Ocean Biogeochemistry

Oceans account for 50% of the anthropogenic CO2 released into the atmosphere. During the past 15 years an international programme, the Joint Global Ocean Flux Study (JGOFS), has been studying the ocean carbon cycle to quantify and model the biological and physical processes whereby CO2 is pumped from the ocean's surface to the depths of the ocean, where it can remain for hundreds of years. This project is one of the largest multi-disciplinary studies of the oceans ever carried out and this book synthesises the results. It covers all aspects of the topic ranging from air-sea exchange with CO2, the role of physical mixing, the uptake of CO2 by marine algae, the fluxes of carbon and nitrogen through the marine food chain to the subsequent export of carbon to the depths of the ocean. Special emphasis is laid on predicting future climatic change.

Contenu

Acknowledgements.- References.- 1 Biogeochemical Provinces: Towards a JGOFS Synthesis.- 1.1 Plankton Community Structure and Distribution.- 1.2 Partitioning the Oceans.- 1.3 Primary Production in Ocean Domains and Provinces.- 1.3.1 Adding up Global PP Observations.- 1.4 Bacterial Production and DOC Flux.- 1.5 A Provincial Outlook.- Acknowledgements.- References.- 2 Physical Transport of Nutrients and the Maintenance of Biological Production.- 2.1 Introduction.- 2.2 Global Overturning Circulation and Nutrient Transport.- 2.2.1 Overturning Circulation and Water-Mass Distributions.- 2.2.2 Southern Ocean.- 2.2.3 Nutrient Supply to the Northern Basins.- 2.2.4 Summary.- 2.3 Convection.- 2.3.1 Vertical Transfer of Nutrients.- 2.3.2 Biophysical Interactions and Convection.- 2.3.3 Limited Role of Convection.- 2.3.4 Summary.- 2.4 Wind-Driven Circulations: Gyres and Boundary Currents.- 2.4.1 Wind-Induced Upwelling and Gyre Circulations.- 2.4.2 Gyre-Scale Circulations.- 2.4.3 Subduction and Fluid Transfer into the Seasonal Boundary Layer.- 2.4.4 Oligotrophic Subtropical Gyres.- 2.4.5 Western Boundary Transport of Nutrients.- 2.4.6 Summary.- 2.5 Smaller-Scale Circulations: Mesoscale Eddies, Waves and Sub-Mesoscale Fronts.- 2.5.1 Formation of Mesoscale Eddies and Sub-Mesoscale Fronts.- 2.5.2 Local Response to Planetary Waves, Eddies and Fronts.- 2.5.3 Far Field Effects: Eddy Transport and Diffusion.- 2.5.4 Summary.- 2.6 Interannual and Long-Term Variability.- 2.6.1 Coupled Atmosphere-Ocean Changes: ENSO.- 2.6.2 North Atlantic Oscillation.- 2.6.3 Changes in Overturning Circulation.- 2.6.4 Summary.- 2.7 Conclusions.- Acknowledgements.- Notes.- References.- 3 Continental Margin Exchanges.- 3.1 Introduction.- 3.2 Recycling Systems.- 3.3 Export Systems.- 3.4 Coastal Upwelling Systems.- 3.5 California Current System.- 3.6 Humboldt Current System.- 3.7 Benguela Current System.- 3.8 Monsoonal Upwelling Systems.- 3.9 Biogeochemical Budgeting.- 3.10 The Arctic Shelves.- 3.10.1 Introduction.- 3.10.2 The Arctic Ocean As a Mediterranean, Shelf-Dominated Sea.- 3.10.3 The Shelves of the Arctic Ocean.- 3.10.4 Barents Shelf.- 3.10.5 Kara Shelf.- 3.10.6 Laptev Shelf.- 3.10.7 East Siberian and Chukchi Shelves.- 3.10.8 Beaufort Shelf.- 3.10.9 The Mackenzie Shelf of the Beaufort Sea as a Case Study.- 3.10.10 Shelf to Basin Sediment Transport in the Arctic.- 3.10.11 CH4, DMS (Dimethyl-Sulphide) Production in the Arctic.- 3.10.12 A Budget for the Arctic Shelves.- 3.10.13 Global Change; Speculation on Consequences for Arctic Shelves.- 3.11 Marginal Seas.- 3.11.1 High Latitude Marginal Seas.- 3.11.2 Semi-Enclosed Marginal Seas.- 3.11.3 Initial Synthesis.- 3.11.4 Future Research.- 3.11.5 Summary.- Acknowledgments.- References.- Apendix 3.1 - Continental Margins: Site Descriptions.- 4 Phytoplankton and Their Role in Primary, New, and Export Production.- 4.1 Introduction.- 4.1.1 A Brief Introduction to Phytoplankton.- 4.1.2 Photosynthesis and Primary Production.- 4.1.3 Measuring Photosynthesis and Net Primary Production in the Sea.- 4.1.4 A Brief History of the Measurement of Primary Productivity in the Oceans.