Abstract
Abstract. Calving-front dynamics is an important control on Greenland's ice mass balance. Ice front retreat of marine-terminating glaciers may, for example, lead to a loss in resistive stress, which ultimately results in glacier acceleration and thinning. Over the past decade, it has been suggested that such retreats may be triggered by warm and salty Atlantic Water, which is typically found at a depth below 200–300 m. An increase in subglacial water discharge at glacier ice fronts due to enhanced surface runoff may also be responsible for an intensification of undercutting and calving. An increase in ocean thermal forcing or subglacial discharge therefore has the potential to destabilize marine-terminating glaciers along the coast of Greenland. It remains unclear which glaciers are currently stable but may retreat in the future and how far inland and how fast they will retreat. Here, we quantify the sensitivity and vulnerability of marine-terminating glaciers along the northwest coast of Greenland (from 72.5 to 76∘ N) to ocean forcing and subglacial discharge using the Ice Sheet System Model (ISSM). We rely on a parameterization of undercutting based on ocean thermal forcing and subglacial discharge and use ocean temperature and salinity from high-resolution ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II) simulations at the fjord mouth to constrain the ocean thermal forcing. The ice flow model includes a calving law based on a tensile von Mises criterion. We find that some glaciers, such as Dietrichson Gletscher or Alison Glacier, are sensitive to small increases in ocean thermal forcing, while others, such as Illullip Sermia or Cornell Gletscher, are remarkably stable, even in a +3 ∘C ocean warming scenario. Under the most intense experiment, we find that Hayes Gletscher retreats by more than 50 km inland by 2100 into a deep trough, and its velocity increases by a factor of 3 over only 23 years. The model confirms that ice–ocean interactions can trigger extensive and rapid glacier retreat, but the bed controls the rate and magnitude of the retreat. Under current oceanic and atmospheric conditions, we find that this sector of the Greenland ice sheet alone will contribute more than 1 cm to sea level rise and up to 3 cm by 2100 under the most extreme scenario.
Highlights
Over the past 2 decades, many glaciers along the northwest coast of Greenland have been retreating and accelerating, sometimes dramatically (e.g., Moon et al, 2012; Wood et al, 2018)
We find that the rate and extent of ice front retreat is strongly dependent on the bed topography: ice fronts are stable on topographic bumps and prograde bed slopes and unstable on retrograde bed slope, which is consistent with previous studies (e.g., Warren, 1991; Bassis, 2013; Carr et al, 2015; Catania et al, 2018; Wood et al, 2018)
We find that some glaciers, such as Alison Gletscher or Upernavik Isstrøm S, are more sensitive to small increases in ocean thermal forcing, while others, such as Cornell Gletscher or Qeqertarsuup Sermia, are very difficult to destabilize, even under a +3 ◦C increase in ocean thermal forcing
Summary
Over the past 2 decades, many glaciers along the northwest coast of Greenland have been retreating and accelerating, sometimes dramatically (e.g., Moon et al, 2012; Wood et al, 2018). It has been suggested that the retreat of these glaciers is initiated by the presence of warm and salty subsurface Atlantic Water (AW) in the fjords (e.g., Straneo et al, 2010; Straneo and Heimbach, 2013; Rignot et al, 2012; Holland et al, 2008) This water is typically found 200 to 300 m below the surface (e.g., Rignot et al, 2016a; Holland et al, 2008). Surface runoff has been increasing over the past decades (van den Broeke et al, 2009; Fettweis et al, 2013b; Tedesco et al, 2013), which enhances subglacial water discharge at the base of calving fronts This freshwater flux enhances the circulation of the ocean in the fjord (Xu et al, 2012), which in turn further increases the melting rate and the rate of undercutting at the calving face of marine-terminating glaciers.
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