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 (GOCE)
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
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
(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 )
….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?)
C org export comparison HAMOCC5.1 EPPLEY SCHLITZER LAWS gC/m2/yr
HAMOCC5.1 with particle dynamics Seasonal average of no. of marine snow aggregates [no. cm -3 ] ( 0-90m) WinterSpring Autumn Summer 0 50
HAMOCC5.1 with particle dynamics Seasonal average of export [gC/(m 2 *year)] WinterSpring Autumn Summer 0 160
HAMOCC5.1 with particle dynamics Seasonal average of atmosphere to ocean CO 2 flux [gC/(m 2 *year)] Spring Autumn Summer Winter
Vertical distribution of POC global southern ocean
Vertical distribution of POC Equatorial Pacific North Atlantic
dpCO 2 : w poc =5m/d minus w poc =10m/d
dpCO 2 : w poc = 10 m/d minus w poc (agg)
Difference in export production between w poc =5m/d and w poc (agg) gC/(m 2 a)
Difference in export production between w poc =10m/d and w poc (agg) gC/(m 2 a) *10 -8
f-ratio from aggregation
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
surface water pCO 2 : REF HFF-REF ( = -1.7ppm) mean: ppm LSCE results (PISCES): LFF-REF ( = -0.7ppm) BAL-REF ( = -5.1ppm)
weak oceanic sink strong LSCE results (PISCES):
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?