At the current rate of retreat, the vast glaciers, which extend deep into the heart of the ice sheet, could contribute up to 3.4 meters to the global sea level rise over the next few centuries.
Antarctica is covered by two large masses of ice: the ice sheets of East and West Antarctica, which feed many individual glaciers. Due to global warming, WAIS has been accelerating at an accelerated rate over the past few decades. Within the ice sheet, the Thwaites and Pine Island glaciers are especially vulnerable to global warming and are already contributing to rising sea levels.
Now, a new study led by the University of Maine and the British Antarctic Survey, which includes academics from Imperial College London, has measured the local rate of change in sea level, an indirect way of measuring ice loss. around these especially vulnerable glaciers.
They discovered that glaciers have begun to retreat at a rate not seen in the last 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 increases in global sea level.
Co-author Dr. Dylan Rood of the Imperial Department of Earth Science and Engineering said: “Although this vulnerable glacier has been relatively stable over the last millennia, its rate of retreat has been relatively stable. current is accelerating and global sea level is already rising.
“These current high rates of melting ice may indicate that the vital arteries of the heart of the West Antarctic ice sheet have broken, leading to an acceleration of ocean flow that is potentially disastrous for the future. Global sea level in a warming world. Too late to stop the bleeding? “
The paper is published in Nature Geoscience.
Looking for sea shells
During the Middle Holocene period, more than 5,000 years ago, the climate was warmer than it is today, so the sea level was higher and the glaciers smaller. Researchers have wanted to study sea level fluctuations since the mid-Holocene, so they studied the remains of ancient Antarctic beaches, which are now high above modern sea levels.
They examined sea shells and penguin bones on these beaches using radiocarbon dating, a technique that uses the radioactive decay of carbon enclosed in shells and bones as a clock to tell us how long they have been sitting on the level of the beach. mar.
When heavy glaciers land on the ground, they push or “load” the Earth’s surface. After glacier ice melts or “unloads,” the earth “bounces” so that what was once a beach is now higher than sea level. This explains why the local sea level of this land dropped, while globally the melting ice water caused the sea level to rise.
By identifying the exact age of these beaches, they were able to know when each beach appeared and thus reconstruct local, or “relative”, sea level changes over time.
The results showed a steady fall in relative sea levels over the past 5,500 years, which researchers interpret as a result of ice loss just before that time. This pattern is consistent with the relatively stable behavior of the glacier with no evidence of large-scale glacier loss or advance.
They also showed that the relative rate of fall in sea level since the mid-Holocene was almost five times lower than today. Scientists have found that the most likely reason for such a big difference is the rapid loss of recent ice mass.
The researchers also compared their results with existing global models of the dynamics between the ice and the earth’s crust. Their data showed that the models did not accurately represent the history of sea level rise in the area during the Middle and Late Holocene according to their data. This study helps to draw a more accurate picture of the history of the region.
Although their data do not rule out the possibility of minor fluctuations in 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 Holocene to recent times. – and that the current rate of glacier retreat that has doubled over the last 30 years is, in fact, unprecedented in the last 5,500 years.
The lead author, Professor Brenda Hall of the University of Maine, said: “The relative change in sea level allows you to see the large-scale loading and unloading of crust by ice. For example, the advance of the glacier, which would result in a load of crust, would reduce the relative rate of fall from sea level or even cause the earth to sink below sea level. “
Stop the bleeding
To better predict the future fate of the ice sheet and its impact on global sea level, the International Collaboration of Thwaites Glaciers (ITGC), the largest joint field science program in the United Kingdom and the United States never performed in Antarctica, with which imperial researchers are involved. , will improve our understanding of the past behavior of the Thwaites Glacier during weather conditions similar to the current ones.
There are also important tracks buried under the ice. To solve these mysteries, researchers will drill ice from the glacier to pick up the rock below, which may contain evidence of whether current melting acceleration rates are reversible or not.