Atlantic Water intrusion triggers rapid retreat and regime change at previously stable Greenland glacier

Abstract

Discharge from Greenland’s marine-terminating glaciers contribute to half of all mass loss from the ice sheet, but the factors forcing their retreat are complex and contested. Here, we examine K.I.V Steenstrups Nordre Bræ (‘Steenstrup’), which, between 2018—2021, retreated ~7 km, thinned by ~20%, doubled in ice discharge, and quadrupled in flow speed. This rate of acceleration is unprecedented amongst Greenland’s glaciers, and now places Steenstrup in the top 10% of glaciers by contribution to Greenland’s discharge. In contrast to expected behaviour from a shallow, grounded tidewater glacier, Steenstrup was insensitive to high surface temperatures that destabilised many regional glaciers in 2016, responding instead to an extreme anomaly in deeper Atlantic Water (AW) in 2018. Steenstrup’s behaviour highlights that, as AW intrusions occur at increasingly shallow depths, even apparently long-term stable glaciers with high sills are vulnerable to sudden and rapid retreat.

Ocean warming drives rapid dynamic activation of marine-terminating glacier on the west Antarctic Peninsula

“…Our results demonstrate that such tipping points can increase ice discharge extremely rapidly, in Cadman Glacier's case by 28.1% in 13 months. Other glaciers on the Antarctic Peninsula may be vulnerable to similar sudden acceleration and retreat, where bed conditions and bathymetry allow, similar to heterogeneous patterns of tidewater glacier retreat controlled by bed topography observed in Greenland 61,62 . For example, the largest glacier on the west coast, Fleming Glacier, has a floating tongue and is grounded on a retrograde bed slope, similar to Cadman Glacier 63 .…”

Seasonal Changes of Mélange Thickness Coincide With Greenland Calving Dynamics

“…The model can be used to further explore how the mélange thickness at the terminus evolves with ice-ocean interactions that influence calving dynamics, including ocean tides [14], ocean warming [40,20,21], and subglacial plumes [56,13].…”

“…at Steenstrup [40]. Given that mélange thickness dictates its buttressing force, the impacts of submarine melting and subglacial discharge on calving will be amplified by melting and thinning the mélange.…”

“…Remote sensing observations on many Greenland glacier termini have shown significant terminusposition seasonality, with advance in winter and retreat in spring to summer through enhanced calving [37,38,39]. Previous studies have attributed seasonal calving dynamics to buttressing from ice mélange [18,15,40]. To investigate whether there are correlations between ice mélange thickness and calving dynamics on other glaciers, we use ICESat-2 observations of mélange surface elevation.…”