Abstract
Abstract. Calving is an important mass-loss process for many glaciers worldwide, and has been assumed to respond to a variety of environmental influences. We present a grounded, flowline tidewater glacier model using a physically-based calving mechanism, applied to Helheim Glacier, eastern Greenland. By qualitatively examining both modelled size and frequency of calving events, and the subsequent dynamic response, the model is found to realistically reproduce key aspects of observed calving behaviour. Experiments explore four environmental variables which have been suggested to affect calving rates: water depth in crevasses, basal water pressure, undercutting of the calving face by submarine melt and backstress from ice mélange. Of the four variables, only crevasse water depth and basal water pressure were found to have a significant effect on terminus behaviour when applied at a realistic magnitude. These results are in contrast to previous modelling studies, which have suggested that ocean temperatures could strongly influence the calving front. The results raise the possibility that Greenland outlet glaciers could respond to the recent trend of increased surface melt observed in Greenland more strongly than previously thought, as surface ablation can strongly affect water depth in crevasses and water pressure at the glacier bed.
Highlights
Calving is an important mass loss process for both ice sheets and smaller tidewater glaciers (e.g., Church et al, 2001; Rignot and Thomas, 2002; Blaszczyk et al, 2009) and plays a strong role in tidewater glacier dynamics (Meier and Post, 1987)
In the context of previous debate over whether dynamic changes in tidewater glaciers are triggered at the terminus or by changes in velocity, the results from these two sets of experiments suggest that either mechanism may have a strong influence on glacier dynamics
In response to previous debate over whether glacier retreat is triggered first by glacier acceleration or increases in calving rate, the model results indicate that either process has the potential to cause terminus retreat and it may be more enlightening to consider the specific mechanisms involved
Summary
Calving is an important mass loss process for both ice sheets and smaller tidewater glaciers (e.g., Church et al, 2001; Rignot and Thomas, 2002; Blaszczyk et al, 2009) and plays a strong role in tidewater glacier dynamics (Meier and Post, 1987). Reduction in backstress from proglacial ice mélange, which can otherwise provide a stabilising force to the calving face and inhibit calving (Nick et al, 2009; Amundson and Truffer, 2010) These mechanisms depend on atmospheric and ocean temperatures driving either surface or submarine ice melt. By including calving in an ice flow model it is possible to experiment with applying these environmental forcing factors separately and deduce the likely sensitivity of tidewater glaciers to them. In this paper our time-evolving, flowline model of Helheim Glacier is tested for sensitivity to the four main environmental inputs outlined above
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