An analysis of yearly layers in cave deposits from India and China, published Nov. 5 in Science, found that eight ice-age warmings linked to stronger Atlantic circulation each lasted more than a century, averaging about 180 years—far longer than the decades indicated by Greenland ice-core records.
The warmings, called Dansgaard–Oeschger events, were sudden shifts during the last glacial period. Scientists study them to understand how ocean circulation affects climate. To time the events, researchers measured oxygen-isotope patterns in stalagmites from caves in northeast India and southwest China.
They combined these records with cave data published earlier. They compared the results with climate-model simulations. The cave records indicate that each transition lasted more than 100 years.
The corresponding signals in Greenland ice cores shifted in less than 70 years. The researchers say the difference reflects what the records capture. Retreating sea ice in the northeastern North Atlantic triggered a rapid change in the atmosphere that appeared in Greenland’s records.
But this shift did not represent the full recovery of ocean circulation. Their simulations suggest the Atlantic Meridional Overturning Circulation (AMOC) grew stronger still later, as sea ice continued to retreat in the northwestern North Atlantic. The team says the cave records better track this longer process.
Greenland’s isotope signal mainly records the faster atmospheric response. The findings help scientists better understand how sudden past climate changes were. But the glacial events do not provide a direct timeline for possible future AMOC changes under modern warming.