Summary

Its polar glacial setting, sea ice cover, and great depth combine to make the Antarctic continental shelf a unique sedimentary environment. A myriad of glacial settings occurs along the Pacific Sector of the Antarctic continental margin, which extends from the Antarctic Peninsula to the Ross Sea. These range from vast ice shelves, the largest being the Ross Ice Shelf, to mountainous coasts where valley glaciers flow into the sea. The Ross Sea continental shelf is the most thoroughly studied portion of the margin.

At present, outlet glaciers play the greatest role in delivering sediment to the continental shelf. Many sediment-laden icebergs have been observed in the region, but most are relatively small. Large ice shelves deposit the bulk of their debris near their grounding lines. Large tabular icebergs calved from the ice shelves are therefore mostly barren of sediment. The concentration of ice-rafted debris in surface sediments decreases sharply seaward of the continental shelf, which implies that most debris-laden icebergs melt before reaching the South Pacific Ocean. Even on the continental shelf, ice-rafted debris comprises a relatively small proportion of surface sediments. Sediments of the inner shelf consist mainly of terrigenous silt, with variable concentrations of siliceous biogenic material (mostly diatom frustules). The only areas where marine currents are winnowing fine-grained sediments to produce coarse-grained deposits is on shallow banks and at the shelf edge and upper slope. Sediment gravity flow processes are active sedimentary agents on the continental slope and on those portions of the continental shelf where glacial erosion has resulted in steep gradients. Piston cores have penetrated through these surface sediments into relict deposits that are mainly of glacial origin. These include glacial marine sediments as well as till.

An extensive belt of fine-grained terrigenous sediment surrounds the Antarctic continent. The northern limits of this belt corresponds approximately with a divergence in the direction of bottom current flow directions. Turbidity currents also play an active role in the dispersal of terrigenous sediments on the abyssal floor. An extensive siliceous ooze belt is situated north of the terrigenous sediment belt and coresponds approximately to the Antarctic Convergence. North of this belt, calcareous sediments blanket those portions of the abyssal floor that are shallower than 4,500 m, which is taken as the level of the Carbonate Compensation Depth. Below this, pelagic clays are accumulating. This overall sediment distribution pattern is disrupted by strong bottom currents, which winnow fine-grained sediments as they settle to the seafloor and actually scour the seafloor in some areas. Bottom photographs show lag deposits and current ripples within scour zones. These scour zones are also marked by extensive zones of manganese deposits.

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