A constraint upon the basal water distribution and thermal state of the Greenland Ice Sheet from radar bed echoes
File(s)
Published version
Author(s)
Type
Journal Article
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.
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.
Date Issued
2018-09-05
Date Acceptance
2018-08-07
Citation
The Cryosphere, 2018, 12, pp.2831-2854
ISSN
1994-0416
Publisher
Copernicus Publications
Start Page
2831
End Page
2854
Journal / Book Title
The Cryosphere
Volume
12
Copyright Statement
© 2018 Author(s). This work is distributed under
the Creative Commons Attribution 4.0 License. https://creativecommons.org/licenses/by/4.0/
the Creative Commons Attribution 4.0 License. https://creativecommons.org/licenses/by/4.0/
License URL
Sponsor
Natural Environment Research Council (NERC)
Grant Number
GEOG.RE2356
Subjects
Science & Technology
Physical Sciences
Geography, Physical
Geosciences, Multidisciplinary
Physical Geography
Geology
WEST ANTARCTICA
THWAITES GLACIER
SUBGLACIAL LAKE
HEAT-FLUX
NORTHEAST GREENLAND
JAKOBSHAVN ISBRAE
GROUNDING-ZONE
SHEAR-MARGIN
DATA SET
BENEATH
0405 Oceanography
0406 Physical Geography And Environmental Geoscience
Meteorology & Atmospheric Sciences
Publication Status
Published
Date Publish Online
2018-09-05