The imprint of anthropogenic CO2 in the Arctic Ocean: evidence from planktic δ13C data from watercolumn and sediment surfaces

δ13C values of N. pachyderma (sin.) from the water column and from core top sediments are compared in order to determine the 13C decrease caused by the addition of anthropogenic CO2 to the atmosphere. This effect, which is referred to as the surface ocean Suess effect, is estimated to be about −0.9‰(±0.2‰) within the Arctic Ocean halocline waters and to about −0.6‰(±0.1‰) in the Atlantic-derived waters of the southern Nansen Basin. This means that the area where the Arctic Ocean halocline waters are formed, the Arctic shelf regions, are relatively well ventilated with respect to CO2. Nevertheless, δ13C of dissolved inorganic carbon (δ13CDIC) in the Arctic Ocean halocline waters is far from isotopic equilibrium. Absolute values of δ13C of N. pachyderma (sin.) covary with the surface ocean Suess effect, and we interprete changes in both parameters as a reflection of the degree of ventilation of the waters on the shelf sea. Measurements of δ13C of N. pachyderma (sin.) in the Arctic Ocean from plankton tows reveal a “vital effect” of about −2‰, significantly different from other published values. A first-order estimate of the total anthropogenic carbon inventory shows, that despite of its permanent sea-ice cover, the Arctic Ocean, with 2% of the global ocean area, is responsible for about 4–6% of the global ocean's CO2 uptake.