Open Ocean Modelling of the Carbon Cycle and Air-Sea CO 2 Fluxes

1. Open Ocean Modelling of the Carbon Cycle and Air-Sea CO2 Fluxes Science Element 3a of CASIX Steve Spall (Met Office)

2. The Talk • What are the aims? • Who are the main contributors? • What tools will we use? • Some preliminary results • What will we be developing? • How we fit in with the rest of CASIX • Measuring how well we are doing

3. Aims • Produce estimates of air-sea fluxes of CO2, focused on the North Atlantic, using a high resolution GCM • Improve these estimates by assimilating Earth Observation data into the carbon cycle model • Integrate other developments under CASIX into the GCM to also improve the CO2 flux estimates

4. Rosa Barciela • Met Office • Setting up the model • Performing model simulation • Looking at resolution sensitivity • Providing boundary data for shelf seas • Mike Bell • Met Office • Oversee work with the FOAM model • Advise on aspects of FOAM simulations • Advise on data assimilation techniques • Member of the CASIX management group The Main Contributors

5. John Hemmings • SOC • Develop assimilation techniques • Assess simulations including assimilation • Advise on and implement improvements to assimilation and the carbon cycle model • Steve Spall • Met Office • Oversee work in this science element of CASIX • Advise on implementation of the carbon cycle model • Integrate new improvements into the model • Member of the CASIX Scientific Steering Committee • Ian Totterdell • SOC • Advise on implementation and improvements to the carbon cycle model • Advise on data assimilation techniques

6. What tools will we use? • Coupling together two models… • FOAM • Forecasting Ocean Assimilation Model • HadOCC • Hadley Centre Ocean Carbon Cycle model

7. FOAM • Can be run at different resolutions for different domains

8. HadOCC • ‘NPZD’ ecosystem model • Coupled to carbon and alkalinity • Transported around the ocean by physical processes • Normally used for climate studies

9. Nutrient supply driving biological carbon uptake Enhanced eddies Control Suppressed eddies From a 1/3° North Atlantic Ocean Model Resolution Sensitivity • Eddies enhance biological uptake of carbon • Using FOAM at higher resolution may improve the simulation of air-sea CO2 fluxes Figure from Oschlies and Garcon (Nature, 1998)

10. Preliminary Results • Comparison of SeaWiFS chlorophyll against the model • Run for early 2000 • Some encouraging results, some work to do

12. What will we be developing? • HadOCC integrated into FOAM and demonstrated at different resolutions • Assimilation methods for Ocean Colour in the ocean carbon cycle model • 10 year hind-cast simulation to provide estimates of air-sea CO2 fluxes • Improved assimilation methods, making use of new Earth Observation products where available

13. How we fit in with the rest of CASIX • Provide boundary conditions for shelf seas models • Implement new parameterisations of air-sea gas exchange • Integrate developments from interface modelling • Provide estimates of air-sea CO2 fluxes for the development of climatologies

14. Measuring how we are doing • Useful to measure how well the model is doing • Good quantity to test is ocean pCO2 • A useful graphical representation is a Taylor diagram • An example of a measure of model accuracy

15. Taylor Diagrams • Take a data set and sub-sample the model • Plot the correlation between model and data and the ratio of standard deviations • Want to move towards the point ‘Obs’

16. Summary • Coupling of the HadOCC ocean carbon cycle model into the Met Office open ocean forecasting model • Aim is to provide hind-cast estimates of air-sea CO2 fluxes • Develop assimilation for the ocean carbon cycle to improve these estimates • Integrate developments from other elements of CASIX