Investigating Persistent Polynya Structure and Variability at Pine Island Glacier, West Antarctica, Using Seal-borne Measurements and Thermal Remote Sensing

Antarcticas ice shelves play a critical role in modulating ice loss to the ocean by buttressing grounded ice upstream. Persistent polynyas are open water areas that are maintained by winds and/or ocean heat, often occurring near ice-shelf fronts. Although persistent polynyas are key sites of consistent interaction between atmosphere, ocean, ice-shelves, and sub-ice-shelf ocean cavities, in situ observations are sparse due to the logistical constraints of collecting field measurements in Antarctica. Here we used temperature and salinity observations derived from seal-borne satellite-linked CTD tags deployed in 2014 and 2019 (January to October) in conjunction with MODerate resolution Imaging Spectroradiometer (MODIS) visible and thermal imagery to investigate the spatial, temporal, and structural variability of polynyas near Pine Island Glacier (PIG). We found anomalously warm (>1) monthly surface ocean (< 300 m) temperatures near the ice front in wintertime (May to September) in both 2014 and 2019, consistent with our remote sensing observations and coincident with known polynya locations. This warmer temperature signal extends more than 20 km west of the PIG front in both instrumental records, suggesting the widespread presence of open wintertime polynyas near the western shear margin of the glacier. This warm water, combined with strong circulation beneath the ice shelf may contribute to increased margin fracturing, mechanical weakening, and rift initiation up-glacier. Our results demonstrate the potential of using seal tag measurements to investigate persistent polynyas at PIG on sub-annual timescales, allowing for more frequent observations than available via ship-borne methods. Used in tandem with remote sensing observations, our findings provide insight into key polynya properties and frontal ice-ocean processes at PIG, which can be extended elsewhere on the Amundsen coast in regions with similar hydrographic conditions.