Southern Ocean response to the Annular Mode: Inorganic and organic carbon fluxes

Inorganic and organic carbon fluxes

Judith Hauck, Christoph V ¨olker, Tingting Wang, Martin Losch, Dieter Wolf-Gladrow, Mario Hoppema

Alfred Wegener Institute for Polar and Marine Research

Bjerknes coference

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

The Southern Ocean

Hoppema et al., 2004

The Southern Ocean

Hoppema et al., 2004

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

The Southern Ocean

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BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

Southern Annular Mode (SAM) SAM Index:

Sea level pressure anomalies between the subpolar low and and the subtropical high-pressure systems

stronger than usual

Negative: pressure gradient weaker than usual

Trend toward its positive phase(Marshall et al., 2003, Thompson et al., 2011)

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

Southern Annular Mode (SAM) SAM Index:

Sea level pressure anomalies between the subpolar low and and the subtropical high-pressure systems Positive: pressure gradient stronger than usual

Negative: pressure gradient weaker than usual

Trend toward its positive phase(Marshall et al., 2003, Thompson et al., 2011)

Southern Annular Mode (SAM) SAM Index:

Sea level pressure anomalies between the subpolar low and and the subtropical high-pressure systems Positive: pressure gradient stronger than usual

Negative: pressure gradient weaker than usual

Trend toward its positive phase(Marshall et al., 2003, Thompson et al., 2011)

1950 1960 1970 1980 1990 2000 2010

−5

−4

−3

−2

−1 0 1 2 3

SAM Index

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

Southern Annular Mode (SAM)

Polar Front

Antarctic shelf

surface ocean

deep ocean Increased

westerlies

Antarctica

atmosphere

Southern Annular Mode (SAM)

Polar Front

Antarctic shelf

surface ocean

deep ocean Increased

westerlies

Antarctica

atmosphere

Counter-acting transport by eddies?

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

Ecosystem Model REcoM-2

Chemistry C / ALK / N / Si / Fe

Small Phytoplankton C / N / CaCO3 / Chl

Diatoms C / N / Si / Chl

Zooplankton C / N

Detritus C / N / Si / CaCO3

Dissolved Organic Material C / N

Geider et al., 1998; Schartau et al., 2007; Hohn et al., 2009; Hauck et al., GBC, under review

Ecosystem Model REcoM-2

Chemistry C / ALK / N / Si / Fe

CO2 dust/Fe

Small Phytoplankton C / N / CaCO3 / Chl

Diatoms C / N / Si / Chl

Zooplankton C / N

Detritus C / N / Si / CaCO3

Dissolved Organic Material C / N

Geider et al., 1998; Schartau et al., 2007; Hohn et al., 2009; Hauck et al., GBC, under review

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

Model runs

1900 1947 2010

Atm CO2

Climatological forcing (CORE)

Climatological dust

Inter-annual varying forcing (NCEP-R1)

Monthly dust (1979-2010)

Model runs

1900 1947 2010

Atm CO2

Climatological forcing (CORE)

Climatological dust

Inter-annual varying forcing (NCEP-R1)

Monthly dust (1979-2010)

Only changes due to perturbed atmospheric forcing

Changes due to atm CO2 increase AND perturbed atmospheric forcing

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

Mena model state: carbonate system

average∆DIC 9.6µmol L⁻¹

average∆Alk 30.2µmol L⁻¹

Mean model state: phytoplankton limitations

Feb Feb

Nanophytoplankton Diatoms

Si-limitation N-limitation

Fe-limitation

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

Regression to SAM

Satellite-derived SST (°C) response

per unit increase SAM Index

-0.4 -0.2 0 0.2 0.4 ^{−0.5 −0.25 0 0.25 0.5}

Modelled SST (°C) response

per unit increase SAM Index

Regression to SAM

−0.05 0 0.05 0.1 0.15

Modelled total chlorophyll response

(mg m^-3 per unit increase SAM)

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

Regression to SAM

−0.05 0 0.05 0.1 0.15

Modelled total chlorophyll response

(mg m^-3 per unit increase SAM)

Polar Front

south north

iron addition + deepening MLD

chlorophyll increase

iron addition + deepening MLD

chlorophyll decrease

Regression to SAM

−0.05 0 0.05 0.1 0.15

Modelled total chlorophyll response

(mg m^-3 per unit increase SAM)

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

Inter-annual variability

Carbon budget

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

Carbon budget

Carbon budget

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

Carbon budget

summing up: carbon flux anomalies for +SAM

Hauck et al., GBC, under review

BACKGROUND INTER-ANNUALVARIABILITY CONCLUSIONS

SAM-related carbon budget summary

upwelling of DIC south of polar front≈balanced by northward Ekman transport and downwelling north of polar front

changes in gas exchange and biological carbon export are of similar magnitude, but much smaller than advective changes

SAM related air-sea CO₂flux in S.O. is 0.09±0.03 PgC yr⁻¹, similar to a recent eddy-resolving study (Dufour,