A window for carbon uptake in the southern subtropical Indian Ocean

Abstract

Atmospheric CO2 sinks in the southern Indian Ocean was examined for their seasonal, interannual and interdecadal variability. Two distinct zones of CO2 uptake are identified; located in the 15°S–35°S band is the northern box where CO2 uptake is dominated by the solubility pump, and in the latitudinal range of 35°S–50°S is the southern box where both the solubility and biological pump are equal players. The anthropogenic CO2 inventories appear to be a result of deepening subduction of CO2 and subsequent invasion into the northern domain. The seasonal and interannual variability of CO2 sinks to the north are rather surface trapped, while the deep CO2 variability is found to be coherent with the atmospheric forcing, consistent with decadal wind stress curl anomalies. This is a step towards separating the secular trends of deep ocean CO2 from its natural variability in the analysis region.