Antarctica’s melting ice could seriously raise the level of the world’s oceans. Already trillions of tons of ice have been lost. And little by little, researchers are identifying the warning signs of the looming collapse.
In Antarctica, there is an ice barrier that scientists call the Larsen Platform. Bordering the Weddell Sea, it essentially consists of three segments. Finally, not really. Since the Larsen A platform, the northernmost, collapsed in January 1995. And Larsen B experienced the same tragic fate in February 2002. Today, PennState University researchers(United States) tell us about the drama that began to unfold a few years earlier.
Antarctica could collapse in just a decade
Let’s first remember that these platforms are like tongues of ice floating on the water. Of course, the warming of the air and the ocean weakens these structures. But the processes that lead to their collapse have so far remained unknown to scientists – even though they are important to understand. Because these ice shelves behave like buttresses, barriers that prevent land ice from flowing into the sea, and thus contributing to the rise in the level of the oceans.
“Larsen B didn’t hold a lot of ground ice. Its loss was therefore not very significant for sea level. But it offers an exceptional laboratory to learn the warning signs and processes of loss of sea ice.explains Richard Alley, professor of geosciences, in a PennState press release.
The researchers say that, naturally, platforms calve. Understand that they lose large pieces that form icebergs. Then, they accumulate ice for decades, before calving again. But Larsen B, in connection with climatic anomalies, suddenly began to experience more frequent and smaller calvings. At the same time, the warm waters dug channels under the pack ice and modified its geometry and its resistance. And the ice began to flow faster out to sea. These could be early warning signs of sea ice destabilization.
The researchers add that as the ice retreated, it moved away from the rocky islands that served as the platform’s anchor point. A bit like removing one by one the thumbtacks holding a poster to the wall. The distribution of these anchor points would also have played a key role in the destabilization of the Larsen B ice shelf. This will help to better understand the dynamics of Antarctica in the context of global warming.
Already trillions of tons of ice lost
And to make even better forecasts of what lies ahead, University of Leeds researchers (United Kingdom) have studied a region a little further south of West Antarctica, the bay of the Amundsen Sea. It has twenty glaciers which, if they were to melt, would raise the level of the world’s oceans by more than a meter. However, it is also the region of Antarctica reputed to evolve most rapidly under the effect of climate change. So the researchers wanted to know how much.
They worked on what they call the « balance sheet » from the bay of the Amundsen Sea. They determined the difference between the mass of ice gained through snowfall and the mass of ice lost through calving. As a result, over the past 25 years, the region has lost more than 3,000 billion tons of ice. Enough to drown Manhattan under… 61 kilometers of water!
This work confirms the essential role of ocean temperature in the melting of the ice in West Antarctica. They also show how important extreme snowfall events are for glacier dynamics. Between 2009 and 2013, a snowy drought caused sea levels to rise 25% more than average. On the other hand, the very heavy snowfalls of 2019 and 2020 reduced the phenomenon by half.
