HR: 16:30h
AN: C44A-03 INVITED    [Abstracts]
TI: Expanding Ice Sheets on the Antarctic Peninsula during the Plio/Pleistocene Recorded in Continental Rise Sediment Drifts
AU: * Cowan, E A
EM: cowanea@appstate.edu
AF: Appalachian State University, Department of Geology, ASU Box 32067, Boone, NC 28608, United States
AU: Hillenbrand, C
EM: hilc@bas.ac.uk
AF: British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 OET, United Kingdom
AB: Sediment drifts on the continental rise west of the Antarctic Peninsula are located within 125 km from the continental shelf edge, the main contributor of terrigenous sediment during both glacial and interglacial periods. The composition of drift deposits continuously recorded changes in ice sheet volume and thermal regime as well as sea surface temperatures (SSTs) and sea ice extent. The coarse-grained terrigenous sediment (pebbles and coarse sand), a proxy for iceberg-rafted debris (IRD), was analyzed in sediments spanning the last 3.1 m.y. at Ocean Drilling Program (ODP) Sites 1101 and 1096. IRD is deposited in both glacial intervals, dominated by fine-grained laminated mud and interglacial units consisting of bioturbated muds enriched in biogenic components. Contents of biogenic opal, which reflect diatom abundance, are relatively high from 3.1-2.2 Ma. Calcareous nannofossils are present within interglacial sediments from 2.2-0.76 Ma. Both findings suggest warm SSTs and limited sea ice over the drifts during interglacial periods before the Late Pleistocene. Quartz grains picked from the IRD fraction and imaged with a scanning electron microscope (SEM) show an abrupt change in surface microtextures at 1.35 Ma. During the Late Pliocene to Early Pleistocene, many quartz grains are completely weathered and only a few show signs of crushing and abrasion, indicating that glaciers were too small to inundate the Antarctic Peninsula topography. Debris shed from mountain peaks was transported supraglacially or englacially allowing weathered grains to pass unmodified through the glaciers. Glaciers expanded in size during glacial periods from 1.35-0.76 Ma. The IRD accumulation during those periods was very high and diverse dropstone lithologies document supply from sources throughout the Antarctica Peninsula. Conditions that spawned the large polar ice sheet identified at the Last Glacial Maximum have been present on the Antarctic Peninsula during glacial periods since approximately 0.76 Ma. Since then, IRD supply has been relatively low and maxima in IRD content occurred during interglacials when sedimentation rates were low. Pebble shapes indicate the dominance of basal glacial transport paths. Quartz sand grains show high relief, fracture and abrasion common under thick ice and dropstone lithologies are more restricted.
DE: 0732 Icebergs
DE: 3022 Marine sediments: processes and transport
DE: 3036 Ocean drilling
DE: 4926 Glacial
SC: Cryosphere [C]
MN: 2007 Fall Meeting