Prominent uptake of anthropogenic CO2 by the Southern Ocean via Antarctic Intermediate Water

Carbon dioxide is the focal point in research and debate on past and future global change. The Southern Ocean plays a prominent role in the redistribution of CO2 between atmospheric and oceanic reservoirs. There are suggestions now that Antarctic Intermediate Water (AAIW), which is formed at the Polar Front, plays an outstanding role in the sequestration of anthropogenic CO2 taken up by the Southern Ocean. We want to validate the hypothesis that the AAIW constitutes a major actor in the anthropogenically perturbed carbon cycle. Validation will be done versus field data of the longest existing (since 1984) oceanic record of combined sections of CO2, transient tracers, hydrography and nutrients at the Greenwich meridian. Moreover, new dedicated CO2 and accompanying data are proposed to be collected during a cruise into the Southern Ocean. The anthropogenic CO2 signal in the AAIW will be derived from several recently proposed concepts for resolving anthropogenic CO2 from contemporary CO2 and auxiliary data. Rigorous comparison of these different concepts should lead to improved application of them in the Southern Ocean, while applying different concepts constitutes a further constraint for the anthropogenic CO2 inventory. An estimate will be provided of the total annual anthropogenic CO2 uptake by the AAIW. Interannual variability of the AAIW along isopycnals is proposed to be investigated using the time-series data of CO2, transient tracers and nutrients. Correlations between the different properties will give insight in the causes of variability. Interannual variability will be related to the Antarctic Circumpolar Wave decadal variability.