Scientists, with the help of elephant seals, have solved a 30-year mystery surrounding the formation of the Antarctic bottom water, a dense cold water filling in most of the ocean deep basins. The formation and circulation of Antarctic bottom water is a key process of the global ocean circulation and therefore of the earth’s climate. Scientists believed that the cold, dense bottom waters of the global ocean originated at three different locations in Antarctica - the Weddell Sea, the Ross Sea and the Adélie Coast of East Antarctica. Thirty years ago, a fourth source was speculated to exist somewhere in the Prydz Bay region, but until now scientists have been unable to confirm if, where and how it was being formed.
In a paper published in Nature Geoscience, a fourth stream of Antarctic bottom water has finally been described through sophisticated satellite data, oceanographic moorings and with the crucial help of elephant seals. Understanding how and where Antarctic bottom water is formed is an important step when you want to better predict the long-term climate change, says Fabien Roquet, postdoctoral researcher at the Meteorological Institute of the Stockholm University, who co-authored the study.
In 2008 and 2009, as part of the International Polar Year, Japanese scientists from the Institute of Low Temperature Science, Hokkaido University and the Tokyo University of Marine Technology deployed instruments off the continental shelf at Cape Darnley, north-west of the Amery Ice Shelf, Antarctica. These data showed the presence of a very cold and saline water flowing downslope to form the Antarctic Bottom Water. However it remained to determine where this water was coming from, which was achieved by attaching instruments on the fur of a few elephant seals. The seals went to an area of the coastline that no ship was ever going to get to, particularly in the middle of winter, and allowed us to sample the most extreme dense shelf water ever measured anywhere around Antarctica. “The data from elephant seal instruments have enabled us to determine the trajectory of how the heavy, salty water flows and thus we were able to identify the location of its origin. It has been shown that this cold salty water coming from Cape Darnely at a place where there is a massive formation of sea ice”, says Fabien Roquet.