Abstract
Abstract. The accelerated ice flow of ice streams that reach far into the interior of the ice sheets is associated with lubrication of the ice sheet base by basal meltwater. However, the amount of basal melting under the large ice streams – such as the Northeast Greenland Ice Stream (NEGIS) – is largely unknown. In situ measurements of basal melt rates are important from various perspectives as they indicate the heat budget, the hydrological regime and the relative importance of sliding in glacier motion. The few previous estimates of basal melt rates in the NEGIS region were 0.1 m a−1 and more, based on radiostratigraphy methods. These findings raised the question of the heat source, since even an increased geothermal heat flux could not deliver the necessary amount of heat. Here, we present basal melt rates at the recent deep drill site EastGRIP, located in the centre of NEGIS. Within 2 subsequent years, we found basal melt rates of 0.19±0.04 m a−1 that are based on analysis of repeated phase-sensitive radar measurements. In order to quantify the contribution of processes that contribute to melting, we carried out an assessment of the energy balance at the interface and found the subglacial water system to play a key role in facilitating such high melt rates.
Highlights
Ice sheet models are used to quantify the contribution of the Greenland Ice Sheet (GrIS) to future sea-level rise under different climatic scenarios
The distinctive extent of Greenland’s largest ice stream – the Northeast Greenland Ice Stream (NEGIS, Fig. 1) – can only be reproduced well if a higher-order approximation is considered for the momentum balance and initial states are based on inversion (Goelzer et al, 2018) or involve subglacial hydrological models (Smith-Johnsen et al, 2020a)
The dynamic thinning of the ice derived from the two scenarios ranges from −0.181 m a−1 ( Hεconst) to −0.194 m a−1 ( Hεsim)
Summary
Ice sheet models are used to quantify the contribution of the Greenland Ice Sheet (GrIS) to future sea-level rise under different climatic scenarios In these simulations, the distinctive extent of Greenland’s largest ice stream – the Northeast Greenland Ice Stream (NEGIS, Fig. 1) – can only be reproduced well if a higher-order approximation is considered for the momentum balance and initial states are based on inversion (Goelzer et al, 2018) or involve subglacial hydrological models (Smith-Johnsen et al, 2020a). The NEGIS is the only large ice stream in Greenland, extending from a distance of 100 km from the ice divide over a length of about 700 km towards the coast (Fahnestock et al, 1993, 2001b; Joughin et al, 2001) It drains about 12 % of Greenland’s ice through three major outlet glaciers Nioghalvfjerdsbrae, Zachariæ Isstrøm and Storstrømmen Glacier (Rignot and Mouginot, 2012). It is expected and projected that NEGIS will contribute significantly to sea-level rise in the future (Khan et al, 2014), highlighting the importance of understanding the general ice-flow dynamics and its driving mechanisms
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