Antarctica’s Doomsday Glacier is losing ice at its fastest rate in 5,500 years, raising concerns about the ice sheet’s future and the possibility of catastrophic sea level rise caused by the frozen continent’s melting ice. The finding comes from a study of prehistoric sea-deposits of penguin bones and limpet shells found on the shores surrounding the ‘doomsday’ Thwaites Glacier and its northern neighbour, the Pine Island Glacier, both located on the West Antarctic Ice Sheet. Antarctica’s glacial melt, driven by climate change, is advancing faster than ever before in recorded history, researchers reported late last week in the journal Nature Geoscience.
As one of Antarctica’s fastest-melting glaciers, Thwaites has earned its nickname. Since the 1980s, Thwaites has lost an estimated 595bn tonnes of ice, contributing to a 4% rise in global sea levels. Thwaites and the Pine Island Glacier, cover enormous expanses - Thwaites has a surface area of about 192,000sq km, making it nearly as big as Great Britain and Pine Island 162,300sq km. As the sea-facing ends of the glaciers are positioned above a bowl-like ocean basin, both are exposed on their undersides to currents of warm, dense, salty water. This warm water isn’t just melting the glaciers where they extend into the Amundsen Sea, but it is also whittling away at them from underneath, unpinning them from their main anchoring points located to the north. Additionally, this melt from below weakens the glaciers and makes them more prone to surface fractures, which could spread across the entire ice sheet, and potentially cause it to shatter. If the entirety of the West Antarctic Ice Sheet were to break up and melt into the sea, it would elevate global sea levels by approximately 11ft.
To compare the glaciers’ melt rates today with those of the distant past, scientists looked for clues on Antarctic beaches close to where the glaciers terminated at the ocean. Ice weighs down land, so as some of that frozen weight melted and drained into the sea toward the end of the last ice age (around 11,500 years ago) the land rebounded to reveal shorelines that were previously hidden beneath the waves. By measuring the ages and heights of nearly two dozen shorelines, the scientists hoped to discover how quickly ice disappeared from the land before advancing again.
The researchers estimated the ages of the shorelines by collecting ancient shells and tiny fragments of penguin bones, before analysing the ancient biomatter with radiocarbon dating. After dating penguin bones and shells from more than 20 different shorelines, the scientists found that the oldest and highest beach began to form roughly 5,500 years ago. From that moment in time until about 30 years ago, ice loss exposed the shorelines at a rate of about 3.5mm each year, the researchers reported. But over the past three decades, the rate of shoreline advance has skyrocketed — up to 40mm per year. Although these vulnerable glaciers were relatively stable during the past few millennia, their current rate of retreat is accelerating and already raising global sea levels.
What this means for the future of Antarctica’s glaciers and ice sheet — and vulnerable coastlines around the globe — is unclear. The researchers’ findings, while alarming, don’t address how many times the glaciers may have retreated and readvanced across recorded history. The scientists hope to figure this out by drilling through the ice to sample rock of the landmass underneath it, which could show if the current rate of melt is reversible, or if the glaciers have truly passed a point of no return.
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