Abstract
Abstract. Ice mass loss from the Greenland ice sheet is the largest single contributor to sea level rise in the 21st century. The mass loss rate has accelerated in recent decades mainly due to thinning and retreat of its outlet glaciers. The diverse calving mechanisms responsible for tidewater glacier retreat are not fully understood yet. Since a tidewater glacier’s sensitivity to external forcings depends on its calving style, detailed insight into calving processes is necessary to improve projections of ice sheet mass loss by calving. As tidewater glaciers are mostly thinning, their calving styles are expected to change. Here, we study calving behaviour changes under a thinning regime at Bowdoin Glacier, north-western Greenland, by combining field and remote-sensing data from 2015 to 2019. Previous studies showed that major calving events in 2015 and 2017 were driven by hydro-fracturing and melt-undercutting. New observations from uncrewed aerial vehicle (UAV) imagery and a GPS network installed at the calving front in 2019 suggest ungrounding and buoyant calving have recently occurred as they show (1) increasing tidal modulation of vertical motion compared to previous years, (2) absence of a surface crevasse prior to calving, and (3) uplift and horizontal surface compression prior to calving. Furthermore, an inventory of calving events from 2015 to 2019 based on satellite imagery provides additional support for a change towards buoyant calving since it shows an increasing occurrence of calving events outside of the melt season. The observed change in calving style could lead to a possible retreat of the terminus, which has been stable since 2013. We therefore highlight the need for high-resolution monitoring to detect changing calving styles and numerical models that cover the full spectrum of calving mechanisms to improve projections of ice sheet mass loss by calving.
Highlights
Greenland’s tidewater glaciers have been observed to accelerate, thin, and retreat faster than any other part of the ice sheet (e.g. Pritchard et al, 2009; Hill et al, 2017; IMBIE Team, 2019)
Previous studies showed that in July 2015 and July 2017, large-scale calving events on Bowdoin Glacier were triggered by surface crevasses, facilitated by melt-undercutting, and propagated by hydro-fracturing (Jouvet et al, 2017; van Dongen et al, 2020c, d)
Our new observations suggest that the calving behaviour of Bowdoin Glacier may have changed since towards predominantly buoyant calving in response to dynamic thinning
Summary
Greenland’s tidewater glaciers have been observed to accelerate, thin, and retreat faster than any other part of the ice sheet (e.g. Pritchard et al, 2009; Hill et al, 2017; IMBIE Team, 2019). Greenland’s tidewater glaciers have been observed to accelerate, thin, and retreat faster than any other part of the ice sheet Projections of future ice sheet mass loss, and thereby of sea level rise, depend on the capability to predict tidewater glacier behaviour. Despite recent advances in observing and modelling calving mechanisms, fundamental gaps in our understanding of outlet glacier sensitivity to climate change remain, such as quantification of the ice–ocean interaction and understanding of glacier behaviour under near-buoyant and super-buoyant conditions (Benn and Åström, 2018; Catania et al, 2020). Observations show that for some tidewater glaciers, largescale infrequent calving events dominate the ice mass loss. H. van Dongen et al.: Calving-style change Bowdoin Glacier over small frequent events (Walter et al, 2010; James et al, 2014; Åström et al, 2014; Medrzycka et al, 2016). As the physical processes triggering small- and large-scale events differ (Medrzycka et al, 2016), it is important to understand the mechanisms behind large-scale events. Benn and Åström (2018) describe four main calving mechanisms
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