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

Abstract

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 m-3, 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 -0.08 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 ΔpCO2 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. Copyright 2005 by the American Geophysical Union.