Researchers used robotic ocean gliders to investigate the rapidly melting ice sheets off the coast of West Antarctica that are predicted to be a major contributor to rising ocean levels.
Warm water near the coast is believed to be the main cause of the ice melt, but researchers are still unsure how the water ends up near the cold land in the first place, Caltech reported. The robots revealed swirling ocean eddies have a strong influence on the transportation of these warm waters, and these findings could help scientists determine how fast this ice is melting.
"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 lead author Andrew Thompson, assistant professor of environmental science and engineering. "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 gliders are only about six feet long and are energy efficient, allowing them to take measurements at lower depths for longer periods of time. When the robots surface every few hours they "call" the researchers through a mobile phone to relay the information they've collected.
The gliders were dropped off the coast of the Antarctic peninsula in January 2012, and spent the next two months exploring the local sea and collecting temperature and salinity readings.
"If it was only temperature that determined density, you'd always have warm water at the top and cold water at the bottom. But in the ocean you also have to factor in salinity; the higher the salinity is in the water, the more dense that water is and the more likely it is to sink to the bottom," Thompson said.
The robots revealed the source of the mysterious warm water was eddies, which are caused by ocean currents. The phenomenon can be compared to someone putting a spoon in their coffee.
"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," Thompson said.
In the future the researchers plan to combine meteorological data with those collected by the gliders in hopes of gaining even more insight into the warm water in the region. They will also use the robots to look at a particularly rough patch of ocean between the southern tip of South America and Antarctica, called the Drake Passage. These observations will provide insight into the exchange of carbon dioxide between the atmosphere and ocean.
"With the Waveglider, we can measure not just the ocean properties, but atmospheric properties as well, such as wind speed and wind direction. So we'll get to actually see what's happening at the air-sea interface," Thompson said.
The findings were published Nov. 10 in the journal Nature Geoscience.
