GLACIAL-INTERGLACIAL DEPOSITION ON A SEDIMENT DRIFT ON THE PACIFIC MARGIN OF THE ANTARCTIC PENINSULA

On the continental rise west of the Antarctic Peninsula there are nine large mounds interpreted as sediment drifts, separated by turbidity c urrent channels. Drift 7 is 150 km long, 70 km wide and up to 700 m hi gh and is asymmetric, with steep sides on the south-east (towards the continent) and south-west, and gentle slopes to north-west and north-e ast. Cores on the gentle sides of the drift show a cyclicity between b rown, bioturbated, diatom-bearing mud with foraminifera and radiolaria ns, and grey, laminated, barren mud. Biostratigraphic evidence is cons istent with a Late Quaternary age. Detailed lithostratigraphy and magn etic susceptibility data allow precise correlation over distances of t ens of kilometres. On the basis of chemostratigraphy, the brown sedime nt is interpreted as interglacial (isotope stages 1 and 5) and the gre y as glacial (stages 2-4 and 6). Sedimentation rates are 3.0-5.5 cm ka (-1). Cores on the steep sides of the drift recovered a condensed sect ion with thinner cycles and hiatuses. Fine grain size, very poor sorti ng and the absence of a mode in the silt size range indicate depositio n from suspension with only weak current activity. There is little evi dence for cyclic changes in bottom current strength. Supply of sedimen t to the benthic nepheloid layer was by entrainment of mud from turbid ity currents, and by settling of pelagic material (biogenic grains, IR D, sediment suspended in meltwater plumes). Cyclic changes in sediment supply include more biogenic supply in interglacials with less sea ic e cover, more terrigenous supply from turbidites in glacials with ice sheets grounded to the shelf edge, and changes in IRD content.