Ancient Shellfish Rewrite History of El Niño Cycles in Our Oceans

El Niño is one of the most powerful drivers of climate change on our planet, and understanding its history is crucial when it comes to understanding how it affects the current climate. Now, ancient shells are revealing a bit more about the past history of El Niño and have shown that it was just as strong and possibly as frequent as the ones that we experience today.

In the past, scientists believed that the El Niño Southern Oscillation in the tropical Pacific Ocean was far weaker in ancient times due to a different configuration of the Earth's orbit.

"We thought we understood what influences the El Niño made of climate variation, and we've been able to show that we actually don't understand it very well," said Julian Sachs, one of the researchers, in a news release.

The scientists examined 25-foot-tall piles of shells from Mesodesma donacium clams that were eaten and then discarded over centuries into piles called middens. The researchers analyzed the shell layers in order to understand what temperatures the oceans were at the time. This, in turn, revealed one to three-year-long records of monthly temperature of the Pacific Ocean along the coast of Peru.

It turns out that 10,000 years ago, the El Niño cycles were strong. Then, roughly 7,000 years ago the shells showed a shift to the central Pacific of the most severe El Niño impacts, followed by a lull in the strength and occurrence of El Niño from about 6,000 to 4,000 years ago.

"Climate models and a variety of datasets had concluded that El Niños were essentially nonexistent, did not occur, before 6,000 to 8,000 years ago," said Sachs. "Our results very clearly show that this is not the case, and suggest that current understand of the El Niño system is incomplete."

The findings could help scientists better understand the El Niño systems of today. This, in turn, will help climate models and allow researchers to better predict how our world's climate with change in the future.

The findings are published in the journal Science.