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Globally, glaciers are shrinking in response to climate change, with implications for global sea level rise as well as downstream ecosystems and water resources. Sliding at the ice-bed interface (basal motion) provides a mechanism for glaciers to respond rapidly to climate change. While the short-term dynamics of glacier basal motion (< 10 years) have received substantial attention, little is known about how basal motion and its sensitivity to subglacial hydrology changes over long (> 50 year) timescales – this knowledge is required for accurate prediction of future glacier change. We compare historical data with modern estimates from field-collected and remotely-sensed data at Athabasca Glacier and show that, between 1961 and 2019, the glacier thinned by 51 meter ( - 18 %). However, a concurrent increase in surface slope results in minimal change in the average driving stress (-10 kilopascal, - 7%). These geometric changes coincide with a uniform surface slow down of surface velocity (-15 meter a-1, -45%). Historical observations and simplified ice modeling suggest that declining basal motion accounts for most of this slow down (63 % at a minimum). A decline in basal motion can be explained by increasing basal friction resulting from geometric change in addition to increasing meltwater flux through an efficient subglacial hydrologic system. There is some evidence that changes in basal motion in the overdeepened reach are responsible for slowing basal motion several km up-glacier. These results highlight the need to include time-varying dynamics of basal motion in glacier models and analyses. These findings suggest declining basal motion may reduce the flux of ice to lower elevations, helping to mitigate glacier mass loss in a warming climate.
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Reduced basal motion responsible for 50 years of declining ice velocities on Athabasca Glacier
Abstract The time-evolution of glacier basal motion remains poorly constrained, despite its importance in understanding the response of glaciers to climate warming. Athabasca Glacier provides an ideal site for observing changes in basal motion over long timescales. Studies from the 1960s provide an in situ baseline dataset constraining ice deformation and basal motion. We use two complementary numerical flow models to investigate changes along a well-studied transverse profile and throughout a larger study area. A cross-sectional flow model allows us to calculate transverse englacial velocity fields to simulate modern and historical conditions. We subsequently use a 3-D numerical ice flow model, Icepack, to estimate changes in basal friction by inverting known surface velocities. Our results reproduce observed velocities well using standard values for flow parameters. They show that basal motion declined significantly (30–40%) and this constitutes the majority (50–80%) of the observed decrease in surface velocities. At the same time, basal resistive stress has remained nearly constant and now balances a much larger fraction of the driving stress. The decline in basal motion over multiple decades of climate warming could serve as a stabilizing feedback mechanism, slowing ice transport to lower elevations, and therefore moderating future mass loss rates.
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- PAR ID:
- 10560834
- Publisher / Repository:
- Cambridge University Press
- Date Published:
- Journal Name:
- Journal of Glaciology
- ISSN:
- 0022-1430
- Page Range / eLocation ID:
- 1 to 13
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Globally, glaciers are shrinking in response to climate change, with implications for global sea level rise as well as downstream ecosystems and water resources. Sliding at the ice‐bed interface (basal motion) provides a mechanism for glaciers to respond rapidly to climate change. While the short‐term dynamics of glacier basal motion (<10 years) have received substantial attention, little is known about how basal motion and its sensitivity to subglacial hydrology changes over long (>50 year) timescales—this knowledge is required for accurate prediction of future glacier change. We compare historical data with modern estimates from field and satellite data at Athabasca Glacier and show that the glacier thinned by 60 m (−21%) over 1961–2020. However, a concurrent increase in surface slope results in minimal change in the average driving stress (−6 kPa and −4%). These geometric changes coincide with relatively uniform slowing (−15 m a−1and −45%). Simplified ice modeling suggests that declining basal motion accounts for most of this slow down (91% on average and 46% at minimum). A decline in basal motion can be explained by increasing basal friction resulting from geometric change in addition to increasing meltwater flux through a more efficient subglacial hydrologic system. These results highlight the need to include time‐varying dynamics of basal motion in glacier models and analyses. If these findings are generalizable, they suggest that declining basal motion reduces the flux of ice to lower elevations, helping to mitigate glacier mass loss in a warming climate.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1017/jog.2024.51
