Paleo-ice sheet dynamics on the northwest Greenland continental shelf

Abstract

Increasing temperatures in the ocean and atmosphere result in the decline of the modern ice sheets in both hemispheres, causing global sea-level rise. Direct records on these ice-sheet dynamics are sparse as most observations were first initiated in the last century. Although ice-core analyses and satellite data from the polar regions increase our knowledge of modern ice flow and ice-sheet dynamics, the reconstruction and investigation of these dynamics during past glacial cycles is required to predict future scenarios for ice-sheet dynamics. Erosional and depositional glacial landforms that developed under the paleo-ice sheet and at its margin are used to reconstruct past ice-sheet extends and dynamics. These glacial landforms indicate the flow direction of past ice-streams that drained the former ice-sheet. They indicate the maximum ice-sheet extent as well as ice-sheet stabilizations or re-advances during ice-sheet retreat. This thesis focuses on the analysis of the Greenland ice-sheet dynamics since the last glacial maximum (LGM, 26.5-19 ka BP). The analysis is based on the identification and investigation of glacial landforms on the seabed of Melville Bay, on the northwest Greenland continental shelf. This region in northeast Baffin Bay hosts three large crossshelf troughs. They were formed by ice-streams advancing to the shelf edge during past glacial cycles. They are among the widest and deepest cross-shelf troughs of the continental shelf of Greenland. High-resolution bathymetry, which is necessary for identification of glacial landforms at the seabed in and adjacent to these troughs is limited in this remote region due to harsh sea-ice conditions. Thus, detailed reconstructions of LGM ice-sheet dynamics and their timing in Melville Bay are incomplete. In this thesis, I present new high-resolution bathymetry data from the northeast Baffin Bay that I investigated for submarine glacial landforms. The data have been recorded in 2010 with RV Polarstern and in 2015 with RV Maria S. Merian. This study aims to reconstruct the Greenland Ice Sheet dynamics since the LGM by inferring glacial processes and their relative chronology from the distribution and configuration of glacial landforms. The presented results show that the ice streams extended to the shelf edge and subsequent retreat of the ice streams varied between the glacial cross-shelf troughs in Melville Bay. Local ice domes on the shallow banks between the cross-shelf troughs are inferred from the distribution of glacial landforms. A newly discovered trough network on the inner continental shelf extends from the large cross-shelf troughs towards the fjords under the modern ice sheet. It was likely formed by a former ice sheet. Steep ridges in the north of Melville Bay are likely related to Proterozoic volcanic dyke swarms that to some extent confined former meltwater and ice-stream pathways. The results of this thesis improve our understanding of the northwest Greenland ice-sheet dynamics during past glacials and indicate that at least some glacial processes are related to underlying bedrock morphology.