Glacial–interglacial deposition on a sediment drift on the Pacific margin of the Antarctic Peninsula

摘要

On the continental rise west of the Antarctic Peninsula there are nine large mounds interpreted as sediment drifts, separated by turbidity current channels. Drift 7 is 150 km long, 70 km wide and up to 700 m high and is asymmetric, with steep sides on the south-east (towards the continent) and south-west, and gentle slopes to north-west and north-east. Cores on the gentle sides of the drift show a cyclicity between brown, bioturbated, diatom-bearing mud with foraminifera and radiolarians, and grey, laminated, barren mud. Biostratigraphic evidence is consistent with a Late Quatermary age. Detailed lithostratigraphy and magnetic susceptibility data allow precise correlation over distances of tens of kilometres. On the basis of chemostratigraphy, the brown sediment is interpreted as interglacial (isotope stages 1 and 5) and the grey 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 section with thinner cycles and hiatuses. Fine grain size, very poor sorting and the absence of a mode in the silt size range indicate deposition from suspension with only weak current activity. There is little evidence for cyclic changes in bottom current strength. Supply of sediment to the benthic nepheloid layer was by entrainment of mud from turbidity currents, and by setting of pelagic material (biogenic grains, IRD, sediment suspended in meltwater plumes). Cyclic changes in sediment supply include more biogenic supply in interglacials with less sea ice cover, more terrigenous supply from turbidites in glacials with ice sheets grounded to the shelf edge, and changes in IRD content