Winter Distribution of Meltwater in Front of Pine Island Ice Shelf Revealed by Seals

Pine Island Glacier is an important contributor to future sea-level rise, and its mass loss is thought to be driven by interaction with the ocean. Here we assess the response of Pine Island Ice Shelf (PIIS) to the ocean by quantifying the meltwater fraction of water in Pine Island Bay with novel wintertime measurements. In August 2014, instrumented seals collected temperature and salinity profiles in front of PIIS. Comparison with the ship-based profiles collected in February reveals significant differences in water properties and glacial meltwater content between February (mid-summer) and August (mid-winter). The water was generally colder in winter than in summer as expected. Close to the ice shelf calving front however, slightly fresher and warmer water was detected in the upper 600 m in winter suggesting higher meltwater content here. The meltwater signature is more easily observed in winter when the surrounding water is close to freezing than in summer when the upper water column is warmed by solar radiation. The meltwater content is highest along the PIIS calving front. A layer of meltwater-rich water was detected at about 500 m of depth along the calving front. Some meltwater is sufficiently buoyant in winter to rise to the surface at the calving front and was detected as a warm and meltwater-rich signature in the top 100-200 m. In summer, higher meltwater content is found at the southwestern end of the calving front where the meltwater outflow has previously been identified in summer campaigns. However, this pattern reversed in winter - higher meltwater content was found in winter at the northeastern end of the calving front. We speculate that this might indicate a reversed wintertime circulation in this region. A well-defined meltwater plume spread to the north about 10 km away from PIIS in winter.