The Role of Air-Sea Exchange in Geochemical Cycling

This book arises from a NATO-sponsored Advanced Study Institute on 'The Role of Air-Sea Exchange in Geochemical Cycling' held at Bombann@§. near Bordeaux, France. from 16 to 27 September 1985. The chapters of the book are the written versions of the lectures given at the Institute. The aim of the book is to give a comprehensive up-to-date coverage of the subject. presented in a teaching mode. The chapters contain much recent research material and attempt to give the reader an understanding of how the role of air-sea exchange in geochemical cycling can be quantitatively assessed. In the last decade, major advances in the fields of marine and atmospheric chemistry have underlined the role of physical, chemical and biological processes at and near the air-sea interface in a number of geochemical cycles (C. S, N, metals etc ... ). Further, there is strong concern over the anthropogenic perturbation of these cycles on both regional and global scales. The first part of the book (Chapters 1 to 8) provides a review of topics fundamental to such studies. These topics include concepts in geochemical modelling, assessment of atmospheric transport from sources to the oceans. description of mixing and transport processes within the ocean for both dissolved and particulate materials, quantification of air-sea fluxes for both gases and particles, photochemical transformations in the atmospheric and oceanic boundary layers.

Contenu

Basic Concepts In Geochemical Modelling.- 1. Introduction.- 2.First Order Models.- 2.1. First order decay reaction.- 2.2. Instantaneous perturbation in a first order decay model.- 2.3. First order production model.- 3. Heterogeneous Catalysis and Enzymatic Type Reactions.- 4. Reversible Reactions.- 5. Model with Coupled Components in the Reservoir.- 6. Second Order Reactions.- 7. Periodic Fluctuations.- 8. Coupling of Reservoirs.- 9. Conclusions.- Atmospheric Pathways to the Oceans.- 1. Introduction.- 2. Atmospheric Structure and Transports.- 2.1. Boundary layer.- 2.2. Cloud scale transport.- 2.3. Storms and midlatitude circulation.- 2.4. Global scale exchange.- 3. Variability and Representativeness.- 3.1. Seasonal and interannual variability.- 3.2. Representativeness of observations.- 4. Modeling of Atmospheric Transport.- 4.1. Source identification models.- 4.2. Mechanistic models.- 4.3. Tropospheric chemistry system models.- Modeling Oceanic Transport of Dissolved Constituents.- 1. Introduction.- 2. Box Models.- 3. Advection-Diffusion Models.- 4. Equations of Motion.- 5. Conclusion.- Vertical Transport of Particles within the Ocean.- 1. Introduction.- 2. Determination of the Lognormal Coefficients L, ? and of N.- 2.1. Particle size data collection.- 2.2. Calculation of the coefficients L, ? and N from data.- 3. Determination of Suspended Particulate Matter Physical Properties using Lognormal coefficients.- 3.1. Surface area concentration.- 3.2. Mass concentration.- 3.3. Vertical fluxes.- 3.4. Residence time.- 3.5. Application to the open sea.- 4. Suspended Particulate Matter Sedimentation with Dissolution Process.- 4.1. Sedimentation at steady state.- 4.2. Sedimentation at non steady state.- 5. Conclusion.- 6. Appendix.- 6.1. Specific properties of the lognormal law.- 6.2. Evaluation of the lognormal coefficients.- Air-Sea Gas Exchange Rates: Introduction and Synthesis.- 1. Introduction.- 2. Basic Principles.- 3. Models.- 3.1. Film model.- 3.2. Surface renewal models.- 3.3. Boundary-layer models.- 4. Laboratory (Wind Tunnel) Studies.- 4.1. Smooth surface regime.- 4.2. Rough surface regime.- 4.3. Breaking wave (bubble) regime.- 5. Field Measurements.- 5.1. Box method.- 5.2. Dissolved gas balance method.- 5.3. Micrometeorological techniques.- 5.4. Natural and bomb-produced 14C.- 5.5. The radon deficiency method.- 5.6. Sulphur hexafluoride.- 5.7. Summary.- 6. Synthesis.- 6.1. Comparison with field data.- The Ocean as a Source for Atmospheric Particles.- 1. Introduction.- 2. The ? ?E/?r Model.