“Although the ACC plays an important role in tomorrow’s climate, our understanding of its behaviour is still extremely limited,” says Dr Shuzhuang Wu, a researcher at the Marine Geosciences Section of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and first author of the study released in Nature Communications. “In order to remove the related uncertainties in the climate models and to improve future forecasts, we urgently need paleo-data, which we can use to reconstruct the conditions and behaviour of the ACC in the past.”
The only constriction on the ACC’s circular route is the Drake Passage between the southern tip of South America and the Northern tip of the Antarctic Peninsula. Here, no less than 150 million cubic metres of ocean water per second force their way through the Passage – more than 150 times the amount of water flowing in all of Earth’s rivers. This bottleneck is an ideal place to observe changes in the overall current. Accordingly, in 2016, AWI researchers travelled to the Drake Passage on board the research icebreaker Polarstern to investigate the sediment deposits from past millennia. “The bottom current here is so strong that in many places the sediment is simply washed away,” explains the leader of the expedition and co-author of the study, Dr Frank Lamy. “Nevertheless, using the Polarstern’s sediment echo sounder, we were able to detect the pockets of sediment and collect samples, including a core from a depth of 3,100 meters, measuring more than 14 metres in length. This was a significant achievement, since the last comparable cores from the Drake Passage dated back to the 1960s.”
The sediments from the new core accumulated over the last 140,000 years. As such, they cover an entire glacial-interglacial cycle, and contain information from the last glacial period, which began 115,000 years ago and ended 11,700 years ago, as well as from the preceding Eemian interglacial period, which began 126,000 years ago.