Modeling glaciers and ice sheets in Greenland and Antarctica with an emphasis on embedded modeling and subglacial hydrology.

摘要

Recent observations in Greenland and Antarctica highlight the importance of ice-ocean interaction and the role of subglacial water. These processes influence the mass balance of ice sheets but are currently not well-represented in models used for sea level estimations. Here, we reproduce the observations numerically to investigate their influence on ice dynamics and improve prognostic modeling.;Recent acceleration and retreat of several Greenland outlet glaciers have led to significant mass loss from the ice sheet. The mechanisms responsible for triggering the change in dynamics are poorly understood and their interactions uncertain. Here, the dynamics of Helheim Glacier are simulated with real climate input to investigate the glacier's response to realistic forcings. Results show that changes in surface mass balance, calving events or submarine melt rates at the grounding line can individually reproduce the observed behavior of the glacier.;Acceleration of ice streams is also observed in Antarctica, where large subglacial drainage networks exist. The acceleration of Byrd Glacier has been linked to a sub-glacial lake discharge event and lasted at least nine months. How does basal water influence ice sheet flow and ice stream dynamics in East Antarctica? Simulating the acceleration of Byrd Glacier with a basal water flow model incorporated in the ice sheet model shows there is an active basal water system underneath the Byrd catchment area and that sliding processes contribute to the overall velocity field.;Widespread subglacial water systems are also observed under the ablation zone of the Greenland Ice Sheet. Summer speed-up of the ice sheet due to enhanced basal sliding is linked to the seasonal increase of surface melt water production. A numerical ice sheet model coupled to a subglacial water model is used to investigate the influence of seasonal melt water on the sliding process. We find that ice acceleration declines quickly as drainage systems adapt their capacity, and that the process is strongly seasonal. This process will not influence sea level significantly.;This work shows that ice dynamics are sensitive to numerous boundary perturbations which remain poorly understood, but should be investigated further and included in prognostic models.