Clam shells could provide vital clue to understanding ancient climate change

Clam shells left behind after ancient people’s meals could offer a vital clue to understanding ancient climate change.

New tools can work out the sea surface temperature and overall climate from the shell of tiny pale surf clams - which are the size of a fingernail and found on beaches around the world.

The shells were consumed by ancient civilisations and could offer snapshots of what the climate was like up to 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 behaviours, which may have been the case in ancient civilisations as well."

Read more: Melting snow in Himalayas drives growth of green sea slime visible from space

Like trees and tree rings, clams create layers in their shells as they grow.

Warner drilled along the shell to collect samples at each interval of time during the clam's lifespan to get a snapshot of the ocean temperature.

Warner says that the relationship between the layers is precise enough to offer a way to measure ocean temperature.

He added: "Using the relationship between the chemistry of the shell and the ocean temperature, we found Donax obesuluscan 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.”

Watch: What is a 'Climatarian'?

Read more: A 1988 warning about climate change was mostly right

Warner and colleagues are working on 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 is characterised by warmer than normal ocean temperatures, increased rainfall and more tropical storms and hurricanes in the southern U.S.

Warner's study sites are in northern Peru, which is one of the areas most impacted by ENSO.

To capture the sea surface temperature from different phases of ENSO, the researchers collected 18 surf clams from markets and coastal beaches in 2012, 2014 and 2016.

This new research used a species of short-lived surf clam called Donax obesulus, which has not been used to reconstruct climate before.

Read more: Why economists worry that reversing climate change is hopeless

In a separate, forthcoming paper, Warner collaborated with fellow archeologist Aleksa Alaica, a postdoctoral researcher at the University of Alberta to analyse the surf clam Donax obesulus found at an archaeological site in the Jequetepeque Valley in northern Peru.

They also discovered that the ancient people, who lived at this site, preferentially harvested larger individual clams, which indicates a fisheries management practice in place more than 2,000 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.

Watch: HSBC warns clients they must have a plan to exit coal