Antarctica is covered by two enormous ice masses: the East and West Antarctic Ice Sheets, which feed many individual glaciers. Due to a warming climate, the Western WAIS has been shrinking at an accelerating rate in recent decades. Within the ice sheet, the Antarctic Thwaites and Pine Island glaciers are particularly vulnerable to global warming and are already contributing to sea-level rise.
A new study led by the University of Maine and the British Antarctic Survey, including academics from Imperial College London, has measured the rate of local sea-level change – an indirect way of measuring ice loss – around these particularly vulnerable glaciers.
They found that glaciers have begun to recede at a rate not seen in the last 5,500 years. With areas of 192,000 km2 (nearly the size of the island of Great Britain) and 162,300 km2 respectively, the Thwaites and Pine Island glaciers have the potential to cause large rises in global sea level.
Co-author of the paper published in the scientific journal Nature Geoscience, Dylan Rood, said in a statement Thursday that the findings “reveal that although these vulnerable glaciers were relatively stable over the last few millennia, their current rate of retreat is accelerating and already global sea level rises.
“These currently elevated rates of ice melt may indicate that those vital arteries at the heart of the West Antarctic Ice Sheet have ruptured, leading to accelerated flow into the ocean that is potentially disastrous for future global ice levels.” sea in a warming world. Is it too late to stop the bleeding?” asks Rood, a researcher at the Department of Earth Sciences and Engineering at Imperial College.
During the mid-Holocene period, more than 5,000 years ago, the climate was warmer than it is today, and therefore sea levels were higher and glaciers were smaller. The researchers wanted to study fluctuations in sea level since the mid-Holocene, so they studied the remains of ancient Antarctic beaches, which today rise above modern sea level.
They examined marine shells and penguin bones on these beaches using radiocarbon dating, a technique that uses the radioactive decay of carbon locked up in shells and bones like a clock to tell us how long they have lain above sea level.
When heavy glaciers settle on the land, they push down or “load” the Earth’s surface. After the ice from the glaciers melts or “discharges”, the land “bounces back” so that what was once a beach is now higher than sea level. This explains why local sea levels fell for this land, while globally water from melting ice caused global sea levels to rise.
By pinpointing the precise age of these beaches, they were able to tell when each beach appeared and thus reconstruct changes in local or ‘relative’ sea level over time. The results showed a steady drop in relative sea level over the past 5,500 years, which the researchers interpret as a result of ice loss just before that time. This pattern is consistent with relatively stable glacial behaviour with no evidence of large-scale glacial loss or advance.
The researchers also showed that the rate of relative sea-level decline since the mid-Holocene was almost five times less than what is measured today. The scientists found that the most likely reason for such a large difference is the recent rapid loss of ice mass.
The experts also compared their results with existing global models of the dynamics between ice and the Earth’s crust. Their data showed that the models did not accurately represent the area’s sea-level rise history during the middle and late Holocene based on their data. This study helps paint a more accurate picture of the region’s history.
Although their data do not exclude the possibility of minor fluctuations of the Thwaites and Pine Island glaciers over the past 5,500 years, the researchers concluded that the simplest interpretation of their data is that these glaciers have been relatively stable from the mid-Holocene to recent times. and that the current rate of glacier retreat, which has doubled in the last 30 years, is unprecedented in the last 5,500 years.
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