SALSA EM: Mapping Subglacial Groundwater in Antarctica

During November 2018 to January 2019 we will be carrying out an extensive EM survey on the Whillans ice stream to map subglacial groundwater.  We will collect both passive magnetotelluric (MT) data as well as active-source EM data, as described in our feasibility study paper.  This project is in collaboration with Matt Siegfried (Stanford U./Colorado School of Mines) and Helen Fricker (UC San Diego).

Also follow our field work with photos posted to Matt Siegfried’s twitter account:
https://twitter.com/MinesGlaciology

Funding Source: NSF Award 1643917

Map of the study region on the lower Whillans/Mercer ice streams showing locations of known active subglacial lakes (blue outlines) [Fricker and Scambos, 2009], predicted hydrologic flowpaths (cyan lines) [Carter et al., 2012], seismic survey locations (pink lines) [Horgan et al., 2012, 2013a,b], locations where the subglacial system was directly sampled through borehole access (green stars), and proposed EM/MT survey locations (purple lines). Insets show survey sites in detail with individual station locations shown as purple triangles. Background imagery from Scambos et al. [2007]; adapted from Siegfried et al. [2016].
Ground-based EM methods for subglacial imaging. The active-source EM method uses a transient or frequency-domain pulse of current in a large horizontal loop to induce currents in the ground. The resulting magnetic-field response function is measured at one or more receiver stations. The passive magnetotelluric method uses measurements of time variations in the naturally occurring horizontal electric and magnetic fields to estimate the frequency-dependent impedance response at a series of stations. For both techniques, the responses can be converted into electrical-conductivity models using non-linear inversion methods.
Bulk electrical resistivity of sediments shown as a function of pore fluid salinity and sediment porosity. Bulk resistivity was computed using Archie’s law with exponent m = 1.5 and temperature 0ºC. The resistivity of pore-water (100% porosity) is from the Practical Salinity Scale 1978 (Perkin and Lewis, 1980). Red dots show direct water measurements from West Lake Bonney (WLB) at 5 and 38 m depth (Spigel and Priscu, 1996) and Casey Station (CS) jokulhlaup outflow (Goodwin, 1988). The dashed green line shows pore water resistivity at Subglacial Lake Whillans (SLW) rapidly decreasing from the lake bottom to 0.4 m into the sediments (Christner and others, 2014; Michaud and others, 2016). For reference, the resistivity of ice greatly exceeds 10 4 ohm-m.

 

Publications

Siegert, Martin J; Kulessa, Bernd; Bougamont, Marion; Christoffersen, Poul; Key, Kerry; Andersen, Kristoffer R; Booth, Adam D; Smith, Andrew M

Antarctic subglacial groundwater: a concept paper on its measurement and potential influence on ice flow Journal Article

Geological Society, London, Special Publications, pp. SP461.8–17, 2017.

Links

Key, Kerry; Siegfried, Matthew R

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

Journal of Glaciology, 331 , pp. 1–17, 2017.

Links