Velocity response of Petermann Glacier, northwest Greenland to past and future calving events

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 north-west 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 ( 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.

Calving at Ryder Glacier, Northern Greenland

“…Similar explanations have been provided for the differing behavior of Ryder and Petermann glaciers; Petermann glacier has retreated in recent decades whilst Ryder glacier has been relatively stable (e.g., Hill et al., 2017, 2018; Rückamp et al., 2019) In Sherard Osborn Fjord, a recently mapped shallow bathymetric sill in front of Ryder glacier substantially reduces the intrusion of warm water of Atlantic origin into the cavity beneath the floating glacier tongue so that cool water temperatures prevail at the grounding line (Jakobsson et al., 2020). In Petermann Fjord, the situation is different: a deeper sill in front of the Petermann glacier (Jakobsson et al., 2018) allows for the inflow of deep, warm water which has the potential to reach the Petermann glacier’s grounding line and contribute to melting in the cavity beneath the ice tongue (Johnson et al., 2011).…”

“…Ryder glacier has displayed cyclic behavior with periods of steady advance interrupted by abrupt and substantial retreats (Hill et al., 2018; Murray et al., 2015). Ice flux across the grounding line is estimated to be 1.9–2.4 km 3 /yr (Joughin et al., 1999), and is approximately in balance with satellite‐derived figures of combined aerial and submarine melt (Wilson et al., 2017).…”

“…The associated reduction in buttressing has led to an acceleration of the floating and grounded parts of the glacier (Rückamp et al., 2019). During the period 1948–2015, Petermann experienced a net retreat of, on average, 311 m a −1 (Hill et al., 2018).…”

Tidal Modulation of Buoyant Flow and Basal Melt Beneath Petermann Gletscher Ice Shelf, Greenland

“…This sustained retreat highlights the relationship between stronger basal melting and destabilization of another Greenland ice shelf. Future changes to the subglacial runoff flux beneath the ice shelf will dictate its stability, with increased flux likely leading to the eventual removal of PGIS (Reilly et al, 2019) and accelerated ice discharge from the Greenland ice sheet (Hill et al, 2018).…”

Summer surface melt thins Petermann Gletscher Ice Shelf by enhancing channelized basal melt

“…This occurred most recently to major outlet glaciers Jakobshavn Isbrae (Holland and others, 2008) and Zachariae Isstrom (Mouginot and others, 2015). After losing their ice shelf, the land-based portion of each glacier began to accelerate and retreat as the buttressing effect of the ice shelf no longer inhibited its seaward flow (Hill and others, 2018). At present only three large Greenland outlet glaciers extend in a floating ice shelf >10 km long (Higgins, 1991): Nioghalvfjerdsfjorden Glacier (also known as 79 North Glacier), Ryder Glacier, and Petermann Gletscher.…”