Abstract
Abstract. Ice discharge from large ice sheets plays a direct role in determining rates of sea-level rise. We map present-day Antarctic-wide surface velocities using Landsat 7 and 8 imagery spanning 2013–2015 and compare to earlier estimates derived from synthetic aperture radar, revealing heterogeneous changes in ice flow since ∼ 2008. The new mapping provides complete coastal and inland coverage of ice velocity north of 82.4° S with a mean error of < 10 m yr−1, resulting from multiple overlapping image pairs acquired during the daylight period. Using an optimized flux gate, ice discharge from Antarctica is 1929 ± 40 Gigatons per year (Gt yr−1) in 2015, an increase of 36 ± 15 Gt yr−1 from the time of the radar mapping. Flow accelerations across the grounding lines of West Antarctica's Amundsen Sea Embayment, Getz Ice Shelf and Marguerite Bay on the western Antarctic Peninsula, account for 88 % of this increase. In contrast, glaciers draining the East Antarctic Ice Sheet have been remarkably constant over the period of observation. Including modeled rates of snow accumulation and basal melt, the Antarctic ice sheet lost ice at an average rate of 183 ± 94 Gt yr−1 between 2008 and 2015. The modest increase in ice discharge over the past 7 years is contrasted by high rates of ice sheet mass loss and distinct spatial patters of elevation lowering. The West Antarctic Ice Sheet is experiencing high rates of mass loss and displays distinct patterns of elevation lowering that point to a dynamic imbalance. We find modest increase in ice discharge over the past 7 years, which suggests that the recent pattern of mass loss in Antarctica is part of a longer-term phase of enhanced glacier flow initiated in the decades leading up to the first continent-wide radar mapping of ice flow.
Highlights
The Antarctic ice sheet receives roughly 2000 Gt (∼ 5.5 mm sea-level equivalent) of precipitation each year with > 90 % of this mass leaving as solid ice discharge to the ocean and the remaining < 10 % leaving in the form of sublimation, wind-driven snow transport, meltwater runoff and basal melt
All three studies show near balance to slightly positive mass changes for the East Antarctic Ice Sheet and large losses for the West Antarctic Ice Sheet and the Antarctic Peninsula, all of which agree well with the results presented here when considering uncertainties and differences in study periods
Glaciers and ice streams feeding major ice shelves were remarkably steady with small heterogeneous changes in velocity
Summary
The Antarctic ice sheet receives roughly 2000 Gt (∼ 5.5 mm sea-level equivalent) of precipitation each year with > 90 % of this mass leaving as solid ice discharge to the ocean and the remaining < 10 % leaving in the form of sublimation, wind-driven snow transport, meltwater runoff and basal melt. Recent studies indicate significant mass loss from the Antarctic ice sheet that is likely accelerating (Harig and Simons, 2015; Helm et al, 2014; Martín-Español et al, 2016; McMillan et al, 2014; Rignot et al, 2011b; Shepherd et al, 2012; Velicogna, 2009). Understanding how this imbalance evolves is critical to providing meaningful projections of sea-level change. This requires circum-Antarctic measurements of surface velocity on fine spatial scale and with sufficient accuracy (∼ 10 m yr−1) to observe regionally coherent changes in flow.
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