Subglacial discharge accelerates future retreat of Denman and Scott Glaciers, East Antarctica

Abstract

Ice shelf basal melting is the primary mechanism driving mass loss from the Antarctic Ice Sheet, yet it is unknown how the localized melt enhancement from subglacial discharge will affect future Antarctic glacial retreat. We develop a parameterization of ice shelf basal melt that accounts for both ocean and subglacial discharge forcing and apply it in future projections of Denman and Scott Glaciers, East Antarctica, through 2300. In forward simulations, subglacial discharge accelerates the onset of retreat of these systems into the deepest continental trench on Earth by 25 years. During this retreat, Denman Glacier alone contributes 0.33 millimeters per year to global sea level rise, comparable to half of the contemporary sea level contribution of the entire Antarctic Ice Sheet. Our results stress the importance of resolving complex interactions between the ice, ocean, and subglacial environments in future Antarctic Ice Sheet projections.

Fig. 1.. Study area.

(A) Model domain featuring bed topography (17) below grounded ice, satellite inferred ice shelf basal melting rates (12) over floating ice, and modeled (31) bottom ocean temperature on 1 January 2017 in front of the ice shelf. The yellow flowline is used in (C); the black solid line denotes the initial modeled grounding line and ice front (GL and IF, respectively), and the white dotted line denotes the region over which ocean conditions are averaged. The inset in the top left corner provides a schematic of East Antarctica, where the solid black contour denotes the model domain. (B) As in (A) but zoomed into the grounding zone of Denman Glacier, showing observed (18) grounding lines at 1996 (dotted orange) and 2018 (solid orange), as well as the initial modeled grounding line (solid black). (C) Vertical cross section along the yellow flowline in (A) through Denman Glacier. The red line denotes the region of stabilizing prograde bed topography; the horizontal dashed line denotes sea level, and the vertical dotted line denotes the location of the present-day grounding line.

Fig. 2.. Modeled and observed ice shelf melt rates.

(A) Mean 2017–2018 modeled basal melting rates from simulation SSP5-8.5_SD, (B) satellite inferred (12) melt rates averaged between 2010 and 2018, and (C and D) the SSP5-8.5_SD melt contribution from subglacial discharge (computed by subtracting the mean 2017–2018 melt fields computed in SSP5-8.5_SD from SSP5-8.5_NO-SD) within the Denman and Scott Glacier grounding zones. Bed topography (17) is shaded below grounded ice, and the modeled channelized subglacial discharge flux is overlain. The solid black line denotes the initial modeled grounding line position, and the dotted black rectangles in (A) encompass the domains of (C) and (D).

Fig. 3.. Future grounding line retreat.

(A) Modeled 2300 grounding lines overlain onto a three-dimensional surface plot of bed topography (17), where solid and dashed lines denote subglacial discharge (_SD) and non-subglacial discharge (_NO-SD) simulation results, respectively. The white dotted contour outlines the domain for (B) to (D). The solid and dashed gray arrows denote the realized and expected retreat path of Scott Glacier, respectively. (B to D) Modeled grounding lines at (B) 2220, (C) 2240, and (D) 2260 overlain onto bed topography and modeled subglacial discharge over grounded ice, and the modeled ice shelf basal melt rate from experiment SSP1-2.6_SD at the corresponding year over floating ice. In all panels, the thick black line denotes the present-day modeled grounding line, and thin contours over grounded ice denote sea level (bed topography at 0 m).

Fig. 4.. Ice shelf melt and sea level rise time series.

Time series of (A) total integrated basal melt within 50 km of the Denman and Scott Glacier grounding line discharge locations, (B) domain sea level contribution (positive values indicate sea level rise), and (C) the sea level contribution trend computed as the time derivative of the sea level contribution time series through 2300. In all panels, solid and dashed lines denote subglacial discharge (_SD) and non-subglacial discharge (_NO-SD) simulations, respectively. Gray lines in (B) and (C) denote results from SSP5-8.5 experiments in which ocean forcing is randomly organized between 2100 and 2300 (see Materials and Methods).