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

Christian Haas,Greg H Leonard,Justin F Beckers,Alex J Gough,Patricia J Langhorne,Gemma M Brett,Daniel Price,Wolfgang Rack

doi:10.5194/tc-15-247-2021

Abstract

Abstract. Basal melting of ice shelves can result in the outflow of supercooled ice shelf water, which can lead to the formation of a sub-ice platelet layer (SIPL) below adjacent sea ice. McMurdo Sound, located in the southern Ross Sea, Antarctica, is well known for the occurrence of a SIPL linked to ice shelf water outflow from under the McMurdo Ice Shelf. Airborne, single-frequency, frequency-domain electromagnetic induction (AEM) surveys were performed in November of 2009, 2011, 2013, 2016, and 2017 to map the thickness and spatial distribution of the landfast sea ice and underlying porous SIPL. We developed a simple method to retrieve the thickness of the consolidated ice and SIPL from the EM in-phase and quadrature components, supported by EM forward modelling and calibrated and validated by drill-hole measurements. Linear regression of EM in-phase measurements of apparent SIPL thickness and drill-hole measurements of “true” SIPL thickness yields a scaling factor of 0.3 to 0.4 and rms error of 0.47 m. EM forward modelling suggests that this corresponds to SIPL conductivities between 900 and 1800 mS m−1, with associated SIPL solid fractions between 0.09 and 0.47. The AEM surveys showed the spatial distribution and thickness of the SIPL well, with SIPL thicknesses of up to 8 m near the ice shelf front. They indicate interannual SIPL thickness variability of up to 2 m. In addition, they reveal high-resolution spatial information about the small-scale SIPL thickness variability and indicate the presence of persistent peaks in SIPL thickness that may be linked to the geometry of the outflow from under the ice shelf.

Highlights

McMurdo Sound is an approximately 55 km wide sound in the southern Ross Sea, Antarctica, located between Ross Island and the Transantarctic Mountains in Victoria Land (Fig. 1a)
We have presented results from five AEM ice thickness surveys of the landfast ice in McMurdo Sound in November of 2009, 2011, 2013, 2016, and 2017 with the aim of describing the spatial and interannual variability of the sub-ice platelet layer (SIPL) known to exist below the fast ice
We have presented a simple method to obtain approximate SIPL thickness and conductivity information from the in-phase and quadrature components of single-frequency AEM data, which were calibrated and validated with drill-hole measurements

Summary

Introduction

McMurdo Sound is an approximately 55 km wide sound in the southern Ross Sea, Antarctica, located between Ross Island and the Transantarctic Mountains in Victoria Land (Fig. 1a). For most of the year, McMurdo Sound is covered by landfast sea ice. The fast ice is mostly composed of first-year ice which usually breaks out during the summer months (Kim et al, 2018). In some years some smaller regions of fast ice mostly near the coast or ice shelf edge may persist through one or several summers to form thick multiyear landfast ice. In particular between 2003 and 2011 the southern parts of McMurdo Sound remained permanently covered by thick multiyear ice that had initially formed due to the shelter from swell and currents by the large grounded iceberg B15 further north (Robinson and Williams, 2012; Brunt et al, 2006; Kim et al, 2018)

Methods

Results

Discussion

Conclusion