Impact of glacio-lacustrine interactions on ice-sheet dynamics

Abstract

Geological records show that large proglacial lakes existed along the land-terminating margins of the Quaternary ice sheets. The major lakes formed in basins that were left deeply depressed due to delayed glacial isostatic adjustment (GIA) when the ice sheets retreated. As the environment around the retreating ice margin is quite dynamic, the lake basins constantly change. Where an ice sheet and proglacial lake are in contact, the dynamics are similar to a marine terminating ice-sheet margin. Such lacustrine boundary conditions cause changes in the ice-sheet’s geometry, stress balance and frontal ablation and therefore affect its entire mass balance. Despite this, dynamically evolving proglacial lakes have rarely been considered in detail in ice-sheet modelling endeavors.

In this Ph.D. project, the impact of proglacial lakes on the ice-sheet dynamics are investigated using numerical methods. For this reason, I implemented a new proglacial lake boundary model into the Parallel Ice Sheet Model (PISM). This model computes the lake basins each timestep according to the dynamic geometry of the ice-sheet and topography. The lake–ice interface is implemented as a generalization of the marine boundary of PISM.

In the first study, the underlying algorithm, LakeCC, is tested to determine if it is capable of reconstructing known lakes. Therefore, it is applied to paleo-topographic reconstructions of North America. In a second study, the impact of the PISM-LakeCC model on the ice-sheet dynamics is tested by running several simplified experiments of the glacial retreat of the North American ice sheets after the Last Glacial Maximum (LGM). Compared to control runs, the lake experiments exhibit an accelerated glacial retreat. Furthermore, for the Laurentide ice sheet (LIS), the presence of lakes triggers a process similar to marine ice sheet instability (MISI), which causes the final collapse of the ice saddle over Hudson Bay.