POSSIBLE TRIGGERS FOR HOLOCENE MELTWATER PRODUCTION AT HIGH ELEVATION ALLUVIAL FANS IN THE DRY VALLEYS, EAST ANTARCTICA

Surface processes can provide clues into past regional temperature and precipitation conditions. Here we investigate the conditions and possible triggers needed to activate meltwater production at high-elevation alluvial fans in the McMurdo Dry Valleys of Antarctica. Alluvial fan deposition in Antarctica requires sufficient energy (i.e. heat) at the Earth’s surface to cause melting of ice and snow, which then enables sediment transport. Today the studied fans are inactive but optically stimulated luminescence (OSL) dating results show at least two episodes of deposition during the Holocene. This evidence for meltwater production at high elevation appears at odds with nearby geomorphic evidence (including but not limited to: long-term preservation of buried ice, noncryoturbated soils, and sustained slope stability), which suggests extremely cold and desert conditions throughout the Holocene in the same McMurdo Dry Valleys micro-climatic zone. We assessed climate conditions necessary for sufficient snow bank melting by analyzing surface temperatures (using adiabatically adjusted empirical meteorological data) at active alluvial fans in the McMurdo Dry Valleys. We identified short, high insolation events during the summer as a possible trigger for high-elevation alluvial fan deposition. Whereas Huybers and Denton demonstrated that increased summer warmth in Antarctica is largely controlled by long duration summers (i.e. an increase in cumulative positive degree days) which is a function of orbital variability, our results suggest that short intense summers may be the ideal climate responsible for high-elevation alluvial fan activity. The McMurdo Dry Valleys received peak daily insolation ~2 kya; within error of the most recent fan deposit with a date of 1-3 kya. Further testing is required to determine if additional forcing factors such as warmer oceans and/or decreased sea ice play a role in increased temperatures as has been suggested by regional climate model output.