Brine, englacial structure and basal properties near the terminus of McMurdo Ice Shelf, Antarctica

Abstract

ABSTRACT. We collected ∼1300 km of ground-penetrating radar profiles over McMurdo Ice Shelf, Antarctica, using frequencies between 40 and 400 MHz to determine extent, continuity and depth to the brine. We also used profiles to determine meteoric ice thickness and locate englacial features, which may suggest ice shelf instability. The brine extends 9-13 km inland from the ice shelf terminus and covers the entire region between Ross, White and Black Islands. Jump unconformities and basal fractures exist in the brine and ice shelf, respectively, suggesting prior fracturing and re-suturing. One 100 MHz profile, the most distal from the ice shelf edge while still being situated over the brine, simultaneously imaged the brine and bottom of meteoric ice. This suggests a negative brine salinity gradient moving away from the terminus. The meteoric ice bottom was also imaged in a few select locations through blue ice in the ablation zone near Black Island. We suggest that brine, sediment-rich ice and poor antenna coupling on rough ice attenuates the signal in this area. When combined with other recent mass-balance and structural glaciology studies of MIS, our results could contribute to one of the most high-resolution physical models of an ice shelf in Antarctica.

Airborne mapping of the sub-ice platelet layer under fast ice in McMurdo Sound, Antarctica

“…Its course is more northerly as it may be constrained by the 200 m isobath. While the ice shelf thickness measurements near the front are uncalibrated, they are generally in agreement with thicknesses from 1960(McCrae, 1984 and from 2015 (Campbell et al, 2017). 480…”

“…We have presented results from five AEM ice thickness surveys of the landfast ice in McMurdo Sound in November of 2009, 2013, 2016, and 2017 with the aim to describe the spatial and interannual variability of the sub-ice platelet layer (SIPL) 575 known to exist below the fast ice. We have presented a simple method to obtain approximate SIPL thickness and conductivity information from the inphase and quadrature components of single-frequency AEM data, that was calibrated and validated with drill-hole measurements.…”

“…We have carried out five surveys over the fast ice in McMurdo Sound, in November of 2009, 2013, 2016, and 2017 1), i.e. in the end of winter when ice thickness was near its maximum.…”

Structure and stability of the McMurdo Ice Shelf Transition Zone and glaciated hillside near Scott Base, Antarctica

“…The near-surface conformable stratigraphy (0-5 m depth) is likely recent accumulation and reworked snow cover from yearly road construction operations over heavily deformed and fractured ice (5-10 m depth). The strong GPR horizons at 12-15 m in depth likely represent discontinuous marine ice frozen onto the bottom of the meteoric ice (as also seen in Campbell et al 2017). Within the TZ Road GPR profiles, vertical noise bands appear to originate from specific horizons near a 5 m depth.…”

“…We used the same software to pick bedrock TWTT and associated bedrock depth based on the wave velocity for ice. Interpretation of GPR profiles follow methods outlined by Campbell et al (2017).…”