Influence of damage and basal friction on the grounding line dynamics

• Main Author: Brondex, Julien
• Other Authors: Institut des Géosciences de l’Environnement (IGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut de Recherche pour le Développement (IRD)-Université Grenoble Alpes 2016-2019 (UGA 2016-2019 ), Université Grenoble Alpes, Olivier Gagliardini, Fabien Gillet-Chaulet
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2017
• Subjects: Modelling; Basal friction; Damage; Grounding line; Finite element method; Ligne d'échouage; Méthode des éléments finis; Modélisation; Frottement basal; Endommagement; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Antarc*; antartic*; Ice Sheet; Ice Shelves
• Online Access: https://tel.archives-ouvertes.fr/tel-01730867; https://tel.archives-ouvertes.fr/tel-01730867/document; https://tel.archives-ouvertes.fr/tel-01730867/file/BRONDEX_2017_archivage.pdf

The Antartic ice sheet represents the world's largest potential contributor to sea level rise. Over 80 % of Antarctica's grounded ice drains through its fringing ice shelves which surround close to 45 % of the continent's shore. Because of Archimède' principle, the contribution of the ice to sea level is accounted for as soon as it flows through the grounding line, which defines the limit beyond which ice grounded on the bedrock starts floating on the ocean. Therefore, realistic modelling of grounding line dynamics is crucial to produce trustworthy projections of future sea level rise. This dynamics is affected by a number of physical processes, some of which are not properly represented in current ice flow models. This PhD thesis focuses on two of these processes: damage of ice on the one hand and basal friction related to basal hydrology on the other hand.Damage accounts for the degradation of ice mechanical properties due to the presence of fractures and crevasses, commonly observed at the surface of glaciers. Damage affects ice flow by lowering ice viscosity. The evolution of damage is governed by a pure advection equation, the numerical resolution of which requires stabilisation methods. We show that, for numerical resolutions associated to acceptable calculation times, grounding line dynamics is sensitive to the choice of this method, which seriously complicates the modelling of damage processes.Ice flow models account for basal friction through the use of friction laws, i.e. the mathematical relationship between basal drag and sliding velocities. Several formulations of these laws have been proposed over the last decades based on theoretical arguments. Some of these formulations explicitly include the effect of basal water which is present in the subglacial drainage system and the pressure of which eases basal motion. Unfortunately, the temporal and spatial scales at stake in glaciology make it impossible to validate these different formulations in situ and large-scale ice flow models usually make use of ...