Recent sediment remolding on a deep shelf, Ross Sea: implications for radiocarbon dating of Antarctic marine sediments

Coarse, bioclastic rich sands have been widely reported from the banks of t he Antarctic continental shelf but their origin is still poorly known. We r eport on a suite of coarse sediments recovered from the top of the Mawson B ank in the northwestern Ross Sea. Radiocarbon ages of biogenic calcite, for modern and apparently late Pleistocene deposits, range from 1085 +/- 45 to 20,895 +/- 250 yr B.P.. Discovery of soft tissue (Ascidian) preserved as a n incrustation on a pebble at 2 m depth indicates aggregation of the sedime nt within several months or a year of core recovery. Radiocarbon ages of ac id insoluble organic matter (aiom) are less than those of the foraminifera calcite. The aiom ages are also reversed in sequence, indicating reworking of the sediment during deposition. These observations and a review of recen tly published literature suggest that much of the bank top sediment in Anta rctica is presently undergoing remobilization, under the influence of stron g currents and/or icebergs even under interglacical (high-stand) sea levels . These observations point out the need for careful, integrated studies on high latitude marine sediment cores before resultant "ages" alone are used as the foundation for paleoglacial reconstructions. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.