Underwater Robot Makes Puzzling Find on Antarctic Sea Ice Thickness

Antarctica's ice paradox has yet another puzzling layer. Not only is the amount of sea ice increasing each year, but an underwater robot now shows the ice is also much thicker than was previously thought, a new study reports.

According to climate models, the region's sea ice should be shrinking each year because of global warming. Instead, satellite observations show the ice is expanding, and the continent's sea ice has set new records for the past three winters. At the same time, Antarctica's ice sheet (the glacial ice on land) is melting and retreating. Measuring sea ice thickness is a crucial step in understanding what's driving growth of sea ice, said study co-author Ted Maksym, an oceanographer at the Woods Hole Oceanographic Institution in Massachusetts.

"If we don't know how much ice is there is, we can't validate the models we use to understand the global climate," Maksym said. The findings were published Monday in the journal Nature Geoscience.

Much of Antarctica's floating sea ice is underwater, hidden from satellites. And the thickest ice is also hardest to reach, Maksym said. Over the last four years, the researchers have mapped the bottom of sea ice with an underwater robot, or autonomous underwater vehicle (AUV), during two research cruises. The AUV can swim to a depth of about 100 feet (30 meters) and has upward-looking sonar. "With the AUV, you can get under ice that is either difficult to access or difficult to drill, and in each region, we found some really thick ice, thicker than had been measured anywhere else," Maksym said.

Almost all of the sea ice that forms during the Antarctic winter melts during the summer, so scientists had assumed it never grew very thick. Previous studies suggested the ice was usually 3 to 6 feet (1 to 2 meters) thick, with a few rare spots up to 16 feet (5 meters) in thickness. The robot sub surveys showed the thickness was 4.6 to 18 feet (1.4 to 5.5 meters). The thickest ice was about 65 feet (20 meters) thick, in the Bellingshausen Sea, Maksym told Live Science.

— Becky Oskin, LiveScience

This is a condensed version of a report from Live Science. Read the full report. Follow Becky Oskin @beckyoskin. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.