Sedimentary and geomorphological signature of the Northeast Greenland Ice Stream (NEGIS) on the continental shelf

Abstract

The Northeast Greenland Ice Stream (NEGIS) drains 16% of the Greenland Ice Sheet (GrIS), hence it is important to understand how the NEGIS might respond to the ongoing and future atmospheric and oceanic warming. Exploring longer term records of NEGIS dynamics during the Last Glacial Maximum (LGM) and the Holocene is one way to improve confidence in NEGIS modelling. This study uses glacial sedimentology and geomorphology to determine the characteristics and depositional origin of sediment on the northeast Greenland continental shelf, providing an insight into past NEGIS dynamics. Five gravity cores, together with sub-bottom acoustic profiles, were retrieved from the Norske and Westwind cross-shelf troughs. These have revealed the presence of massive and stratified diamictons, and laminated, stratified, and massive muds. Drumlins, mega-scale glacial lineations (MSGLs), sediment wedges and iceberg ploughmarks have also been identified.

Subglacial deformation, and possibly lodgement, produced till, drumlins, and MSGLs during the LGM advance of the NEGIS. During retreat, deposition took place at the grounding line via debris flow processes, which contributed to the formation of asymmetrical sediment wedges. Beyond the grounding line, sediment was deposited and reworked by iceberg rafting, suspension settling from meltwater plumes, mass flow activity, and iceberg keel scouring.

Sediment wedges at the shelf edge in Westwind Trough provide confirmation that the NEGIS reached the outer shelf at the LGM. Ice withdrawal from the shelf edge in Westwind Trough took place in a step-like manner and was driven by iceberg calving. Iceberg calving also drove ice recession through mid Norske Trough, and this recession was punctuated by a grounding line readvance that could have been related to Younger Dryas cooling. The NEGIS likely moved into inner Norske Trough during the early Holocene, with retreat partially generated by melting at the ice margin at this time. Different grounding line regimes (ice shelf vs grounded tidewater) may have been present in Norske and Westwind troughs during retreat.