Capabilities and performance of Elmer/Ice, a new-generation ice sheet model

Abstract

Abstract. The Fourth IPCC Assessment Report concluded that ice sheet flow models, in their current state, were unable to provide accurate forecast for the increase of polar ice sheet discharge and the associated contribution to sea level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice flow models, and as a result a significant number of new ice sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the opensource multi-physics code Elmer. It was one of the first fullStokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger-scale problems, earning the status of an ice sheet model. Here, we summarise almost 10 yr of development performed by different groups. Elmer/Ice solves the full-Stokes equations, for isotropic but also anisotropic ice rheology, resolves the grounding line dynamics as a contact problem, and contains various basal friction laws. Derived fields, like the age of the ice, the strain rate or stress, can also be computed. Elmer/Ice includes two recently proposed inverse methods to infer badly known parameters. Elmer is a highly parallelised code thanks to recent developments and the implementation of a block preconditioned solver for the Stokes system. In this paper, all these components are presented in detail, as well as the numerical performance of the Stokes solver and developments planned for the future.

Subglacial flood path development during a rapidly rising jökulhlaup from the western Skaftá cauldron, Vatnajökull, Iceland

“…A hypsometric curve, i.e. lake water volume as a function of ice-shelf elevation, for the lowering of the ice shelf was calculated with the full-Stokes ice-dynamic model Elmer/Ice (Gagliardini and others, 2013) by simulating the emptying of a cylindrically symmetric subglacial lake below an ice cover with the approximate dimensions of the western Skaftá cauldron. The question to be addressed by the simulation is whether the subglacial water body maintains a similar shape as the ice shelf is lowered and the lake is emptied or whether the lake geometry changes substantially due to internal shear within the ice shelf near the lake edge such that the grounding line at the lateral boundary moves inward as the shelf lowers.…”

“…Gagliardini and others, 2013), and a constant uniform positive surface mass balance b s . The stress-free upper surface is assumed to have a smooth geometry, ignoring the dynamic effect of surface crevasses that are observed to be formed in a concentric pattern during the subsidence of the ice shelf.…”

“…At each node, the normal force exerted by the ice on the bedrock is compared with the water pressure at that location and the ice allowed to separate from the bed in case the water pressure is higher (see Gagliardini and others, 2013). The lake is assumed to be hydraulically connected to the atmosphere through water passageways such as crevasses or moulins.…”

“…Outflow from the subglacial lake and transient storage of water in the subglacial flood path are derived and used, together with water temperature measurements in the subglacial lake and near the terminus, to shed light on the dynamics of the flood path development for this type of flood. The emptying of a cylindrically symmetric subglacial lake is simulated with the full-Stokes ice-dynamic model Elmer/Ice (Gagliardini and others, 2013) to deduce a relationship between water volume in the lake and iceshelf elevation for calculations of outflow from the lake and for analysing the size of the subglacial lake in relation to the observed dimensions of the ice-surface depression.…”

Inverse solution of surface mass balance of Midtre Lovénbreen, Svalbard

“…In this study we use the high-resolution full-stress ice flow model Elmer/Ice (Gagliardini and others, 2013). In contrast to a previous application using the same model that focused on a prognostic simulation of ML (Zwinger and Moore, 2009), we develop a method inspired by inverse modelling to resolve the past SMB distribution over the glacier.…”