HOLOCENE SUMMER MELT POTENTIAL IN THE ANTARCTIC DRY VALLEYS: EVIDENCE FROM HIGH ELEVATION ALLUVIAL FAN ACTIVITY

Landforms inland and at high elevations within the Antarctic McMurdo Dry Valleys (MDV) are considered some of the most stable geomorphic features on the planet, some of which appear largely intact since the Pliocene. We investigated a series of high elevation alluvial fans, in the MDV, seeking evidence for more recent activity. Distinct sedimentary units within the alluvial fans, representing episodes of high meltwater production, have been dated via optically stimulated luminescence (OSL). The ages of significant meltwater production in the upper stratigraphy range from 1 - 14 ky before present; however, there exists a cluster of significant meltwater events between 1-3 ky and a second cluster between 8-11 ky. Here we use an insolation model to illustrate that high-elevation fan activity in the MDV is a function of increased summer insolation; however, the orbital forcing mechanism responsible for high melt potential at 1-3 kya differs from the forcing at 8-11 kya. The melting events between 8-11 kya are likely a result of long duration summers. This is consistent with the findings of Huybers and Denton who demonstrated that increased summer warmth in Antarctica, and perhaps the sensitivity of terrestrial ice sheets, is largely controlled by long duration summers (i.e. an increase in cumulative positive degree days). However, we identified shorter, but higher-intensity summers, i.e. a function of precession, as a possible trigger for high-elevation alluvial fan deposition between 1-3 kya. Our results suggest that short intense summers may be equally, if not more important, for creating the ideal climate for high-elevation snow melt potential and thus alluvial fan activity in the MDV. Regional climate models are being run to determine if insolation alone may be responsible for melting events or if additional forcing factors such as warmer oceans and/or decreased regional sea ice play a role in increased temperatures and melt in the MDV. This finding may provide clues for the precise environment required for Quaternary melting conditions for alpine glaciers in the MDV and perhaps the nearby East Antarctic Ice Sheet.