Indication of high basal melting at EastGRIP drill site on the Northeast Greenland Ice Stream

The origin of Greenland’s largest ice stream – the Northeast Greenland Ice Stream (NEGIS) – is located far inland of the Greenland Ice Sheet. High surface flow velocities in the center of NEGIS are attributed to the lubrication of the ice sheet base facilitated by basal melt water. In order to derive basal melt rates at the EastGRIP drill site (~2668 m thick ice), we performed in-situ measurements with an autonomous phase-sensitive radar (ApRES; Brennan et al., 2014; Nicholls et al., 2015) in two consecutive years. The precise processing method (Stewart et al., 2019 and Vankova et al., 2020) detects englacial and basal vertical displacements, but it is limited due to noisy data in the lower half of the ice column. Thus, we made assumptions for the vertical strain in the lower half and adapted simulation results (Rückamp et al., 2020). We found melt rates ranging from 0.16 to 0.22 m/a, which is extremely large for inland ice. However, our results are only slightly above melt rates from previous studies (Fahnestock et al., 2001 and MacGregor et al., 2016) which found melt rates of 0.10 m/a and more through airborne radar measurements (evaluated using radiostratigraphy methods) in the vicinity of EastGRIP. Melt rates of >0.16 m/a require a heat flux into the ice of >1.55 W/m² which is not exclusively the geothermal heat flux, as also the subglacial hydrological system may supply a significant heat flux into the ice.