HR: 0800h
AN: C21B-1090    [Abstracts]
TI: Last Glacial Maximum extent and timing of ice retreat in the Lambert Glacier-Amery Ice Shelf region
AU: * White, D A
EM: dwhite@els.mq.edu.au
AF: Department of Physical Geography, Macquarie University, Macqurie University, NSW 2109 Australia
AU: Gore, D B
EM: dgore@els.mq.edu.au
AF: Department of Physical Geography, Macquarie University, Macqurie University, NSW 2109 Australia
AU: Fink, D
EM: fink@ansto.gov.au
AF: Australian Nuclear Science and Technology Organisation (ANSTO), Environment Division, PMB1, Menai, NSW 2122 Australia
AU: Ferguson, R
C21B-1090 AF: Department of Physical Geography, Macquarie University, Macqurie University, NSW 2109 Australia
AB: The response of the East Antarctic Ice Sheet (EAIS) to global climatic and sea level changes that occurred during the last glacial cycle provide important clues to the dynamics of the ice sheet, and it's potential response to future global change. While it is possible to estimate many parameters of the EAIS using methods such as isostatic rebound, marine d180, numerical models and ice core gas content, none provide direct evidence of former ice volumes and geometries that are critical in assessing how the EAIS responded to forcing parameters. We present an overview of the recent program of 26Al and 10Be exposure age dating of the last local Glacial Maximum (lGM) moraines and erratics in the Lambert Glacier-Amery Ice Shelf drainage system (LG-AIS), that presently drains up to one fifth of the entire East Antarctic Ice Sheet. We contrast these results with existing data from the surrounding area to examine how the convergent ice flow and strong ice streaming of the LG-AIS affected the response of this system to global changes during this time. The lGM moraine heights in the LG-AIS indicate a relatively moderate advance of the ice sheet in this region and can account for no more than ~0.5 m of eustatic sea level rise since 20 ka BP, and are consistent with the both the most recent glacio-hydro-isostatic models that predict former ice heights based on post lGM sea level changes in the LG-AIS, and marine records that indicate that ice did not reach the continental shelf break in this region at the lGM. The small amount of ice thickening precludes this area as a significant source of sea level rise since 20 ka BP, including during MWP-1a. The low ice profiles also suggest that ice streaming occurred in the LG-AIS at the lGM. The pattern of deglaciation following the lGM in and around the LG-AIS was complex. Slow ice downwasting in the middle reaches of the system (near Loewe Massif) began at ~16-15 ka BP and had reached the modern glacial margin by ~11 ka BP. The initial drawdown in this area was coincident with the decoupling of ice from the bed under the modern Amery Ice shelf at AM02. However, ice remained grounded on the shallower banks of Prydz Bay until ~13 ka, confirming a relatively slow ice drawdown, and no large scale ice sheet collapse in this area MWP-1a. Also, while downwasting in the southern Prince Charles Mountains probably began at a similar time as the coastal reaches of the LG-AIS, most of the ice retreat occurred between 10-8 ka BP. This pattern suggests that while deglaciation of the coastal regions of the ice sheet were controlled by both sea level rise and subglacial topography, snow accumulation and ice dynamics may be more important in the inland reaches of large ice drainage systems. The cosmogenic isotope ages provide robust evidence that the LG-AIS deglaciated between 3-6 ka earlier than the surrounding coastal oases and ranges. This early deglaciation suggests that areas of strong ice streaming, with their relatively low ice profiles are more sensitive to changes in external forcing parameters such as eustatic sea level and increased temperatures than the higher, and thus more heavily grounded regions of the ice sheet.
DE: 0726 Ice sheets
DE: 0730 Ice streams
DE: 0774 Dynamics
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
DE: 9310 Antarctica (4207)
SC: Cryosphere [C]
MN: Fall Meeting 2005