Spatial climatic variation and its control on glacier equilibrium line altitude in Taylor Valley, Antarctica

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The altitude of the equilibrium line (ELA) is an important variable describing a glacier because it helps to define the relation between the local climate and distribution of glacier mass. For the glaciers in the McMurdo Dry Valleys of Antarctica, the ELA rises rapidly with distance from the coast at a rate of about 30 m km-1, which is almost an order of magnitude greater than rates found in temperate glacier regimes. In one of the dry valleys, Taylor Valley, the ELA trend is not smooth but exhibits an abrupt shift of about 700 m yielding a local gradient of about 70 m km-1. The geographic location of the shift coincides with the Nussbaum Riegel, a ridge in the middle of the valley, which apparently exerts a strong control on the climatic pattern in Taylor Valley. To reveal the specific climatic factors responsible for the abrupt shift in ELA, we applied a theoretical analysis of ELA response to step changes in climate. Model results predicted an ELA rise of 729 m, which compares favorably to the observed 700 m change. The two most important climatic factors are differences in precipitation and wind speed. Whereas precipitation is expected to be a major factor determining ELA position for glaciers worldwide, because it determines the rate of mass accumulation, wind speed has not been previously recognized. In polar regions, where melting is typically absent, sublimation is the only significant process by which glaciers lose mass and its rate largely depends on wind speed rather than temperature. These findings highlight the sensitivity of polar glaciers to climatic differences over short distances, which have profound effects on the ELA and, in turn, glacier geometry. This study also points to the importance of understanding spatial differences in climates before piecing together a temporal climatic history based on data derived from different glaciers.

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Global and Planetary Change

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