Increase in Anthropogenic CO2 in the Caribbean Sea Over the Period of 1997-2003 and its Implications Toward the Carbon Cycle in the Gulf of Mexico

Inorganic carbon data from two separate surveys (WOCE and CLIVAR) along the transect A22 within the Caribbean Sea were examined for increase in anthropogenic CO2 (Canthro) concentration in this semi-enclosed basin over a six year period (1997-2003). Using multiple approaches, we found that Canthro gradually decreased with depth along most of the surveyed transect. However, in the northern end of the A22 near Puerto Rico, we observed both significantly greater increase in Canthro at depth (>1000 m) than the rest of this transect and a mid-depth (~2000 m) Canthro maximum. Furthermore, despite relatively large uncertainties, we also found that Canthro exhibited a homogeneous, albeit small (~1 μmol/kg), increase in the deep waters south of above high Canthro zone. These observations are presumably caused by deep water circulation in the Caribbean Sea. In the Venezuelan Basin where A22 is located, deep water predominantly comes from adjacent North Atlantic intermediate water through a shallow sill (Anegada Passage, ~1915 m). The rate of Canthro increase in the deep water below this sill thus depends on the flux of the intermediate North Atlantic water, due to limited direct exchange between the deep waters in the Caribbean Sea and in the open ocean basin. This work may have important implications toward the understanding of CO2 uptake in other semi-enclosed basins under the rising atmospheric CO2 conditions. A study is currently underway to investigate this problem in the Gulf of Mexico.