Figure 1. A. Geographic extent of a stable Antarctic Ice Sheet for different mean temperatures at sea level (5, 9, 10, 15, 19, and 20 K) above current temperatures (Huybrechts, 1990). The higher temperature models provide a guide as to which areas would have developed ice cover during the earliest phases of Cenozoic cooling. At the highest model temperature (+20 K), the ice sheet is small, centered in the Gamburtsev Mountains, from which drainage flows into Prydz Bay. At lower temperatures, the ice extends toward the coast, first reaching it in Prydz Bay and the Ross Sea. B. Development of shelf sequence geometry under the influence of glacial ice. When ice extends to the shelf break, sediment in basal ice is delivered to the upper slope, which then progrades. The shelf may erode or receive a blanket of compact till forming topsets. During periods of reduced ice cover, the shelf and slope receive siliciclastic sediment from icebergs and biogenic sediment from phytoplankton production in the water column.

Figure 2. A. Overview map of the proposed primary Leg 188 drill sites in respect to port of origin (Freemantle) and final port (Hobart). B. Map of the East Antarctic coastline between 50°E and 90°E, showing the location of Prydz Bay, the Mac Robertson Shelf, Mawson Station, Leg 119 drill sites (squares), and proposed priority one (red circles [web]/black circles [print]) and contingency (white circles [web]/gray circles [print]) drill sites for Leg 188.

Figure 3. Map of Antarctic ice sheets showing drainage divides and flow lines. Prydz Bay is the downstream end of the Lambert Glacier-Amery Ice Shelf drainage basin, which originates entirely in the East Antarctic Ice Sheet. The convergent flow lines feeding the Amery Ice Shelf mean that it responds more sensitively to changes in the interior than other parts of the east Antarctic coast.

Figure 4. Location of Prydz Channel Trough Mouth fan and Wilkins and Wild Drifts. Arrows indicate flow lines of Lambert Glacier during major ice advances.

Figure 5. Model of sediment drift formation along the Antarctic continental margin (Rebesco et al., 1997). During glacial maxima, till transported to the shelf edge slumps, forming sediment gravity flows. Turbidity currents thus formed move down the slope to the rise, where suspended fine sediments are entrained by west-flowing bottom currents and deposited in the drifts west of the submarine canyons.

Figure 6. Interpretation of seismic line through Leg 119 drill sites in Prydz Bay (Cooper et al., 1991a). Shaded area is the part of seismic Sequence PS.2A not sampled by Site 742. Sequence PS.2B comprises Cretaceous nonmarine sediments and Site 742, which bottomed in Eocene glacial sediment. Thus, the lower part of Sequence PS.2A will be drilled to date the oldest glacial sediments in Prydz Bay and to sample any preglacial Cenozoic deposits.

Figure 7. Map showing bathymetry of the Wild Drift, seismic lines, and proposed drill sites.

Figure 8. Seismic section across Wilkins Drift. Seismic horizons:
P3 – Onset of current influenced drift deposition (Oligocene?)
P2 – Onset of Antarctic glaciation? (Eocene?)
P1 – Cretaceous?

Figure 9. Seismic section (north-south) through the Prydz Channel trough mouth fan showing Surface PP.15, which marks the start of trough mouth fan sedimentation and the first cutting of the Prydz Channel.

Figure 10. Model of trough mouth fan sedimentation. A. When the ice stream extends to the continental shelf edge, debris in basal ice and the mobile debris layer at the glacier sole mostly bypass the shelf and are delivered to the shelf edge, where they are redistributed by debris flows and turbidity currents. Fine sediment is entrained in buoyant meltwater plumes and settles on the fan surface. B. During interglacials, the ice has retreated inshore from the shelf edge. Biogenic sedimentation, ice rafting, and minor reworking by slope processes predominate. Ice keel ploughing at the shelf edge results in some remobilization of glacial sediment.

Figure 11. Bathymetric map showing the location of Iceberg Alley, proposed ODP sites, seismic lines, and gravity cores.

Figure 12. A. Seismic line collected with a generator-injector (GI) gun source (Line 186/1901) along the axis of Iceberg Alley. Siliceous mud and ooze appears as a faint horizontally layered unit overlying dipping Paleogene sediments. Proposed ODP sites are indicated. B. A 3.5-kHz echo sounder line collected along the axis of Iceberg Alley. The sediments show horizontal layering in sileceous mud and diatom ooze (SMO) deposits. Proposed ODP sites and existing gravity cores indicated.

Figure 13. Generalized section across Prydz Bay illustrating the Leg 188 drilling strategy. The strategy consists of (1) one hole (Site PBS-2A) drilling the lower part of the Paleogene section (Sequence PS.2A); (2) one hole (Site PBF-6A) drilling the Prydz Channel trough mouth fan to date the development of cross-shelf channels and trough mouth fans and determine the number of times the Lambert Glacier reached the shelf edge from the late Miocene? to the present; and (3) one hole (Site PBD-12B) to investigate glacial-interglacial variations in continental rise sedimentation from the Oligocene to Pleistocene.

Figure 14. Location of primary drill sites on the Prydz Bay shelf, slope, and rise.

Figure 15. Location of alternate sites on the Prydz Bay shelf, slope, and rise.

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