The feasibility of imaging subglacial hydrology beneath ice streams with ground-based electromagnetics

Key, Kerry; Siegfried, Matthew R.

doi:10.1017/jog.2017.36

Cited by 29 publications

(34 citation statements)

References 113 publications

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“…To validate and constrain hydrological process models, geophysical observations should be collected in targeted locations where large-scale transitions are observed (e.g., Schroeder et al, 2013) and non-steady-state behavior in the hydrological regime is possible (e.g., Smith et al, 2009;2017). This effort should include repeat radar and seismic surveys, installation of autonomous GPS and phase-sensitive radar stations, and development of novel techniques for mapping subglacial conductivity structure , Foley et al, 2016, Key and Siegfried, 2017 in review).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

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How much, how fast?: A science review and outlook for research on the instability of Antarctica's Thwaites Glacier in the 21st century

Scambos¹,

Bell²,

Alley³

et al. 2017

Global and Planetary Change

154

158

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Constraining how much and how fast the West Antarctic Ice Sheet (WAIS) will change in the coming decades has recently been identified as the highest priority in Antarctic research (National Academies, 2015). Here we review recent research on WAIS and outline further scientific objectives for the area now identified as the most likely to undergo near-term significant change: Thwaites Glacier and the adjacent Amundsen Sea. Multiple lines of evidence point to an ongoing rapid loss of ice in this region in response to changing atmospheric and oceanic conditions. Models of the ice sheet's dynamic behavior indicate a potential for greatly accelerated ice loss as ocean-driven melting at the Thwaites Glacier grounding zone and nearby areas leads to thinning, faster flow, and retreat. A complete retreat of the Thwaites Glacier basin would raise global sea level by more than three meters by entraining ice from adjacent catchments. This scenario could occur over the next few centuries, and faster ice loss could occur through processes omitted from most ice flow models such as hydrofracture and ice cliff failure, which have been observed in recent rapid ice retreats elsewhere. Increased basal melt at the grounding zone and increased potential for hydrofracture due to enhanced surface melt could initiate a more rapid collapse of Thwaites Glacier within the next few decades. words

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Section: Accepted Manuscriptmentioning

confidence: 99%

“…This effort should include repeat radar and seismic surveys, installation of autonomous GPS and phase-sensitive radar stations, and development of novel techniques for mapping subglacial conductivity structure , Foley et al, 2016, Key and Siegfried, 2017 in review).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

How much, how fast?: A science review and outlook for research on the instability of Antarctica's Thwaites Glacier in the 21st century

Scambos¹,

Bell²,

Alley³

et al. 2017

Global and Planetary Change

154

158

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“…The hydrologic system underlying large ice sheets and glaciers can have a significant effect on the dynamics of the overlying ice motion (e.g., Kamb 1987;Bell 2008). In a synthetic study, Key and Siegfried (2017) explore the feasibility of investigating the processes occurring at the basal zone of ice sheets using EM approaches that have been applied to hydrologic systems in temperate regions. They show that with favourable data quality (data errors of 1% at high frequencies up to 1000 Hz), a thin local 3 Ωm subglacial lake of ~ 5 m thickness and 2 km lateral extent would be detectable under ~ 1 km of overlying ice sheet using MT or FDEM.…”

Section: Ice Sheet and Glacier Dynamicsmentioning

confidence: 99%

“…1). Future potential exists for studies of ice sheet and glacial dynamics, and characterisation of subglacial hydrologic systems (Key and Siegfried 2017;Siegert et al 2018); however, the applicability and success of these studies may be hampered by the challenges of acquiring high-quality electric field data at the required periods without the inclusion of active source methods.…”

Section: Introductionmentioning

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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“…base, for which only few direct observations exist (Fisher et al, 2015;Key and Siegfried, 2017;Maier et al, 2019;Pattyn and Morlighem, 2020).…”

mentioning

confidence: 99%

Sensitivity of ice sheet surface velocity and elevation to variations in basal friction and topography in the Full Stokes and Shallow Shelf Approximation frameworks

Cheng

Kirchner

Lötstedt

2020

Preprint

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Abstract. Predictions of future mass loss from ice sheets are afflicted with uncertainty, caused, among others, by insufficient understanding of spatio-temporally variable processes at the inaccessible base of ice sheets for which few direct observations exist and of which basal friction is a prime example. Here, we use an inverse modeling approach and the associated time-dependent adjoint equations, derived in the framework of a Full Stokes model and a Shallow Shelf/Shelfy Stream Approximation model, respectively, to determine the sensitivity of ice sheet surface velocities and elevation to perturbations in basal friction and basal topography. Analytical and numerical examples are presented showing the importance of including the time dependent kinematic free surface equation for the elevation and its adjoint, in particular for observations of the elevation. A closed form of the analytical solutions to the adjoint equations is given for a two dimensional vertical ice in steady state under the Shallow Shelf Approximation. There is a delay in time between a perturbation at the ice base and the observation of the change in elevation. A perturbation at the base in the topography has a direct effect in space at the surface above the perturbation and a perturbation in the friction is propagated directly to the surface in time. Perturbations with long wavelength and low frequency will propagate to the surface while those of short wavelength and high frequency are damped.

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The feasibility of imaging subglacial hydrology beneath ice streams with ground-based electromagnetics

Cited by 29 publications

References 113 publications

How much, how fast?: A science review and outlook for research on the instability of Antarctica's Thwaites Glacier in the 21st century

How much, how fast?: A science review and outlook for research on the instability of Antarctica's Thwaites Glacier in the 21st century

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

Sensitivity of ice sheet surface velocity and elevation to variations in basal friction and topography in the Full Stokes and Shallow Shelf Approximation frameworks

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