That Antarctica is melting is not in question – surface area is easily measured. The same goes for the surrounding seawater melting it. One question plaguing researchers, though, was how exactly that warmer water came in contact with the icy continent. Now, using dolphin-like robotic gliders, researchers from Caltech have found that storm-like underwater eddies beneath the continent play a role in transitioning warmer waters to the ice sheets.

“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,” explains lead author Andrew Thompson, assistant professor of environmental science and engineering at Caltech. “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.”

Traditional methods for measuring water temperature rely on ships dropping equipment into the sea. This is obviously a problem if you want to measure the water temperature beneath a continent, as ships cannot get to the source of the warm water. Since it’s not at the surface, satellite imaging doesn’t tell the whole story, either.

The gliders, on the other hand, are small (only about five feet long) and extremely energy efficient. This allows them to explore for much longer periods of time than any manned vessel could. Every few hours, the gliders surface and “call” the parent vessel via a device in the glider’s tail. Researchers can then download all data the glider has collected in real time.

The glider name is aptly applied – they have no propellers, and work by taking in (or jettisoning) seawater to change buoyancy. When the glider sinks or floats, the shape of the wings transfers vertical lift into horizontal movement, like an aircraft would. The gliders have been in use since early 2012.

They’ve found that, oddly, the warmest water isn’t at the surface (as density principles would predict), but rather sandwiched between the surface and the depths due to differences in salinity. The stamina of the gliders were able to observe over many months that eddies (swirling storm-like features similar to weather patterns topside) were responsible for moving the warm water up and out toward the ice sheets.

“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 says. “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.”