According to a new study, heat from the depths of the ocean has been approaching Antarctica, threatening the ice shelves that circulate across the continent.
Until now, scientists did not have enough ocean observations to detect the warming trend.
In a new one, published this Tuesday in Communications Earth & Environmentresearchers compiled long-term ocean measurements collected by ships and robotic floating devices to show that a warm mass called “circumpolar deep water” expanded and moved towards the Antarctic continental shelf in recent 20 years.
“It’s worrying, because this warm water could flow beneath Antarctica’s ice shelves, melting them from below and destabilizing them,” says the study’s first author, Joshua Lanham.
According to , ice shelves play an important role in containing the ice sheets and glaciers of the interior of Antarctica, which together contain enough fresh water to raise sea levels by about 58 metros.
This is the first time scientists have observed a change in marine heat across the entire Southern Ocean.
“It is something that had been predicted by climate models due to global warming, but that we had not yet observed in the data”, adds Lanham.
Previous observations of the Southern Ocean, which surrounds Antarctica, have been limited to samples recorded by ships about once a decade.
This information provided temperature, salinity and nutrient data across the entire water column. However, without continuous data, there is less certainty regarding long-term changes in heat distribution.
The researchers supplemented the ship’s measurements with publicly available data collected by a global network of autonomous buoys, which float in the upper layer of the ocean. These calls provide continuous snapshots of the ocean, but the program has not been in operation for as long as ships have been collecting detailed hydrographic data.
Using machine learning, researchers took data from Argo buoys and combined it with long-term patterns extracted from ship measurements to build a new record that captures detailed monthly snapshots of the past four decades, allowing them to discover changing warm waters.
“In the past, ice caps were protected by a tub of cold water, preventing them from melting. Now, it appears that ocean circulation has changed, and it’s almost as if someone had turned on the hot water tap and now the tub is warming up,” says the study’s co-author, Sarah Purkey.
More than 90% of excess heat resulting from global warming is stored in the ocean, with the Southern Ocean being responsible for absorbing most of the heat originating from anthropogenic.
In the frigid waters around the poles, extremely cold, dense water forms that sinks to the depths of the ocean. As water sinks, it drags heat, carbon and nutrients with it, setting in motion a global “conveyor belt” of currents, including water. Atlantic Meridional Return Circulation (AMOC), which transports water across the Atlantic.
Climate models indicate that warmer air temperatures and additional freshwater from melting ice are reducing the formation of this dense water in the North Atlanticwhich could lead to a .
Similar changes have recently been predicted for the Southern Ocean. Climate models have suggested that production of cold, dense water will decrease in Antarcticacausing warmer circumpolar deep water to move landward to take up the space left by the receding cold water.
