Diverse geomorphological regimes underlie the Northeast Greenland Ice Stream

Approximately 17% of the modern Greenland Ice Sheet is drained via the Northeast Greenland Ice Stream (NEGIS), which extends ~600 km into the interior of the ice sheet. The NEGIS is generally thought to be topographically unconstrained, as the onset of fast flowing ice is not confined to or channeled by a distinct valley.

In our study, we investigate the subglacial topography along the length of the NEGIS, from its onset to its divergence into its outlet glaciers, in order to ascertain the characteristics of the subglacial conditions beneath the ice stream. We analyse airborne radio-echo sounding surveys collected using the AWI airborne ultra-wideband radar system during 2018 and 2022, alongside selected survey lines from Operation IceBridge. We use the metrics of hypsometry, topographic roughness, and valley morphometry, to elucidate three geomorphologically distinct regions over which the NEGIS flows.

The region at the onset of the NEGIS exhibits very low small-scale roughness, low relief, and a lack of valleys, indicating a likely sedimentary basin. Downstream of this, the subglacial environment changes, increasing in small-scale roughness following a topographic step. Here, two major overdeepened troughs control the ice flow. As the ice stream starts to diverge, the subglacial topography evolves again into smaller, more alpine-like valleys, akin to the eastern subglacial highlands which previously hosted Pliocene ice caps. The differences in these geomorphological regimes underlying the NEGIS are likely to be attributable to changing geological provinces, which in this area are poorly constrained. In addition, whilst these regimes appear to have little effect on the location of the onset of the ice stream and its shear margins, the subglacial topography downstream has a distinct impact on ice stream geometry by channeling or reinforcing ice flow direction. In contrast to the fact that the NEGIS is generally thought of as topographically unconstrained, this study indicates that topography is in fact influencing the ice stream. We will also present first results on quantifying this effect, through the derivation of 3-dimensional mass flux balance and its relation to topography.

This study provides new insights into the subglacial environment along the NEGIS, which, despite the acquisition of large amounts of bed elevation data in recent years, has yet to be fully characterised. Furthermore, it emphasises the highly variable conditions which can affect and facilitate fast ice flow, indicating that no one single process controls the ice stream.