At the current rate of retreat, the vast glaciers, which stretch deep into the core of the ice sheet, could contribute up to 3.4 meters to global sea level rise over the next few centuries.
Antarctica is covered by two huge masses of ice: the East and West Antarctic Ice Sheets, which feed many individual glaciers. Due to global warming, the WAIS has been thinning at an accelerating rate over the past few decades. Within the ice sheet, the Thwaites and Pine Island glaciers are particularly vulnerable to global warming and are already contributing to sea level rise.
Now a new study 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 the loss of ice – around these particularly vulnerable glaciers.
They discovered that the glaciers had begun to retreat at a rate not seen in the past 5,500 years. With areas of 192,000 km2 (almost 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 sea level rises globally.
Co-author Dr Dylan Rood of Imperial’s Department of Earth Science and Engineering said: “We reveal that although these vulnerable glaciers have been relatively stable over the past millennia, their rate current recession is accelerating and is already raising global sea levels.
“These currently high rates of ice melt may signal that these vital arteries in the heart of the West Antarctic Ice Sheet have ruptured, leading to accelerated outflow into the ocean, which is potentially disastrous for the future. global sea level in a warming world. Is it too late to stop the bleeding?”
The paper is published in nature geoscience.
Search for shells
In the middle of the Holocene, more than 5,000 years ago, the climate was warmer than today and therefore the sea level was higher and the glaciers were smaller. The researchers wanted to study sea level fluctuations since the mid-Holocene, so they studied the remnants of ancient Antarctic beaches, which today are elevated above modern sea level.
They examined penguin shells and bones on these beaches using radiocarbon dating – a technique that uses the radioactive decay of carbon locked in shells and bones like a clock to tell us how long they have been living for. sit above sea level.
When heavy glaciers rest on the ground, they push or “load” the surface of the Earth. After the melting or “unloading” of ice from the glaciers, the land “bounces back” so that what was once a beach is now higher than sea level. This explains why the local sea level for this land has sunk, while globally water from melting ice has caused global sea levels to rise.
By identifying the precise age of these beaches, they were able to tell when each beach appeared and thus reconstruct changes in the local or “relative” sea level over time.
The results showed a steady decline in relative sea level over the past 5,500 years, which the researchers interpret as the result of ice loss just before that time. This pattern is consistent with relatively stable glacier behavior without evidence of large-scale glacier loss or advance.
They also showed that the rate of relative sea level fall since the mid-Holocene was almost five times lower than that measured today. Scientists have found that the most likely reason for such a difference is the recent rapid loss of ice mass.
The researchers also compared their results to existing global models of the dynamics between ice and the Earth’s crust. Their data showed that the models did not accurately represent the region’s sea level rise history during the mid to late Holocene based on their data. This study helps paint a more accurate picture of the region’s history.
Although their data does 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 since mid-Holocene to recent times. — and that the current rate of glacier retreat which has doubled in the past 30 years is, indeed, unprecedented in the past 5,500 years.
Lead author Professor Brenda Hall from the University of Maine said: “Relative sea level change allows you to see large-scale loading and unloading of crust by ice. For example, the re-advancement of glaciers, which would lead to crustal loading, slow the rate of relative sea level decline or even potentially cause land to submerge below sea level.”
Stop the bleeding
To better predict the future fate of the ice sheet and its impact on global sea levels, the International Thwaites Glacier Collaboration (ITGC) – the largest joint Anglo-American field science program ever conducted in Antarctica – to which Imperial researchers are involved, will improve our understanding of the past behavior of the Thwaites Glacier under climatic conditions similar to those of today.
Important clues are also buried deep under the ice. To solve these mysteries, researchers will drill through the ice of the glacier to collect rocks underneath, which may contain evidence on whether or not current rates of melt acceleration are reversible.
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