Variations of biogenic particle flux in the southern Atlantic section of the Subantarctic Zone during the late Quaternary: Evidence from sedimentary 231Pa and 230Thex ex

Variations of intensity and composition of biogenic particle flux at the northern boundary of the present Polar Frontal Zone in the Atlantic sector of the Southern Ocean are indicators of major changes of paleoenvironmental conditions on glacialrinterglacial time scales during the Late Quaternary. In order to estimate those past changes, sediment accumulation patterns of two piston cores, one from just north and one just south of the present day position of the Subantarctic Front were reconstructed. Using the 230Th method large contributions of laterally supplied material were quantified and used toex correct sediment accumulation rates. During the last glacial focussing of biogenic opal-dominated material exceeded the original contribution from the surface water above by a maximum factor of 8.7. The initial activity ratio of 231Pa r230Thex ex was used as tracer for biogenic particle flux and composition and indicates that during the glacial stages 2 and 4 the area of high opal productivity was situated above the location of the southern core whereas the northern core has not been reached by this northward shift during the last 130 kyr as shown by the pattern of focussing-corrected bulk accumulation rates. If the position of the Antarctic Polar Front has remained at the northern boundary of the high opal productivity area during the last 130 kyr, the results suggest that was located exactly between the two core sites during glacial stages 2 and 4. A two-box modeling approach involving particle flux and boundary scavenging intensity of 231Pa was applied to estimate the possible range of the 231Pa r230Th ratio recorded in Southern Ocean sediments. Previous estimates on the export of 231Pa fromex e