About 9,000 years agowhen global temperatures increased with the end of the Last Ice Age, the ice ofEast Antarctica they suffered one particularly rapid fusion: the cause of this amplification was the effect of melt water on ocean circulation. The researchers managed to reconstruct the sequence of events, a real “ripple effect“, which led to the acceleration of the melting of the cap. The discovery, published in the journal Nature Geosciencewas made by an international team led by the National Institute of Polar Research of Japan: it is important because this phenomenon can happen again with current global warming, resulting in a accelerated global sea level rise.
The ripple effect that led to the melting of Antarctic ice 9,000 years ago
The researchers analyzed the marine sediment cores collected in Lützow-Holm Bay, along the north-eastern coast of Antarctica, during the Japanese Antarctic Research Expeditions (JARE) between 1980 and 2023. Thanks to sedimentological, micropaleontological and geochemical analyses (particularly measurements of beryllium isotope ratios), the researchers were able to reconstruct past environmental changes in the bay and its surroundings. It turned out that about 9000 years ago the influx of deep, warm circumpolar marine waters. To understand the cause, the researchers conducted simulations that highlighted how the origin was melting of ice of other areas of the Antarctic ice sheet, due to rising temperatures. The water produced by the melting spread throughout the ocean surrounding Antarctica and, being sweet and consequently too light to sink, formed a superficial layer that did not mix with the warmer, deeper water. This phenomenon altered ocean circulation and allowed warm water to reach the ocean-floating ice shelf in Lützow-Holm Bay while maintaining its temperature.
The heat began to consume the base of the platform and this, as it disintegrated, was no longer able to support the ice on the mainland, which therefore began to slide more rapidly towards the sea. This new supply of cold and fresh water in turn encouraged the circulation of deep warm waters, which accelerated the melting of the ice: it was therefore a so-called “feedback” mechanismor of feedbackwhich involves effects that follow one another in a chain until they come back to influence the starting process.
A phenomenon that can repeat itself with global warming
The study highlights how in Antarctica the melting of ice in a certain area can also strongly influence that of other distant areas of the ice cap. The mechanism, which at the end of the Last Ice Age was triggered by a climate change of natural origin, can be reactivated in the presence of current global warming. Recent observations indicate that already now portions of the East Antarctic ice sheetwhich include for example the Pine Island and Thwaites glaciers, they are retreating at an accelerating pace due to the influx of deep warm waters. The ripple effect would lead to a accelerated global sea level rise and climate models will have to take this into account when developing future scenarios. Professor Suganuma, author of the study, concludes: “This study provides essential data and modeling evidence that will facilitate more accurate predictions of the future behavior of the Antarctic ice sheets. The feedback cascades identified in this study serve to underline the idea that small regional alterations can potentially generate global consequences”.
