Abstract
Abstract. Iceberg calving accounts for between 30 % and 60 % of net mass loss from the Greenland Ice Sheet, which has intensified and is now the single largest contributor to global sea level rise in the cryosphere. Changes to calving rates and the dynamics of calving glaciers represent a significant uncertainty in projections of future sea level rise. A growing body of observational evidence suggests that calving glaciers respond rapidly to regional environmental change, but predictive capacity is limited by the lack of suitable models capable of simulating calving mechanisms realistically. Here, we use a 3-D full-Stokes calving model to investigate the environmental sensitivity of Store Glacier, a large outlet glacier in West Greenland. We focus on two environmental processes: undercutting by submarine melting and buttressing by ice mélange, and our results indicate that Store Glacier is likely to be able to withstand moderate warming perturbations in which the former is increased by 50 % and the latter reduced by 50 %. However, severe perturbation with a doubling of submarine melt rates or a complete loss of ice mélange destabilises the calving front in our model runs. Furthermore, our analysis reveals that stress and fracture patterns at Store's terminus are complex and varied, primarily due to the influence of basal topography. Calving style and environmental sensitivity vary greatly, with propagation of surface crevasses significantly influencing iceberg production in the northern side, whereas basal crevasses dominate in the south. Any future retreat is likely to be initiated in the southern side by a combination of increased submarine melt rates in summer and reduced mélange strength in winter. The lateral variability, as well as the importance of rotational and bending forces at the terminus, underlines the importance of using the 3-D full-Stokes stress solution when modelling Greenland's calving glaciers.
Highlights
Iceberg calving and submarine melt are important ablation mechanisms in the cryosphere, collectively accounting for around half of the net annual ice loss in Greenland over the last decade and more when warm subtropical waters periodically flow into coastal seas and fjords (Rignot and Kanagaratnam, 2006; Holland et al, 2008; Straneo et al, 2010; Christoffersen et al, 2011)
The importance of calving as a contributor to global sea level rise is demonstrated by the sustained retreat, acceleration and dynamic thinning triggered at the termini of many Greenlandic outlet glaciers in the past 2 decades (Howat et al, 2005; Holland et al, 2008; Rignot and Kanagaratnam, 2006)
The starting point is a present-day control simulation which includes three types of climate forcing on the terminus: (1) distributed submarine ice-wall melting at the submerged portion of the terminus, (2) concentrated submarine melting associated with convective plumes forming at two known locations where glacial meltwater is subglacially discharged, and (3) ice mélange buttressing
Summary
Iceberg calving and submarine melt are important ablation mechanisms in the cryosphere, collectively accounting for around half of the net annual ice loss in Greenland over the last decade (van den Broeke et al, 2009) and more (up to two-thirds) when warm subtropical waters periodically flow into coastal seas and fjords (Rignot and Kanagaratnam, 2006; Holland et al, 2008; Straneo et al, 2010; Christoffersen et al, 2011). The importance of calving as a contributor to global sea level rise is demonstrated by the sustained retreat, acceleration and dynamic thinning triggered at the termini of many Greenlandic outlet glaciers in the past 2 decades (Howat et al, 2005; Holland et al, 2008; Rignot and Kanagaratnam, 2006). Recent observational studies (James et al, 2014; Murray et al, 2015; Chudley et al, 2019; Medrzycka et al, 2016; Luckman et al, 2015) have captured the calving process in unprecedented detail, yet the physical links between calving and climate remain poorly understood.
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