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Clam shells left behind after ancient people’s meals could offer a vital clue to understanding ancient climate change.
New tools can calculate the sea surface temperature and climate from tiny pale surfclams, which are smaller than a fingernail. They are found on beaches around the globe.
The shells were eaten in ancient civilisations. They could be used to provide snapshots of What the climate was like 3,000 years ago.
Jacob Warner of the LSU Department of Geography & Anthropology said, “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 civilisations as well.”
As they grow, clams form layers in their shells just like trees and tree rings.
Warner dug along the shell to take samples at every time point during the clam’s lifetime to get an instant snapshot of the ocean temperature.
Warner claims that the relationship between the layers is accurate enough to allow for a method to measure ocean temperature.
Warner says that Donax obesuluscan records sea surface temperature very well by using the relationship between the chemistry and ocean temperature. With this information, we can push this back in time and reconstruct what the temperature and climate was in the past.”
Warner and colleagues are working tracking a climate phenomenon that affects a large part of the world called the El Niño Southern Oscillation, or ENSO.
The warm phase of ENSO includes higher than normal ocean temperatures, higher rainfall, and more tropical storms or hurricanes in the southern U.S.
Warner’s study sites can be found in northern Peru which is one of ENSO’s most affected areas.
The researchers collected 18 surf clams from coastal beaches and markets in 2012, 2014, and 2016 to capture the sea surface temperature at different phases of ENSO.
This new research used Donax obesulus, a short-lived species of surf clam that was not previously used to reconstruct climate.
Warner collaborated with Aleksa Alaica (a postdoctoral researcher at University of Alberta) to analyze the surf clam Donax obsulus discovered at an archeological site in the Jequetepeque Valley, northern Peru.
They also discovered that ancient people who lived at this site preferred to harvest larger individual crabs. This suggests that there was a fisheries management system in place more than 2000 years ago.
Warner is currently reconstructing past climate using clam shells collected at another archeological site called Caylán in the Nepeña Valley of north-central Peru that was occupied about 2,200-2,600 years ago.
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