The Rate of Air-Sea CO2 Exchange: Chemical Enhancement and Catalysis by Marine Microalgae.

Contents

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Overview

Chapter 1 : Introduction: The Rate of Air-Sea CO2 Exchange

1.1 : The ocean carbon cycle and global climate

1.1.1 : CO2 and global climate.
1.1.2 : The chemistry of the carbonate system in seawater
1.1.3 : Rate determining factors for transfer of CO2 between the atmosphere and the ocean: the solubility and biological pumps.
1.1.4 : Future changes in the solubility and biological pumps
1.1.5 : But why measure the rate of CO2 transfer across the air-sea interface?

1.2 : Measuring the rate of air-sea CO2 exchange.

1.2.1 : Introduction to air-water gas transfer: thermodynamic and kinetic parameters
1.2.2 : Units of the transfer velocity, solubility and flux.
1.2.3 : Various approaches to deriving a parameterization of the transfer velocity -overview
1.2.4 : Models of air-sea gas exchange, Schmidt number dependence
1.2.5 : Measurements of the transfer velocity in laboratory tanks and wind tunnels.
1.2.6 : Measurements of the transfer velocities of inert gases in lakes
1.2.7 : Dual and triple tracer technique at sea
1.2.8 : Radon measurements
1.2.9 : Why not measure the CO2 transfer velocity directly at sea?
1.2.10 : Measurements on the air side of the interface: Eddy correlation
1.2.11 : Carbon 14C budget
1.2.12 : Summary of parameterisations of the transfer velocity

1.3 : Calculating the net global air-sea CO2 flux.

1.3.1 : Introduction
1.3.2 : Measurement of pCO2 in seawater
1.3.3 : Variability in water pCO2
1.3.4 : Interpolation between pCO2 measurements.
1.3.5 : Combining pCO2 and transfer velocity: problems of averaging.
1.3.6 : Examples of Global Air-Sea CO2 Flux Calculations
1.3.7 : Other approaches to global flux calculations
1.3.8 : A common misunderstanding regarding the net and gross air-sea CO2 fluxes

1.4 : Other physical factors influencing the transfer velocity

1.4.1 : Bubbles
1.4.2 : The "Thermal Skin" effect
1.4.3 : Effect of evaporation, condensation and rain.
1.4.4 : Irreversible thermodynamic coupling between heat and matter fluxes?
1.4.5 : Surface Organic Films

1.5 : Enhancement of the transfer velocity by chemical reaction

1.5.1 : Theory: reaction and diffusion
1.5.2 : The rate of hydration of carbonic acid
1.5.3 : Algebraic reaction-diffusion models for air-sea CO2 transfer.
1.5.4 : Iterative reaction-diffusion models for air-sea CO2 transfer
1.5.5 : Laboratory measurements of chemical enhancement
1.5.6 : Effect of chemical enhancement on the net global air-sea flux

Chapter 2 : Introduction: Carbonic Anhydrase in Marine Algae and the Sea-surface Microlayer

2.1 : Carbonic anhydrase and air-sea CO2 exchange

2.2 : Carbonic Anhydrase in mammalian respiration

2.2.1 : Discovery of carbonic anhydrase
2.2.2 : Structure and Mechanism

2.3 : Carbonic anhydrase in photosynthesis

2.3.1 : Evolution of plant carbonic anhydrase
2.3.2 : Functions and location of carbonic anhydrase in marine microalgae
2.3.3 : Species of marine microalgae with carbonic anhydrase
2.3.4 : Physiological response to low pCO2, and the "Zinc hypothesis".

