Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

Stephen Cornford ,Gunter Leguy,Johannes Feldmann,Rob Arthern,Gaël Durand,Hongju Yu,Julia Christmann,G Hilmar Gudmundsson,Matthew J Hoffman,William H Lipscomb,Thiago Dias Dos Santos,Martin Rückamp,Chris Borstad,David Pollard,Nacho Merino,Thomas Kleiner,Mathieu Morlighem,Angelika Humbert,David M Goldberg ,Hélène Seroussi ,C Williams ,Xylar Asay‐Davis

doi:10.5194/tc-14-2283-2020

Abstract

Abstract. We present the result of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+. MISMIP+ is intended to be a benchmark for ice-flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient to model buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments first tests that models are able to maintain a steady state with the grounding line located on a retrograde slope due to buttressing and then explore scenarios where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. The majority of participating models passed the first test and then produced similar responses to the loss of buttressing. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions – notably the difference between the simpler and more complete treatments of englacial stress but also the differences between numerical methods – taking a secondary role.

Highlights

A number of ice-flow models have been developed in the last decade that simulate fast-flowing ice streams and ice shelves as well as larger, slower-moving ice masses
A substantial portion of variability in the results can be explained by straightforward groupings of the participating models: for example models that make use of the Weertman (1957) friction rule see slower grounding line migration than models employing either the Schoof (2005) or Tsai et al (2015) rules
We have presented the results of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+

Summary

Introduction

A number of ice-flow models have been developed in the last decade that simulate fast-flowing ice streams and ice shelves as well as larger, slower-moving ice masses. Models designed to simulate the creeping flow of continental ice sheets over glacial cycles are typically based on the shallow ice approximation (SIA), which considers only vertical shear stresses, while more complete approximations are needed for ice shelves and ice streams. The simplest model that can be applied is the shallow-shelf/shelfy-stream approximation (MacAyeal, 1989), which includes horizontal normal and shear stresses and requires the solution of vertically integrated, two-dimensional stress balance equations. More complete models include the L1Lx class of vertically integrated models (Hindmarsh, 2004; Schoof and Hindmarsh, 2010), which resemble the SSA in many respects; the higher-order (HO) models (Pattyn, 2003), which require the solution of simplified three-dimensional stress equations; and the complete Stokes models that include all viscous stresses (Le Meur et al, 2004)

Results

Discussion

Conclusion