Climate Change Institute

Constraints on the Last Ross Sea Ice Sheet from Glacial Deposits in the Southern Transantarctic Mountains

Beardmore Glacier, Antarctica

Brenda Hall, Gordon Bromley

Dec. 4 – Dec. 31, 2010

During the last glacial maximum (LGM) the Antarctic Ice Sheet filled the Ross Embayment to a northern limit near Coulman Island.  Its LGM limit and initial retreat history have been studied extensively in the marine realm and along the Victoria Land Coast as far south as Hatherton Glacier.  Nonetheless, important questions about the thickness, dynamics and retreat history remain unresolved.  Most critically the profile of the ice that occupied the Ross Sea Embayment is uncertain, because we lack dated geological constraints on ice thickness for much of the southern Transantarctic Mountains, and the question of whether low-gradient ice streams extended across the Ross Sea during the LGM is unresolved.  In addition, although the ice-retreat history from the northern Ross Sea is established, the later stages are undated.  The paucity of data permits different models of LGM ice thickness and deglaciation, with very different implications for ice-sheet dynamics and future evolution.  These questions combine to highlight an important gap in our knowledge of Antarctic ice sheet history.  Answering them would make a significant contribution to our understanding of the magnitude and timing of postglacial sea-level change and the potential contribution of Antarctica to future sea-level rise.

For this reason we are studying the former thickness and retreat history of glaciers flowing through the Transantarctic Mountains (TAMs) into the southern Ross Sea.

We are mapping and dating lateral moraine deposits along the lower reaches of major glaciers flowing through the TAMs from Amundsen Glacier to Beardmore Glacier.  Our results will date the LGM and constrain the thickness of ice leaving the mountains and flowing into the Ross Sea.

We are dating erratics and moraines below the LGM level at the same sites to establish the timing of ice thinning.  The comparison between this record in the southern Ross Sea and behavior at the grounding line far to the north will help to establish whether the ice sheet was lightly grounded in the Ross Sea and able to transmit longitudinal stresses over long distances.

By extending our age transects down to the level of floating ice at the mouth of each glacier we will date the migration of the grounding line along the TAMs.  These dates will allow us to distinguish between models of ice retreat, which have important implications for former ice configuration and dynamics, and to constrain the contribution from Ross Sea deglaciation to global sea level through the late Holocene.