Modeling ice shelf weakening with the material point method and damage mechanics
Abstract
Mechanical weakening of ice shelves reduces their ability to restrain discharge of grounded ice into the ocean and should be included in large-scale ice flow models when making projections of ice sheet evolution and sea level rise. Here, we simulate mechanical weakening of ice shelves and calving events using a material point method (MPM) for shallow shelf ice flow coupled with creep damage mechanics. MPM is a particle variation of the finite element method. Particles discretize the ice domain, carry all variables, and advect with the flow within an updated Lagrangian framework. Equations are solved on a grid with the particles serving as moving integration points with modified shape functions. The advantages of our MPM model are quick updates and error-free advection for damage, thickness, ice front position, and grounding line position. Error-free advection is essential for preserving sharp gradients in the damage field over time.
We test the MPM-damage model on both an idealized marine ice sheet and the Larsen C ice sheet-ice shelf system. We run the model for the idealized system forward from a non-damaged steady state. Damage accumulates at shear margins, and a rift initiates and propagates to result in a calving event. The ice sheet responds to the damage accumulation with increased flow speeds, thinning, and grounding line retreat. The damage evolution appears to be realistic, and its strong feedback on ice flow shows the necessity of including fracture-induced weakening in projections of ice sheet evolution. For the Larsen C system, we initialize the ice geometry and velocity using satellite data from 2015. We determine the initial damage and friction fields by solving an inverse problem. When run forward, the simulation reproduces observed rift propagation and the resultant calving event of iceberg A-68 in 2017. We also experiment with diagnosing stability of ice shelves by testing their response to potential triggers of collapse or weakening, such as thinning, hydrofracture, calving, and ungrounding from pinning points.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.C34A..02H
- Keywords:
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- 0726 Ice sheets;
- CRYOSPHEREDE: 0728 Ice shelves;
- CRYOSPHEREDE: 0730 Ice streams;
- CRYOSPHEREDE: 0798 Modeling;
- CRYOSPHERE