Deep Channels Linking Antarctic Glacier's Underside to Ocean Could Hasten Melting

BY EARTH INSTITUTE |SEPTEMBER 9, 2020

Newly discovered deep seabed channels beneath the Thwaites Glacier in West Antarctica may be pathways for warm ocean water to melt the undersides of the ice, and contribute to sea level rise, say scientists. The scientists have based their conclusions on data from two research missions, using aircraft and a ship.

Researchers from the UK- and U.S.-led International Thwaites Glacier Collaborationcollected the data from the glacier and adjoining Dotson and Crosson ice shelves during January–March 2019. While one team collected airborne data flying over the glacier and its adjoining ice shelf in a British Antarctic Survey aircraft, the other mapped the sea floor at the ice front from the U.S. Antarctic Program’s icebreaker Nathaniel B Palmer. Two research papers published this week in the journal The Cryosphere describe the discovery.

By flying geophysical instruments over the glacier, the researchers were able to map a system of channels and cavities extending some 100 kilometers back from the front of its floating ice shelf to where the ice sits on land, the so-called grounding line. Some of the features are 800 meters deep. The researchers say the maps give them for the first time a clear view of the pathways along which warm water may potentially reach the underside of the glacier, causing it to melt.

Above, a Twin Otter plane belonging to the British Antarctic Survey en route to Antarctica’s Thwaites Glacier. Below, leading edge of the glacier’s floating ice shelf; at this point, the ice sits about 70 meters above the water, with another 480 meters below the surface. (Both photos: Dave Porter/Lamont-Doherty Earth Observatory)

Dave Porter, a glaciologist at Columbia University’s Lamont Doherty Earth Observatory, who flew over Thwaites Glacier for the airborne survey, said, “Being able to see firsthand the changes occurring [there] was both awe-inspiring and disconcerting.”

Thwaites Glacier covers 192,000 square kilometers (74,000 square miles), equivalent to the area of Great Britain or the state of Florida. It is believed to be particularly susceptible to climate and ocean changes. During the past 30 years, the overall rate of ice loss from the Thwaites and its neighboring glaciers has increased more than fivefold. Already, ice draining from Thwaites into the adjoining Amundsen Sea accounts for about 4 percent of global sea level rise. A runaway collapse of the glacier could lead to an increase in sea levels of around 65 centimeters (25 inches). Scientists want to find out how quickly this could happen.

Lead author Tom Jordan, a geophysicist at British Antarctic Survey, said of the hidden features, “They form the critical link between the ocean and the glacier. The offshore channels, along with an adjacent cavity system, are very likely to be the route by which warm ocean water passes underneath the ice shelf up to the grounding line, where the ice meets the bed.”

Exceptional sea-ice breakup in early 2019 enabled the team on the Nathaniel B Palmerto survey more than 2,000 square kilometers of sea floor at the glacier’s ice front. The area surveyed had previously been hidden beneath part of the floating ice shelf extending from Thwaites Glacier, which broke off in 2002, and in most subsequent years the area was inaccessible due to thick sea-ice cover. The team’s findings reveal that the sea floor is generally deeper and has more deep channels leading toward the grounding line under the ice shelf than was previously thought.

“We found the coastal sea floor, which is incredibly rugged, is a really good analogue for the bed beneath the present-day Thwaites Glacier both in terms of its shape and rock type,” said Kelly Hogan, a British Antarctic Survey marine geophysicist. “By examining retreat patterns over this sea-floor terrain, we will be able to help numerical modelers and glaciologists in their quest to predict future retreat.”

Adapted from a press release by the British Antarctic Survey and the European Geosciences Union.