Abstract
AbstractWe present a novel method to estimate dynamic ice loss of Greenland's three largest outlet glaciers: Jakobshavn Isbræ, Kangerlussuaq Glacier, and Helheim Glacier. We use Global Navigation Satellite System (GNSS) stations attached to bedrock to measure elastic displacements of the solid Earth caused by dynamic thinning near the glacier terminus. When we compare our results with discharge, we find a time lag between glacier speedup/slowdown and onset of dynamic thinning/thickening. Our results show that dynamic thinning/thickening on Jakobshavn Isbræ occurs 0.87 ± 0.07 years before speedup/slowdown. This implies that using GNSS time series we are able to predict speedup/slowdown of Jakobshavn Isbræ by up to 10.4 months. For Kangerlussuaq Glacier the lag between thinning/thickening and speedup/slowdown is 0.37 ± 0.17 years (4.4 months). Our methodology and results could be important for studies that attempt to model and understand mechanisms controlling short‐term dynamic fluctuations of outlet glaciers in Greenland.
Highlights
The mass loss of the Greenland Ice Sheet (GrIS) has been accelerating during the last quarter of a century (Bamber et al, 2018; Mouginot et al, 2019; Shepherd et al, 2020) with rapid and record-high icesheet-wide losses in 2012 and 2019 (Nghiem et al, 2012; Sasgen et al, 2020)
It should be noted that fluctuations in detrended dynamic ice loss are small for Kangerlussuaq Glacier (KG), whereas JI fluctuations vary between −20 Gt and +10 Gt, and Helheim Glacier (HG) between −5 and +10 Gt
Changes in dynamic ice loss at major outlet glaciers produce large elastic signals at nearby Global Navigation Satellite System (GNSS) stations, but these signals decay in space much more rapidly than do the signals produced by major shifts in surface mass balance (SMB)
Summary
The mass loss of the Greenland Ice Sheet (GrIS) has been accelerating during the last quarter of a century (Bamber et al, 2018; Mouginot et al, 2019; Shepherd et al, 2020) with rapid and record-high icesheet-wide losses in 2012 and 2019 (Nghiem et al, 2012; Sasgen et al, 2020). GNSS stations are uplifting due to a combination of Glacial Isostatic Adjustment (GIA, caused by past ice-ocean mass exchange) and Earth's near instantaneous elastic response to present-day ice mass changes (Bevis et al, 2012). The Earth's elastic response is due to a combination of dynamic thinning of glaciers and surface mass balance (SMB) processes. These two contributors to surface elevation changes have different spatial patterns. The major advantage of using GNSS data is the very high temporal resolution (daily) of elastic uplift estimates, caused by daily mass loss variability of the nearby glacier. We develop a relation between GNSS uplift and accumulated ice discharge for each glacier to examine recent ice variability
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