Physical properties in the shear margin of the Northeast Greenland Ice Stream

The North-East Greenland Ice Stream (NEGIS) is a major contributor to ice loss experienced by the Greenland Ice Sheet. Our current understanding of the mechanics of this highly dynamic feature is limited compared to the surrounding slowly deforming ice sheet, but significant for enhancing ice flow models and attaining more accurate sea-level rise projections. Especially the shear margins of an ice stream are the regions where, in addition to the ice stream bed, a large part of the deformation occurs. To study the deformation processes that are active in the shear margins on the basis of sub-surface ice samples will contribute to our understanding of how fast flow in ice streams is enabled. The East Greenland Ice-core Project drilled the first deep ice core in such a fast-flowing regime at the onset of NEGIS, reaching bedrock at approximately 2670 m. The EGRIP ice core data provide a comprehensive record of the crystal-preferred orientation (CPO) throughout the core. Additionally, short cores of approximately 100 m length (S5, ExS5-1, ExS5-2) were drilled in 2019 and 2022 in the shear margin south-east of the main core drilling site.

We present results from CPO analysis of these three cores, supported by density data and temperature profiles from the boreholes. Comparing our results with those from the main core reveals the effect of shear localisation in the margin on the physical properties of the ice, and highlights the significant lateral variation between the three locations set in the shear margin within distances of 2-3 km.