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.