Decadal increases of anthropogenic CO2 in the subtropical South Atlantic Ocean along 30°S

Abstract

Using high-quality data for dissolved inorganic carbon and related properties obtained about 10 years apart (1992/1993-2003), We examined decadal increases of anthropogenic CO2 (ΔnCTCAL) along 30°S (WHP A10 section) in the subtropical South Atlantic. Significant ΔnCTCAL was detectable down to an isopycnal surface of σθ = 27.3 (∼1000 m water depth). Averaged ΔnCTCAL in Sub-Antarctic Mode Water (SAMW; 26.6-27.0 σθ, 350-700 m) was 6.8 ± 1.6 μmol kg-1 and that in Antarctic Intermediate Water (AAIW; 27.1-27.4 σθ, 700-1200 m) was 3.6 ± 1.4 μmol kg-1. In SAMW, ΔnCTCAL was higher by ∼7 μmol kg-1 west of 15°W than east of it, while ΔnCTCAL in AAIW did not show such a distinct east-west difference. For deep waters, significant ΔnCTCAL was detected in Antarctic Bottom Water at depths greater than 4500 m in the Cape Basin (longitude 2°E-10°E). No significant ΔnCTCAL could be detected for North Atlantic Deep Water (NADW). We attributed ΔnCTCAL being higher west of 15°W in SAMW to differences of water mass distributions and flows. From a water column inventory, we estimated the uptake rate of anthropogenic CO2 over the decade from 1992/1993 to 2003 to be 0.6 ± 0.1 mol m-2 a-1, which is half the rate in the South Pacific (1.0 ± 0.4 mol m-2 a-1). Copyright 2008 by the American Geophysical Union.