Radar detection of the brine extent at McMurdo Ice Shelf, Antarctica, and its control by snow accumulation

Abstract

We derive the surface density and brine infiltration depth/extent at McMurdo Ice Shelf, Antarctica, from combined analysis of radar profiles and radar statistical reconnaissance of the surface from 2011 to 2012 austral summer airborne observations. Most of the brine boundaries appear controlled, directly or indirectly, by the snow accumulation pattern. The infiltration is bounded westward by an ablation area and resides just above the pore close‐off depth over most of its extent. The eastern brine limit matches a light‐snow corridor, suggesting a reversed pressure gradient at depth that might sharply slow down the infiltration. Brine into ice is confirmed at the deepest locations north and east of Williams Field. The ice‐ocean interface is undetected west of the infiltrated zone, except in localized patches. We hypothesize this echo‐free zone to be due to high scattering below the surface, possibly from a network of accreted ice and/or ice platelets at the ice‐ocean interface.

The internal structure of the Brunt Ice Shelf from ice-penetrating radar analysis and implications for ice shelf fracture

“…1) and forms the southernmost portion of a complex ice shelf that incorporates the Stancomb-Wills Glacier Tongue and the Riiser-Larsen Ice Shelf to the east. The Brunt Ice Shelf flows northwest from the coast of Coats Land with a speed of > 500 m a −1 at the calving front, although there is strong temporal variability in the flow regime (Gudmundsson et al, 2017). The flow is restrained by grounding at the McDonald Ice Rumples (Fig.…”

“…Thus the region around Halley Research Station is a unique place to study the impact of ice shelf structural heterogeneity on fracture propagation because dynamic changes are underway within a well-monitored environment and the station provides a logistic hub to undertake extensive ground-penetrating radar survey. The rate and direction of propagation of Halloween Crack changed when the crack tip entered a region of thicker ice shelf thought to comprise closely spaced blocks of meteoric ice (De Rydt et al, 2017). In this paper, we use radar results to determine the degree of heterogeneity in ice shelf internal structures and discuss how this came to be.…”

Revised text and figures

“…4 and 5). It is also possible that undulations in the firn may, in part, be due to horizontal shortening induced by historic changes in flow speed of the ice shelf (Gudmundsson et al, 2017).…”

“…Only at one instance did Chasm 1 propagate through an area of meteoric ice (red cir- Fig. 12), which coincided with a period of significantly slower propagation rates (De Rydt et al, 2017).…”

Supplementary material to "Brief Communication: Widespread potential for seawater infiltration on Antarctic ice shelves"

“…Ross -78.9568 179.9229 N (Chiang and Langway, 1978) R7 Brunt -75.4 -25.5 Y (Thomas, 1975) (Neal, 1979) Ross --"Transition from valley glacier to ice shelf" (Robin et al, 1970) Larsen C -68 -60 Near rifts in ice shelf (Smith, 1972;Smith and Evans, 1972) Wordie --Towards edges of shelf (Swithinbank, 1968) Wilkins --Map in Figure 4 ( Vaughan et al, 1993) McMurdo --Map in Figure 5 ( Grima et al, 2016) Brunt -75.31 -26.7 Attributed to basal marine ice by Walford (1964) but to brine infiltration by Swithinbank (1968) (Swithinbank, 1968;Walford, 1964) (Fretwell et al, 2013). Bar charts show the percentage area of selected ice shelves covered by the brine zone, defined with a threshold for firn permeability of 750 kg m -3 (red), 800 kg m -3 (yellow) and 830 kg m -3 (blue).…”