pressure cells.

Figure 3. (A) General circulation of the atmosphere and wind-driven ocean surface pattern during the Early Jurassic, northern hemisphere summer; (B) southern hemisphere summer; Black arrows represent ocean currents.

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Monsoonal conditions would have been restricted to the far western margins of the Tethys Ocean, between 5 ºN and 25ºS (Kutzbach, 1985; Moore et al., 1993; Röhl, et al., 2001; Arias and Whatley, 2004). During the summer (Figure 3A), low-pressure over the polar ocean and over the central Laurasia (over the central part of the Eurasian continent) would create a north-south temperature gradient, which would generate easterlies surface winds along the western and central part of the EES and westerlies at the northern part of the European Epicontinental Sea. In winter (Figure 3B), land cools and the warm pressure lowpressure cells are replaced by high-pressure cells over the north-eastern coast of the North America and central Asia landmasses. Now the strongest winds would be the easterlies. In winter, the stability and the low moisture of the cold air is responsible of winter easterlies which might be stronger than summer easterlies (Figure 4).

Figure 4. Sea level pressure and surface layer winds for the Pliensbachian (a) northern hemisphere summer (b) northern hemisphere winter (adapted from Parrish et al., 1982; Scotese and Summerhayes, 1986; Chandler et al., 1992).

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Figure 5. Schematic diagram showing the ocean circulation pattern derived from climate models over the EES in the Early Jurassic time.

Considering this atmospheric general circulation pattern (Figure 4), the ocean current pattern may have special characteristics (Figure 5). The easterlies winds would set in motion the water masses along the southern part of the European Epicontinental Sea in a westerly direction creating a westward current. When this current reaches the western portion of the European Epicontinental Sea (eastern coast of North America), would rotate and by the Coriolis Effect (the Coriolis effects forces the water of the upper layer to move at right angles to the wind, causing it to flow meridional toward the equator) would deflect northward forming a western boundary current (such as the present Gulf Stream) to higher latitudes. This current would carry warm waters towards the northeastern parts of the European Epicontinental Sea and by the Coriolis Effect and the continental landmasses should go round creating an eastern boundary current (such as, the present Benguela Current). Western and eastern boundary currents would combine to create a subtropical-tropical clockwise gyre. Therefore, the prevalent ocean circulation pattern would be described as a clockwise gyre in the central parts of the European Epicontinental Sea. This wind pattern may also explain the entrance of a "warm Tethyan current" which would keep the polar sea ice-free in the winter. During the summer, low-pressure cells are sited over the polar ocean and over the central Laurasia and may be responsible for the formation of weak westerlies winds at the northern part of the European Epicontinental. These winds, which flow southwest to northeast direction, could transport cold water from the Arctic Ocean to the European Epicontinental Sea throughout the Norwegian-Greenland Strait. Both current are going to dominate most of the European shallow seas during part of the Early Jurassic and configure the distribution pattern of the fossil assemblages.

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To contrast this palaeocurrents model, we can consider the information which coming from the fossil record. The vision of the pattern of distribution of several fossil groups (mainly ammonites, bivalves and brachiopods) allow obtaining information about the palaeoceanographical history of the Early Jurassic Epicontinental Sea. During the Early Jurassic, the fossil record indicate the entrance and exit of fossil faunas between the warm waters of the Tethys Ocean and the cold waters of the European Epicontinental Sea along the southern margin of the European Epicontinental Sea and through the Iberian-Moorish Strait around the Iberian Peninsula (Arias and Whatley, 2004). Distribution pattern of the Early Jurassic fossil groups seem to indicate a similar general palaeocurrents patterns, with a continuum faunal exchange between both realms (Ager, 1956; Howarth, 1973; Stevens, 1973; Elmi et al, 1974, 1982, 1989; Ager and Walley, 1977; Mouterde and Dommergues, 1980; Almeras and Moulan, 1982; Dommergues, 1982; Enay and Mangold, 1982; Thierry, 1982; Cariou et al., 1985; Almeras and Elmi, 1987; Doyle, 1987; Hallam, 1987; Dommergues and Marchand, 1988; Almeras and Faure, 2000; Meister and Stampfly, 2000; Arias and Whatley, 2004).

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EARLY JURASSIC OSTRACODA, PALEOCIRCULATION AND WATER MASSES Ostracods are microscopic crustaceans (usually 90% probability) while it is very unlikely (