Variability of the net air-sea CO₂ flux inferred from shipboard and satellite measurements in the Southern Ocean south of Tasmania and New Zealand

Yvan Rangama (1) , Jacqueline Boutin (1) , Jacqueline Etcheto (1) , Liliane Merlivat (1) , Taro Takahashi (2) , Bruno Delille (3) , M. Frankignoulle (3) , Dorothee C. E. Bakker (4)

1 LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
2 LDEO - Lamont-Doherty Earth Observatory
3 Unité d'Océanographie Chimique
4 School of Environmental Sciences [Norwich]

We determine the distribution of oceanic CO₂ partial pressure (pCO₂) with respect to remotely sensed parameters (sea surface temperature (SST) and chlorophyll (Chl)) in order to gain an understanding of the small-scale (10-100 km) pCO₂ variability and to estimate the net air-sea CO₂ flux in the region (125°E-205°E; 45°S-60°S), which represents 22% of the Southern Ocean area between 45°S and 60°S. We split the study area into several biogeochemical provinces. In chlorophyll-poor regions, pCO₂ is negatively correlated with SST, indicating that pCO₂ is mostly controlled by mixing processes. For Chl > 0.37 mg m³ , pCO₂ is negatively correlated with Chl, indicating that pCO₂ variability is mostly controlled by carbon fixation by biological activity. We deduce fields of pCO₂ and of air-sea CO₂ fluxes from satellite parameters using pCO₂-SST, pCO₂-chlorophyll relationships and air-sea gas exchange coefficient, K, from satellite wind speed. We estimate an oceanic CO₂ sink from December 1997 to December 1998 of À0.08 GtC yr^-1 with an error of 0.03 GtC yr^-1. This sink is approximately 38% smaller than that computed from the Takahashi et al. (2002) climatological distribution of DpCO₂ for the 1995 year but with the same K (-0.13 GtC yr^-1). When we correct ocean pCO₂ for the interannual variability between 1995 and 1998, the difference is even larger, and we cannot reconcile both estimates in February-March and from June to November. This strengthens the need of new in situ measurements for validating extrapolation methods and for improving knowledge of interannual pCO₂ variability.

Domaines: Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]; Milieux et Changements globaux

Yvan Rangama, Jacqueline Boutin, Jacqueline Etcheto, Liliane Merlivat, Taro Takahashi, et al.. Variability of the net air-sea CO₂ flux inferred from shipboard and satellite measurements in the Southern Ocean south of Tasmania and New Zealand. Journal of Geophysical Research, 2005, 110, pp.C09005. ⟨10.1029/2004JC002619⟩. ⟨hal-00124824⟩