Salt in the ocean’s surface has been steadily reducing since the 1950’s, which prevents the warmer waters underneath from mixing and cooling back down as it should.

Ocean Depths Feel Impact of Global Warming

Researchers from McGill University have found that the salt in the ocean’s surface has been steadily reducing since the 1950’s, which prevents the warmer waters underneath from mixing and cooling back down as it should.

Using data and measurements from studies conducted over a 60-year span, the researchers found that the reduction of salt in the ocean’s surface prevents water from effectively mixing to cool the overall temperature of the ocean. The researchers also studied several climate models which predict a rise in precipitation in the Southern Ocean as atmospheric carbon dioxide level increase.

"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, lead author of the paper.

The McGill study also helps explain why Antarctic Bottom Water has been shrinking over the last 20 years.

"The waters exposed in the Weddell polynya became very cold, making them very dense, so that they sunk down to become Antarctic Bottom Water that spread throughout the global ocean. This source of dense water was equal to at least twice the flow of all the rivers of the world combined, but with the surface capped by freshwater, it has been cut off,” said Eric Galbraith, study co-author and McGill University professor.

"Although our analysis suggests it's unlikely, it's always possible that the giant polynya will manage to reappear in the next century," Galbraith said. "If it does, it will release decades worth of heat and carbon from the deep ocean to the atmosphere in a pulse of warming."

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