Principal Investigators - Brenda Hall,
John Stone and Howard Conway (University of Washington)
Graduate Students - Gordon Bromley, Claire Todd (University of Washington)
The stability of the marine West Antarctic Ice Sheet (WAIS) remains a significant unresolved problem in predicting future sea level change (IPCC, 2001). Some recent observations of the ice sheet support a negative mass balance (Shabtaie and Bentley, 1987; Jacobs et al., 1992, 1996, Shepherd et al., 2001), whereas others argue the opposite (Joughin and Tulaczyk, 2002). Differences between these short-term results may stem, in part, from temporal fluctuations in flow. In comparison, geologic observations provide evidence of behavior over a much longer time scale than glaciological monitoring and remote sensing, and therefore can help to constrain the evolutionary trajectory of the WAIS. Our recent work involving glacial geologic mapping, dating and ice-penetrating radar surveys suggests that deglaciation of both the Ross Sea Embayment and coastal Marie Byrd Land continued into the late Holocene, and leaves open the possibility of ongoing deglaciation and grounding-line retreat. However, our previous study in the Ross Sea Embayment was based on only three locations the southern Scott Coast, Hatherton Glacier, and Roosevelt Island all of which lie far to the north of the present grounding line (Conway et al., 1999). To investigate whether recession has ended, or if the rate and pattern of deglaciation inferred from the previous study applies to the present grounding line, we need to extend this work to the southern Ross Sea Embayment.
We will reconstruct the level of Reedy Glacier, in the far southern Transantarctic Mountains, from the LGM through to the present day. Because the grounding line has not yet passed Reedy Glacier, it, unlike other outlet glaciers crossing the Transantarctic Mountains, will have recorded recent changes in the thickness of ice in the Ross Sea. The deglaciation chronology of Reedy Glacier therefore can indicate whether Holocene retreat of the WAIS grounding-line ended thousands of years ago, or is continuing at the present day. We will carry out an integrated glaciologic, glacial-geologic, and exposure-dating project to map and date past levels of Reedy Glacier. Over two field seasons, we will map moraines and erratic distributions at sites along the length of the glacier. We will date the moraines directly with cosmogenic isotopes, and, if possible, couple these results with radiocarbon dates on organic material from ice-marginal melt ponds. This will allow us to correlate moraines along the glacier and to establish its gradient through time. We will obtain radar profiles across the glacier at several locations and measure present-day flow speeds with GPS, as the basis for developing a flow-line model to relate our observations to the grounding-line position downstream. Ultimately, the mapping, dating and ice-modeling components of the study will be integrated into a reconstruction that defines changes in ice thickness in the southernmost Ross Sea since the LGM, and relates these changes to the history of grounding-line retreat.
Our work directly addresses key goals of the West Antarctic Ice Sheet Initiative, which are to understand the dynamics, recent history and possible future behavior of the West Antarctic Ice Sheet.