2.4 : The potential for enrichment of carbonic anhydrase in the sea-surface microlayer

2.4.1 : Introduction to the problem
2.4.2 : Collecting samples for measuring surface microlayer enrichment
2.4.3 : Measurements of enriched biological activity the sea-surface microlayer
2.4.4 : Measured enrichments of proteins and zinc in the microlayer

2.5 : Enzyme kinetics and CA activity

2.5.1 : Definitions
2.5.2 : Stage 1: Initial Velocity experiments
2.5.3 : Equilibrium conditions
2.5.4 : Stage 2: CO2 transfer in a steady state reaction-diffusion system
2.5.5 : Calculations used by other investigators

2.6 : Measurement of carbonic anhydrase and its activity

2.6.1 : Activity measurements (electrode, spectrophotometric, manometric)
2.6.2 : Measurements of detecting catalysed CO2 uptake by algal cells
2.6.3 : Purification of CA on gels and determination of molecular mass

2.7 : Enzyme kinetic constants for CA reported in the literature

2.7.1 : Kinetic constants kcat and Km
2.7.2 : Effect of temperature
2.7.3 : Anion Inhibition

Chapter 3 : Early Calculations and Experimental Observations

3.1 : Introduction

3.2 : Development of a simple physiological model to relate CA production to water pCO2 and temperature.

3.2.1 : Summary of Riebesell's model for CO2 supply to a "typical diatom"
  • 3.2.1.1 : Reaction- Diffusion model
  • 3.2.1.2 : Comparison with stagnant film model
    3.2.2 : Adding carbonic anhydrase to the model
    3.2.3 : Increase of growth rate due to carbonic anhydrase, as a function of pCO2 and temperature

    3.3 : Preliminary estimate of potential impact of carbonic anhydrase on air-sea CO2 exchange

    3.3.1 : Catalysed chemical enhancement of the air-sea CO2 exchange rate
    3.3.2 : Calculating the average transfer velocity using the Rayleigh windspeed distribution
    3.3.3 : Applying physiological distribution of carbonic anhydrase as a function of pCO2
    3.3.4 : The different effect of the enzyme distribution on 14C and 12C fluxes.
    3.3.5 : Limitations of these calculations: temperature variation, pCO2 distribution, and intercorrelation between parameters.

    3.4 : Gas exchange experiments -various options

    3.4.1 : Oxygen and pH measurements in an open laboratory tank
    3.4.2 : Methods of measuring pCO2 for gas transfer experiments
    3.4.3 : Other ideas for gas exchange experiments

    3.5 : Fluorescence measurements of Carbonic Anhydrase

    3.5.1 : Introduction
    3.5.2 : Principle of the fluorescence technique
    3.5.3 : Results and conclusions

    3.6 : Conclusions and Strategy for further work

    Chapter 4 : Design and Principles of Steady-State-Tank

    4.1 : A holistic experiment achieved by a steady-state method?

    4.2 : Advantages and disadvantages of the steady -state method.

    4.3 : Principle of steady-state CO2 gas exchange calculation

    4.4 : Timescale for approach to steady state

    4.4.1 : Equations describing approach to steady state in the headspace for CO2
    4.4.2 : Computer model of approach to steady-state

    4.5 : Low-solubility inert gases

    4.5.1 : Problem with steady-state measurement of transfer velocity
    4.5.2 : Principle for measuring SF6 transfer velocity
    4.5.3 : Principle for measuring Oxygen transfer velocity

    4.6 : Design and Construction of the Steady-State Tank

    4.6.1 : Shape and Dimensions
    4.6.2 : Materials
    4.6.3 : Gas tight headspaces
    4.6.4 : Temperature Control

    4.7 : Stirring

    4.7.1 : Water Stirring
    4.7.2 : Air Stirring
    4.7.3 : Discussion of relative importance of air and water stirring

    Chapter 5 : Operation of steady-state gas exchange tank

    5.1 : Note on evolution of the system and choice of factors to vary

    5.2 : Seawater composition

    5.2.1 : Sources
    5.2.2 : Filtering and Cleaning
    5.2.3 : Added Nutrients
    5.2.4 : Added bovine enzyme and/or inhibitor
    5.2.5 : Lowering the water pCO2

    5.3 : Source of Algal cultures

    5.3.1 : North Sea spring bloom samples
    5.3.2 : Preparation of cultures
    5.3.3 : Light

