The oceanic sink for anthropogenic CO2 since the mid 1990s

The ocean has continued to take up anthropogenic CO2 from the atmosphere since the 1990s, but so far, we do not have a direct global-scale data-based quantification of this uptake. Here, we address this gap and determine the oceanic accumulation of anthropogenic CO2 between the 1990s and the mid-2000s. We compare inorganic carbon observations from the recent global repeat hydrography program with observations from the 1990s and use an eMLR method on the sea-water property C* to separate the anthropogenic CO2 component from the total change in DIC. We evaluate these results with several independent estimates, permitting us to assess the uncertainties. The initial results indicate a global increase in inventory of about 25 Pg C between 1994 and 2006, which amounts to an uptake of about 2.1 Pg C yr-1 over this period. This flux is currently rather uncertain and is at the lower end of most other estimates (e.g., atmospheric data and ocean inversions). If correct, the ocean sink would have been smaller than expected from the increase in atmospheric CO2.