Climate Change Behind Trapped Heat in Oceanic Depths

Disappearance of ice-free regions in Antarctica is linked with climate change, according to a new study.

Satellite images taken during 1970s showed huge ice-free regions- called polynya- in the Weddell Sea. The Weddell polynya closed after three years. Other researchers had found that warm waters in the region had prevented the ice from forming in the region.

The event hasn't reoccurred in the past forty years. Now, researchers at McGill University have found that this 'rare event' was actually a common phenomenon in Antarctica until global warming started heating things up.

For the study, researchers worked with their colleagues at University of Pennsylvania to analyze data from the past 60 years.

They found that the ocean surface has been getting less salty in the past few decades, which has prevented the water underneath from mixing with the top layer. Thus, the heat trapped in deep oceanic water hasn't had an escape route in 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, at McGill University and lead author of the paper.

According to researchers, their observations gel with the current climate models, which predict that the Southern Ocean will become wetter with the rise in carbon dioxide levels.

"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," said Jaime Palter, a professor in McGill's Department of Atmospheric and Oceanic Sciences and co-author of the study, according to a news release. "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."

Also, the study explains why the Antarctic Bottom Water has been drying up in the past few years. The Antarctic Bottom Water is present just above the sea floor. This water is salty, cold and dense and plays an important role in ventilation of the ocean and carbon cycle.

Cold waters in the Weddell polynya sunk to the sea floor and formed the Antarctic Bottom Water, which then spread throughout the sea floor, researchers said.

In other words, disruption of a critical oceanic phenomenon has led to deep ocean waters trapping high levels of heat and carbon. According to the researchers, it is possible that the polynya might reappear and release several years' carbon from "deep ocean to the atmosphere in a pulse of warming."

The study is published in the journal Nature Climate Change.