The warm waters of the deep ocean are already approaching dangerously close to Antarctica and threaten to melt its ice shelves from below, which may be critical because the destabilization of these ices could cause a significant rise in sea level on a global scale.
This has been confirmed by an international team of researchers, led by the University of Cambridge, who have compiled ocean measurements taken over decades by ships and robotic floating devices to demonstrate that a warm mass, called ‘circumpolar deep water’, has expanded and is moving towards the Antarctic continental shelf; today they publish the results of their work in the journal Communications Earth and Environment.
Researchers have reconstructed four decades of ocean changes and confirmed for the first time through direct observations that global warming is altering Southern Ocean currents in worrying ways, and that those changes impact the ocean’s ability to regulate carbon and heat across the planet.
“It is worrying, because this warm water can seep under the Antarctic ice shelves, melting them from below and destabilizing them,” said Joshua Lanham, lead author of the study at Cambridge Earth Sciences, and specified that climate models had predicted this change due to global warming, but the researchers had not confirmed it with data.
The ice shelves play an important role in containing the ice sheets and glaciers in the interior of Antarctica, which together retain enough fresh water to raise sea level by about 58 meters, the University highlighted in the summary of the work.
Previous observations of the Southern Ocean, which surrounds Antarctica, were limited to surveys recorded by ships about once a decade, and that information, collected as part of a long-running international program, provided detailed data on temperature, salinity and nutrients throughout the water column, but without continuous data scientists had more uncertainty about long-term changes in heat distribution.
Now, researchers have supplemented the ship’s measurements with publicly available data collected by a global network of autonomous buoys drifting across the ocean surface; These buoys, known as ‘Argo’, provide continuous snapshots of the ocean, but the program has not been in operation as long as ships that compile detailed hydrographic sections.
Using machine learning technologies, the researchers took the Argo data and combined it with long-term patterns extracted from ship measurements to build a new record that captures detailed monthly snapshots over the past four decades, allowing them to discover the change in warm waters.
The ice sheets are protected by a mass of cold water that prevents them from melting, but now everything indicates that ocean circulation has changed; “It’s like someone turned on the hot water tap and the water was getting hot,” said Professor Sarah Purkey, one of the lead authors, from the Scripps Institution of Oceanography (University of California).
In the frigid waters surrounding the poles, extremely cold and dense water forms and sinks to the depths of the ocean and as it sinks, it absorbs heat, carbon and nutrients, setting in motion a global network of currents.
“Climate models, including those used by the Intergovernmental Panel on Climate Change (IPCC) that advises the UNO, indicate that rising air temperatures and freshwater input from melting ice are reducing the formation of this dense water mass in the North Atlantic, and researchers have now corroborated that this scenario is manifested in real observations, with the implications it has for how carbon, nutrients and heat circulate through the global ocean.”
