Abstract
Abstract. The Greenland Ice Sheet (GrIS) is losing mass in response to recent climatic and oceanic warming. Since the mid-1990s, tidewater outlet glaciers across the ice sheet have thinned, retreated, and accelerated, but recent changes in northern Greenland have been comparatively understudied. Consequently, the dynamic response (i.e. changes in surface elevation and velocity) of these outlet glaciers to changes at their termini, particularly calving from floating ice tongues, is poorly constrained. Here we use satellite imagery and historical maps to produce an unprecedented 68-year record of terminus change across 18 major outlet glaciers and combine this with previously published surface elevation and velocity datasets. Overall, recent (1995–2015) retreat rates were higher than at any time in the previous 47 years (since 1948). Despite increased retreat rates from the 1990s, there was distinct variability in dynamic glacier behaviour depending on whether the terminus was grounded or floating. Grounded glaciers accelerated and thinned in response to retreat over the last 2 decades, while most glaciers terminating in ice tongues appeared dynamically insensitive to recent ice tongue retreat and/or total collapse. We also identify glacier geometry (e.g. fjord width, basal topography, and ice tongue confinement) as an important influence on the dynamic adjustment of glaciers to changes at their termini. Recent grounded outlet glacier retreat and ice tongue loss across northern Greenland suggest that the region is undergoing rapid change and could soon contribute substantially to sea level rise via the loss of grounded ice.
Highlights
Mass loss from the Greenland Ice Sheet (GrIS) has accelerated since the early 2000s, compared to the 1970s and 1980s (Kjeldsen et al, 2015; Rignot et al, 2008), and could contribute 0.45–0.82 m of sea level rise by the end of the 21st century (Church et al, 2013)
In addition to the long-term record of frontal position change (1948–2015), we further assess the variability of retreat rates across northern Greenland, by presenting mean retreat rates across five decadal time periods (1976–1985, 1986–1995, 1996–2005, 2006–2015) in Fig. 4a–e, except for the earliest epoch (1948–1975), which spans 27 years due to image availability
Our results showed that grounded outlet glaciers which retreated into deeper fjords had higher retreat rates (e.g. Tracy, Harald Moltke Bræ, and Heilprin), than those with shallower basal troughs (e.g. Academy and Marie-Sophie)
Summary
Mass loss from the Greenland Ice Sheet (GrIS) has accelerated since the early 2000s, compared to the 1970s and 1980s (Kjeldsen et al, 2015; Rignot et al, 2008), and could contribute 0.45–0.82 m of sea level rise by the end of the 21st century (Church et al, 2013). Recent mass loss has been attributed to both a negative surface mass balance and increased ice discharge from marine-terminating glaciers (van den Broeke et al, 2016; Enderlin et al, 2014). The latter has contributed ∼ 40 % of total mass loss across the GrIS since 1991 (van den Broeke et al, 2016), and increased mass loss was synchronous with widespread glacier acceleration from 1996 to 2010 (Carr et al, 2017b; Joughin et al, 2010; Moon et al, 2012; Rignot and Kanagaratnam, 2006). Tidewater glaciers can behave in a cyclic man-
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