A constraint upon the basal water distribution and thermal state of the Greenland Ice Sheet from radar bed echoes

Jordan, Thomas; Williams, C.; Schroeder, Dustin M.; Martos, Yasmina M.; Cooper, Michael A.; Siegert, Martín J.; Paden, John; Huybrechts, Philippe; Bamber, Jonathan

doi:10.5194/tc-12-2831-2018

Cited by 43 publications

(43 citation statements)

References 99 publications

(218 reference statements)

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“…The reflection coefficient can provide a constraint on where the bed is frozen or thawed, the reach and character of ocean water at the grounding line, and basal conditions of ice streams (Peters and others, 2005; Jacobel and others, 2009; Ashmore and others, 2014; Christianson and others, 2016). The presence and volume of inferred basal water bodies have also been used to place constraints on the basal thermal state and/or geothermal flux, while layer drawdown has also been used to constrain basal melt rates and geothermal flux (Fahnestock and others, 2001; Catania and others, 2006; Buchardt and Dahl-Jensen, 2007; Schroeder and others, 2014b; Rezvanbehbahani and others, 2017, 2019; Seroussi and others, 2017; Jordan and others, 2018a,b).…”

Section: Ice Sheet and Glacier Bed Conditionsmentioning

confidence: 99%

Five decades of radioglaciology

et al. 2020

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Radar sounding is a powerful geophysical approach for characterizing the subsurface conditions of terrestrial and planetary ice masses at local to global scales. As a result, a wide array of orbital, airborne, ground-based, and in situ instruments, platforms and data analysis approaches for radioglaciology have been developed, applied or proposed. Terrestrially, airborne radar sounding has been used in glaciology to observe ice thickness, basal topography and englacial layers for five decades. More recently, radar sounding data have also been exploited to estimate the extent and configuration of subglacial water, the geometry of subglacial bedforms and the subglacial and englacial thermal states of ice sheets. Planetary radar sounders have observed, or are planned to observe, the subsurfaces and near-surfaces of Mars, Earth's Moon, comets and the icy moons of Jupiter. In this review paper, and the thematic issue of the Annals of Glaciology on ‘Five decades of radioglaciology’ to which it belongs, we present recent advances in the fields of radar systems, missions, signal processing, data analysis, modeling and scientific interpretation. Our review presents progress in these fields since the last radio-glaciological Annals of Glaciology issue of 2014, the context of their history and future prospects.

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Section: Ice Sheet and Glacier Bed Conditionsmentioning

confidence: 99%

Five decades of radioglaciology

et al. 2020

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“…The unaltered nature, and geological interpretation, of this feature further lend credibility to our interpretation of low ξ values as denoting a hard bed. Additionally, recent assessment of the basal thermal state, and basal water prediction derived from RES, suggest that this region is not predominantly 'wet' (MacGregor et al, 2016;Jordan et al, 2018;Chu et al, 2018) further indicating that the interpretation of water 5 ponding is unlikely to hold here.…”

Section: Igneous Intrusion Petermann Glaciermentioning

confidence: 83%

“…The vertical (depth-range) resolution varies from ∼ 4.3 to 20 m, where the horizontal (along-track) resolution is typically ∼30 to 60 m. Precise breakdown of the radar data coverage by field season and radar instrument class can be found in MacGregor et al (2015) (Fig. 1) and Jordan et al (2018) 5 (Fig. 1), respectively.…”

Section: Ice-penetrating Radar Systems and Survey Coveragementioning

confidence: 95%

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Subglacial roughness of the Greenland Ice Sheet: relationship with contemporary ice velocity and geology

