Robotic gliders are the newest trend in marine exploration

Robo-dolphins exploring polar ice sheets

Three dolphin-like robots have been collecting data on melting of Antarctic ice as part of a pioneering study demonstrating the value of automated systems for environmental science.

The two-metre long robots, each costing about $240,000 (£150,000), were deployed in the Weddell Sea off Antarctica in January 2012 by a team led by researchers from the California Institute of Technology.

Carried by the ocean currents and vortices, the robots glided in water for two months measuring temperature and salinity.

The data helped the scientists to better understand how ocean currents transporting warm water towards Antarctica add to the disruption of the fragile ice sheets. The results of the study were described in an article published in the journal Nature Geoscience.

"When you have a melting slab of ice, it can either melt from above because the atmosphere is getting warmer or it can melt from below because the ocean is warm," said the study’s lead author Andrew Thompson. "All of our evidence points to ocean warming as the most important factor affecting these ice shelves, so we wanted to understand the physics of how the heat gets there."

The use of the battery-powered underwater drones immensely simplified the data collection process. Traditionally, researchers would have to send a survey ship into the area of interest, at a cost of at least $30,000 a day, which, in the case of the Southern Ocean, is "rather challenging," Caltech says.

The ability of those teams to collect data from aboard such a ship would be largely limited by how deep their instruments can reach.

The drones, on the contrary, can be left alone for months, diving up to one kilometre deep to paint the most accurate picture. Each glider's ability to dive is controlled by a simple pump that pushes fluid into an internal compartment to change its buoyancy.

The robotic dolphins surface every few hours to send data to the researchers via a mobile-phone connection, allowing for near real-time data assessment.

This constant access to up-to-date information has helped the researchers better understand how ocean vortices contribute to the transportation of warm water towards the coast of Antarctica. Due to their short-lived and unstable nature, these phenomena are hard to study using other methods such as satellite observation or ship measurements.

"Ocean currents are variable, and so if you go just one time, what you measure might not be what the current looks like a day later. It's sort of like the weather – you know it's going to be warm in the summer and cold in the winter, but on a day-to-day basis it could be cold in the summer just because a storm came in," Thompson said. "Eddies do the same thing in the ocean, so unless you understand how the temperature of currents is changing from day to day – information we can actually collect with the gliders – then you can't understand what the long-term heat transport is."

Even though one of the gliders, made by Norway’s marine technology company Kongsberg, got lost, the mission was still cheaper than a similar research trip made in 2007 by a ship, the researchers said.

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