Abstract
Abstract. Simulations of ice sheet evolution over glacial cycles require integration of observational constraints using ensemble studies with fast ice sheet models. These include physical parameterisations with uncertainties, for example, relating to grounding-line migration. More complete ice dynamic models are slow and have thus far only be applied for < 1000 years, leaving many model parameters unconstrained. Here we apply a 3D thermomechanically coupled full-Stokes ice sheet model to the Ekström Ice Shelf embayment, East Antarctica, over a full glacial cycle (40 000 years). We test the model response to differing ocean bed properties that provide an envelope of potential ocean substrates seawards of today's grounding line. The end-member scenarios include a hard, high-friction ocean bed and a soft, low-friction ocean bed. We find that predicted ice volumes differ by > 50 % under almost equal forcing. Grounding-line positions differ by up to 49 km, show significant hysteresis, and migrate non-steadily in both scenarios with long quiescent phases disrupted by leaps of rapid migration. The simulations quantify the evolution of two different ice sheet geometries (namely thick and slow vs. thin and fast), triggered by the variable grounding-line migration over the differing ocean beds. Our study extends the timescales of 3D full-Stokes by an order of magnitude compared to previous studies with the help of parallelisation. The extended time frame for full-Stokes models is a first step towards better understanding other processes such as erosion and sediment redistribution in the ice shelf cavity impacting the entire catchment geometry.
Highlights
Shortcomings in the description of ice dynamics remain one of the limitations for projecting the evolution of the Greenland and Antarctic ice sheets (Pachauri et al, 2014)
Due to the high computational costs of full-Stokes (FS) models that solve the complete ice dynamical equations, current longterm (> 1000 years) ice sheet simulations rely on simplifications to the ice dynamical equations
While there is no speed-up for the “classic” solver setup using the direct solver MUltifrontal Massively Parallel sparse direct Solver (MUMPS), there is a linear speedup for the ParStokes solver up to ∼ 700 computer processing units (CPUs) before the rate of speed-up tapers off and vanishes for more than 1536 CPUs
Summary
Shortcomings in the description of ice dynamics remain one of the limitations for projecting the evolution of the Greenland and Antarctic ice sheets (Pachauri et al, 2014). Due to the high computational costs of full-Stokes (FS) models that solve the complete ice dynamical equations, current longterm (> 1000 years) ice sheet simulations rely on simplifications to the ice dynamical equations. This choice is justified because it allows for ensemble modelling and tuning of unknown parameters using observations. There are two drawbacks to this approach. It is uncertain whether the transition zone between grounded and floating ice is adequately represented in existing long-term simulations (Pattyn and Durand, 2013).
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