Calving Multiplier Effect Controlled by Calving Front Geometry

Abstract:

Quantifying the impact of submarine melting on calving is absolutely central to understanding the response of marine-terminating glaciers to ocean forcing. Modeling and observational studies have shown the potential for submarine melting to amplify calving (the calving multiplier effect), but there is little consensus as to under what conditions this occurs. Furthermore, the process has not yet been parameterised so that it can be included in the large-scale models used for sea level projection.

Here, with help from full-Stokes Elmer/Ice simulations, we propose an analytical basis for understanding the presence or absence of the calving multiplier effect. We show that as a calving front becomes undercut it becomes more susceptible to both serac failure (calving only of ice that is undercut) and rotational failure (full thickness calving of ice behind the grounding line). By deriving analytical thresholds for these two forms of calving, based on the depth-mean shear and calving front moment, respectively, we suggest that the dominant calving style is determined by the calving front geometry. Well-grounded glaciers are more likely to experience serac failure and no calving multiplier effect, while glaciers that are close to flotation are more likely to experience rotational failure and the calving multiplier effect. The shape of the undercut is also important, with linear undercutting in particular promoting the calving multiplier effect. Our study offers a quantitative framework for understanding where and when the calving multiplier effect occurs, and, therefore, a route to parameterising the effect in ice sheet-scale models.