Abstract
AbstractThe Northeast Greenland Ice Stream (NEGIS) is an important dynamic component for the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The geometric boundary conditions and in particular the nature of the subglacial bed of the NEGIS are essential to understand its ice flow dynamics. We present a record of more than 8000 km of radar survey lines of multi-channel, ultra-wideband radio echo sounding data covering an area of 24 000 km2, centered on the drill site for the East Greenland Ice-core Project (EGRIP), in the upper part of the NEGIS catchment. Our data yield a new detailed model of ice-thickness distribution and basal topography in the region. The enhanced resolution of our bed topography model shows features which we interpret to be caused by erosional activity, potentially over several glacial–interglacial cycles. Off-nadir reflections from the ice–bed interface in the center of the ice stream indicate a streamlined bed with elongated subglacial landforms. Our new bed topography model will help to improve the basal boundary conditions of NEGIS prescribed for ice flow models and thus foster an improved understanding of the ice-dynamic setting.
Highlights
The Greenland ice sheet (GrIS) is the second largest land ice mass on Earth and one of the largest contributors to global sea-level rise (Rignot and others, 2011; Gardner and others, 2013; Khan and others, 2014)
In contrast to flow of outlet glaciers, which often drain ice through bedrock channels or valleys, the high flow velocities of ice streams extend further into the interior of the ice sheet. In some cases their location is not controlled by the bed topography and their boundaries are characterized by narrow shear zones (Truffer and Echelmeyer, 2003)
We observe a gradual decrease of ice thickness from the onset of the Northeast Greenland Ice Stream (NEGIS) close to the ice divide toward northeast (Fig. 2)
Summary
The Greenland ice sheet (GrIS) is the second largest land ice mass on Earth and one of the largest contributors to global sea-level rise (Rignot and others, 2011; Gardner and others, 2013; Khan and others, 2014). In contrast to flow of outlet glaciers, which often drain ice through bedrock channels or valleys, the high flow velocities of ice streams extend further into the interior of the ice sheet In some cases their location is not controlled by the bed topography and their boundaries are characterized by narrow shear zones (Truffer and Echelmeyer, 2003). Modeling studies reveal that an interpretation of isochrones of ice streams is challenging without a detailed knowledge of the bed topography (Leysinger Vieli and others, 2007) These existing limitations motivated the acquisition of new high-resolution ice thickness data to improve available bed topographies around NEGIS, in order to help interpret basal structures and thereby determine ice–substrate interaction within NEGIS and in its vicinity (Keisling and others, 2014; Vallelonga and others, 2014). For ice thickness ranging from 2000 to 3000 m our error, σr, ranges from 13 to 17 m
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