Dynamic ice-sheet models are necessary to predict the response of the WAIS to future climate change and our confidence in the predictive capabilities of these models increases when they successfully simulate the past history of the WAIS. However, observational data that can serve as benchmarks for ice-sheet models, such as past ice elevations, are still quite poorly constrained in many key sectors of the WAIS. Our research involves field mapping of glacial deposits combined with cosmogenic surface exposure dating (³He, ²¹Ne, and ¹⁰Be). We have targeted past ice elevation variations from the interior of the WAIS. Our field site is located at the Ohio Range The location lies close to the head of the Mercer ice stream near the ice divide.

Our field mapping and cosmogenic dating of glacial erratics indicates maximum ice elevations of ~125 m above the modern ice-sheet surface occurred at ~11.5 ka The deglacial chronology prohibits interior WAIS as a contribution to meltwater pulse 1A. Our observational data of ice elevation variations compare well with predictions of a thermomechanical ice-sheet model that incorporates very low basal shear stress downstream of the present day grounding line. We conclude that ice streams in the Ross Sea Embayment had thin, low-slope profiles during the last glacial period and WAIS ice elevations during this period were several hundred meters lower than previous reconstructions. This conclusion implies that the WAIS ice volume was smaller than has been proposed, which has important implications for interpretation of bedrock uplift rates in the Ross Embayment that typically assume thicker ice loads during the LGM, and for the contribution of the WAIS to Holocene sea-level rise.

Click here for the publication

We are currently working on reconstructing a long-term history of the ice sheet using ²¹Ne and ¹⁰Be measurements on bedrock surfaces. Our results show that surfaces that are 60m above present day ice levels have been mostly exposed (>90% of the time) over the past 5 Myrs. We also find

1) ice elevations during the last glaciation were the highest over the past 5 Myrs. Our results are consistent with the idea that decreasing temperatures decreases basal slip and thereby increases ice elevation/volume.

2) ice elevations never exceeded 150m above present day levels over the past 10 Myrs.

3) erosion rates in the interior of the Antarctic continent over the last 10 Myrs are only ~20-30 cm/Ma, comparable to erosion rates in the Dry Valleys. It appears that the entire Antarctic continent has been mostly in a deep freeze since the late Miocene.

For some neat pictures of the Ohio Range click here