Rapid invasion of anthropogenic CO2 into the deep circulation of the Weddell Gyre.

Abstract

Data are presented for total carbon dioxide (TCO2), oxygen and nutrients from 14 cruises covering two repeat sections across the Weddell Gyre, from 1973 to 2010. Assessments of the rate of increase in anthropogenic CO2 (Cant) are made at three locations. Along the Prime Meridian, TCO2 is observed to steadily increase in the bottom water. Accompanying changes in silicate, nitrate and oxygen confirm the non-steady state of the Weddell circulation. The rate of increase in TCO2 of +0.12±0.05 μmol kg(-1) yr(-1) therefore poses an upper limit to the rate of increase in Cant. By contrast, the bottom water located in the central Weddell Sea exhibits no significant increase in TCO2, suggesting that this water is less well ventilated at the southern margins of the Weddell Sea. At the tip of the Antarctic Peninsula (i.e. the formation region of the bottom water found at the Prime Meridian), the high rate of increase in TCO2 over time observed at the lowest temperatures suggests that nearly full equilibration occurs with the anthropogenic CO2 of the atmosphere. This observation constitutes rare evidence for the possibility that ice cover is not a major impediment for uptake of Cant in this prominent deep water formation region.