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Tidewater glaciers: Melting underwater far faster than previously estimated?

July 25, 2019

A tidewater glacier in Alaska is melting underwater at rates upwards of two orders of magnitude greater than what is currently estimated, sonar surveys reveal. The study's results, based on direct measurements, suggest that some glaciers may be in "hotter water" than previously thought. Like vast frozen rivers, tidewater glaciers flow from the land and into the sea, forming a partially submerged ice-ocean boundary. However, unlike terrestrial glaciers, which are often sequestered to high-altitudes, tidewater glaciers can be far more dynamic and subject to ongoing changes driven by underwater melting and iceberg calving where the ocean meets the ice. While it is widely recognized that ice loss from these glaciers influences both the rate of sea level rise and potentially global ocean circulation - a primary driver of global climate - the understanding of the dynamics of tidewater glacier melt, particularly as a response to accelerated warming in high-latitude glacier environments, is largely predicated upon sparse data, indirect inferences and an unconstrained theoretical model of subsurface melting. To date, suggest the authors of this study, no direct measurements of submarine melting at tidewater glacier fronts have been made. To address this lack of direct observations, David Sutherland and colleagues conducted repeat multibeam sonar surveys of the submerged face of the LeConte Glacier in Southeast Alaska. Along with other ocean, ice and atmospheric measurements collected in August 2016 and May 2017, the sonar images were used to document and create a time-variable, three-dimensional record of changes in the glacier face that could be linked to melting and calving patterns. Sutherland et al. discovered seasonally increasing submarine melt across the glacier face and at rates far greater than theory-based predictions. Their results, they say, suggest a pressing need to reevaluate existing models of tidewater glacier ice loss.
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American Association for the Advancement of Science

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