Climate Change Linked to Disappearance of Ice Free Regions in Antarctica
A team of international scientists says that climate change is responsible for the recent disappearance of the ice free regions known as polynya in the Antarctica.
The first satellite images of Antarctica taken during the mid-1970s exposed a huge ice free region within the ice pack of the Weddell Sea. These ice free regions known as Polynya closed after three years. Researchers believed that it was the presence of warm water in the region that prevented the formation of the ice.
It has been over 40 years and the huge polynya, the size of New Zealand, has not reappeared. The scientists declared it as a rare natural occurrence.
However, the new study led by researchers at McGill University claims that the Weddell polynya of the 1970s may have been the last event, of what was earlier a common feature of southern Ocean, and is currently suppressed due to the effects of the accelerating climate change on the salinity of the ocean.
Working in collaboration with researchers at the University of Pennsylvania, the team examined data collected over the last 60 years. They identified that since the 1950s the surface of the ocean has been gradually reducing in salinity. The blanket of fresh water on top of the ocean prevented the water trapped underneath to mix with the top layer. Due to this, the ocean heat was trapped with no escape route. This has been the condition for several years.
"Deep ocean waters only mix directly to the surface in a few small regions of the global ocean, so this has effectively shut one of the main conduits for deep ocean heat to escape," says Casimir de Lavergne, a recent graduate of McGill's Master's program in Atmospheric and Oceanic Sciences and lead author of the paper.
The researchers say their observations match with the latest climate models that predict a rise in precipitation in the Southern Ocean as the levels of atmospheric carbon dioxide increase.
"This agrees with the observations, and fits with a well-accepted principle that a warming planet will see dryer regions become dryer and wetter regions become wetter," says Jaime Palter, a professor in McGill's Department of Atmospheric and Oceanic Sciences and co-author of the study. "True to form, the polar Southern Ocean - as a wet place - has indeed become wetter. And in response to the surface ocean freshening, the polynyas simulated by the models also disappeared."
In recent years it was discovered that the Antarctic Bottom Water that fills the deepest layers of the World Ocean was drying up. The water that was exposed to Weddell polynya turned extremely cold, dense and sank to the bottom and spread throughout the sea floor.
"Although our analysis suggests it's unlikely, it's always possible that the giant polynya will manage to reappear in the next century," Galbraith adds. "If it does, it will release decades-worth of heat and carbon from the deep ocean to the atmosphere in a pulse of warming."
The finding was documented in the journal Nature Climate Change.