Thermal structure and basal sliding parametrisation at Pine Island Glacier – a 3-D full-Stokes model study

N Wilkens,M Rückamp,D Rippin,J Behrens,T Kleiner,A Humbert

doi:10.5194/tc-9-675-2015

Abstract

Abstract. Pine Island Glacier is one of the fastest changing glaciers of the Antarctic Ice Sheet and therefore of scientific interest. The glacier holds enough ice to raise the global sea level significantly (~ 0.5 m) when fully melted. The question addressed by numerous modelling studies of the glacier focuses on whether the observed changes are a start of an uncontrolled and accelerating retreat. The movement of the glacier is, in the fast-flowing areas, dominated by basal motion. In modelling studies the parametrisation of the basal motion is therefore crucial. Inversion methods are commonly applied to reproduce the complex surface flow structure of Pine Island Glacier by using information of the observed surface velocity field to constrain, among other things, basal sliding. We introduce two different approaches of combining a physical parameter, the basal roughness, with basal sliding parametrisations. This way basal sliding is again connected closer to its original formulation. We show that the basal roughness is an important and helpful parameter to consider and that many features of the flow structure can be reproduced with these approaches.

Highlights

In the past decades the fastest changes in ice flow velocity, ice thickness and grounding line retreat in the Antarctic Ice Sheet have been observed in the region of Pine Island Glacier (PIG), Amundsen Sea Embayment, West Antarctica (Rignot, 2008, 1998; Wingham et al, 2009; Joughin et al, 2010; Park et al, 2013; Helm et al, 2014)
As the inversion for basal sliding parameters is not sufficient for the physical understanding of basal motion, we focus on basal sliding parametrisations that consider measured basal roughness distributions
We have shown that the complex surface flow structure of PIG could be well reproduced with our simplified approach of an inversion for a basal sliding parameter β2 in the reference simulation

Summary

Introduction

In the past decades the fastest changes in ice flow velocity, ice thickness and grounding line retreat in the Antarctic Ice Sheet have been observed in the region of Pine Island Glacier (PIG), Amundsen Sea Embayment, West Antarctica (Rignot, 2008, 1998; Wingham et al, 2009; Joughin et al, 2010; Park et al, 2013; Helm et al, 2014). The bed lies below sea level in large areas, making it part of a so-called marine ice sheet. In combination with a retrograde bed, which slopes down from the ocean towards the centre of the glacier, this setting was postulated to be intrinsically unstable by the so-called “Marine Ice Sheet Instability” hypothesis (Hughes, 1973). This hypothesis is still up for debate (Vaughan, 2008; Gudmundsson et al, 2012), while the trigger for the changes is thought to be enhanced ocean melting of the ice shelf (Dutrieux et al, 2014)

Results

Discussion

Conclusion