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Clam shells hold key to reconstruct historical climate change records

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Archeologists have discovered a way to reconstruct past changes in the climate by analyzing the shells of surf clams, a food consumed by people for thousands of years.

Detailing their research in the journal , archeologists from Louisiana State University in the U.S., tracking the climate phenomenon called the El Nino South Oscillation (ENSO), the warm phase of which is characterized by warmer ocean temperatures, increased rainfall and hurricanes in the southern U.S., worked at sites in northern Peru, collecting surf clam specimens from local markets and beaches in 2012, 2014 and 2016.

Northern Peru is one of the areas most affected by ENSO, with the cold, deep water off the coast making it one of the most productive fisheries in the world, . When a warm ENSO event occurs, it can result in fisheries dying off.

Using a short-lived species of surf clam for the first time, called Donax obesulus, the archeologists examined the shells they collected over the years. Clams create layers in their shells as they grow, similar to tree rings, and by drilling along the shell to collect samples, the researchers were able to get a snapshot of what the ocean temperature was as the shell grew.

“Using the relationship between the chemistry of the shell and the ocean temperature, we found Donax obesulus can record sea surface temperature pretty well. With this information, we can push this back in time and reconstruct what the temperature and climate was in the past,†said lead author Jacob Warner in the release.

Because ancient civilizations consumed surf clams and left them at archeologically significant sites, researchers can reconstruct the climate and its fluctuations from nearly 3,000 years ago.

Warner, of Lousiana State University in the U.S., also collaborated with University of Alberta archeologist Aleksa Alaica at a separate archeological site in the Jequetepeque Valley in northern Peru where, by analyzing Donax obesulus shells, the team gained insight into the ancient civilization that lived there.

Alaica and Warner found the clam shells were bigger during warmer ENSO events, making them a good source of evidence for paleoclimate study. They also discovered that the ancient people who lived at the site preferentially harvested larger individual clams, which indicated a fisheries management practice in place more than 2,000 years ago.

“The equipment available now, compared to the past, is precise and powerful enough to be able to reveal the sea surface temperature and the overall climate at a specific location when the clam was building its shell. This gives us archaeologists and paleoclimatologists another tool in our proverbial toolbox to reconstruct past climate. As we know today, climate can influence all kinds of practices and behaviors, which may have been the case in ancient civilizations as well,†Warner said in the release.

Warner is continuing his use of clam shells to reconstruct historical climate change at another archeological site in north-central Peru known as Caylan, in the Nepena Valley, which was occupied between 2,200 to 2,600 years ago.

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