At the end of the last ice age, an armada of icebergs, each twice the height of the Empire State Building, broke off from the shoreline of Antarctica. According to a new study in the Proceedings of the National Academy of Sciences, they were created when a 280,000-square-kilometer (108,000-square-mile) section of the colossal Ross Ice Shelf collapsed in just 1,500 years.
The current stability of Antarctic ice shelves, the floating seaward extensions of ice sheets, is incredibly low. Man-made climate change is leading to unprecedented degrees of warming, causing the undersides of huge ice masses to melt and weaken. As a result, Larsen-A in the Antarctic Peninsula collapsed in 1995, followed by Larsen-B in 2002. Larsen-C, which is roughly 2.5 times the size of Wales, is due to follow suit.
Although these land-anchored ice shelves do not significantly contribute to sea level rise as they tumble into the ocean, they are acting as barricades for the landlocked ice sheets behind them. When removed, these enormous sheets may begin to join their watery grave, dramatically raising sea levels. For these reasons, researchers are keen to try and predict the future of gigantic ice shelves, and the Ross Ice Shelf, which is currently the size of France, is no exception to this.
The research vessel peeking at the ancient striations within the basin. L. Simkins/Rice University
“At the height of the last ice age, we know that the sheet of ice covering the Antarctic continent was larger and thicker than it is today,” said John Anderson, a professor of oceanography at Rice University and co-author of the paper, in a statement. “This continent-enveloping ice sheet extended all the way to the continental shelf, and in western Antarctica it filled the entire Ross Sea basin.”
Up to 18,000 years ago, this basin was packed with thick, heavy ice all the way down to the seafloor. The team decided to look for the telltale signatures of the movement of ice, large grooves in the seafloor known as striations, within this basin. To accomplish this, they used cutting-edge seafloor mapping systems aboard a U.S. research vessel – the most sensitive ever employed in the Antarctic.
By tracing the paths of these massive striations, they found that around 10,000 years ago, as the ice age ended, a huge number of icebergs broke off from the shelf and pushed themselves out to sea. As this happened, the remaining part of the shelf retreated back onto the land as the warmer and more acidic sea eroded its exposed front.
Within 1,500 years, an area the size of Colorado had fallen into the sea. There’s a chance that in our rapidly warming world, such collapses could become more commonplace, unleashing massive volumes of ice on the continent into the oceans.
When Larsen-B broke apart, the glaciers behind it began to move forwards toward the sea 10 times faster than they used to. If the Ross Ice Shelf follows the same path, a fleet of glaciers could plunge into the sea soon afterwards. Worryingly, the modern day Ross Ice Shelf is considered by glaciologists to be unstable, behaving in a similar way to its ancient predecessor prior to its dramatic, rapid collapse.