Abstract
Abstract. The effect of the North Atlantic Ocean on the Greenland Ice Sheet through submarine melting of Greenland's tidewater glacier calving fronts is thought to be a key driver of widespread glacier retreat, dynamic mass loss and sea level contribution from the ice sheet. Despite its critical importance, problems of process complexity and scale hinder efforts to represent the influence of submarine melting in ice-sheet-scale models. Here we propose parameterizing tidewater glacier terminus position as a simple linear function of submarine melting, with submarine melting in turn estimated as a function of subglacial discharge and ocean temperature. The relationship is tested, calibrated and validated using datasets of terminus position, subglacial discharge and ocean temperature covering the full ice sheet and surrounding ocean from the period 1960–2018. We demonstrate a statistically significant link between multi-decadal tidewater glacier terminus position change and submarine melting and show that the proposed parameterization has predictive power when considering a population of glaciers. An illustrative 21st century projection is considered, suggesting that tidewater glaciers in Greenland will undergo little further retreat in a low-emission RCP2.6 scenario. In contrast, a high-emission RCP8.5 scenario results in a median retreat of 4.2 km, with a quarter of tidewater glaciers experiencing retreat exceeding 10 km. Our study provides a long-term and ice-sheet-wide assessment of the sensitivity of tidewater glaciers to submarine melting and proposes a practical and empirically validated means of incorporating ocean forcing into models of the Greenland ice sheet.
Highlights
Discharge of ice from marine-terminating glaciers around the margin of the Greenland Ice Sheet is responsible for 9.1 mm of Greenland’s 1972–2018 total sea level contribution of 13.7 mm (Mouginot et al, 2019) and, together with increased surface melting, has resulted in Greenland becoming the fastest-growing contributor to global sea level (Chen et al, 2017)
We draw on detailed modeling of submarine melting at tidewater glacier calving fronts, together with the observation that tidewater glacier retreat is most frequent in the summer when plumes are active, to suggest estimating submarine melting at each glacier by Q0.4 thermal forcing (TF), where Q is the summer (June–July–August) mean subglacial discharge
We find a statistically significant relationship between parameterized submarine melt rate and terminus position at the ice sheet scale and that variability in submarine melting can explain more than 50 % of variability in terminus position at 105 of the 191 glaciers considered
Summary
Discharge of ice from marine-terminating glaciers around the margin of the Greenland Ice Sheet is responsible for 9.1 mm of Greenland’s 1972–2018 total sea level contribution of 13.7 mm (Mouginot et al, 2019) and, together with increased surface melting, has resulted in Greenland becoming the fastest-growing contributor to global sea level (Chen et al, 2017). Increased discharge from tidewater glaciers is understood to be a response to a warming of the ocean and fjords surrounding the ice sheet that, in concert with increased surface melting and subglacial discharge, has resulted in increased submarine melting and calving at tidewater glacier termini (Straneo and Heimbach, 2013). Considering first the ocean processes, the Greenland ice sheet interacts directly with the ocean at around 300 tidewater glacier calving fronts that are several kilometers wide and several hundred meters deep (Rignot and Mouginot, 2012).
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