Title: Decadal (1994-2008) change in the carbon isotope ratio in the eastern South Pacific Ocean
Authors: Young Ho Ko, Kitack Lee, Paul D. Quay, and Richard A. Feely
Journal: GLOBAL BIOGEOCHEMICAL CYCLES
Abstract:
We determined the 14 year change in the anthropogenic CO2 inventory in the eastern South Pacific Ocean along the 110¡ÆW meridian from 67¡ÆS to 21¡ÆN, using seawater ¥ä13C data sets collected in 1994 and 2008. The vertical integral of the 14 year ¥ä13C change was assessed in five latitude bands and found to be greatest (14.7¢¶m yr1) in the subpolar band (38¡ÆS–55¡ÆS) and smallest (3.0¢¶m yr1) in the tropical band (21¡ÆN–18¡ÆS). The ¥ä13C change in each of the latitudinal bands was primarily caused by inputs of anthropogenic CO2 via air-sea exchange and transport. More than 50% of the total anthropogenic CO2 was added to the subpolar band via the northward movement of Antarctic Intermediate Water (AAIW) from the south, and the remaining 50% was added via air-sea exchange. We also calculated the ratio of the temporal change in ¥ä13C to the change in dissolved inorganic carbon, which is a measure of the efficiency of oceanic uptake of anthropogenic CO2. The ratio for AAIW in 1994 (0.017¢¶(¥ìmol kg1)1) was greater than that in 2008 (0.010¢¶(¥ìmol kg1)1) based on the change in preformed ¥ä13C and dissolved inorganic carbon (DIC), indicating reduced efficiency of CO2 uptake by the Southern Ocean in 2008 relative to that in 1994. AAIW remained at the surface for a shorter period in 2008 relative to 1994, and thus would have taken up less atmospheric CO2 prior to subduction. The projected reduction in this ratio indicates a weakening of CO2 uptake by the Southern Ocean in the future.