Until now, scientists have measured ice thickness using satellite images, visual estimates, and by drilling holes in the ice itself. But in Antarctica, much of the floating ice is actually underwater, with ice so thick that drilling and satellite images just don't work. For the past four years, a team of researchers from the US, UK, and Australia have been deploying an autonomous underwater vehicle they call SeaBED to explore areas that divers and other machinery can't reach and, using sonar, measure the ice's thickness from the bottom looking up, reports UPI. They're now reporting in the journal Nature Geoscience that, while a lot of ice remains to be measured, they've been surprised to find ice as thick as 65 feet.
Because most of the ice in Antarctica melts away during the summer months, scientists had long assumed it wouldn't be terribly thick—previous research has indicated it's usually 3 to 6 feet thick, and in some places as many as 16 feet thick, reports LiveScience. But what they've found thus far has averaged 4.6 to 18 feet, with measurements maxing out at 65 feet in the Bellingshausen Sea. Sea ice has actually been growing in Antarctica by 1.2% to 1.8% a year since 1979, though the increases are mainly in the Ross Sea (it's decreased significantly in the Bellingshausen and Amundsen seas), adds LiveScience. Scientists say these regional differences are likely due to stronger winds or more meltwater from the Antarctic ice sheet. (See a few more theories about the increasing ice.)