Modeling Glacial Lake Washburn - Insight into the LGM

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Non-technical Project DescriptionGeologic field evidence of ancient lake level fluctuations in coastal Taylor Valley in the McMurdo Dry Valleys of Antarctica has been related to advances (higher lake levels) and retreats (lower lake levels) of the Ross Ice Sheet into the valley mouth during and since the last Glacial Maximum (24,000 to 13,000 years ago). The ancient lake record provides some of the most complete terrestrial geologic evidence of inferred Antarctic ice-sheet changes at the height of the most recent bipolar glaciation. Different interpretations of geologic deposits have led to two alternate hypotheses about how far inland the Ross Ice Sheet advanced to produce high lake levels during the Last Glacial Maximum. One hypothesis suggests that limited ice advances into the valley were associated with larger lakes, whereas the alternative suggests that more extensive ice advances were associated with much smaller lakes (by five times). The local extent of ice advances has implications for the overall size of the Ross Ice Sheet and its impact on sea level. This project will resolve the different interpretations by modeling the environmental conditions under which different sized lakes would form, with the hypothesis that one of the lake sizes would be more likely to occur. In addition, the team will discover the environmental conditions that allow large lakes to form and be maintained when average air temperatures were much colder than today, an observation not supported by modern observations. Technical Project DescriptionA geomorphic record of lake level change in the McMurdo Dry Valleys will be used to infer environmental conditions during the Last Glacial Maximum (LGM) providing a climatic record over an 11,000-year period from 24,000 to about 13,000 years before present. Notable events during this period include the termination of the LGM global sea level low-stand, subsequent rapidly rising sea levels, and two episodes of abrupt sea level rise including meltwater pulse 1A. Specifically, the project will model lake level changes of Glacial Lake Washburn in Taylor Valley, the best documented paleo-lake in the region. Its level changed radically (100s m) over millennial time scales providing a strong signal of environmental change. Established energy balance models developed for the current climate and glaciological setting in Taylor Valley will be adapted to LGM conditions to model paleo-lake levels using estimated paleo-environmental conditions that include an atmosphere known to be cooler by -4 to -8 degrees Celsius. To define the range (uncertainty) of plausible environmental conditions that result in the same lake level a Monte Carlo-style approach is adopted. The results will provide a new perspective on past Antarctic climate and contribute to the debate on Antarctic sources to sea level rise. The project will provide training for a Ph.D. student.