DRAMATIC TOPOGRAPHIC CHANGES IN THE MCMURDO DRY VALLEYS, ANTARCTICA (Invited Presentation)

Field observations of coastal and lowland regions in the McMurdo Dry Valleys (MDV) suggest they are on the threshold of rapid topographic change due to thermokarst erosion and subsidence. In contrast, the high elevation upland landscapes in the MDV represent some of the most stable surfaces on Earth. A number of landscapes have undergone dramatic and unprecedented landscape changes over the past decade and the commonality between all changes appears to be sediment on ice acting as a catalyst for melting. To document the magnitude and spatial pattern of these changes we compared a 2001 LiDAR elevation model to one we flew in 2014. Results showed extensive fluvial erosion and deposition. The Garwood River (Garwood Valley) had incised >3 m into massive ice permafrost, smaller streams in Taylor Valley have experienced widespread erosion of down-cutting and/or bank undercutting, and regional buried ice deposits in all coastal valleys have been ablating to form thermokarst ponds and slumps. The glaciers have been thinning in the ablation zone and becoming rougher.

We hypothesize that these ice-related changes result from warming soils due to increased solar radiation during the 1990s, a period of decreasing summer air temperatures. The time series of the summer air temperatures and elevated solar radiation have shown no significant trends since. The cause of increasing solar radiation is probably due to increasing atmospheric transmissivity in the years after the eruption of Mt. Pinatubo. The warming soils also warmed the stream waters which enhanced thermal erosion of the permafrost and deposits of buried massive ice. We hypothesize that the trigger for the deep down cutting of the Garwood and other rivers was probably the unusual melt season of 2001/02 when a flood of water eroded the channel bottom close to the massive ice permafrost. Taken together, these changes are probably triggering important responses in fluvial hydrology, geochemistry, and biological community structure and function in this region. Work is underway to investigate these responses.

The observed changes do not appear to be linked to climate warming but rather to climate variability. However, the changes do provide a harbinger of what to expect if and when climate warming envelops the McMurdo Dry Valleys.