Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)

Abstract

Abstract. The Northeast Greenland Ice Stream (NEGIS) is the sole interior Greenlandic ice stream. Fast flow initiates near the summit dome, and the ice stream terminates approximately 1000 km downstream in three large outlet glaciers that calve into the Greenland Sea. To better understand this important system, in the summer of 2012 we drilled a 67 m firn core and conducted ground-based radio-echo sounding (RES) and active-source seismic surveys at a site approximately 150 km downstream from the onset of streaming flow (NEGIS firn core, 75 • 37.61 N, 35 • 56.49 W). The site is representative of the upper part of the ice stream, while also being in a crevasse-free area for safe surface operations.Annual cycles were observed for insoluble dust, sodium and ammonium concentrations and for electrolytic conductivity, allowing a seasonally resolved chronology covering the past 400 yr. Annual layer thicknesses averaged 0.11 m ice equivalent (i.e.) for the period 1607-2011, although accumulation varied between 0.08 and 0.14 m i.e., likely due to flowrelated changes in surface topography. Tracing of RES layers from the NGRIP (North Greenland Ice Core Project) ice core site shows that the ice at NEGIS preserves a climatic record of at least the past 51 kyr. We demonstrate that deep ice core drilling in this location can provide a reliable Holocene and late-glacial climate record, as well as helping to constrain the past dynamics and ice-lithosphere interactions of the Greenland Ice Sheet.

Missing Evidence of Widespread Subglacial Lakes at Recovery Glacier, Antarctica

“…We found that the area down to 0 ∘ E/W shows a layered structure down to the lower third or quarter of the ice thickness. In this respect, Recovery Glacier is similar to the North East Greenland Ice Stream as shown in Vallelonga et al (2014). Layers within the ice are supposed to lower, once ice flows across a subglacial lake, as shown in Gudlaugsson et al (2016) and Leysinger Vieli et al (2007).…”

Physical Conditions of Fast Glacier Flow: 2. Variable Extent of Anisotropic Ice and Soft Basal Sediment From Seismic Reflection Data Acquired on Store Glacier, West Greenland

“…However, more recent evidence has revealed the presence of sediments beneath several areas of the GrIS (Walter et al, 2014). Christianson et al (2014) and Vallelonga et al (2014) recently identified dilatant till beneath the onset of the Northeast Greenland Ice Stream, demonstrating that the single largest ice stream in Greenland has soft basal conditions that are very similar to those observed more frequently beneath Antarctic ice streams. In west Greenland glacial sediments are widespread on the continental shelf (Dowdeswell et al, 2014;Hogan et al, 2012) and are also likely to be present subglacially.…”

Radiostratigraphy and age structure of the Greenland Ice Sheet

“…By virtue of its accessibility and smaller size relative to the East and West Antarctic ice sheets, the Greenland Ice Sheet (GrIS) has been more comprehensively surveyed by ice-penetrating radar than those Antarctic ice masses. Multiple institutions have regularly collected and analyzed radar data from the GrIS since the 1960s [Gudmandsen, 1975;Jacobel and Hodge, 1995;Dahl-Jensen et al, 1997, 2003Fahnestock et al, 2001aFahnestock et al, , 2001bNixdorf and Göktas, 2001;Baldwin et al, 2003;Legarsky and Gao, 2006;Buchardt, 2009;Catania and Neumann, 2010;Bamber et al, 2013;Christianson et al, 2014;Vallelonga et al, 2014;Keisling et al, 2014]. Despite these advantages, previous efforts to directly map and interpret the radiostratigraphy of the GrIS are limited with respect to the data now available.…”