Six massive glaciers in West Antarctica are moving faster than they did 40 years ago, causing more ice to discharge into the ocean and global sea level to rise, according to new research. The amount of ice draining collectively from those half-dozen glaciers increased by 77 percent from 1973 to 2013, scientists report this month in Geophysical Research Letters, a journal of the American Geophysical Union. Pine Island Glacier, the most active of the studied glaciers, has accelerated by 75 percent in 40 years, according to the paper. Thwaites Glacier, the widest glacier, started to accelerate in 2006, following a decade of stability.
The study is the first to look at the ice coming off the six most active West Antarctic glaciers over such an extended time period, said Jeremie Mouginot, a glaciologist at University of California-Irvine (UC-Irvine) who co-authored the paper. Almost 10 percent of the world's sea-level rise per year comes from just these six glaciers, he said.
"What we found was a sustained increase in ice discharge—which has a significant impact on sea level rise," he said.
The researchers studied the Pine Island, Thwaites, Haynes, Smith, Pope and Kohler glaciers, all of which discharge ice into a vast bay known as the Amundsen Sea Embayment in West Antarctica.
The amount of ice released by these six glaciers each year is comparable to the amount of ice draining from the entire Greenland Ice Sheet annually, Mouginot said. If melted completely, the glaciers' disappearance would raise sea levels another 1.2 meters (four feet), according to co-author and UC-Irvine Professor Eric Rignot.
The decades of increasing speeds and ice loss are "a strong indication of a major, long-term leakage of ice into the ocean from that sector of Antarctica," noted Rignot.
This region is considered the potential leak point for Antarctica because of the low seabed. The only thing holding it in is the ice shelf," said Robert Thomas, a glaciologist at the NASA Wallops Flight Facility, in Wallops Island, Va., who was not involved in the study. Ice shelves are platforms of permanent floating ice that form where glaciers meet the sea. In West Antarctica, ice shelves prevent the glaciers investigated in the study from slipping more rapidly into the ocean.