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Back to Young UTIG Researchers Talks
Radar Studies of Accreting Ice
From Subglacial Lake Vostok in East Antarctica
By Suzanne Oliason.
Abstract:
Lake Vostok, the largest of Antarctica’s subglacial lakes, is located in East Antarctica. Valuable information concerning the present day conditions of the lake and its climate-cycle history can be found by studying models of glacier ice thickness (Hulbe 1998). In the 2000-2001 season, UTIG recorded airborne ice penetrating radar sounding data over Lake Vostok. Radar sounding instrumentation uses electromagnetic frequencies of tens of megahertz to create images of the ice layers, bedrock and lake surface. From these images, ice thickness is obtained by "picking" the ice sheet’s surface and bed. The current criterion for determining what is picked as the bed is to pick the earliest echo. This method, however, is not applicable to the data collected from Vostok, because the earliest echo might not be the actual bed. New criteria explaining the existence of this "shadow bed" must be created in order to determine the correct ice thickness. In the Lake Vostok transect, there appears to be a shadow that corresponds to the lake and one that corresponds to the bedrock. It is possible that the origin of the shadow over the bedrock, or "mountains," differs from that of the shadow over the lake. In regards to this dilemma, I formulated hypotheses that apply to each facet of the problem. Hypotheses regarding the shadow over the lake are that it is the interface between glacier ice and ice frozen on from the lake or that it results from rock inclusions frozen to the base of the glacier ice as it moves over the shoreline of the lake. The mountain shadow could be attributed to the lake ice/glacier ice interface moving up over the bedrock, the radar reflecting off bedrock to the side of the plane and superimposing this image above the actual bedrock image, or the stress of the glacier ice on the bed realigning ice crystals or "plucking" rock inclusions from adjacent mountaintops. Through testing these hypotheses and determining the outcome of the data, new criteria was formulated and followed for accurate picking of the bedrock.
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