    5.4 : Chlorophyll measurement

    5.5 : pCO2 measurements

    5.5.1 : Overview of LiCOR Non-dispersive infra-red gas analyser
    5.5.2 : Water vapour
    5.5.3 : Reference gases
    5.5.4 : Computer readout.
    5.5.5 : Contamination problem
    5.5.6 : Memory problem
    5.5.7 : Pressure variation

    5.6 : Gas flow rates

    5.7 : Gas flow system for supplying air with controlled pCO2

    5.8 : Normal procedure for CO2 gas exchange measurement

    5.9 : Total CO2

    5.10 : Alkalinity and pH

    5.11 : SF6 gas exchange

    5.11.1 : Spiking the tank to create a disequilibrium
    5.11.2 : Measurement procedure
    5.11.3 : Calibration
    5.11.4 : Calculation of transfer velocity
    5.11.5 : Uncertainty regarding the equilibrium SF6 concentration

    5.12 : Oxygen gas exchange

    5.12.1 : Creating a disequilibrium
    5.12.2 : Measurement
    5.12.3 : Calculation of the transfer velocity
    5.12.4 : Some problems with the oxygen measurements

    Chapter 6 : Analysis of measured CO2 data from steady-state tank

    6.1 : Measured Quantities

    6.2 : Thermodynamic and Kinetic constants

    6.3 : Seawater chemistry

    6.4 : Predicted CO2 transfer velocity, plus uncatalysed enhancement

    6.5 : Measured CO2 transfer velocities and their error ranges

    6.6 : Weighted average transfer velocities

    6.7 : Calculation of Total and Biological Carbon

    Chapter 7 : CO2 exchange without algae: Results and Discussion

    7.1 : Overview

    7.2 : Effect of water paddle speed.

    7.2.1 Acidified Seawater and MilliQ water (diffusion only: effect of salinity)
    7.2.2 Seawater (effect of chemical enhancement)

    7.3 : Effect of temperature

    7.3.1 Measurements and predictions
    7.3.2 Effect of temperature on thermodynamic and kinetic constants

    7.4 : Schmidt number relationship

    7.4.1 Sulphurhexafluoride / Oxygen comparison
    7.4.2 Derivation from salinity and temperature variation measurements.

    7.5 : Effect of pCO2 on the enhanced transfer velocity

    7.5.1 Effect of water pCO2
    7.5.2 Influx and Efflux measurements: Effect of air pCO2?
    7.5.3 pCO2 effect in the real ocean

    7.6 : Effect of adding bovine carbonic anhydrase

    7.6.1 Early measurements of catalyzed CO2 transfer
    7.6.2 Effect of temperature on enzyme activity and lifetime
    7.6.3 Effect of enzyme concentration, enzyme inhibitor, and pCO2
    7.6.4 Comparison of measured and predicted catalysis

    7.7 : Difference between measured and predicted chemical enhancement.

    7.8 : Comparison with previous measurements of chemical enhancement

    7.8.1 Measurements of chemical enhancement in published literature
    7.8.2 Data from measurements by Law, Frankignoulle, and Watson, PML 1993

    7.9 : Conclusions

    Chapter 8 : CO2 exchange rates with algae: results and discussion

    8.1 : Overview

    8.2 : General features of the graphs describing blooms

    8.2.1 : Gas exchange plot
    8.2.2 : Carbon budget plot

    8.3 : Results from each algal bloom

    8.3.1 : First Dunaliella bloom
    8.3.2 : Second Dunaliella bloom
    8.3.3 : Phaeodactylum bloom
    8.3.4 : Amphidinium bloom
    8.3.5 : Phaeocystis samples from the North Sea spring bloom
    8.3.6 : Third Dunaliella bloom
    8.3.7 : Fourth Dunaliella bloom
    8.3.8 : Skeletonema bloom
    8.3.9 : Emiliana Huxleyi bloom

    8.4 : Comparison of CO2 transfer velocities with and without algae.

