A paleoproductivity transect across the Antarctic Circumpolar Current in the Late Quaternary South Atlantic

The global significance of the Southern Ocean as a carbon sink as well as the individual dynamics and budgets are still open questions. The response of the biogeochemical system to climate changes and related processes were studied by looking at marine archives from a north-south transect across the Antarctic Circumpolar Current (ACC) in the southeast Atlantic sector of the Southern Ocean. Paleoproductivity was calculated from total (marine) Corg and accumulation rates by the equation of Stein (1991) for four ODP Leg 177 sites. High-resolution series (sample spacing between 500 and 820 years) were taken from Sites 1089, 1091, 1093 and 1094 from Recent down to 500 kyr. The Bender (2002) Vostok ice core age model was used to map the stratigraphic data (O-isotopes, bio-, lithostratigraphy and seasurface paleotemperatures) on equal scales and to allow comparisons to dust and other climate records from ice cores.Site 1089 in the Subantarctic Zone shows the highest Corg and paleoproductivity values. Maxima of about 100-150 gC (per square meter and year) were reached during cold intervals and minima of about 50 gC during climate optima. The paleoproductivity record shows a significant precession related periodicity pattern. This pattern fades to the south were it becomes progressively replaced by the 100-kyr cycle. Paleoproductivity values decreased from Sites 1091 via 1093, both in the Polar Frontal Zone, to 1094 in the Antarctic Zone. Maxima below 100 gC were reached at the end of glaciations just before terminations, and were immediately followed by minima of about 15 gC during peak surface temperature conditions.References:Stein, R., 1991. Accumulation of organic carbon in marine sediments. In: Bhattacharji, S., Friedman, G.M., Neugebauer, H.J., Seilacher, A. Eds. , Lecture Notes in Earth Sciences. Springer-Verlag, Berlin, p. 217.Bender, M.L., 2002. Orbital tuning chronology for the Vostok climate record supported by trapped gas composition. Earth and Planetary Science Letters, 204, 275-289.