HR: 15:10h
AN: C13A-07    [Abstracts]
TI: Subglacial Processes and Flow Dynamics of Former Antarctic Ice Streams Reconstructed From Marine Geology and Geophysics
AU: * O'Cofaigh, C
EM: colm.o'cofaigh@durham.ac.uk
AF: Department of Geography, Durham University, Science Site, South Road, Durham, DH13LE United Kingdom
AU: Evans, J
EM: je10007@cam.ac.uk
AF: Scott Polar Research Institute, University of Cambridge, Lensfield Road, Cambridge, CB21ER United Kingdom
AU: Dowdeswell, J A
EM: jd16@cam.ac.uk
AF: Scott Polar Research Institute, University of Cambridge, Lensfield Road, Cambridge, CB21ER United Kingdom
AU: Larter, R D
EM: rdla@bas.ac.uk
AF: British Antarctic Survey, High Cross, Madingley Road , Cambridge, CB30ET United Kingdom
AU: Hillenbrand, C
EM: hilc@bas.ac.uk
AF: British Antarctic Survey, High Cross, Madingley Road , Cambridge, CB30ET United Kingdom
AB: Recent marine geophysical and geological research from the Antarctic continental margin has resulted in significant advances to our understanding of the extent, timing and dynamic behaviour of the West Antarctic Ice Sheet (WAIS) and the Antarctic Peninsula Ice Sheet (APIS) during the Late Quaternary, as well as the processes and conditions at the former ice-sheet bed. This research indicates an extensive WAIS and APIS at the last glacial maximum (LGM). The ice sheet was positioned at, or close to, the shelf edge around the Peninsula, the Bellingshausen Sea and Pine Island Bay. In all these areas large glacial troughs extend across the continental shelf, and sedimentary and geomorphic evidence from these troughs indicates that they were occupied by grounded paleo-ice streams during, or immediately following, the LGM. This evidence includes elongate subglacial bedforms (mega-scale glacial lineations) that can extend for up to 20 km and which are formed in weak deformation till. Deformation tills have been identified and mapped in all the paleo-ice stream troughs investigated to date. Macro-sedimentological, micromorphological and geotechnical data indicate that pervasive till deformation beneath these ice streams took place over vertical thicknesses of several metres, and that this was associated with significant advection of sediment towards the former grounding line. Subglacial geology appears to have exerted a major control on ice stream development. The transition from crystalline bedrock to a sedimentary substrate within these troughs characteristically marks the onset of streaming flow. However, in Marguerite Trough streaming flow appears to have commenced over the crystalline bedrock by enhanced basal sliding, with the highest flow velocities occurring over the sedimentary substrate further downflow by subglacial deformation. This indicates spatial variation in the mechanism of rapid flow beneath individual ice streams. Subglacial meltwater channels eroded into crystalline bedrock in the inner parts of Pine Island Bay and Marguerite Trough demonstrate evacuation of meltwater beneath these ice streams. Such features are likely the product of erosion over several glacial cycles and thus only provide maximum estimates of meltwater discharge. A variety of geomorphic features imaged on geophysical records and supplemented by investigations of core sedimentology, indicate that the rate of ice stream retreat was variable between the different bathymetric troughs. For example, slow ice stream recession in the Larsen-A and western Ross Sea regions contrasts markedly with the Marguerite Trough ice stream which underwent rapid retreat across much of its bed. This implies marked variations in paleo-ice stream dynamics during regional deglaciation. Antarctic paleo-ice streams do not appear to have responded uniformly to external forcing such as climate warming or relative sea level rise during deglaciation. This suggests that "local" factors (e.g., bathymetry, ice stream drainage basin size and ice flux) may have been the dominant controls on Antarctic ice-stream behaviour during Late Quaternary deglaciation.
DE: 1827 Glaciology (0736, 0776, 1863)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4207 Arctic and Antarctic oceanography (9310, 9315)
DE: 4556 Sea level: variations and mean (1222, 1225, 1641)
DE: 9310 Antarctica (4207)
SC: Cryosphere [C]
MN: Fall Meeting 2005