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

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.

[1]  Antony J. Payne,et al.  An improved Antarctic dataset for high resolution numerical ice sheet models (ALBMAP v1) , 2010 .

[2]  P. Kanagaratnam,et al.  Accelerated Sea-Level Rise from West Antarctica , 2004, Science.

[3]  Robin E. Bell,et al.  Progressive unpinning of Thwaites Glacier from newly identified offshore ridge: Constraints from aerogravity , 2011 .

[4]  D. J. Wingham,et al.  Conditions for a steady ice sheet–ice shelf junction , 2008 .

[5]  Douglas R. Macayeal,et al.  Large‐scale ice flow over a viscous basal sediment: Theory and application to ice stream B, Antarctica , 1989 .

[6]  Anton Eisenhauer,et al.  Rapid sea-level rise and reef back-stepping at the close of the last interglacial highstand , 2009, Nature.

[7]  Stefano Schiavon,et al.  Climate Change 2007: The Physical Science Basis. , 2007 .

[8]  C. Schoof Ice sheet grounding line dynamics: Steady states, stability, and hysteresis , 2007 .

[9]  T. Zwinger,et al.  The ISMIP-HOM benchmark experiments performed using the Finite-Element code Elmer , 2008 .

[10]  Kelly M. Brunt,et al.  Mapping the grounding zone of the Amery Ice Shelf, East Antarctica using InSAR, MODIS and ICESat , 2009, Antarctic Science.

[11]  Gaël Durand,et al.  Full Stokes modeling of marine ice sheets: influence of the grid size , 2009, Annals of Glaciology.

[12]  D. Goldberg Numerical and theoretical treatment of grounding line movement and ice shelf buttressing in marine ice sheets , 2009 .

[13]  T. Zwinger,et al.  Marine ice sheet dynamics: Hysteresis and neutral equilibrium , 2009 .

[14]  Franco Brezzi,et al.  Virtual bubbles and Galerkin-least-squares type methods (Ga.L.S.) , 1993 .

[15]  David Pollard,et al.  Modelling West Antarctic ice sheet growth and collapse through the past five million years , 2009, Nature.

[16]  F. Pattyn A new three-dimensional higher-order thermomechanical ice sheet model: Basic sensitivity, ice stream development, and ice flow across subglacial lakes , 2003 .

[17]  Antony J. Payne,et al.  Assessing the ability of numerical ice sheet models to simulate grounding line migration , 2005 .

[18]  Eric Rignot,et al.  Recent Antarctic ice mass loss from radar interferometry and regional climate modelling , 2008 .

[19]  L. Morland Thermomechanical balances of ice sheet flows , 1984 .

[20]  J. Ruokolainen,et al.  Glacier flow modelling: a comparison of the Shallow Ice Approximation and the full-Stokes solution , 2004 .

[21]  R. Hindmarsh,et al.  Coupling of ice‐shelf melting and buttressing is a key process in ice‐sheets dynamics , 2010 .

[22]  A. Abe‐Ouchi,et al.  Effects of first-order stress gradients in an ice sheet evaluated by a three-dimensional thermomechanical coupled model , 2003, Annals of Glaciology.

[23]  Eric Rignot,et al.  Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise , 2011 .

[24]  Rupert Gladstone,et al.  Grounding line migration in an adaptive mesh ice sheet model , 2010 .

[25]  J. Weertman,et al.  Stability of the Junction of an Ice Sheet and an Ice Shelf , 1974, Journal of Glaciology.

[26]  Corinne Le Quéré,et al.  Climate Change 2013: The Physical Science Basis , 2013 .

[27]  Richard F. Katz,et al.  Stability of ice-sheet grounding lines , 2010, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[28]  K. Hutter Theoretical Glaciology: Material Science of Ice and the Mechanics of Glaciers and Ice Sheets , 1983 .

[29]  David G. Vaughan,et al.  BEDMAP: a new ice thickness and subglacial topographic model of Antarctica , 2001 .

[30]  H. Blatter Velocity and stress fields in grounded glaciers: a simple algorithm for including deviatoric stress gradients , 1995 .