Sub-bottom profiling and sedimentological studies in the southern Weddell Sea, Antarctica: evidence for large-scale erosional/depositional processes

Abstract

Low-frequency echo-sounder profiles (3.5 kHz and Parasound systems), surface sediments, and sediment cores were taken from the continental margin of the southern Weddell Sea during four cruises of the R.V. Polarstern between 1985/86 and 1988/89. Nine sediment echo types were classified, mapped and interpreted and verified using sedimentological data. The results provide evidence of large-scale erosional and depositional processes on the continental margin of the southern Weddell Sea. During the last glacial maximum, the Antarctic ice sheet advanced to the continental shelf edge directly north of the Crary Trough, where it overdeepened the shelf by erosion. The supply of eroded material presumably initiated sediment gravity transport processes on the slope in the extension of the Crary Trough. A combination of high energy gravitational transport, such as by turbidity currents, and contour current activity probably caused westward migration of a zone of erosion along the steep, 200–400 m high western flank of an asymmetrical channel extending down the slope. Within the channel, predominantly coarse-grained sediments were deposited, whereas to the west of it, fine-grained levee sedimentation occurred on a sediment ridge. Probably after decoupling of the ice masses, large amounts of sediment were deposited at the sill north of the Crary Trough and at the shallow shelf edge further to the west. Grounding of icebergs resulted in redeposition and compaction of glaciomarine sediments on the continental shelf. Following the retreat of the ice from the shelf edge, sediment gravity transport is inferred to have ceased at the slope. The modern situation is characterized by the flow of high velocity Ice Shelf Water across the shelf edge and at the upper continental slope to the west across the channel-levee complex. On the lower slope today, the current velocities of the remaining Ice Shelf Water are probably not strong enough to cause erosion along the steep western channel flank.