Deep channels link ocean to Antarctic glacier

Researchers from UK and US International Thwaites Glacier Collaboration (ITGC), collected 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 ice shelf in a British Antarctic Survey Twin Otter aircraft, the other mapped the sea floor at the ice front from the US Antarctic Program icebreaker RV Nathaniel B Palmer.

Publishing this month (9 September) in the journal The Cryosphere the two research papers describe the discovery. Thwaites Glacier covers 192,000 square kilometres (74,000 square miles) -- the size of Great Britain or the US state of Florida -- and is particularly susceptible to climate and ocean changes.

Over the past 30 years, the overall rate of ice loss from Thwaites and its neighbouring glaciers has increased more than 5-fold. Already, ice draining from Thwaites into the Amundsen Sea accounts for about four percent of global sea-level rise. A run-away collapse of the glacier could lead to a significant increase in sea levels of around 65 cm (25 inches) and scientists want to find out how quickly this could happen.

Lead author Dr Tom Jordan, an aero-geophysicist at British Antarctic Survey (BAS), who led the airborne survey, says:

"It was fantastic to be able to map the channels and cavity system hidden beneath the ice shelf; they are deeper than expected -- some are more than 800 metres deep. They form the critical link between the ocean and the glacier.

"The offshore channels, along with the 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."

Dave Porter at LDEO Columbia University, who flew over Thwaites Glacier for the airborne survey, says:

"Flying over the recently-collapsed ice tongue and being able to see first-hand the changes occurring at Thwaites Glacier was both awe inspiring and disconcerting, but also gratifying to know the airborne data we were collecting would help reveal the hidden structures below."

Exceptional sea-ice break up in early 2019 enabled the team on the RV Nathaniel B Palmer to survey over 2000 square kilometres 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 the sea floor is generally deeper and has more deep channels leading towards the grounding line under the ice shelf than was previously thought.

Lead author, Dr Kelly Hogan, is a marine geophysicist at BAS. She was part of the team surveying the seabed. She says:

"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. By examining retreat patterns over this sea-floor terrain we will be able to help numerical modellers and glaciologists in their quest to predict future retreat.

"This research has filled a critical data gap. Together the new coastal sea floor maps and the cavity maps track the deep channels for over 100 km to where the glacier sits on the bed. For the first time we have a clear view of the pathways along which warm water can reach the underside of the glacier, causing it to melt and contribute to global sea-level rise."

Glossary

Ice shelf -- is a large floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are only found in Antarctica, Greenland, Canada, and the Russian Arctic.

Ice sheet -- also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km2 (19,000 sq mi).

Glacier -- is a huge mass of ice that moves slowly over land. The term "glacier" comes from the French word glace (glah-SAY), which means ice. Glaciers are often called "rivers of ice."