The Southern Ocean sink for atmospheric CO2

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The Southern Ocean sink for atmospheric CO2

• Nicolas Gruber(1), S. Fletcher-Mikaloff(1),
• A. Jacobson(2), M. Gloor(2), J.L. Sarmiento(2)
• Department of Atmospheric and Oceanic Sciences
  IGPP, UCLA
• AOS Program, Princeton University

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TWO VIEWS OF CO2 FLUXES IN THE
SOUTHERN OCEAN
Takahashi et al. (2002) u2 a la Wanninkhof et
al. (2001)
TRANSCOM Gurney et al. (2002)
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INVERSION OF OCEAN INTERIOR OBSERVATIONS
AS A CONSTRAINT ON CO2 FLUXES

• Basis functions are model simulated footprints of
  unit emissions from a number of fixed regions
• Estimate linear combination of basis functions
  that fits observations in a least squares sense.
• Inversion is analogous to linear regression

footprints
fluxes
obs
Premultiply both sides by inverse of A
estimated fluxes
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OCEAN INVERSION RESULTS
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COMPARISON WITH
TAKAHASHI AND TRANSCOM
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MODEL SENSITIVITY
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DATA DCant and DCgasex
DCgasex DICobs - DCbio - DCant - const

DCant estimated by DC method
Gruber et al., (1996)
Gruber and Sarmiento (2002)
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Summary

• Our inversion of ocean interior DCant and DCgasex
  data suggests that the Southern Ocean south of
  44ºS is currently about neutral with regard to
  the atmosphere.

• This neutral flux is due to a compensation
  between outgassing of natural CO2 and uptake of
  anthropogenic CO2.

• Our inversion results suggest a weaker Southern
  Ocean sink for atmospheric CO2 than inferred by
  Takahashi et al. (2002). Possible reasons for the
  discrepancy are
• - inversion biases (model transport, data)
• - summer bias of DpCO2 data

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THE CHANGE OF SOUTHERN OCEAN
CO2 FLUXES OVER TIME
(mol m-2 yr-1)
Pre-industrial CO2 fluxes
1995 CO2 fluxes
KVLOW-AILOW model
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NATURAL VS ANTHROPOGENIC CO2 FLUXES
IN THE SOUTHERN OCEAN
(mol m-2 yr-1)
Pre-industrial CO2 fluxes
1995 Anthropogenic CO2 fluxes
KVLOW-AILOW model