Shells in Peru help to understand El Niño

Scientists studying the shells found along the coast of Peru say they can track changes in ocean temperatures over time, “reading” the smallest changes in shell structure. They hope this will lead to a better understanding of the El Niño Southern Oscillation (ENSO), a weather pattern that affects ocean heat and often brings more rain and tropical storms to parts of the world.

The hard shells of bivalve species such as clams and oysters tend to grow in layers throughout their lives. When archaeologists and paleoclimatologists study these tiny shell layers, they can see clues to past weather conditions. The idea is a lot like studying the growth rings of a tree to understand its history.

“The equipment available now, compared to the past, is accurate and powerful enough to reveal the sea surface temperature and general climate at a specific location when the mollusc was building its shell,” explains doctoral candidate Jacob Warner at Louisiana State University in the United States and lead author of a new research article published in the journal chemical geology .

“As we know today, weather can influence all kinds of practices and behaviors, which may have been the case in ancient civilizations as well,” adds Warner.

Clam shells Donax obesulus

The team studied the shells of molluscs Donax obesulus , which has never been used in this type of search before. Similar work has been successfully carried out in another short-lived species, the Mesodesma donacium, But these molluscs are no longer found in the northern part of Peru, where the research is focused.

The team used precision holes to sample the shells, marking time intervals that contribute to an overall picture of the shells. ocean temperatures as the bark grew.

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“Using the relationship between shell chemistry and ocean temperature, we found that Donax obesulus it can record sea surface temperature very well,” Warner said. One of the things they look at, for example, is the proportion of specific oxygen isotopes found in the composition of shells.

“With this information, we can go back in time and reconstruct what the temperature and climate were like in the past,” he said.

looking for better alternatives

But because these types of clams only live for three to five years, they cannot provide long time lines for ocean temperature trends. Warner is collaborating with other research teams to make comparisons with projectiles that are thousands of years old. He is also working on previous meteorological records in Caylán, in the Nepeña Valley, Peru.

Among those other scientists is Aleksa Alaica, a postdoctoral researcher at the University of Alberta who has analyzed surfing molluscs. Donax obesulus found at an archaeological site in the Jequetepeque Valley, Peru. They were part of the diet of ancient peoples who lived there thousands of years ago, and the shells remain in ancient settlements. Alaica is finding that shell sizes were larger during the hottest ENSO events.

“This collaborative study shows the power of simple methods to examine complex issues. Our work highlights the multiple factors that affect the growth of the cascara and the resilience of communities in the past to respond to climatic and social changes”, said Alaica.

By Lauren Fagan. Article in English

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