Elephant seals have been used as living monitoring devices to show that freshwater input from melting Antarctic ice shelves suppresses the formation of dense bottom waters that are vital in driving heat around the globe. The findings, reported in Nature Communications this week, suggest that enhanced melting under a future warming climate could potentially put an end to bottom water formation.

As the seas surrounding Antarctica freeze during the winter, the rejection of salt from the sea-ice matrix leads to the formation of extremely dense surface waters, which eventually sink to form bottom waters that drive the globe’s deep ocean circulation. The majority of dense waters are produced in polynya systems - areas of particularly intense sea-ice formation - which exist in only a few key areas. Prydz Bay, East Antarctica, hosts three such polynya systems, yet available data suggest the area produces less-dense waters than expected, questioning its contribution to the globally important bottom waters. Unfortunately, data for the Prydz Bay region are limited, particularly during the winter months when human access to the region is impossible.

To tackle this problem of inaccessibility, Guy Williams and colleagues enlisted the help of local elephant seals. Using small instruments attached to the seals, the authors were able to collect vital temperature and salinity data throughout the year, and also across the entire Prydz Bay region. The authors are able to show that although the Pryz Bay polynyas do indeed produce dense surface waters, the density is significantly reduced through the input of freshwaters sourced from the melting of local ice shelves.

The authors propose that increased melting of local ice shelves under a warming climate might further limit the formation of important dense waters.