    8.4.1 : Explanation of the composite plots
    8.4.2 : Discussion of composite plots and identification of catalysis effect
    8.4.3 : Comparison with literature reports of CA activity in these species

    8.5 : Surface Algal Films

    8.5.1 : General features of films
    8.5.2 : End of the first Dunaliella Bloom
    8.5.3 : End of Phaeodactylum bloom
    8.5.4 : End of fourth Dunaliella bloom
    8.5.5 : End of Emiliana Huxleyi bloom
    8.5.6 : Conclusions regarding the effect of surface films

    8.6 : Conclusions regarding algal catalysis

    Chapter 9 : The Effect of Catalysed and Uncatalysed Enhancement on the Net Global Air-Sea CO2 Flux.

    9.1 : Overview

    9.2 : Source of Data

    9.2.1 : Windspeed and Temperature
    9.2.2 : DpCO2 and pH
    9.2.3 : Chlorophyll
    9.2.4 : Land and Ocean Area
    9.2.5 : Summary of input data

    9.3 : Calculation Method

    9.3.1 : Basic calculation of the transfer velocity and chemical enhancement
    9.3.2 : Multiplying the rate of reaction between CO2 and OH- by a factor of six to match the experimental results.
    9.3.3 : Use of Rayleigh distribution to split weekly windspeeds
    9.3.4 : Distribution of Carbonic Anhydrase enzyme catalysis -based on chlorophyll and physiology

    9.4 : Summary of Calculation Options

    9.5 : Computation method

    9.5.1 : The scale of the calculation
    9.5.2 : Summary of Computer programs
    9.5.3 : Global Flux Calculation program
    9.5.4 : Program structure
    9.5.5 : Program to generate global maps and monthly -latitude-band-plots

    9.6 : Results: CO2 gas exchange without enzyme catalysis

    9.6.1 : Gas exchange rate and air-sea CO2 flux without chemical enhancement
    9.6.2 : Effect of uncatalysed chemical enhancement
    9.6.3 : Effect of Rayleigh splitting of weekly winds on chemical enhancement
    9.6.4 : Effect of Wanninkhof parameterisation on chemical enhancement
    9.6.5 : Effect of increasing rate of reaction of CO2 with OH- by a factor of six

    9.7 : Results including catalysis by Carbonic Anhydrase Enzyme

    9.7.1 : Discussion of global average effects of enzyme catalysis
    9.7.2 : The spatial and temporal variability of enzyme catalysis
    9.7.3 : Overall scale of enzyme catalysis effect

    Chapter 10 : Summary, Conclusions and Future Work

    10.1 : Results from tank experiments without algae

    10.1.1 : Uncatalysed enhancement
    10.1.2 : Measurements with added bovine enzyme

    10.2 : Results from tank experiments with algal blooms

    10.2.1 : Evidence of enzyme catalysis
    10.2.2 : Direct uptake of CO2 by surface films

    10.3 : Effect of chemical enhancement and enzyme catalysis on the net global air-sea CO2 flux

    10.3.1 : Background
    10.3.2 : Results of calculations -uncatalysed
    10.3.3 : Results of calculations -with catalysis
    10.3.4 : Resolving the inert tracer / 14C discrepancy

    10.4 : Intercorrelations in future global CO2 flux calculations

    10.5 : Proposals for future investigation

    10.5.1 : Direct CO2 uptake by surface algal films
    10.5.2 : Other experiments and improvements

    10.6 : Concluding thoughts

    Appendix: Fluorescence Measurements of Carbonic Anhydrase

    A.1 Experimental Methods
    A.1.1 : Fluorescence measurement
    A.1.2 : Chemicals
    A.2 : Calibration experiments
    A.3 : Measurements in seawater collected from an algal bloom in the North Sea
    A.4 : Measurements of microlayer enrichment in a laboratory tank.
    A.5 : Decline in CA-DA fluorescence over time
    A.6 : Potential improvements

    REFERENCES


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