Helheim Glacier Poised for Dramatic Retreat

Abstract

The Greenland Ice Sheet (GrIS) is a major contributor to global sea-level rise (Bamber et al., 2018;van den Broeke et al., 2016). Approximately 50% of Greenland's mass loss is due to increasing ice loss from its marine-terminating outlet glaciers (The IMBIE Team, 2020). This is particularly prominent in the southeast where ice discharge increased from an average of 136 ± 6 Gt yr −1 during 1972-1980 to an average of 160 ± 2 Gt yr −1 during 2010-2018(Mouginot et al., 2019, totaling ∼25% of the ice-sheet-wide mass loss due to ice discharge since 1990. Located at the head of Sermilik Fjord, Helheim Glacier (66.4°N, 38°W) is one of the largest and fastest-flowing glaciers in Greenland, contributing 6-7% of the total ice discharge from the GrIS (Mankoff et al., 2020).

Seasonal and Multiyear Flow Variability on the Prince of Wales Icefield, Ellesmere Island: 2009–2019

“…(2020) and Van Wychen et al. (2016, 2021) and similar to observations at Helheim Glacier (Williams et al., 2021), we suggest that beginning in 2014, Trinity and Wykeham glaciers have transitioned to a flow type of dynamic thinning which is strongly influenced by subglacial topography. In contrast to previous studies from this region (Millan et al., 2017, Harcourt et al., 2020; Van Wychen et al., 2016, 2021), we find that Trinity and Wykeham, while having undergone an overall increase in velocity since 2009, have not accelerated consistently as previously suggested, and are likely strongly influenced by subglacial topography which result in multiyear repeating periods of acceleration.…”

“…Similar to our findings for Trinity and Wykeham glaciers, Williams et al. (2021) identified a shift in dynamics (i.e., terminus velocity and retreat) on Helheim between 2014 and 2019, again coinciding with acceleration and retreat in the near terminus area, a region which is currently near (within 50 m) flotation. It is expected that continued mass loss, thinning, and retreat down the retrograde slope located in the lowermost 5 km of the terminus of Helheim will result in dramatic retreat.…”

“…Consistent with the findings of Harcourt et al (2020) and Van Wychen et al (2016, 2021 and similar to observations at Helheim Glacier (Williams et al, 2021), we suggest that beginning in 2014, Trinity and Wykeham glaciers have transitioned to a flow type of dynamic thinning which is strongly influenced by subglacial topography. In contrast to previous studies from this region (Millan et al, 2017, Harcourt et al, 2020Van Wychen et al, 2016, 2021, we find that Trinity and Wykeham, while having undergone an overall increase in velocity While Trinity and Wykeham glaciers are both currently grounded on basal pinning points, if thinning continues at the current rate, it is likely that a destabilization of their termini will occur, resulting in further acceleration in velocity and retreat in terminus position similar to that expected and previously observed at Helheim Glacier.…”

“…Evidence of sustained thinning and near-flotation of the termini of both glaciers, in combination with this velocity increase, leads us to believe that Trinity and Wykeham glaciers are responding to external forcing by switching between seasonal flow and flow dominated by dynamic thinning. Both glaciers are grounded below sea level for a distance of 30-40 km up-glacier from their termini, and patterns of thinning, increased buoyancy, and acceleration are similar to those observed during the collapse of Columbia Glacier (Cuffey & Paterson, 2010;Van der Veen, 1996, 2002 and more recently at Helheim Glacier (Williams et al, 2021). Based on our observations, we expect thinning, retreat, and acceleration of Trinity and Wykeham to continue in multiyear repeating periods, controlled by subglacial topography.…”

Meltwater drainage and iceberg calving observed in high-spatiotemporal resolution at Helheim Glacier, Greenland

“…As of 2019, Helheim Glacier had retreated farther and thinned more than at any other time in the observational record (Williams and others, 2021). The glacier may retreat rapidly in the future (Williams and others, 2021), but it has relatively low global sea-level contribution potential; although it occupies a deep subglacial fjord, the fjord is relatively narrow and the bed rises above sea level to the sides and inland (Nick and others, 2013; Felikson and others, 2021).…”