Decadal increases of anthropogenic CO2 in the South Pacific subtropical ocean along 32°S

Abstract

To estimate decadal increases of anthropogenic CO2 in the ocean, distributions of dissolved inorganic carbon (CT) corrected by apparent oxygen utilization and salinity (nCTANT) were investigated along the World Ocean Circulation Experiment (WOCE Hydrographic Programme (WHP)) P6 section based on data obtained 10 years apart. Significant increases of nCTCAL were detected down to 1500 m (≅27.5σ0) water depth, above which the Sub-Antarctic Mode Water (SAMW) and the Antarctic Intermediate Water (AAIW) are found. The decadal increases of nCTCAL on the isopycnal surfaces (26.6-26.σθ) of SAMW were higher (5-8 μmol kg-1) to the east of 160°W than to the west of it, while the increases in AAIW were almost constant on the isopycnal surfaces (27.0-27.5σθ). The averaged increases of nCTCAL in SAMW and AAIW were 10 ± 3.1 and 4.1 ± 2.0 μmol kg-1, respectively. Small but significant increases of nCTCAL and salinity-normalized CT (nCT) were also found (approximately 3.0 and 5.0 μmol kg-1, respectively) in abyssal waters occupying depths greater than 3500 m at longitude 180°-160°W, which correspond to Circumpolar Deep Water. Spatial differences of anthropogenic CO2 accumulation are discussed in terms of water mass distributions. The water column inventory of increases of anthropogenic CO2 in the South Pacific subtropical ocean was estimated to be 1.0 ± 0.4 mol m-2 yr-1, which is almost the same as that previously reported. Copyright 2007 by the American Geophysical Union.