Oceanographic and physiographic controls on modern sedimentation within Antarctic fjords

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Abstract
Physical oceanographic data and modern surface sediments were collected from eleven fjords along the western side of the Antarctic Peninsula and South Shetland Islands. Surface sediment samples (62) were analyzed for texture and total organic carbon content. The distribution of biogenic and terrigenous facies within the fjords is controlled by bay geometry and oceanographic regime. Climate plays a secondary role but, along with ice drainage basin size, controls the rate of terrigenous supply to the glacial marine environment. Specifically, fjords along the Danco Coast and Palmer Archipelago with a high length to width ratio tend to have bottom sediments that are arenaceous where ice-rafted sediment is released preferentially at the head of the fjord. Biogenic facies are favored where the bay geometry is complex. Where such complexity exists, separate oceanographic regimes develop that lead to separation of terrigenous and biogenic sediments. Processes of interflow (mid- and deep-water turbid cold tongues) and Coriolis deflection produce terrigenous facies along the inner fjord and western edges of a fjord system. Warm outer bay waters tend to develop a stable eddy circulation pattern that favors the productivity of phytoplankton in the surface layers. Outer bays are therefore floored with organic-rich siliceous muds and ice-rafted material. Only in the South Shetland Islands is melt-water input significant enough to generate estuarine circulation within the fjord, but here strong bottom currents result in arenaceous bottom sediments with no biogenic facies. Ice-rafted diamictons are produced proximal to the edges of small tide-water glaciers in the South Shetlands. The facies relationships established in this study provide a strong reference for paleoclimatic studies that utilize downcore measurements of texture and organic carbon.

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