Combining observational data from Argo floats and satellites with global circulation models, a team led by the University of Washington and MIT showed that as the surface of the Southern Ocean heats up, warm water is blown northward by currents. It will eventually end up around the north pole.
At the same time, new water is entering the Southern Ocean from the coldest and deepest basins on Earth. This deep water represents the tail-end of an incredibly slow-moving oceanic conveyor belt that begins centuries earlier in the North Atlantic. In other words, the sea water encircling Antarctica hails from a time before the industrial revolution or human-caused climate change were even a thing.
“The Southern Ocean is unique because it’s bringing water up from several thousand meters [as much as 3km],” lead study author Kyle Armour said in a statement. “You have a lot of water coming to the surface, and that water hasn’t seen the atmosphere for hundreds of years.”
Armour stressed that his study did not directly address warming on the Antarctic ice sheet per se, which is most affected by the coastal waters lapping up directly on the shoreline. “The mechanism we’ve identified slows the warming of the open ocean around Antarctica — but not these coastal waters directly”. Indeed, continental Antarctica and much of the coastline have been warming at a rate more comparable to the rest of the world.
The growth of sea ice surrounding Antarctica, however, may be facilitated by Armour’s mechanism of deep cold water. He’s also investigating other factors that could be contributing. “So far, we think [sea ice expansion] may be related to changes in the winds around Antarctica, which have been linked to stratospheric ozone depletion,” he said.
