A synthesis of the basal thermal state of the Greenland Ice Sheet

MacGregor, Joseph A.; Fahnestock, M. A.; Catania, G. A.; Aschwanden, Andy; Clow, Gary D.; Colgan, William; Gogineni, S.; Morlighem, Mathieu; Nowicki, Sophie; Paden, John; Price, Stephen; Seroussi, H. L.

doi:10.1002/2015jf003803

Cited by 144 publications

(253 citation statements)

References 104 publications

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“…5.1). In this analysis we compare the RES-derived data with the Greenland bed digital elevation model (DEM) (Bamber et al, 2013a) and the predicted basal thermal state (MacGregor et al, 2016). Secondly, by comparing the theoretical predictions of the self-affine radar scattering model with the observed relationship between the Hurst exponent and waveform abruptness, we quantitatively assess topographic control upon radar scattering (Sect.…”

Section: Resultsmentioning

confidence: 99%

“…6 flight-track maps for the RES-derived roughness and scattering data are compared with the Greenland bed DEM (Bamber et al, 2013a) and the predicted basal thermal state (Fig. 11 in MacGregor et al, 2016). The flighttrack maps all demonstrate a high degree of spatial structure, with some notable correlations present (both between each other and the DEM).…”

Section: Maps For Self-affine Roughness and Radar Scattering In Northmentioning

confidence: 99%

“…Notably, the basal traction parameterisation -which encapsulates the thermal state, basal roughness, and lithology -is potentially the largest single geophysical uncertainty in projections of the response of ice sheets to climate change (Ritz et al, 2015). Distinction between frozen and thawed regions of the glacier bed is particularly important in constraining ice dynamics, since appreciable basal motion can only occur in regions where the glacier bed is wet (Weertman, 1957;Nye, 1970;MacGregor et al, 2016). Airborne radio-echo sounding (RES) is the only existing remote sensing technique that can acquire bed data with sufficient spatial coverage to enable subglacial information to be obtained across the ice sheets (refer to Pritchard (2014) and Bamber et al (2013a) for recent Antarctic and Greenland coverage maps).…”

Section: Introductionmentioning

confidence: 99%

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Self-affine subglacial roughness: consequences for radar scattering and basal water discrimination in northern Greenland

et al. 2017

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Abstract. Subglacial roughness can be determined at a variety of length scales from radio-echo sounding (RES) data either via statistical analysis of topography or inferred from basal radar scattering. Past studies have demonstrated that subglacial terrain exhibits self-affine (power law) roughness scaling behaviour, but existing radar scattering models do not take this into account. Here, using RES data from northern Greenland, we introduce a self-affine statistical framework that enables a consistent integration of topographicscale roughness with the electromagnetic theory of radar scattering. We demonstrate that the degree of radar scattering, quantified using the waveform abruptness (pulse peakiness), is topographically controlled by the Hurst (roughness power law) exponent. Notably, specular bed reflections are associated with a lower Hurst exponent, with diffuse scattering associated with a higher Hurst exponent. Abrupt waveforms (specular reflections) have previously been used as a RES diagnostic for basal water, and to test this assumption we compare our radar scattering map with a recent prediction for the basal thermal state. We demonstrate that the majority of thawed regions (above pressure melting point) exhibit a diffuse scattering signature, which is in contradiction to the prior approach. Self-affine statistics provide a generalised model for subglacial terrain and can improve our understanding of the relationship between basal properties and ice-sheet dynamics.

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Section: Resultsmentioning

confidence: 99%

Section: Maps For Self-affine Roughness and Radar Scattering In Northmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Self-affine subglacial roughness: consequences for radar scattering and basal water discrimination in northern Greenland

et al. 2017

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“…The magnitude and extent of basal melt occurring under the GrIS is poorly constrained [56]. Given the rapid flow of many tidewater glaciers, it is important to resolve whether the volume of meltwater generated by frictional heat is critical to their rapid ice motion [6] and if so, to better incorporate this process effectively in to predictive dynamic ice sheet models.…”

Section: Basal Melt Ratesmentioning

confidence: 99%

“…Parts of the interior of the ice sheet are frozen to the bed, and thus have no subglacial drainage. While the precise extent of the area of the ice bed interface which is frozen remains unclear [56], in large part due to uncertainty regarding the geothermal heat flux, modelling from Southwest Greenland suggests that ice at the bed down glacier of the 2000-m ice sheet surface contour would be expected to be at the pressure melting point [52•, 57].…”

Section: Subglacial Meltwater Processesmentioning

confidence: 99%

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Nienow

Sole

Slater

et al. 2017

Curr Clim Change Rep

100

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Purpose of the Review This review discusses the role that meltwater plays within the Greenland ice sheet system. The ice sheet's hydrology is important because it affects mass balance through its impact on meltwater runoff processes and ice dynamics. The review considers recent advances in our understanding of the storage and routing of water through the supraglacial, englacial, and subglacial components of the system and their implications for the ice sheet. Recent Findings There have been dramatic increases in surface meltwater generation and runoff since the early 1990s, both due to increased air temperatures and decreasing surface albedo. Processes in the subglacial drainage system have similarities to valley glaciers and in a warming climate, the efficiency of meltwater routing to the ice sheet margin is likely to increase. The behaviour of the subglacial drainage system appears to limit the impact of increased surface melt on annual rates of ice motion, in sections of the ice sheet that terminate on land, while the large volumes of meltwater routed subglacially deliver significant volumes of sediment and nutrients to downstream ecosystems. Summary Considerable advances have been made recently in our understanding of Greenland ice sheet hydrology and its wider influences. Nevertheless, critical gaps persist both in our understanding of hydrology-dynamics coupling, notably at tidewater glaciers, and in runoff processes which ensure that projecting Greenland's future mass balance remains challenging.

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Northeast sector of the Greenland Ice Sheet to undergo the greatest inland expansion of supraglacial lakes during the 21st century

Ignéczi

Sole

Livingstone

et al. 2016

Geophysical Research Letters

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The formation and rapid drainage of supraglacial lakes (SGL) influences the mass balance and dynamics of the Greenland Ice Sheet (GrIS). Although SGLs are expected to spread inland during the 21st century due to atmospheric warming, less is known about their future spatial distribution and volume. We use GrIS surface elevation model and regional climate model outputs to show that at the end of the 21st century (2070–2099) approximately 9.8 ± 3.9 km3 (+113% compared to 1980‐2009) and 12.6 ± 5 km3 (+174%) of meltwater could be stored in SGLs under moderate and high representative concentration pathways (RCP 4.5 and 8.5), respectively. The largest increase is expected in the northeastern sector of the GrIS (191% in RCP 4.5 and 320% in RCP 8.5), whereas in west Greenland, where the most SGLs are currently observed, the future increase will be relatively moderate (55% in RCP 4.5 and 68% in RCP 8.5).

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A synthesis of the basal thermal state of the Greenland Ice Sheet

Cited by 144 publications

References 104 publications

Self-affine subglacial roughness: consequences for radar scattering and basal water discrimination in northern Greenland

Self-affine subglacial roughness: consequences for radar scattering and basal water discrimination in northern Greenland

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Northeast sector of the Greenland Ice Sheet to undergo the greatest inland expansion of supraglacial lakes during the 21st century

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