Emergent Dynamics From a Position‐Based Calving Function and the Limits of a Rate‐Based Calving Function

Abstract

A wide range of functions are currently available for simulating the calving of marine-terminating glaciers, but there is no consensus on the best approach to represent the calving process in glacier and ice-sheet models. Current assessments of calving functions are often crudely done by fitting functions to observed changes in terminus positions, neglecting the physical processes that drive changes in calving dynamics. Here, we use 3D simulations of synthetic tidewater glacier domains in Elmer/Ice, to determine whether natural behaviors emerge from the crevasse-depth and von Mises calving functions, and to provide a basis for more robust assessments of the potential capabilities of calving functions. The crevasse-depth calving function is shown to be able to simulate both serac and full-thickness calving events and simulates how their relative proportion is altered by changing the ice freeboard or submarine melting. A clear distinction between rate- and position-based calving is shown, with the von Mises calving function unable to respond to imposed changes in topography or freeboard ice. By comparing the two calving functions, it is apparent that the position-based crevasse-depth function more faithfully represents the calving behaviors observed in the natural world. Consequently, future projections should be made using position-based calving functions. Using a position function, calving rates vary with time and glacier state, so cannot be assumed to be a constant function of stress. In essence, a calving function must be able to capture the key physical processes that drive calving. If so, the transitions in calving dynamics will inherently emerge.