Abstract
Abstract. The Northeast Greenland Ice Stream (NEGIS) currently drains more than 10 % of the Greenland Ice Sheet area and has recently undergone significant dynamic changes. It is therefore critical to accurately represent this feature when assessing the future contribution of Greenland to sea level rise. At present, NEGIS is reproduced in ice sheet models by inferring basal conditions using observed surface velocities. This approach helps estimate conditions at the base of the ice sheet but cannot be used to estimate the evolution of basal drag in time, so it is not a good representation of the evolution of the ice sheet in future climate warming scenarios. NEGIS is suggested to be initiated by a geothermal heat flux anomaly close to the ice divide, left behind by the movement of Greenland over the Icelandic plume. However, the heat flux underneath the ice sheet is largely unknown, except for a few direct measurements from deep ice core drill sites. Using the Ice Sheet System Model (ISSM), with ice dynamics coupled to a subglacial hydrology model, we investigate the possibility of initiating NEGIS by inserting heat flux anomalies with various locations and intensities. In our model experiment, a minimum heat flux value of 970 mW m−2 located close to the East Greenland Ice-core Project (EGRIP) is required locally to reproduce the observed NEGIS velocities, giving basal melt rates consistent with previous estimates. The value cannot be attributed to geothermal heat flux alone and we suggest hydrothermal circulation as a potential explanation for the high local heat flux. By including high heat flux and the effect of water on sliding, we successfully reproduce the main characteristics of NEGIS in an ice sheet model without using data assimilation.
Highlights
The Greenland Ice Sheet (GrIS) displays large spatial variations in surface velocity, with a few fast-flowing outlets draining most of the interior (Rignot and Mouginot, 2012)
This indicates that the downstream area of the Northeast Greenland Ice Stream (NEGIS) catchment is largely controlled by topography, while the upstream area is controlled by its basal conditions, which is in agreement with Keisling et al (2014)
The downstream velocities appear to be driven by topography, and the spatial pattern is well captured by the subglacial hydrology model
Summary
The Greenland Ice Sheet (GrIS) displays large spatial variations in surface velocity, with a few fast-flowing outlets draining most of the interior (Rignot and Mouginot, 2012). Recent developments in ice sheet models such as efficient parallel computation (Khroulev and PISM-Authors, 2015), better representation of flow equations (Larour et al, 2012), detailed basal topography (Morlighem et al, 2014) and the inclusion of subglacial hydrology have contributed to greatly improving the representation of this spatially varying flow (Aschwanden et al, 2016) In addition to these advances, inversion for basal friction using surface velocities has proved to be a powerful tool (Morlighem et al, 2013), and models are able to capture most of the complex flow pattern of the ice sheet. We cannot fully rely on inversions for future projections, as basal conditions may evolve as a result of a changing climate and in turn influence ice dynamics
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