NASA satellite image of the Maud Rise polynya. Polynyas can form in sea ice over the open ocean as warm water is brought to the surface by ocean currents. Credit: NASA Earth Observatory
“We now understand that the polynya was caused by a complex interaction between the unique geography of the ocean floor and an unusually strong wind that produced unusually strong ocean currents transporting heat and salt water towards the surface. But it also required the contribution of a very specific key process,” says Fabien Roquet, Professor of Physical Oceanography at the Department of Marine Sciences at the University of Gothenburg, and one of the researchers behind the discovery.
“This upwelling of warmer water explains how the sea ice might melt. But as sea ice melts this leads to a freshening of the surface water, which should in turn put a stop to this upwelling. So, another process must be happening for the polynya to persist. There must be an additional input of salt from somewhere,” says Aditya Narayanan, researcher at the National Oceanographic Centre and main author of the study.
“Ekman transport was the essential missing piece of the puzzle that was necessary to increase the balance of salt and sustain the mixing of salt and heat towards the surface water,” says Fabien Roquet.The effects of a polynya can persist in the ocean for years after they have formed. They can change the way water moves and how currents carry heat towards the continent. The dense waters that form here can spread across the global ocean.