55. Decadal scale carbon dioxide increase and acidification in the Weddell Sea, Southern Ocean

Mario Hoppema (1)*, Steven van Heuven (2), Rob Middag (3), Kim Currie (4), Oliver Huhn (5)

1 Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27515, Germany
2 Netherlands Institute for Sea Research, Texel, the Netherlands
3 Dept. of Chemistry, NIWA/University of Otago Research Centre for Oceanography, Dunedin, 9054, New Zealand

4 NIWA / University of Otago Research Centre for Oceanography, Dunedin, 9054, New Zealand
5 Institute of Environmental Physics, University of Bremen, Bremen, 28359, Germany

Using a suite of cruises spanning several decades, we investigated the time rate of change of Total CO2 (TCO2) and related variables in the surface layer of the Weddell Gyre and adjacent Antarctic Circumpolar Current.

At the Prime Meridian, a significant TCO2 increase was observed, which is clear evidence for the invasion of anthropogenic CO2. In the Weddell Sea Bottom Water at this location, the spatial distribution of the increase in TCO2 bears a high resemblance to that of CFCs, suggesting that the changes in TCO2 have been propagated from the surface. However, other variables like dissolved oxygen and silicate also show trends through time, pointing to non-steady state conditions which might also affect the derived CO2 increase. Near the tip of the Peninsula, the coldest and most recently ventilated waters, hugging the continental slope, exhibit increasing TCO2 over time despite the presence of sea ice.

This indicates that CO2 uptake and acidification occur although sea ice cover is present for a significant period of the year. The CO2 increases/changes were translated into changes of carbonate ion and pH. Additionally, we show data on the partial pressure of CO2 for the Weddell Sea, in particular on the seasonal cycle and the saturation state. We determined seasonal changes in CO2, i.e., drawdown through phytoplankton, which we compared to seasonal changes in trace metals in this region.