Climate Change Institute

Sensitivity of the Antarctic Ice Sheet to the Last Two Glacial/Interglacial Cycles

Brenda Hall, Stephanie Allard, Toby Koffman, Calvin Mako, Robin Arnold, Glenn McKenney

December 2010 – February 2011

What is the role of the Antarctic Ice Sheet (AIS) in Quaternary climate change? Despite its importance to Earth’s climate system, we lack a full understanding of AIS sensitivity to global climate change. The immediate impact of this is our current poor understanding of the ice sheet’s behavior under warming climate and its contribution to future sea-level rise (IPCC 2007).  A full understanding of AIS behavior requires long-term records that extend beyond the observational period. Here, we propose to reconstruct and date precisely the history of marine-based ice in the Ross Sea sector over the last two glacial/interglacial cycles, enabling us to assess potential driving mechanisms (i.e., sea-level rise, ice dynamics, ocean-temperature variations) for ice fluctuations and thus place present ice-sheet behavior in a long-term context.

During the last glacial maximum (LGM), the AIS filled the Ross Embayment. Although much has been done both in the marine and terrestrial settings to constrain its extent, the chronology of the ice sheet, particularly the timing and duration of the maximum and the pattern of initial recession, leaves much to be desired. Virtually nothing is known of the penultimate glaciation, other than it is presumed to have been generally similar to the LGM. These shortcomings greatly limit our ability to understand AIS evolution and the driving mechanisms behind ice-sheet fluctuations.

We are developing a detailed record of ice extent and chronology in the western Ross Embayment for not only the LGM, but also for the penultimate glaciation (Stage 6), from well-dated glacial geologic data in the Royal Society Range. We will map and date precisely deposits in Miers, Marshall, and Garwood Valleys. Not only will we date the maximum positions and place limits on the timing of initial ice advance, but we also will constrain the thinning history from recessional moraines and glaciofluvial terraces below the upper drift limits. We will record the passage of the grounding line past the valley mouths and test between models of ice recession (see main proposal). Chronology will come primarily from high-precision AMS ¹⁴C and multi-collector ICP-MS ²³⁴U/²³⁰Th dating of lake algae and carbonates known to be widespread in the proposed field area.  These data will allow us to produce high-resolution chronologies for the last two glacial/interglacial cycles and place current ice-sheet behavior in context. We also will constrain the Antarctic contribution to global sea-level change (at least from the Ross Sea sector) through this time.