Exceptionally High Geothermal Heat Flux Needed to Sustain the Northeast Greenland Ice Stream

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 hotspots with various locations and intensities. We find that a minimum geothermal heat flux value of 970 mW/m2 located close to EastGRIP is required locally to reproduce the observed NEGIS velocities, consistent with previous estimates. By including high geothermal 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.

Complex Basal Conditions and Their Influence on Ice Flow at the Onset of the Northeast Greenland Ice Stream

“…While this method allows for using basal melt rates as input to quantify transported water volumes, we chose to simply count the number of upstream cells as a measure for potential water pathways. Basal melt rates are poorly constrained for this area, in particular, because the spatial variations in geothermal heat flux are subject to considerable uncertainties (Dow et al, 2018;Jordan et al, 2018;Smith-Johnsen et al, 2019). Nevertheless, we can use the water pathways to estimate the distribution of basal water, particularly for areas where we can infer a thawed base and the generation of meltwater by other methods.…”

“…The increasing ice flow velocity of the onset of the NEGIS in its current geometry would lead to the development a surface trough, which is not consistent with observations. In present ice-sheet models, the NEGIS is reproduced through estimating basal-shear stress from inverse methods informed by surface velocities (Larour et al, 2014;Smith-Johnsen et al, 2019). Estimates of basal resistance are not accurate enough to sufficiently reproduce geometry and surface velocities of ice streams by ice-flow models, as our understanding of processes and conditions is still very limited.…”