Atmospheric variability in West Antarctica : impact on the ocean circulation and on theice-sheet surface mass balance

• Main Author: Donat-Magnin, Marion
• Other Authors: Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes 2016-2019 (UGA 2016-2019 ), Université Grenoble Alpes, Hubert Gallée, Nicolas Jourdain
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2019
• Subjects: Climate variability; Southern Ocean; Antarctic surface mass balance; Climate projections; Regional modelisation; Amundsen; Modélisation atmosphérique régionale; Océan Austral; Bilan de masse de surface; Projections climatiques; Variabilité interannuelle et décennale; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Antarctic; Austral; West Antarctica; Antarc*; Antarctica; Antarctique*; Ice Sheet; Ice Shelf; Ice Shelves
• Online Access: https://theses.hal.science/tel-02475556; https://theses.hal.science/tel-02475556/document; https://theses.hal.science/tel-02475556/file/DONAT-MAGNIN_2019_diffusion.pdf

West Antarctica, and particularly the Amundsen sector, has shown since the 1990s a large increase of mass loss related to coastal glacier acceleration in response to an increase of oceanic melt underneath ice shelves. Ice shelves play a buttressing role for ice-stream and increased oceanic melt therefore lead to ice shelves thinning and glacier acceleration, which contributes to sea level rise. West Antarctica is of particular concern because its configuration is prone to marine ice-sheet instability. It has been suggested that ice shelves weaken under large surface melt in a warmer climate (hydrofracturing), possibly leading to another kind of instability. Instabilities could be slowed down or compensated by future Surface Mass Balance (SMB) that consists mainly of snowfall, sporadic rainfall, and is slightly reduced by sublimation and runoff. The main objective of this PhD work is to model the atmospheric and oceanic processes that will most likely affect the future West Antarctic contribution to sea level rise.First, oceanic projections have been developed using the NEMO ocean model. The ocean circulation induced by ice-shelf basal melting affects the ocean response to future changes in surface winds. Therefore, models that do not represent ice-shelf cavities produce wrong warming patterns around Antarctica. A positive feedback between oceanic melting and grounding-line retreat has been identified and can increase melt rates by a factor of 2.5. These results are strong incentive to couple ocean and ice sheet models, although the projections proposed here are relatively idealized.To run SMB and surface melting projections, an atmospheric model with a fine representation of polar processes, including those related to the snowpack, is needed. MAR is found to be an appropriate tool to simulate the present-day surface climate in the Amundsen region. We find that none of the large climate modes of variability (ASL, SAM, ENSO) explains more than 50% of surface melt and SMB summer variance at the interannual ...