Cooper¹,

Jordan²,

Schroeder³

et al. 2019

Preprint

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The subglacial environment of the Greenland Ice Sheet (GrIS) is poorly constrained, both in its bulk properties, for example geology, presence of sediment, and of water, and interfacial conditions, such as roughness and bed rheology.There is, therefore, limited understanding of how spatially heterogeneous subglacial properties relate to ice-sheet motion.Here, via analysis of two decades worth of radio-echo sounding data, we present a new systematic analysis of subglacial roughness beneath the GrIS. We use two independent methods to quantify subglacial roughness: first, the variability of along-5 track topography-enabling an assessment of roughness anisotropy from pairs of orthogonal transects aligned perpendicular and parallel to ice flow; and second, from bed-echo scattering-enabling assessment of fine-scale bed characteristics. We establish the spatial distribution of subglacial roughness and quantify its relationship with ice flow speed and direction. Overall, the beds of fast-flowing regions are observed to be rougher than the slow-flowing interior. Topographic roughness exhibits an exponential scaling relationship with ice surface velocity parallel, but not perpendicular, to flow direction in fast-flowing 10 regions, and the degree of anisotropy is correlated with ice surface speed. In many slow-flowing regions both roughness methods indicate spatially coherent regions of smooth bed, which, through combination with analyses of underlying geology, we conclude is likely due to the presence of a hard flat bed. Consequently, the study provides scope for a spatially variable hard bed/soft bed boundary constraint for ice-sheet models.

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“…Given enough basal melt, a change in resistivity at the base of the ice column due to the phase change from solid ice to liquid water may allow differentiation between ice sheets with active basal melting and those without. Theoretically then the resistivity at the base of the ice column coupled with estimates of rate of basal melt from complimentary studies (e.g., Jordan et al 2018a, Jordan et al 2018b) can provide information on heat flow. Further the resistivity is dependent on the crystal structure and size and could be used to trace a particular boundary within the ice volume of interest.…”

Section: Ice Sheet and Glacier Dynamicsmentioning

confidence: 99%

On the Use of Electromagnetics for Earth Imaging of the Polar Regions

Hill

2019

Surv Geophys

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The polar regions are host to fundamental unresolved challenges in Earth studies. The nature of these regions necessitates the use of geophysics to address these issues, with electromagnetic and, in particular, magnetotelluric studies finding favour and being applied over a number of different scales. The unique geography and climatic conditions of the polar regions means collecting magnetotelluric data at high latitudes, which presents challenges not typically encountered and may result in significant measurement errors. (1) The very high contact resistance between electrodes and the surficial snow and ice cover (commonly MΩ) can interfere with the electric field measurement. This is overcome by using custom-designed amplifiers placed at the active electrodes to buffer their high impedance contacts.(2) The proximity to the geomagnetic poles requires verification of the fundamental assumption in magnetotellurics that the magnetic source field is a vertically propagating, horizontally polarised plane wave. Behaviour of the polar electro-jet must be assessed to identify increased activity (high energy periods) that create strong current systems and may generate non-planar contributions. (3) The generation of 'blizstatic', localised random electric fields caused by the spin drift of moving charged snow and ice particles that produce significant noise in the electric fields during periods of strong winds. At wind speeds above ~ 10 m s −1 , the effect of the distortion created by the moving snow is broad-band. Station occupation times need to be of sufficient length to ensure data are collected when wind speed is low. (4) Working on glaciated terrain introduces additional safety challenges, e.g., weather, crevasse hazards, etc. Inclusion of a mountaineer in the team, both during the site location planning and onsite operations, allows these hazards to be properly managed. Examples spanning studies covering development and application of novel electromagnetic approaches for the polar regions as well as results from studies addressing a variety of differing geologic questions are presented. Electromagnetic studies focusing on near-surface hydrologic systems, glacial and ice sheet dynamics, as well as large-scale volcanic and tectonic problems are discussed providing an overview of the use of electromagnetic methods to investigate fundamental questions in solid earth studies that have both been completed and are currently ongoing in polar regions.

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A constraint upon the basal water distribution and thermal state of the Greenland Ice Sheet from radar bed echoes

Cited by 43 publications

References 99 publications

Five decades of radioglaciology

Five decades of radioglaciology

Subglacial roughness of the Greenland Ice Sheet: relationship with contemporary ice velocity and geology

On the Use of Electromagnetics for Earth Imaging of the Polar Regions

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