Sensitivity of centennial mass loss projections of the Amundsen basin to the friction law

Abstract

Abstract. Reliable projections of ice sheets' future contributions to sea-level rise require models that are able to accurately simulate grounding-line dynamics, starting from initial states consistent with observations. Here, we simulate the centennial evolution of the Amundsen Sea Embayment in response to a prescribed perturbation in order to assess the sensitivity of mass loss projections to the chosen friction law, depending on the initialisation strategy. To this end, three different model states are constructed by inferring both the initial basal shear stress and viscosity fields with various relative weights. Then, starting from each of these model states, prognostic simulations are carried out using a Weertman, a Schoof and a Budd friction law, with different parameter values. Although the sensitivity of projections to the chosen friction law tends to decrease when more weight is put on viscosity during initialisation, it remains significant for the most physically acceptable of the constructed model states. Independently of the considered model state, the Weertman law systematically predicts the lowest mass losses. In addition, because of its particular dependence on effective pressure, the Budd friction law induces significantly different grounding-line retreat patterns than the other laws and predicts significantly higher mass losses.

Regularized Coulomb Friction Laws for Ice Sheet Sliding: Application to Pine Island Glacier, Antarctica

“…Some other works that employ a regularized Coulomb friction law use an explicit representation of N based on an equivalence with h af (Brondex et al, , ; Nias et al, ), which may be problematic as described above (see also Text S1). When parameterized this way, the regions where Coulomb friction occurs are limited by geometrical constraints to the regions within ~1–15 km of the grounding line (e.g., h af < ~100 m in Figure S2) as described in Text S1.…”

“…Models of ice sheet evolution depend strongly on their selection of the basal friction law (Brondex et al, , ; Joughin, Smith, & Holland, ; Nias et al, ), in which basal shear stress is expressed as τ b = f ( u b , N ), where u b is the speed at which ice slides over its bed. Here N denotes the effective pressure at the ice‐bed interface, defined as the difference between ice‐overburden and basal‐water pressure.…”

Assessment of Sub-Shelf Melting Parameterisations Using theOcean-Ice Sheet Coupled Model NEMO(v3.6)-Elmer/Ice(v8.3)

“…The law behaves as a non-linear power law away from the 15 grounding line and as a Coulomb friction law near the grounding line, thus ensuring a smooth transition of stress state near and at the grounding line. The Schoof friction law was recently compared to various other types of friction laws commonly used in ice-sheet modelling, for an idealised framework (Brondex et al, 2017) and a real drainage basin (Brondex et al, 2018).…”

Parameter sensitivity analysis of dynamic ice sheet models-Numerical computations

“…where C b ≥ 0 is the basal sliding coefficient with a different interpretation than the friction coefficient C in (2.5) and θ and λ are the sliding exponents. Depending on the base conditions, (θ, λ) are for example (3,2), (3,1) and (1, 0) [6]. In this formulation, the volume flux is locally determined by the surface gradient ∇h and the thickness of the ice H. The height evolution is governed by an equation similar to the height equation in (2.5)…”

“…The time constant τ could be e.g. 1 year. Assume that f (Tu)Tu·Tv is approximately constant in time (e.g.…”