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University of Warwick institutional repository: http://go.warwick.ac.uk/wrap A Thesis Submitted for the Degree of PhD at the University of Warwick http://go.warwick.ac.uk/wrap/1125 This thesis is made available online and is protected by original copyright. Please scroll down to view the document itself. Please refer to the repository record for this item for information to help you to cite it. Our policy information is available from the repository home page. Environmental variability in the Gulf of Guinea Large Marine Ecosystem Physical features, forcing and fisheries Nicholas John Hardman-Mountford, M.Sc., B.Sc. (Hons.) A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy University of Warwick Department of Biological Sciences Ecology and Epidemiology Group June 2000 Ai Table of Contents TABLE OF CONTENTS.................................................................................................II LIST OF TABLES AND FIGURES ...............................................................................VI ACKNOWLEDGEMENTS........................................................................................VIII DECLARATION ..........................................................................................................IX ABSTRACT................................................................................................................... X LIST OF ACRONYMS.................................................................................................XI 1 RESEARCH AIMS, RATIONALE AND GLOBAL BACKGROUND......................1 1.1 GLOBAL CONTEXT...............................................................................................1 1.1.1 Focus...........................................................................................................1 1.1.2 Relevance of this study to fisheries.................................................................2 1.1.3 Study region.................................................................................................3 1.1.4 Aims ............................................................................................................4 1.2 THESIS STRUCTURE .............................................................................................5 1.3 OCEANOGRAPHIC REMOTE SENSING FROM SATELLITES.........................................6 1.3.1 Infra-red radiometry .....................................................................................7 1.3.2 Ocean colour................................................................................................7 1.3.3 Radar altimetry .......................................................................................... 10 1.3.4 Future satellites and applications ................................................................ 11 1.4 OCEANOGRAPHIC PRINCIPLES ............................................................................ 12 1.4.1 Shelf-slope dynamics................................................................................... 12 1.4.2 Fronts........................................................................................................ 15 1.4.3 Upwelling dynamics.................................................................................... 17 1.4.4 Internal waves ............................................................................................ 19 1.5 BASIN WIDE DYNAMICS AND OCEAN-ATMOSPHERE COUPLING............................ 22 1.6 ECOLOGICAL PRINCIPLES................................................................................... 25 1.6.1 Comparative analysis of ecosystems............................................................. 26 1.6.2 Fish populations for ecosystem analysis....................................................... 27 1.6.3 Recruitment variability ............................................................................... 29 1.6.4 Ecosystem definition................................................................................... 31 2 OVERVIEW OF CONDITIONS IN THE GULF OF GUINEA LME..................... 35 2.1 SYSTEMS AND SUBSYSTEMS............................................................................... 35 2.2 BATHYMETRY ................................................................................................... 37 2.3 CLIMATOLOGY .................................................................................................. 38 2.3.1 Climate and seasons ................................................................................... 38 2.3.2 Winds......................................................................................................... 38 2.3.3 Rainfall...................................................................................................... 39 2.4 OCEANOGRAPHY............................................................................................... 39 2.4.1 Sea water structure and temperature............................................................ 39 2.4.2 Ocean circulation....................................................................................... 40 2.4.3 Upwelling .................................................................................................. 41 2.5 BIOLOGY .......................................................................................................... 43 2.5.1 Phytoplankton ............................................................................................ 43 2.5.2 Zooplankton............................................................................................... 43 2.5.3 Fish populations and Assemblages............................................................... 44 ii 3 UPWELLING DYNAMICS IN THE GULF OF GUINEA...................................... 48 3.1 WIND DRIVEN EKMAN DIVERGENCE ................................................................... 48 3.2 HEAT GAIN FROM ATMOSPHERE AND COASTAL THERMOHALINE CONVECTION....... 51 3.3 MECHANISMS INVOLVING CURRENTS.................................................................. 52 3.3.1 Geostrophically induced upwelling .............................................................. 52 3.3.2 Advection by currents.................................................................................. 53 3.3.3 Current-cape interaction............................................................................. 53 3.4 LOCALLY FORCED TRAPPED WAVE THEORY ........................................................ 54 3.5 REMOTE FORCING.............................................................................................. 54 3.5.1 Mechanism................................................................................................. 54 3.5.2 Modelling studies ....................................................................................... 55 3.5.3 Observational evidence............................................................................... 58 3.6 INTERANNUAL VARIABILITY IN UPWELLING ........................................................ 63 3.7 DISCUSSION ...................................................................................................... 65 4 REMOTE SENSING OF SST................................................................................. 68 4.1 INTRODUCTION ................................................................................................. 68 4.1.1 Use of remote sensing ................................................................................. 68 4.1.2 Remote sensing of the West African region................................................... 69 4.2 DATA ACQUISITION AND PRE-PROCESSING.......................................................... 70 4.3 CLOUD CONTAMINATION................................................................................... 71 4.4 DATA PROCESSING AND ANALYSIS METHODS..................................................... 72 4.4.1 Temporal statistics (spatial variability)........................................................ 72 4.4.2 Spatial statistics (temporal variability)......................................................... 75 4.4.3 Spectral analysis ........................................................................................ 75 4.4.4 Indices of interannual variability in oceanographic features.......................... 76 4.5 RESULTS ........................................................................................................... 77 4.5.1 Overall....................................................................................................... 77 4.5.2 Seasonal variability.................................................................................... 79 4.5.3 Interannual variability................................................................................ 89 4.6 DISCUSSION ...................................................................................................... 97 4.6.1 Seasonal pattern......................................................................................... 97 4.6.2 Interannual pattern................................................................................... 101 4.6.3 Relevance of features observed to fisheries recruitment............................... 103 4.6.4 Conclusions.............................................................................................. 105 5 DETECTION OF MAJOR PATTERNS IN SST USING PRINCIPAL COMPONENTS ANALYSIS...................................................................................... 106 5.1 INTRODUCTION