{"content":[{"text":"The Cryosphere, 15, 3119–3128, 2021 \n https://doi.org/10.5194/tc-15-3119-2021 \n © Author(s) 2021. This work is distributed under \n the Creative Commons Attribution 4.0 License.","bbox":{"left":0.075926,"top":0.046475,"width":0.320104,"height":0.05967399999999999}},{"text":"Indication of high basal melting at the EastGRIP drill site \n on the Northeast Greenland Ice Stream \n Ole Zeising1,2 and Angelika Humbert1,2 \n 1Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany \n 2Department of Geosciences, University of Bremen, Bremen, Germany","bbox":{"left":0.075926,"top":0.197011,"width":0.692825,"height":0.11599300000000001}},{"text":"Correspondence: Ole Zeising (ole.zeising@awi.de)","bbox":{"left":0.075926,"top":0.323671,"width":0.34207000000000004,"height":0.016156999999999977}},{"text":"Received: 29 January 2021 – Discussion started: 2 February 2021 \n Revised: 21 May 2021 – Accepted: 7 June 2021 – Published: 6 July 2021","bbox":{"left":0.075926,"top":0.35144,"width":0.477316,"height":0.029868000000000006}},{"text":"Abstract. The accelerated ice ﬂow of ice streams that reach \n far into the interior of the ice sheets is associated with lu- \n brication of the ice sheet base by basal meltwater. However, \n the amount of basal melting under the large ice streams – \n such as the Northeast Greenland Ice Stream (NEGIS) – is \n largely unknown. In situ measurements of basal melt rates \n are important from various perspectives as they indicate the \n heat budget, the hydrological regime and the relative impor- \n tance of sliding in glacier motion. The few previous esti- \n mates of basal melt rates in the NEGIS region were 0.1 m a−1 \n and more, based on radiostratigraphy methods. These ﬁnd- \n ings raised the question of the heat source, since even an \n increased geothermal heat ﬂux could not deliver the neces- \n sary amount of heat. Here, we present basal melt rates at \n the recent deep drill site EastGRIP, located in the centre of \n NEGIS. Within 2 subsequent years, we found basal melt rates \n of 0.19 ± 0.04 m a−1 that are based on analysis of repeated \n phase-sensitive radar measurements. In order to quantify the \n contribution of processes that contribute to melting, we car- \n ried out an assessment of the energy balance at the interface \n and found the subglacial water system to play a key role in \n facilitating such high melt rates.","bbox":{"left":0.075926,"top":0.408327,"width":0.39352600000000004,"height":0.32837099999999997}},{"text":"the momentum balance and initial states are based on inver- \n sion (Goelzer et al., 2018) or involve subglacial hydrological \n models (Smith-Johnsen et al., 2020a). Primarily, this is due to \n the model’s inability to accurately represent lubrication and \n thus the subsequent sliding at the ice stream base that occurs. \n The NEGIS is the only large ice stream in Greenland, \n extending from a distance of 100 km from the ice divide \n over a length of about 700 km towards the coast (Fahnestock \n et al., 1993, 2001b; Joughin et al., 2001). It drains about \n 12 % of Greenland’s ice through three major outlet glaciers \n Nioghalvfjerdsbrae, Zachariæ Isstrøm and Storstrømmen \n Glacier (Rignot and Mouginot, 2012). Loss of the ﬂoating \n tongue of Zachariæ Isstrøm has already led to ice ﬂow ac- \n celeration and increased mass loss (Mouginot et al., 2015). \n Consequently, it is expected and projected that NEGIS will \n contribute signiﬁcantly to sea-level rise in the future (Khan \n et al., 2014), highlighting the importance of understanding \n the general ice-ﬂow dynamics and its driving mechanisms. \n One hypothesis for the genesis of NEGIS is locally in- \n creased basal melting at the onset area that enables and en- \n hances basal sliding (Fahnestock et al., 2001a; Christian- \n son et al., 2014; Franke et al., 2021) and forms a subglacial \n hydrological system. The coupling with basal sliding is fa- \n cilitated via the water pressure, so that the sliding velocity \n rises with increasing water pressure (e.g. Beyer et al., 2018; \n Smith-Johnsen et al., 2020a). However, little is known about \n the amount of subglacial water below the up to ∼ 3300 m \n thick ice sheet. \n First estimates of basal melt rates by Fahnestock et al. \n (2001a) and later by Keisling et al. (2014) and MacGregor \n et al. (2016) are based on the interpretation of chronology \n in radiostratigraphy. All three studies found melt rates of","bbox":{"left":0.501851,"top":0.408774,"width":0.3935239999999999,"height":0.47695399999999993}},{"text":"1","bbox":{"left":0.075926,"top":0.780061,"width":0.008136000000000004,"height":0.016156999999999977}},{"text":"Introduction","bbox":{"left":0.100333,"top":0.780061,"width":0.088304,"height":0.016156999999999977}},{"text":"Ice sheet models are used to quantify the contribution of the \n Greenland Ice Sheet (GrIS) to future sea-level rise under dif- \n ferent climatic scenarios. In these simulations, the distinc- \n tive extent of Greenland’s largest ice stream – the Northeast \n Greenland Ice Stream (NEGIS, Fig. 1) – can only be repro- \n duced well if a higher-order approximation is considered for","bbox":{"left":0.075926,"top":0.809287,"width":0.39352000000000004,"height":0.08948}},{"text":"Published by Copernicus Publications on behalf of the European Geosciences Union.","bbox":{"left":0.075926,"top":0.920612,"width":0.5857480000000002,"height":0.016156999999999977}}],"images_bbox":[{"left":0.075926,"top":0.107558,"width":0.069445,"height":0.018551}],"images_bbox_not_text_overlap":[{"left":0.075926,"top":0.107558,"width":0.069445,"height":0.018551}]}