Evidence of Ancient Ocean Upwelling During El Niño Off Peru’s Coast Provides Climate Change Clues

Contact: Margaret Nagle (207) 581-3745

When the oceanic phenomenon El Niño strikes every four to seven years, it wreaks havoc on the world’s weather patterns, fishing and agriculture. University of Maine anthropologist Dan Sandweiss wants to know how ancient civilizations coped with these blows to their way of life.

For the past five years, Sandweiss has been collaborating with researchers at the universities of Alabama and Arizona to study 10,000 years of climate change using seashells from Peruvian archaeological sites. Their work is funded by a $600,000 grant from the National Science Foundation.

The principal investigator on the project is University of Alabama geologist Fred Andrus. Approximately $182,000 of the grant funds the fieldwork led by Sandweiss, a UMaine professor of anthropology and Quaternary and climate studies.

“I’m particularly interested in past climate along the coast of Peru, in the ancient cultures that developed and the resources they used,” says Sandweiss, who also is dean and associate provost for UMaine graduate studies.

To learn about ancient climate, Sandweiss and his colleagues are studying terrestrial and marine samples from past and recent excavations. Those samples include remains of seashells, ancient fruits and plants, some of which came from tombs. Scientists speculate that the fruits and plants were left as food to use in the afterlife; shells were offerings.

Comparing the radiocarbon dates from the plant material and shells helps the researchers determine what was going on in the ocean in relation to climate change.

In particular, they are focusing on upwelling, which typically occurs on western coasts when the ocean churns, bringing cold water to the surface that has long circulated near the ocean floor. With the upwelling comes nutrients that feed plankton, which feed fish.

However, upwelling during an El Niño event churns up warmer, less nutrient-rich water.

For the most part, shells work just like other organisms. While the creatures that live in them grow, the shells grow as well, taking in carbon from the water and the air.

However, when water has circulated at the bottom of the ocean long enough, it becomes like a dead animal, Sandweiss said. It loses its carbon-14 with none to replace it, until upwelling occurs and brings it back to the surface. Mollusks that live in this “old” water yield radiocarbon dates that are older than the shell’s real age. The more deep, nutrient-rich, old water is upwelled, the older the shells will appear to be.

By comparing the shell’s apparent age from carbon dating with that of the fruits and plants gathered from the same levels in the archaeological sites, the scientists can determine what kind of water was upwelling, which in turn reflects important climate parameters. The project focuses on the Middle Holocene Epoch about 4,000-8,000 years ago, when much of the world was warmer than today.

“If we can understand past climate better, we get some clues from what happened the last time the world was warmer and perhaps what will happen with global warming,” Sandweiss says.