Impact of vertical flux simulation on surface pCO2

Joachim Segschneider1, Iris Kriest2,Ernst Maier-Reimer1, Marion Gehlen3, Birgit Schneider3

1Max-Planck-Institute for Meteorology, Hamburg, Germany2IFM-GEOMAR, Kiel, Germany3LSCE, Gif-sur-Yvette, France

EU FP6 IP 511176 (GOCE)

Background

The vertical flux of particulate matter from the surfaceto the ocean floor in biogeochemical models ispresently 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 pCO2, atmosphere-ocean gas exchange and atmospheric pCO2?

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):

wpoc=5 m/d

wpoc=10m/d

w from aggregation scheme (wagg)

….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, CaCo3 shells, detritus (ballast effect)• dust load does not increase settling velocity (important?)

Corg export comparisonHAMOCC5.1 EPPLEY

SCHLITZER LAWS

gC/m2/yr

HAMOCC5.1 with particle dynamics

Seasonal average of no. of marine snow aggregates [no. cm-3] ( 0-90m)

Winter Spring

AutumnSummer

0

50

HAMOCC5.1 with particle dynamics

Seasonal average of export production @90m [gC/(m2*year)]

Winter Spring

AutumnSummer

0

160

HAMOCC5.1 with particle dynamics

Seasonal average of atmosphere to ocean CO2 flux [gC/(m2*year)]

Spring

AutumnSummer

Winter

-200

200

Vertical distribution of POC

globalsouthernocean

Vertical distribution of POC

EquatorialPacific

NorthAtlantic

dpCO2 : wpoc=5m/d minus wpoc=10m/d

dpCO2 : wpoc= 10 m/d minus wpoc (agg)

Difference in export production between wpoc=5m/d and wpoc (agg)

gC/(m2 a)

Difference in export production between wpoc=10m/d and wpoc (agg)

gC/(m2 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 annualmean

POC-flux PE-ratio (EP/PP) air-sea CO2 flux

surface water pCO2: REF HFF-REF (= -1.7ppm)

mean: 274.5 ppm

LSCE results (PISCES):

LFF-REF (= -0.7ppm) BAL-REF (= -5.1ppm)

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gLSCE results (PISCES):

CONCLUSIONS

• simulated surface water pCO2 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?