Decadal-Scale Increases of Anthropogenic CO 2 in Antarctic Bottom Water in the Indian and Western Pacific Sectors of the Southern Ocean

Abstract

We determined decadal-scale increases of anthropogenic CO 2 in the water column using data sets collected 17 years apart (1994–1996 and 2012–2013) along a transect at nominal 62°S in the Indian and western Pacific sectors of the Southern Ocean. Large increases of anthropogenic CO 2 (up to 9.1 ± 1.5 μmol/kg), closely following atmospheric CO 2 increases, were found in Antarctic Bottom Water (AABW), previously considered a small sink of anthropogenic CO 2 . Vertical distributions of anthropogenic CO 2 increases showed significant positive correlations with those of changes in CFC-12 and SF 6 , implying that the distributions were mainly controlled by physical processes such as ventilation and circulation. Calculated uptake rates of anthropogenic CO 2 by AABW were between 0.29 and 0.39 mol·m −2 ·yr −1 in five longitudinal segments of the transect. In accounting for the large increase of anthropogenic CO 2 in AABW, sea surface conditions in the formation region of AABW are important.