Abstract
Abstract. Dynamic ice discharge from outlet glaciers across the Greenland Ice Sheet has increased since the beginning of the 21st century. Calving from floating ice tongues that buttress these outlets can accelerate ice flow and discharge of grounded ice. However, little is known about the dynamic impact of ice tongue loss in Greenland compared to ice shelf collapse in Antarctica. The rapidly flowing (∼1000 m a−1) Petermann Glacier in northwest Greenland has one of the ice sheet's last remaining ice tongues, but it lost ∼50 %–60 % (∼40 km in length) of this tongue via two large calving events in 2010 and 2012. The glacier showed a limited velocity response to these calving events, but it is unclear how sensitive it is to future ice tongue loss. Here, we use an ice flow model (Úa) to assess the instantaneous velocity response of Petermann Glacier to past and future calving events. Our results confirm that the glacier was dynamically insensitive to large calving events in 2010 and 2012 (<10 % annual acceleration). We then simulate the future loss of similarly sized sections to the 2012 calving event (∼8 km long) of the ice tongue back to the grounding line. We conclude that thin, soft sections of the ice tongue >12 km away from the grounding line provide little frontal buttressing, and removing them is unlikely to significantly increase ice velocity or discharge. However, once calving removes ice within 12 km of the grounding line, loss of these thicker and stiffer sections of ice tongue could perturb stresses at the grounding line enough to substantially increase inland flow speeds (∼900 m a−1), grounded ice discharge, and Petermann Glacier's contribution to global sea level rise.
Highlights
Dynamic ice discharge from marine-terminating outlet glaciers is an important component of recent mass loss from the Greenland Ice Sheet (GrIS) (van den Broeke et al, 2016; Enderlin et al, 2014)
We have shown that the two-horizontal-dimensional model Úa can reproduce the flow of Petermann Glacier before the large calving event in 2010
We expand on previous work and provide new insight into the velocity response of Petermann Glacier to past and future large calving events and eventual ice tongue collapse
Summary
Dynamic ice discharge from marine-terminating outlet glaciers is an important component of recent mass loss from the Greenland Ice Sheet (GrIS) (van den Broeke et al, 2016; Enderlin et al, 2014). Since the 1990s, outlet glaciers in Greenland have been thinning (Pritchard et al, 2009; Krabill et al, 2000), retreating (e.g., Carr et al, 2017; Jensen et al, 2016; Moon and Joughin, 2008), and accelerating (Joughin et al, 2010; Moon et al, 2012) in response to climate–ocean forcing. Marine-terminating glaciers are influenced by ocean warming (e.g., Holland et al, 2008; Mouginot et al, 2015; Straneo and Heimbach, 2013), increased surface air temperatures (Moon and Joughin, 2008), and reduced sea ice concentration in the fjords (Amundson et al, 2010; Shroyer et al, 2017; Reeh et al, 2001). 21st century retreat at two large outlet glaciers in southeast Greenland (Helheim and Kangerlussuaq) was followed by acceleration and ice surface thinning (Howat et al, 2005, 2007; Nick et al, 2009)
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