1. m.racault@uea.ac.uk Changes in the Southern Ocean biological export production over the period 1968-2004 Marie-F. Racault, Corinne Le Quéré & Erik Buitenhuis CARBOOCEAN Annual Meeting Gran Canaria, December 2006

2. Strengthening and poleward shifting of the winds in the Southern Ocean 2004 mean 2004 minus 1967 NCEP winds (m/s)

3. Decrease in the Southern Ocean sink of CO 2 modelled expected observations

4. Changes in Export and Primary Production? Carbon content (PgC/y) of the Southern Ocean Total ΔFCO2 = 0.15 Δ FHeat = 0.01 ΔPP = ? ΔExp = ? ΔDIC = 0.4PgC/y ΔDIC = ? Atmosphere Euphotic zone Deep ocean

5. OPA General Circulation model 0.5-1.5 o x2 o resolution 31 vertical levels Calculated vertical mixing NCEP daily forcing OPA model

6. PISCES-T ecosystem model 2 phyto, 2 zoo., 2 sinking particles Limitation by Fe, P, and Si Initialise with observations in 1948 (Buitenhuis et al., GBC 2006) PISCES-T model

7. Chla (mg/m 3 ) and biological export production (molC/m 2 /y) from the model and based on observations SeaWiFS Chla PISCES-T Chla PISCES-T bio. export Obs. bio. export * * Schlitzer, 2002

8. eratio in the Southern Ocean over the period 1968-2004 mean Export Production (PgC/y) 1.4 Primary Production (PgC/y) 4.7 Southern Ocean eratio mean eratio Exp PP = 0.3

9. eratio in the Southern Ocean (SO) vs. Global Ocean SO mean Export Production (PgC/y) 1.4 8.9 Primary Production (PgC/y) 4.7 61 Global eratio SO mean eratio Exp PP = 0.3 SO global mean global mean eratio Exp PP = 0.15

10. OPA General Circulation model 0.5-1.5 o x2 o resolution 31 vertical levels Calculated vertical mixing NCEP daily forcing Have the changes in circulation induced a trend in the biological export production? Simulation of PISCES-T with observed atmospheric forcing

11. OPA General Circulation model 0.5-1.5 o x2 o resolution 31 vertical levels Calculated vertical mixing NCEP daily forcing from year 1967 repeated onward Have the changes in circulation induced a trend in the biological export production? Simulation of PISCES-T with constant atmospheric forcing

12. PISCES-T with wind forcing PISCES-T with constant wind SeaWiFS Running mean of the Chla Running mean of the Chla anomalies Comparison of the Chla (mg/m 3 ) between PISCES-T and SeaWiFS PISCES-T with wind forcing

13. PISCES-T with constant wind Comparison of the Chla (mg/m 3 ) PISCES-T with wind forcing SeaWiFS PISCES-T with wind forcing

14. Trend in the Southern Ocean Chla (mg/m 3 ) Time series of the Chla induced by changes in circulation PISCES-T with obs. atmo. forcing minus PISCES-T with constant forcing Increase of 0.07 mgChl/m 3 over 38 years

15. Increase in the eratio in the Southern Ocean caused by changes in circulation mean changes Δ Export Production (PgC/y) 0.3 Δ Primary Production (Pgc/y) 0.6 mean eratio PISCES-T eratio with obs. atmo. forcing minus PISCES-T eratio with constant forcing = 0.3 ΔExp ΔPP = 0.57 eratio due to changes in circulation

16. Increase in Export and Primary Production Carbon content (PgC/y) of the Southern Ocean Total ΔFCO2 = 0.15 Δ FHeat = 0.01 ΔPP = 0.6 ΔExp = 0.3 ΔDIC = 0.4PgC/y ΔDIC = 0.4 Atmosphere Euphotic zone Deep ocean

17. Conclusions Further work High eratio in the Southern Ocean Export production compensates 3/4 of the DIC Model results supported by observations Investigate the structure of the ecosystem and estimate its role in this context of circulation changes

18. Further modelling studies Prototype version of PLANKTON 10 currently working Diatoms N 2 fixers Phaeocystis Nanophyto plankton Fe CaCO 3 DMS DOM Mesozoo- plankton Microzoo- plankton Zoopl. filter feeders Bacteria Picophyto plankton Light Si Coccolitho- phorids NO 3 PO 4 NH 4