Representing grounding-line dynamics in Antarctic ice-sheet models

• Main Author: Docquier, David
• Other Authors: Pattyn, Frank, Tison, Jean-Louis, Hindmarsh, Richard, Luparia, Andrea, Hanson, Kael
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: Universite Libre de Bruxelles 2013
• Subjects: Sciences de la terre et du cosmos; Sciences exactes et naturelles; Glaciology > Antarctica; Glaciers > Antarctica; Glaciologie > Antarctique; Glaciers > Antarctique; Transient/Transitoire; Intercomparison/Intercomparaison; Glaciology/Glaciologie; Modeling/Modélisation; Antarctic; West Antarctica; Greenland; Thwaites Glacier; Antarc*; Antarctica; Antarctique*; glacier; Ice Sheet; Ice Shelves
• Online Access: http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209400; https://dipot.ulb.ac.be/dspace/bitstream/2013/209400/4/c5d80d42-5e4c-48e6-9214-94a54c73efd0.txt; https://dipot.ulb.ac.be/dspace/bitstream/2013/209400/1/d543c168-8dd6-49af-9f13-fabc12937e89.txt

Since the mid-20th century, global average temperatures have dramatically risen mostly due to the increasing amount of greenhouse gas emissions in the atmosphere. The effects of this recent global warming are already evident and could be exacerbated in the near future if no real action is taken. Recent ice loss in West Antarctica, monitored by satellite measurements and other techniques, gives cause for concern in such a warming world. A major part of this loss has been driven by warm water masses penetrating underneath the ice shelves in this region. This has led to a flow acceleration of the inland outlet glaciers and a greater discharge of ice to the ocean. The actual resulting contribution of West Antarctica to sea-level rise is estimated to be around 0.2 mm per year between 1992 and 2011, i.e. about one third of the ice-sheet contribution (Antarctica and Greenland), and is expected to increase in the near future. In this thesis, we first clearly demonstrate that modeling grounding-line (the boundary between grounded and floating ice) migration depends on both the numerical approach and the physical approximation of the ice-sheet model used. Ice-sheet models prescribing the ice flux at the grounding line and using appropriate physical level and numerical approach converge to the same steady-state grounding-line position irrespective of the grid size used. However, the transient behavior of those models is less accurate than other models and leads to an overestimated grounding-line discharge. Therefore, they need to be used with particular attention on short time scales. Furthermore, the non-inclusion of vertical shear stress in those models increases the effective viscosity and gives steady-state grounding-line positions further downstream when compared to full-Stokes models. The second major finding of this thesis is the high control of geometry (glacier width and bedrock topography) on Thwaites Glacier, one of the fastest-flowing outlet glaciers in West Antarctica. A flowline finite-difference ...