Robotic ocean gliders discover new answers to why polar ice is melting
Researchers have a new tool in determining how and why polar ice is melting that has already discovered important new information. Scientists say evidence points to warmer oceans having a greater impact on melting ice than warmer air in the atmosphere, but understanding how that warmer water is circulating is crucial to finding out how fast the ice is melting and how quickly ocean levels will rise.
Robotic gliders used by researchers at Caltech and University of East Anglia were able to reach parts of the oceans surrounding Antarctica that couldn't previously be reached. Before the gliders, researchers would lower instruments from ships or count on satellite data to reveal ocean temperatures and conditions, but in the Souther Ocean, those two ways of gathering data just didn't work.
Andrew Thompson, assistant professor of environmental science and engineering at Caltech said, "Observationally, it's a very hard place to get to with ships. Also, the warm water is not at the surface, making satellite observations ineffective."
In Antarctica, the warmest water isn't at the top, as is usually the case. Because of the different water temperatures moving around the area, coupled with salinity which makes water denser, the warmest water is actually sandwiched in the middle layers of the water column. The robotic gliders were able to take temperature readings at multiple depths to show what was really going on below the surface.
The gliders are about six feet long and bullet-shaped. They don't have a propeller; instead batteries power a pump that pushes fluid in and out of a compartment making it either more or less buoyant, causing it to sink or rise to the surface. The glider is very energy efficient, meaning it can dive for long periods and collect more data. The glider sends information back to researchers with a cell phone-like device in its tail that connects to the researchers and automatically sends data whenever it surfaces.
Back in January 2012, the gliders spent two months investigating the waters around the Antarctic Peninsula, diving down to depths of a kilometer and back up again, taking temperature and salinity readings as they went. The researchers have been crunching all of the data the robots gathered and have found out something significant: the heat was being brought in by eddies, swirling underwater storms that are caused by ocean currents.
"Eddies are instabilities that are caused by ocean currents, and we often compare their effect on the ocean to putting a spoon in your coffee," Thompson says. "If you pour milk in your coffee and then you stir it with a spoon, the spoon enhances your ability to mix the milk into the coffee and that is what these eddies do. They are very good at mixing heat and other properties."
The gliders allowed the researchers to see the impact of these eddies because of the depths they could reach and their ability to work for months at a time. Without these new tools, this major cause of warm water reaching Antarctica may not have been discovered.
Now that the researchers know this, they can start monitoring ocean currents more closely to observe these eddies and the warm temperatures they bring in and pair that with meteorological data. In December, the researchers plan to send the gliders to the Drake Passage at the southern tip of South America. The robotic gliders will dive while Wavegliders, another type of marine robot that skims the surface of the water, collect data at the surface.