Seasonal and interannual variabilities in terminus position, glacier velocity, and surface elevation at Helheim and Kangerlussuaq Glaciers from 2008 to 2016

Abstract

The dynamic response of Greenland tidewater glaciers to oceanic and atmospheric change has varied both spatially and temporally. While some of this variability is likely related to regional climate signals, glacier geometry also appears to be important. In this study, we investigated the environmental and geometric controls on the seasonal and interannual evolution of Helheim and Kangerlussuaq Glaciers, Southeast Greenland, from 2008 to 2016, by combining year‐round, satellite measurements of terminus position, glacier velocity, and surface elevation. While Helheim remained relatively stable with a lightly grounded terminus over this time period, Kangerlussuaq continued to lose mass as its grounding line retreated into deeper water. By summer 2011, Kangerlussuaq's grounding line had retreated into shallower water, and the glacier had an ~5 km long floating ice tongue. We also observed seasonal variations in surface velocity and elevation at both glaciers. At Helheim, seasonal speedups and dynamic thinning occurred in the late summer when the terminus was most retreated. At Kangerlussuaq, we observed summer speedups due to surface‐melt‐induced basal lubrication and winter speedups due to ice‐shelf retreat. We suggest that Helheim and Kangerlussuaq behaved differently on a seasonal timescale due to differences in the spatial extent of floating ice near their termini, which affected iceberg‐calving behavior. Given that seasonal speedups and dynamic thinning can alter this spatial extent, these variations may be important for understanding the long‐term evolution of these and other Greenland tidewater glaciers.

Resolving Seasonal Ice Velocity of 45 Greenlandic Glaciers With Very High Temporal Details

“…Our dense observations also enabled us to classify Alison Glacier (16), Upernavik Isstrøm − III (26), and Helheim Glacier (28) as type 1 (Figures S16, S26, S28, S36, and Table 1). For instance, changes in ice front positions at Helheim Glacier (28) and Jakobshavn Isbrae (not measured in this study), two of Greenland's highest discharge glaciers, greatly influence their seasonal velocity variations Kehrl et al, 2017;Lemos et al, 2018). For instance, changes in ice front positions at Helheim Glacier (28) and Jakobshavn Isbrae (not measured in this study), two of Greenland's highest discharge glaciers, greatly influence their seasonal velocity variations Kehrl et al, 2017;Lemos et al, 2018).…”

“…For instance, Mouginot et al (2015Mouginot et al ( ) estimated long-term (1976Mouginot et al ( -2015 velocity changes of Zachariae Isstrøm, northeast Greenland, noting significant speedup after 2012, which was primarily attributed to the disappearance of its floating ice shelf and enhanced subsurface melting of its ice front by the ocean. For some of these glaciers, seasonal ice flow was found to correlate with the changes in ice front position (Howat et al, 2010(Howat et al, , 2008Kehrl et al, 2017;Moon et al, 2014). For some of these glaciers, seasonal ice flow was found to correlate with the changes in ice front position (Howat et al, 2010(Howat et al, , 2008Kehrl et al, 2017;Moon et al, 2014).…”

“…Radar intensity images have been widely used to map the terminus positions of marine-terminating glaciers (Howat et al, 2008;Kehrl et al, 2017;Moon et al, 2014;Vijay & Braun, 2017). We used speckle-reduced Sentinel-1 IW GRD radar intensity images to map ice front positions.…”

The Possible Transition From Glacial Surge to Ice Stream on Vavilov Ice Cap

“…Many tidewater glaciers and ice streams show periodic summer speedups (e.g., Dunse et al, 2015;Kehrl et al, 2017;Neckel et al, 2016;Schellenberger et al, 2017;Sevestre et al, 2018). This is due to seasonal variation in subglacial hydrology that greatly affects the glacier sliding speeds (Sevestre et al, 2018).…”

Ocean‐Induced Melt Triggers Glacier Retreat in Northwest Greenland

“…Several hypotheses have been proposed to explain the variability in glacier response to climate warming, including differences in glacier/fjord geometry (Felikson et al, 2017;Kehrl et al, 2017;Meier & Post, 1987;Porter et al, 2014), atmospheric warming (Moon & Joughin, 2008), subglacial discharge (Bartholomaus et al, 2016;Motyka et al, 2013;Xu et al, 2013), and ocean-induced melting (Larsen et al, 2016;Rignot et al, 2010Rignot et al, , 2016. These analyses suggest a complex interplay between bed topography, enhanced runoff due to atmospheric warming, enhanced ocean-induced ice melt due to ocean warming, and the supply of ice from upstream.…”