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Underwater robots reveal why Antarctic ice caps are melting

Nature Geoscience; Nature Geoscience

Mon, 10 Nov 2014

Researchers at the University of East Anglia (UEA) and the California Institute of Technology have used underwater robots to show how warm water is making its way to the Antarctic ice sheets, causing them to melt.

A discovery mission to the Southern Ocean off Antarctica, one of the most remote and inaccessible oceans of the world, has revealed that swirling ocean eddies transport layers of warm water towards the coast of Antarctica.

It is hoped that the findings, published today in Nature Geoscience, will help refine ocean and climate models, so that scientists can more accurately predict the rate at which ice sheets will retreat and how quickly global sea level will rise as a result.

Three robotic underwater gliders were deployed to explore waters on the Antarctic continental shelf to see how warm water is reaching the coast. This warmer water is normally found hundreds of metres down throughout the Southern Ocean, but how it reaches the shallow water around Antarctica has not been observed before.

The gliders were remotely controlled from Norwich, more than 10,000 miles away, and they sent data back via satellite mobile phone technology every few hours for two months.

Prof Karen Heywood, from UEA's Centre for Ocean and Atmospheric Sciences, said: "Our robots help us to build up a picture of underwater conditions by collecting data on water salinity, temperature, and oxygen levels. The results have identified ocean features that could not feasibly have been studied by any other means.

"This research was particularly challenging because the seawater quickly freezes to form sea ice and can trap the sea gliders, just like Shackleton's ship Endurance was trapped in the same area 100 years ago," she added.

The research team found that warm salty water was managing to reach the Antarctic continental shelf by being transported by eddies - swirling underwater storms that are caused by ocean currents.
"Our research reveals the process by which warm water is being transported towards the ice. It is important because the rapidly melting ice sheets on the coast of West Antarctica are a potential major contributor to rising ocean levels worldwide.

"Physical processes in this area of the Antarctic are important for global climate and chemical cycles. But steep terrain and complex interactions between the atmosphere, sea ice, and water combine to make this particularly challenging for climate models, as well as for making observations. The use of ocean gliders is beginning to revolutionise our understanding of polar ocean processes."

"This is just the start of understanding polar processes, but we hope it will help refine ocean and climate models, and predict future rates of retreat for Antarctic ice shelves."

'Eddy transport as a key component of the Antarctic overturning circulation' is the cover-story for December issue of Nature Geoscience, to be published online on November 10, 2014.