The present and past bottom-current flow regime around the sediment drifts on the continental rise west of the Antarctic Peninsula

Throughout the last decade large sediment drifts located on the upper continental rise west of the Antarctic Peninsula were the target of oceanographic measurements, bathymetric mapping, seismic investigations. shallow sediment coring, and deep-sea drilling by Ocean Drilling Program (ODP) Leg 178. These studies concluded that for most of the late Neogene and Quaternary a generally SW-ward directed bottom current affected the deposition on the drifts. In particular during glacial periods, the deposition was additionally influenced by NW-ward directed transport of terrigenous detritus supplied by turbidity currents from the Antarctic Peninsula continental slope. In a recent study, however, the palaeomagnetic signal of the drift sediments recovered at two ODP Leg 178 sites (1095 and 1101) was interpreted to provide spatial and directional information on the physical record of the NE-ward flowing Antarctic Circumpolar Current (ACC). Here we investigate the link between the clockwise flowing ACC and the generally SW-wards flowing near-bottom contour current. We show that at the ODP Leg 178 sites on the western Antarctic Peninsula continental margin the ACC only affects the ocean circulation above ca. 1000 m water depth. Therefore, the signal of ACC flow might only be archived in the ice-rafted debris (IRD) content of the drift sediments. However, the IRD from the Leg 178 sites accounts for only a small proportion of the drift sediments and is dominantly of local origin. Past variability of bottom-water flow around the sediment drifts was reconstructed on the basis of seismic studies and clay mineralogical and grain-size analyses. These reconstructions provide useful information about both downstream direction and velocity changes of the bottom current and point to its SW-ward flow along the upper rise during at least the last 9.4 Ma.

Details