A three-dimensional full Stokes model of the grounding line dynamics: effect of a pinning point beneath the ice shelf

Abstract

Abstract. The West Antarctic ice sheet is confined by a large area of ice shelves, fed by inland ice through fast flowing ice streams. The dynamics of the grounding line, which is the line-boundary between grounded ice and the downstream ice shelf, has a major influence on the dynamics of the whole ice sheet. However, most ice sheet models use simplifications of the flow equations, as they do not include all the stress components, and are known to fail in their representation of the grounding line dynamics. Here, we present a 3-D full Stokes model of a marine ice sheet, in which the flow problem is coupled with the evolution of the upper and lower free surfaces, and the position of the grounding line is determined by solving a contact problem between the shelf/sheet lower surface and the bedrock. Simulations are performed using the open-source finite-element code Elmer/Ice within a parallel environment. The model's ability to cope with a curved grounding line and the effect of a pinning point beneath the ice shelf are investigated through prognostic simulations. Starting from a steady state, the sea level is slightly decreased to create a contact point between a seamount and the ice shelf. The model predicts a dramatic decrease of the shelf velocities, leading to an advance of the grounding line until both grounded zones merge together, during which an ice rumple forms above the contact area at the pinning point. Finally, we show that once the contact is created, increasing the sea level to its initial value does not release the pinning point and has no effect on the ice dynamics, indicating a stabilising effect of pinning points.

Combining damage and fracture mechanics to model calving

“…The position between the grounded and floating part of the basal boundary, i.e. the grounding line, is part of the solution and is computed solving a contact problem following Durand et al (2009) andFavier et al (2012). The inverse method described in JayAllemand et al (2011) is used to infer the basal friction coefficient C by reducing the mismatch between observed and modelled surface velocities.…”

Parameterization of basal friction near grounding lines in a one-dimensional ice sheet model

“…Stokes models (Durand et al, 2009;Favier et al, 2012), which include all components of the stress tensor, are the most accurate of the widely used iceflow models. However, they can be impractical at continental scales because of their large computational cost, especially in three dimensions.…”

Antarctic ice rise formation, evolution, and stability

“…The numerical experiment consisted in adding a pinning point underneath the ice shelf of a steady state ice sheet. Buttressing induced by the pinning point led to an advance of the grounding line, such as the one caused by the ice rumple in Favier et al [2012], but the ice rise created was not stable and eventually swallowed by the advancing ice sheet.…”

“…Ice rumples are characterized by an overriding ice sheet and hence do not induce horizontal divergence of the main ice flow direction. Their formation has been previously studied numerically by Favier et al [2012], who investigated how local grounding of an ice shelf has an important effect on grounding line advance: pinning of the ice shelf substantially increases buttressing, slows down the ice shelf, and makes the grounding line advance until it engulfs the ice rumple that has formed on top of the pinning point.…”

“…When the contact between an ice shelf and the pinning point is lost, one expects that the subsequent loss of buttressing leads to an acceleration of the ice and subsequent retreat of the grounding line (see the verification experiment by Favier et al [2012]). However, acceleration of an ice sheet due to unpinning of the ice shelf has not been clearly demonstrated so far.…”