Continental Margin Sediments and Ice Sheet History

The mass balance of the EAIS, the nature of the substratum and the continental topography, particularly in the coastal region, determine sediment input to the continental margin. Enhanced input of sediments to the continental margin at ODP Site 693 in the eastern Weddell Sea and development of a prograding wedge started in the latest Miocene and peaked during the earliest Pliocene (Gersonde et al., 1990). The seismic tie between ODP Site 693 and the southern Weddell Sea is uncertain, but Kuvaas and Kristoffersen (1991) suggest that fan development started in the southern Weddell Sea by the early Oligocene (above Reflector W4, Fig. WS-4 and Foldout WS-1), and that about two-thirds of the sediment thickness at the mouth of the present Crary Trough was already in place by the late Miocene (i.e. below Reflector W5). Channel-levee complexes have migrated eastward on the Crary Trough Mouth Fan, and late Miocene and younger deposition constructed a third major channel-levee complex and deposited about 1 km of sediments below the trough mouth (Fig. WS-4 and Foldout WS-1). These age relations imply that the principal input of sediments from East

Antarctica to the Weddell Sea margin from the early Oligocene to the late Miocene originated from a glaciated interior of the continent via the Crary Trough, and that there was effectively no input along the Dronning Maud Land margin. At this point, the significance of a local thickness maximum of glacial sediments north of Lyddan Ice Rise (Rogenhagen et al., 2004) is unclear. The EAIS expanded to the Dronning Maud Land margin during the latest Miocene-earliest Pliocene and formed a prograding wedge below the continental shelf and slope. Sea ice cover has prevented acquisition of the seismic data from west of 45°W and north of the Ronne Ice Shelf (Fig. WS-1) needed to study the depositional geometries of sediments originating from the catchment area of the WAIS. Data from this area also are needed to study the relation between eastern and western sediment source regions.

Moraine complexes on the shelf in the eastern Weddell Sea suggest that the EAIS was grounded on the mid-shelf and did not reach the shelf edge during the LGM (Kristoffersen et al., 2000), except at the mouth of the Crary Trough (Bentley and Anderson, 1998).

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