- 3. The ? ?2E/?t ?r Model.- 4. Comparison of ? ?E/?r and W ?2E/?t ?r Models.- 5. Oceanic Whitecap Coverage.- 6. Global Sea-to-Air Salt Flux.- 7. Toward a Comprehensive Marine Aerosol Generation Model.- The Ocean as a Sink for Atmospheric Particles.- 1. Overview.- 2. Assessement of Wet Deposition.- 3. Field Approach to Dry Deposition.- 4. Accurate Deposition Measurements do not Guarantee Accurate Net Air to Sea Transfer Rates.- 5. Relative Importance of Wet and Dry Removal Rates.- 6. Conclusion.- Atmospheric, Oceanic, and Interfacial Photochemistry as Factors Influencing Air-Sea Exchange Fluxes and Processes.- 1. Introduction.- 2. Environmental Photochemistry.- 2.1. Stratospheric photochemistry.- 2.2. Homogeneous tropospheric photochemistry.- 2.3. Heterogeneous tropospheric photochemistry.- 2.4. Seawater photochemistry.- 2.5. Soil photochemistry.- 3. Interaction of Photochemistry with Air-Sea Exchange Processes.- 3.1. Air-sea gas exchange.- 3.2. Rainout-washout deposition processes.- 3.3. Dry deposition.- 3.4. Marine aerosol generation.- 4. Summary.- Carbon Dioxide: Its Natural Cycle and Anthropogenic Perturbation.- 1. Introduction.- 2. The Natural Cycle of Carbon Dioxide.- 2.1. Reservoirs, fluxes, residence times.- 2.2. Air-sea exchange of CO2.- 2.3. Regional variability of air-sea fluxes.- 2.4. Marine carbonate chemistry.- 2.5. The oceanic carbon cycle.- 2.6. The cycle of oxygen.- 3. Anthropogenic Increase of Atmospheric CO2.- 3.1. Observations and airborne fraction.- 3.2. Modelling the oceanic response to carbon cycle perturbations.- 3.3. CO2 release from the terrestrial biosphere and the "missing CO2 sink".- 3.4. Scenarios for future CO2 concentrations.- 3.5. Carbone isotope perturbations.- 4. Climatic Effects of CO2 Increase.- 5. Natural CO2 Variations.- 5.1. Seasonal variations.- 5.2. Correlation with El Ni?o.- 5.3. Glacial/interglacial changes.- CO2 Air-Sea Exchange during Glacial Times: Importance of Deep Sea Circulation Changes.- 1. Introduction.- 2. Evidence from Polar Ice Cores.- 2.1. Data.- 2.2. Discussion: is the ocean able to absorb the missing CO2?.- 3. Evidence from Deep Sea Sediments.- 3.1. Data.- 3.2. Various hypotheses explaining the sedimentary record.- 3.3. Cadmium as a proxy-indicator for past phosphate.- 4. Broecker's two box Model for the CO2 Cycle.- 5. Evidence for Deep Water Circulation during the Last Climatic Cycle.- 5.1. Geochemical basis.- 5.2. Glacial to interglacial contrasts.- 5.3. Disappearance of North Atlantic Deep Water during the glacial to interglacial transition.- 5.4. Enhanced North Atlantic Deep Wafer formation during the inception of the glaciation.- 6. Conclusion.- Exchange of CO and H2 between Ocean And Atmosphere.- 1. Introduction.- 2. Determination of the Supersaturation Factors of CO and H2.- 3. Spatial and Temporal Changes of dissolved CO and H2.- 4. Processes Sustaining CO and H2 Concentrations in Surface Water.- 4.1. Production processes.- 4.2. Consumption processes.- 4.3. Transport processes.- 5. Calculation of Fluxes by the "Laminar Film Model".- 6. Role of Oceans in the budget of atmospheric CO and H2.- The Air-Sea Exchange of Low Molecular Weight Halocarbon Gases.- 1. Introduction.- 2. Gases for which the Oceans are a net Source for the Atmosphere.- 2.1. Alkyl (mainly Methyl) halides.- 2.2. Haloforms.- 2.3. Other organo-halides.- 3. Gases for which the Oceans are a net Sink for the Atmosphere.- 4. Summary.- Sea-Air Exchange of High-Molecular Weight Synthetic Organic Compounds.- 1. Introduction.- 2. Compounds of Interest.- 3. Sampling/Analytical Aspects of Trace Organics.- 4. Distribution of High Molecular Weight Organics in the Marine Environment.- 4.1. Water and organisms.- 4.2. Atmospheric concentrations.- 4.3. Atmospheric deposition.- 5. Air-Sea Exchange Mechanisms for Synthetic Organics.- 5.1. Dry deposition.- 5.2. Wet deposition.- 5.3. Adsorption and partitioning in surface waters.- 6. Air-Sea Fluxes in the North Pacific.- 7. Relative Importance of Atmospheric Deposition to th…