Abstract
Abstract. There is widespread, but often indirect, evidence that a significant fraction of the bed beneath the Greenland Ice Sheet is thawed (at or above the pressure melting point for ice). This includes the beds of major outlet glaciers and their tributaries and a large area around the NorthGRIP borehole in the ice-sheet interior. The ice-sheet-scale distribution of basal water is, however, poorly constrained by existing observations. In principle, airborne radio-echo sounding (RES) enables the detection of basal water from bed-echo reflectivity, but unambiguous mapping is limited by uncertainty in signal attenuation within the ice. Here we introduce a new, RES diagnostic for basal water that is associated with wet–dry transitions in bed material: bed-echo reflectivity variability. This technique acts as a form of edge detector and is a sufficient, but not necessary, criteria for basal water. However, the technique has the advantage of being attenuation insensitive and suited to combined analysis of over a decade of Operation IceBridge survey data.The basal water predictions are compared with existing analyses of the basal thermal state (frozen and thawed beds) and geothermal heat flux. In addition to the outlet glaciers, we demonstrate widespread water storage in the northern and eastern interior. Notably, we observe a quasilinear corridor of basal water extending from NorthGRIP to Petermann Glacier that spatially correlates with elevated heat flux predicted by a recent magnetic model. Finally, with a general aim to stimulate regional- and process-specific investigations, the basal water predictions are compared with bed topography, subglacial flow paths and ice-sheet motion. The basal water distribution, and its relationship with the thermal state, provides a new constraint for numerical models.
Highlights
Basal water beneath the Greenland Ice Sheet (GrIS) influences and is influenced by, the dynamics and thermodynamics of the overlying ice
The data were taken using a succession of radar instruments: Advanced Coherent Radar Depth Sounder (ACORDS), Multi-Channel Radar Depth Sounder (MCRDS), Multi-Channel Coherent Radar Depth Sounder (MCoRDS), Multi-Channel Coherent Radar Depth Sounder: version 2 (MCoRDS v2), mounted on three airborne platforms: P-3B Orion (P3), DHC-6 Twin Otter (TO) DC8, Douglas DC-8 (DC8) (Paden, 2015)
To demonstrate the robustness of the predictions, we performed a sensitivity analysis with respect to the modelled attenuation correction < N > (Sect. 2.2) The analysis considered a series of increasingly large perturbations to < N > and tested whether σ[R] > 6 dB held for the perturbed model
Summary
Basal water beneath the Greenland Ice Sheet (GrIS) influences and is influenced by, the dynamics and thermodynamics of the overlying ice. A lubricated bed is a necessary condition for basal sliding, which can be responsible for up to about 90 % of the ice surface velocity (van der Veen, 2013). Constraining the spatial distribution of basal water is important, for understanding the dynamic state of the overlying ice and its sensitivity to external forcing. A reliable estimate of the presence of basal water can be used as a boundary condition or as a constraint in numerical modelling and to evaluate model performance and is, as a consequence, an attractive objective. Jordan et al.: Greenland basal water from radar bed echoes
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
