Snow Dynamics in a Polar Desert, McMurdo Dry Valleys, Antarctica

The McMurdo Dry Valleys of Antarctica are a hyper-arid polar desert, receiving less than 10 cm of water equivalent each year. Snow dynamics of the McMurdo Dry Valleys are important to understanding the microbial ecology and possibly the long term hydrology of the region. Snow in the valleys collects in small nivation hollows to form discontinuous patches of snow across the landscape. We propose that seasonal snow on valley floors is ecologically important because it increases the availability of moisture to subnivian soils and insulates the subnivian soils from temperature extremes. In addition, seasonal snow cover may also be responsible for preserving permafrost in areas of greater accumulation. Our study sites in Taylor and Wright Valey include the surrounding areas of Lake Fryxell, Lake Hoare, Lake Bonney, Lake Brownworth, Lake Vanda, and the Labyrinth. Throughout the 2009-10 summer season, the outlines of 3 snow patches at each site were surveyed several times to monitor the areal ablation of snow cover. Snow pits at adjacent snow patches provided snow density profiles. In addition to small-scale observations, remotely sensed images from the WorldView-1 and Quickbird platforms provide valley-scale data at a spatial resolution of up to 60 cm and a temporal resolution of one week on average. Using data available from nearby meteorological stations, an energy balance approach is used in conjunction with field measurements to calculate the ablation rates over the course of the 2009-10 summer for each region. To test how the field measurements reflect ablation rates at the valley scale, an object-based classification technique is used to extract a time series of areal snow cover across the valleys from the remotely sensed imagery. Results show similar ablation rates across the 3 regions in Taylor Valley. However, the three regions in Wright Valley are markedly different. Snow cover near Lake Vanda ablated rapidly, while a significant amount of snow cover on the valley floor persisted in the Lake Brownworth region at the end of the summer season. Results show sublimation dominates the ablation process with relatively small amounts of melt increasing the availability of water to subnivian microbial communities.