Global sea level rise pops up in news headlines once in a while, though the accelerating process is a matter of concern. It is in this connection that one has to analyse news about two research papers published last week in the European Geosciences Union’s journal The Cryosphere. They infer that the newly discovered deep seabed channels beneath Thwaites Glacier in West Antarctica may be the pathway for warm ocean water to melt the underside of the ice.
Data from two research missions, using aircraft and ship, are helping scientists to understand the contribution this huge and remote glacier is likely to make to future global sea level rise. Thwaites Glacier covers 192,000sq km – and is particularly susceptible to climate and ocean changes.
Researchers from the UK- and US-led International Thwaites Glacier Collaboration collected data from the glacier and adjoining Dotson and Crosson ice shelves during January-March 2019. While one team of international researchers collected airborne data flying over the glacier and ice shelf in a British Antarctic Survey (BAS) Twin Otter aircraft, the other mapped the sea floor at the ice front from the US Antarctic Programme icebreaker RV Nathaniel B Palmer.
During the past three decades, the overall rate of ice loss from Thwaites and its neighbouring glaciers has increased more than five-fold. Already, ice draining from Thwaites into the Amundsen Sea accounts for about 4% of global sea-level rise. A run-away collapse of the glacier could lead to a significant increase in sea levels of around 65cm (25in), and scientists want to find out how quickly this could happen.
Lead author Tom Jordan, an aero-geophysicist at BAS, who led the airborne survey, said the channels and cavity system hidden beneath the ice shelf are deeper than expected – some are more than 800m deep. 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 RV Nathaniel B Palmer to survey more than 2,000sq km 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 Kelly Hogan, a marine geophysicist at BAS and a part of the team surveying the seabed, described the coastal sea floor, which is incredibly rugged, as 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, numerical modellers and glaciologists can be helped in their quest to predict future retreat. This research has filled a critical data gap.
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