1. Impact of vertical flux simulation on surface pCO 2 Joachim Segschneider 1, Iris Kriest 2, Ernst Maier-Reimer 1, Marion Gehlen 3, Birgit Schneider 3 1 Max-Planck-Institute for Meteorology, Hamburg, Germany 2 IFM-GEOMAR, Kiel, Germany 3 LSCE, Gif-sur-Yvette, France EU FP6 IP 511176 (GOCE)

2. Background The vertical flux of particulate matter from the surface to the ocean floor in biogeochemical models is presently simulated using 4 different approaches: prescribed globally uniform penetration depth profiles prescribed globally uniform settling velocities regionally varying settling velocities depending on production rates/dust input (ballast effect) regionally varying settling velocities computed from aggregation schemes

3. Addressed question How do these likewise used approaches impact on the surface pCO 2, atmosphere-ocean gas exchange and atmospheric pCO 2 ? Within CarboOcean WP16, this question is addressed using the PISCES (LSCE) and the HAMOCC (MPI-M) models and different schemes for modelling of the export production

4. (1) work at MPI-M… implementation of the aggregation scheme of Kriest et al (2001) into MPIOM/HAMOCC5.1 Three experiments (climatological NCEP forcing, 278ppm): w poc =5 m/d w poc =10m/d w from aggregation scheme (w agg )

5. ….work at MPI-M…. Particle dynamics module computes: number of marine snow aggregates size distribution of marine snow aggregates mass of marine snow aggregates one sinking velocity as function of size and particle density for opal, CaCo 3 shells, detritus (ballast effect) dust load does not increase settling velocity (important?)

6. C org export comparison HAMOCC5.1 EPPLEY SCHLITZER LAWS gC/m2/yr

7. HAMOCC5.1 with particle dynamics Seasonal average of no. of marine snow aggregates [no. cm -3 ] (  0-90m) WinterSpring Autumn Summer 0 50

8. HAMOCC5.1 with particle dynamics Seasonal average of export production @90m [gC/(m 2 *year)] WinterSpring Autumn Summer 0 160

9. HAMOCC5.1 with particle dynamics Seasonal average of atmosphere to ocean CO 2 flux [gC/(m 2 *year)] Spring Autumn Summer Winter -200 200

10. Vertical distribution of POC global southern ocean

11. Vertical distribution of POC Equatorial Pacific North Atlantic

12. dpCO 2 : w poc =5m/d minus w poc =10m/d

13. dpCO 2 : w poc = 10 m/d minus w poc (agg)

14. Difference in export production between w poc =5m/d and w poc (agg) gC/(m 2 a)

15. Difference in export production between w poc =10m/d and w poc (agg) gC/(m 2 a) *10 -8

16. f-ratio from aggregation

17. LSCE results (PISCES): --- REF (Reference, high flux feeding intensity) --- LFF (low flux feeding intensity) --- HFF (high flux feeding intensity) --- BAL (ballast parameterization) global annual mean POC-flux PE-ratio (EP/PP) air-sea CO 2 flux

18. surface water pCO 2 : REF HFF-REF (  = -1.7ppm) mean: 274.5 ppm LSCE results (PISCES): LFF-REF (  = -0.7ppm) BAL-REF (  = -5.1ppm)

19. weak oceanic sink strong LSCE results (PISCES):

20. CONCLUSIONS simulated surface water pCO 2 depends strongly on the choice of vertical transport scheme this can be quantified by the PE-ratio models were tuned using simple parameterisations - do we need to retune them if we take into account regionally varying schemes? are these findings important in the view of future climate projections?