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Using Inclinometry Measurements to Understand the Conditions Controlling Ice Flow, Western Greenland Ice Sheet

Séminaire de N. Maier ( University of Wyoming, USA), Mardi 9 Octobre 2018 a 11h en salle Lliboutry, Bâtiment de Glaciologie

27 septembre 2018, par Fabien Gillet-Chaulet

Using Inclinometry Measurements to Understand the Conditions Controlling Ice Flow, Western Greenland Ice Sheet

Séminaire de Nathan Maier (University of Wyoming, USA)

Sliding and deformation of the Greenland Ice Sheet (GrIS) exert a first-order control on ice sheet mass balance by dictating mass transport to marine outlets and low elevations prone to high melt rates. Yet, direct measurements of deformation and sliding on the GrIS are rare, leaving the partitioning of ice motion unconstrained across the majority of the ice sheet. Here, we analyze data from a unique three-dimensional array of inclinometers installed in eight boreholes at a field site underlain by a hard bed on a land terminating region of the Western GrIS. We find ice motion during the winter is completely dominated by sliding, which comprises 96% of the surface velocity at the field location. The sliding is found to occur over a basal patchwork of alternating sticky and slippery patches tens of meters in scale that facilitates the high basal motion. The high sliding fraction is unexpected given a bedrock basal boundary and location away from fast moving outlets. However, we find deformation motion is fundamentally limited by the stiffness of the cold Greenland ice, such that sliding likely dominates ice flow across much of the GrIS ablation zone.

The deformation, sliding, and surface velocity are also quantified over a three year period to characterize the spatiotemporal variations in ice motion at the field location. It is found that across the length scale an ice thickness, the spatial variability of the surface velocity generally reflects that of the sliding velocity. Spatial variations in sliding and deformation span an order of magnitude, but do not vary smoothly through the domain, and instead cluster into discrete populations. Strong, statistically significant temporal trends in the sliding and deformation fraction are found at some borehole locations, while at other boreholes they are dominated by seasonality. In general, time changes in the deformation velocity mimic that of the sliding velocity, with the highest rates of both recorded in the early melt season and the lowest in winter. Finally, changes in the shape of the deformation profiles suggest a significant change in the basal variability occurs at the onset of the melt season, and again as ice flow returns to winter conditions at the cessation of the melt season. To understand the basal conditions that produce the spatiotemporal variability observed, Elmer/Ice will be used to generate a sweet of flow-line models with varied basal boundaries that will be compared to the in situ measurements of sliding and ice deformation.

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