- 4.1.5 Quantifying Global Net Primary Productivity in the Oceans.- 4.1.6 Export, New and 'True New' Production.- 4.1.7 Elemental Ratios and Constraints on New Production.- 4.1.8 New Production, Export Production, and Net Community Production.- 4.1.9 Measurement of New Production.- 4.1.10 Measurement of Net Community Production.- 4.1.11 Measurement of Export Production.- 4.1.12 Summary of Methods.- 4.2 Synthesis.- 4.2.1 Physical Controls of Export Fluxes: the Importance of Functional Groups.- 4.2.2 Calcium Carbonate Precipitation.- 4.2.3 Primary, New and Export Production and the Global Carbon Cycle on Longer Time Scales.- References.- 5 Carbon Dioxide Fluxes in the Global Ocean.- 5.1 Introduction.- 5.2 The Oceans' Influence on Atmospheric CO2.- 5.2.1 The Ocean Sets the Steady-State Atmospheric CO2 Concentration.- 5.2.2 The Pre-Industrial Steady State.- 5.2.3 Pre-Industrial North-South Transports.- 5.3 How Big is the Global Ocean Sink?.- 5.3.1 1-D Models Calibrated with 14C.- 5.3.2 3-D Models of the Ocean Carbon Cycle.- 5.3.3 13C Changes with Time in the Ocean.- 5.3.4 Atmospheric Observations.- 5.3.5 Observations of the Air-Sea Flux.- 5.3.6 Preformed Total Carbon Methods and the Ocean Inventory of CO2.- 5.3.7 Summary of Recent Estimates of the Ocean Sink.- 5.4 What Processes Control Air-Sea CO2 Flux?.- 5.4.1 Patterns in the Global Survey.- 5.4.2 Comparison Using Models.- 5.4.3 Modelled Future Uptake of Anthropogenic CO2.- 5.5 Variability in the CO2 Signal.- 5.5.1 Seasonal Variation.- 5.5.2 Inter-Annual Variation.- 5.6 The Gas Transfer Velocity.- 5.7 Conclusion: the Next Ten Years.- Acknowledgements.- References.- 6 Water Column Biogeochemistry below the Euphotic Zone.- 6.1 Introduction.- 6.2 The Twilight Zone: Biology, Biogeochemical Processes and Fluxes.- 6.2.1 Biology of the Twilight Zone.- 6.2.2 Nature of the Exported Material and Processes.- 6.2.3 Microbial Production of Nitrous Oxide.- 6.3 The Fluxes of Biogenic Matter versus Depth.- 6.3.1 The Export Flux out of the Euphotic Zone.- 6.3.2 The Export Flux towards the Ocean's Interior (>1000 m).- 6.4 The Variable Composition of the World Ocean Waters along the Conveyor Belt.- 6.5 Conclusions and Perspectives.- 6.5.1 The Ventilation Depth and the ?-Ratio.- 6.5.2 The Role of Mineral Ballasts in the Export of Carbon to the Ocean Interior.- References.- 7 The Impact of Climate Change and Feedback Processes on the Ocean Carbon Cycle.- 7.1 Introduction.- 7.1.1 Climate and Change - Present Status.- 7.1.2 Examples of Feedbacks in the Present and the Geological Past.- 7.2 Feedbacks.- 7.2.1 Definition.- 7.2.2 Identification.- 7.2.3 Classification.- 7.2.4 Magnitude.- 7.2.5 Evolution.- 7.2.6 Interactions between Feedbacks.- 7.2.7 Scales and Response Times.- 7.2.8 Degree of Confidence - Understanding Feedbacks.- 7.3 What do Current Models Predict?.- 7.4 Status of Our Understanding of Feedbacks.- 7.5 Nutrient Dynamics.- 7.6 Phytoplankton and Carbon Limitation.- 7.6.1 Atmospheric Supply of Nutrients.- 7.6.2 Nitrogen Fixation.- 7.6.3 Changes in Nutrient Uptake Stoichiometry - the Redfield Ratio.- 7.6.4 Export Production and Remineralisation in the Deep Ocean.- 7.7 The Calcifiers.- 7.7.1 Biogeochemistry and Feedbacks.- 7.7.2 Global Distributions.- 7.7.3 Controlling Factors, Forcing and Modelling.- 7.7.4 A Case Study - the Bering Sea.- 7.8 Iron Supply to the Oceans.- 7.8.1 How Much of the Ocean Is Iron-Poor?.- 7.8.2 The Supply of Iron to the Ocean.- 7.8.3 Atmospheric Deposition of Iron versus Upwelling Supply.- 7.8.4 Dust Supply - Global Maps and Fluxes.- 7.8.5 Dust Transport - from Soil to Phytoplankton.- 7.8.6 Response by the Biota - Detection.- 7.8.7 The Future - Climate Change and Dust Deposition.- 7.8.8 A Case Study - Uncertainties in Projection.- 7.9 Dimethyl Sulphide and the Biota.- 7.9.1 The CLAW Hypothesis.- 7.9.2 What Produces DMSP/DMS?.- 7.9.3 Global Distributions of DMS.- 7.9.4 The Haptophyte Connection.- 7.10 UV-B and Ozone Depletion.- 7.10.1 Present Status of Ozone Depleti…