Investigating calving dynamics through the development of a new 3D full-Stokes calving model and its application at Jakobshavn Isbrae, West Greenland

Abstract

A new calving algorithm was developed in the finite element model Elmer/Ice that allows unrestricted calving and terminus advance in 3D. The algorithm used the meshing software Mmg to implement anisotropic remeshing and allow for adaptive meshing at each timestep. The development of the algorithm along with the implementation of the crevasse depth calving law produced a new full-Stokes calving model in Elmer/Ice that is laid out in detail in Chapter 4. The new model is shown to be robust and capable of simulating calving across an array of complex geometries. Using a synthetic geometry, the model is applied in Chapter 5 to test a comprehensive list of variables that affect calving dynamics. The simulations show that calving dynamics are predominately altered by fjord or bed geometry, but other factors such as lateral friction or temperature can also alter the simulated calving. Other non-physical model parameters such as mesh resolution or timestep are also shown to have a large impact on modelled calving. Finally, in Chapter 6, the calving model is applied at Jakobshavn Isbrae (Sermeq Kujalleq), Greenland’s largest glacier. This is the first time that the calving dynamics at Jakobshavn Isbrae have been modelled in 3D. This has been a challenge previously due to the large outlet glacier’s dynamic nature. The model is shown to be robust and capable of simulating the calving, but the prediction of calving is underestimated. The crevasse penetration requirement of the crevasse depth calving law needed to be optimised in order for simulations to match observations of advance and retreat, with the optimal crevasse penetration requirement being 94.5\%. Ice-melange back stress was key to winter readvancement and essential for the model to match observations. However, the ultimate position of the terminus was determined by the geometry at the glacier bed. Importantly, this showed a large step forward in modelling capabilities, where unrestricted 3D calving was modelled at a large dynamic tidewater glacier in a continuum. This work is vital to improving our understanding of calving dynamics at tidewater glaciers and therefore enabling calving to be better constrained in future climate projections.