An Improved Model for Tidally-Modulated Grounding Line Migration

Thursday, 18 December 2014: 8:30 AM
Gudmundur Hilmar Gudmundsson, NERC British Antarctic Survey, Cambridge, CB3, United Kingdom and Victor C Tsai, Caltech-Seismological Lab, Pasadena, CA, United States
Understanding the dynamics of the grounding line is necessary for predictions of long-term ice sheet stability. However, despite a growing number of observations of the tidal influence on grounding line migration, this short-timescale migration is poorly understood, with most modeling attempts assuming beam theory to calculate displacements. Here, we present an improved model of tidally-modulated grounding line migration that treats the migration as an elastic fracture problem forced by the additional ocean water pressure from the tide. This new model predicts that the grounding line cannot be assumed to be in hydrostatic equilibrium and furthermore that the migration is inherently asymmetric and non-linear, with migration distances that are not simply proportional to the tidal load. Specifically, grounding line migration is approximately 10 times greater over the high tide part of the tidal cycle compared to low tide, and migration distances are substantially larger than simple flotation arguments would suggest. Numerical tests also show that the dependence of migration distance on elastic moduli and ice sheet thickness are inconsistent with the predictions of beam theory for a wide range of realistic values. Finally, applying the new model to observations in Antarctica results in new estimates of bed slopes, though these estimates remain uncertain due to imperfect knowledge of the relevant parameters.