Abstract
Abstract. Previous studies of Totten Ice Shelf have employed surface velocity measurements to estimate its mass balance and understand its sensitivities to interannual changes in climate forcing. However, displacement measurements acquired over timescales of days to weeks may not accurately characterize long-term flow rates wherein ice velocity fluctuates with the seasons. Quantifying annual mass budgets or analyzing interannual changes in ice velocity requires knowing when and where observations of glacier velocity could be aliased by subannual variability. Here, we analyze 16 years of velocity data for Totten Ice Shelf, which we generate at subannual resolution by applying feature-tracking algorithms to several hundred satellite image pairs. We identify a seasonal cycle characterized by a spring to autumn speedup of more than 100 m yr−1 close to the ice front. The amplitude of the seasonal cycle diminishes with distance from the open ocean, suggesting the presence of a resistive back stress at the ice front that is strongest in winter. Springtime acceleration precedes summer surface melt and is not attributable to thinning from basal melt. We attribute the onset of ice shelf acceleration each spring to the loss of buttressing from the breakup of seasonal landfast sea ice.
Highlights
Totten Glacier in East Antarctica drains the Aurora Subglacial Basin, which is grounded well below sea level (Young et al, 2011; Roberts et al, 2011) and contains enough ice to raise the global sea level by at least 3.5 m (Greenbaum et al, 2015)
The current best estimates of Totten Glacier and Totten Glacier and its ice shelf (TIS) mass budgets have been calculated using a mosaic of surface velocity measurements collected at different times throughout the year (Rignot et al, 2013); these estimates have been built on an unconfirmed assumption that ice velocity does not vary on subannual timescales
Where glacier flow varies throughout the year, it is possible that velocity measurements collected over short time intervals may lead to inaccurate estimates of annual mass balance or incorrect interpretation of interannual changes in velocity
Summary
Totten Glacier in East Antarctica drains the Aurora Subglacial Basin, which is grounded well below sea level (Young et al, 2011; Roberts et al, 2011) and contains enough ice to raise the global sea level by at least 3.5 m (Greenbaum et al, 2015). The current best estimates of Totten Glacier and TIS mass budgets have been calculated using a mosaic of surface velocity measurements collected at different times throughout the year (Rignot et al, 2013); these estimates have been built on an unconfirmed assumption that ice velocity does not vary on subannual timescales. The buttressing strength of ice mélange at Store Glacier in Greenland has been estimated at 30–60 kPa, which is an order of magnitude below the driving stress of the glacier but is sufficient to cause observable subannual changes in glacier velocity up to 16 km from the ice front (Walter et al, 2012; Todd and Christoffersen, 2014). In this paper we find seasonal variability in two independent ice velocity data sets and we consider the potential roles of surface meltwater, ice shelf basal melt, and sea ice buttressing in influencing the flow of TIS at subannual timescales
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