Citation:

tc-12-2831-2018

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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 data combination enabling 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 quasi-linear '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.

Coverage:

Median Latitude: 72.000000 * Median Longitude: -40.000000 * South-bound Latitude: 60.000000 * West-bound Longitude: -65.000000 * North-bound Latitude: 84.000000 * East-bound Longitude: -15.000000

Date/Time Start: 2003-01-01T00:00:00 * Date/Time End: 2014-12-31T00:00:00

Event(s):

Greenland * Latitude Start: 84.000000 * Longitude Start: -65.000000 * Latitude End: 60.000000 * Longitude End: -15.000000 * Location: Greenland

Comment:

The basal water distribution is derived from the ACORDS, MCRDS and MCoRDS airborne radar sensors over 13 field seasons from 2003-2014. The flight-track data is provided as csv files on a season-by-season basis and for the full (13 season) data set. The data columns correspond to: (A) latitude, (B) longitude, (C) water binary value, at a 1 km along-track posting. The water binary value corresponds to: 1 == a 5 km bin with water detected, 0 == a 5 km bin with no water detected, NaN == a 5 km bin with no coverage.

The basal water predictions are shown in Figures 7-10 of Jordan et al. 2018 and correspond to a subset of flight-track data where basal water is present: specifically, where there are rapid horizontal gradients in the bed dielectric (wet/dry transitions). The predictions therefore act as a sufficient constraint upon the basal water distribution rather than being a fully comprehensive flight-track map for basal water extent.

Parameter(s):

#	Name	Short Name	Unit	Principal Investigator	Comment
1	DATE/TIME	Date/Time		Bamber, Jonathan L	Geocode – period start, mostly march
2	DATE/TIME	Date/Time		Bamber, Jonathan L	Geocode – period end, mostly may
3	File content	Content		Bamber, Jonathan L
4	File name	File name		Bamber, Jonathan L
5	File format	File format		Bamber, Jonathan L
6	File size	File size	kByte	Bamber, Jonathan L
7	Uniform resource locator/link to file	URL file		Bamber, Jonathan L

License:

Creative Commons Attribution 3.0 Unported (CC-BY-3.0)

Size:

70 data points

Data

Download dataset as tab-delimited text — use the following character encoding:

1 Date/Time (period start, mostly march)	2 Date/Time (period end, mostly may)	3 Content	4 File name	5 File format	6 File size [kByte]	7 URL file
2003	2003	ACORDS 2003 data, platform P-3B Orion	2003_P3_Water	CSV	311.129	2003_P3_Water.csv
2005	2005	ACORDS 2005 data, platform DHC-6 Twin Otter	2005_TO_Water	CSV	147.839	2005_TO_Water.csv
2006	2006	MCRDS 2006 data, platform DHC-6 Twin Otter	2006_TO_Water	CSV	262.829	2006_TO_Water.csv
2007	2007	MCRDS 2007 data, platform P-3B Orion	2007_P3_Water	CSV	269.663	2007_P3_Water.csv
2008	2008	MCRDS 2008 data, platform DHC-6 Twin Otter	2008_TO_Water	CSV	401.398	2008_TO_Water.csv
2009	2009	MCRDS 2009 data, platform DHC-6 Twin Otter	2009_TO_Water	CSV	194.372	2009_TO_Water.csv
2010	2010	MCoRDs 2010 data, platform Douglas DC-8	2010_DC_Water	CSV	545.712	2010_DC_Water.csv
2010	2010	MCoRDs 2010 data, platform P-3B Orion	2010_P3_Water	CSV	509.739	2010_P3_Water.csv
2011	2011	MCoRDs 2011 data, platform P-3B Orion	2011_P3_Water	CSV	1623.628	2011_P3_Water.csv
2011	2011	MCoRDs 2011 data, platform DHC-6 Twin Otter	2011_TO_Water	CSV	128.213	2011_TO_Water.csv
2012	2012	MCoRDs 2012 data, platform P-3B Orion	2012_P3_Water	CSV	1855.005	2012_P3_Water.csv
2013	2013	MCoRDs 2013 data, platform P-3B Orion	2013_P3_Water	CSV	841.141	2013_P3_Water.csv
2014	2014	MCoRDs 2014 data, platform P-3B Orion	2014_P3_Water	CSV	1915.750	2014_P3_Water.csv
2003	2014	Complete 13 seasons dataset	Fulldataset_13Seasons_Water	CSV	9006.418	Fulldataset_13Seasons_Water.csv