Basal melt at NorthGRIP modeled from borehole, ice-core and radio-echo sounder observations

Abstract

ABSTRACT. From temperature measurements down through the 3001m deep borehole at the North Greenland Icecore Project (NorthGRIP) drill site, it is now clear that the ice at the base, 3080 m below the surface, is at the pressure-melting point. This is supported by the measurements on the ice core where the annual-layer thicknesses show there is bottom melting at the site and upstream from the borehole. Surface velocity measurements, internal radio-echo layers, borehole and ice-core data are used to constrain a timedependent flow model simulating flow along the north-northwest-trending ice-ridge flowline, leading to the NorthGRIP site. Also time-dependent melt rates along the flowline are calculated with a heat-flow model. The results show the geothermal heat flow varies from 50 to 200 mW m^2 along the 100 km section of the modeled flowline. The melt rate at the NorthGRIP site is 0.75 cm a^1, but the deep ice in the NorthGRIP core originated 50 km upstream and has experienced melt rates as high as 1.1cm a^1.

Response of the large-scale subglacial drainage system of Northeast Greenland to surface elevation changes

“…This is in spite of an active ice-stream drainage system (Joughin et al, 2010) and few topographic constraints on most of the ice streams (Bamber et al, 2013a). This is even more surprising since it is well known that liquid water is widespread under large parts of the Greenland Ice Sheet; this has been testified by observations of subglacial water at ice core drill sites (Dahl-Jensen et al, 2003) and from radioecho sounding surveys Oswald and Gogineni, 2008), and it is supported by results from largescale ice-sheet modelling (Greve and Hutter, 1995;Seroussi et al, 2013).…”

“…Anandakrishnan and Alley, 1997;Fahnestock et al, 2001), and recent modelling efforts have begun to address this (e.g. Bougamont et al, 2011;de Fleurian et al, 2014). The coupling between ice flow and subglacial processes is, however, complicated and not easily incorporated into ice-sheet models.…”

Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

“…Wright and Siegert, 2012), there is almost no evidence for subglacial lakes existing beneath the GrIS (although see Ekholm et al, 1998). This seems incongruous given observations detailing the widespread presence of subglacial meltwater at its bed (Dahl-Jensen et al, 2003;Gogineni, 2008, 2012). Is this because there are very few subglacial lakes?…”

“…This includes repeated palaeo-subglacial lake formation in the rugged interior of Marguerite Bay in isolated basins connected by meltwater channels (e.g. Anderson and Oakes -Fretwell, 2008), and the temporary formation of a shallow subglacial lake in Palmer Deep 15 thousand years ago (see Domack et al, 2006). The ice-surface flattening feedback resulting from subglacial lake formation (e.g.…”

High-resolution record of Northern Hemisphere climate extending into the last interglacial period

“…1), was selected on the basis of three criteria that, when satisfied together, should produce dateable ice older than that found in central Greenland: a position on a ridge to reduce deformation by ice flow, flat bedrock, and a lower precipitation rate. The present accumulation rate is 0.19 m ice equivalent yr 21 , the annual mean temperature is 231.5 8C, and the ice near the base originates 50 km upstream of the ice ridge in the direction of Summit 12 . The NGRIP drilling started in 1996, and bedrock was reached in July 2003.…”