A Sea Change
Discovery of ancient clamshells provides new clues to the connection between climate and culture

About the Photo: "Knowing how El Niño got started and how people responded is important if we want to understand how environmental changes affect people today." — Dan Sandweiss

Sidebar Exploring Peru's pyramids Norwegian explorer and scientist Thor Heyerdahl is one of the most famous figures in modern archaeology.

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The summer sun beats unmercifully on the hot dry beaches of northern Peru. Just south of the equator, the landscape is anything but lush. Beyond the river valleys that drain the snowfields of the Andes, there is practically no vegetation. In fact, the Pacific coastline is so barren that NASA once came here to better understand the surface of Mars.

Just outside the industrial town of Chimbote, archaeologist Dan Sandweiss and a Peruvian colleague, Alfredo Narváez, drive their aging Land Cruiser off the PanAmerican Highway and onto a makeshift road of hard cobble that runs atop a ridge above the beach. They've come to look at the ridges, some 15 feet high, that snake for miles up the coast north of Chimbote.

No one knows why the ridges are here or how old they are. They hold far too much rock to be the result of human activity.

Sandweiss, an expert in seashells as they relate to marine resources used by humans, and Narváez strike out across the ridges toward an ancient bay that is now a salt flat. A nearly 8-foot cliff circles the flat like the lip of a giant bowl. The slope is littered with clam, oyster, cockle and scallop shells, most of which have no business being there.

"I had been focusing on shellfish for two years, reading everything I could find. I knew most of the species and knew these shouldn't be here," says Sandweiss of the discovery made in 1980.

Sandweiss took a few of the shells to a malacologist (mollusc specialist) at the Peruvian Institute of the Sea, who made a surprising identification — the shells are warm-water species on the cold-water coast of Peru.

That finding propelled Sandweiss, then a Cornell University graduate student, into the heart of discussions about marine resources, cultural development and climate change. His is a story about institutions and individuals responding to dramatic natural events over which they have no control.

Sandweiss and other archaeologists are listening for the faint echo of those struggles.

Sandweiss, a University of Maine associate professor of anthropology and Quaternary and climate studies, first conducted research on clams as a Yale University student. He analyzed shells and other remains at a historical site in the New Haven, Conn., harbor, harvesting quahogs and weighing the meat. He wanted to understand how significant they might have been in the diets of an earlier generation of residents.

Soon after, he was introduced to Peruvian studies and a controversial theory proposed in 1975 by archaeologist Michael Moseley. Sandweiss' interest in marine resources dovetailed nicely with Moseley's theory that the sea could provide a foundation for ancient cultural development.

At the time, the idea was a bit of heresy. Archaeologists generally agreed that irrigation agriculture — not the sea — was the bedrock of civilization. But Moseley and others demonstrated that in Peru, marine resources fueled a growing population that began building permanent stone structures starting about 6,000 years ago.

In fact, middens, or garbage heaps left in even older settlements, showed heavy dependence on fish and shellfish throughout what is known as Peru's Preceramic Period (about 11000 – 2250 B.C.). It was a time when humans were gradually shifting from living in nomadic hunter-gatherer bands to permanent settlements. In short, Moseley was arguing that clams and culture were intertwined.

Moseley suggested that if Sandweiss really wanted to understand the role of marine resources in Peru's ancient history, he needed to talk to modern fishermen. Sandweiss spent a summer conducting interviews. He became familiar with the fish and shellfish that Peruvian fishermen harvested, and learned about the preservation methods using salt and woven drying racks.

Moseley was right. The information turned out to be a key to the past. At archaeological sites, Sandweiss soon was able to recognize the pattern of postholes and the remains of materials used in fish drying racks.

Sandweiss didn't return to Peru until 1979, when he was a graduate student at Cornell University. His discovery of the ancient clam bed near Chimbote thrust his work into discussions about El Niño, the Pacific Ocean phenomenon that can affect weather around the globe.

Was El Niño an ancient phenomenon and did it affect cultural development in Peru? No one knew, but archaeologists were raising questions. One of them, James Richardson III of the Carnegie Museum of Natural History and the University of Pittsburgh, had found similar evidence farther north along Peru's coast more than 10 years before. His dissertation on molluscs as a possible indicator of a climate change suggested that a shift in species, and thus climate, occurred about 5,800 years ago.

Sandweiss also worked with two other University of Pittsburgh scientists, Harold Rollins and Jack Donahue. At Chimbote, they inspected the beach ridges and shells that Sandweiss found by the ancient bay. They sought to explain the mystery of the warm-water clams found in locations where, today, the cold Peruvian coastal current prevents tropical marine species from getting a foothold.

The strong El Niño of 1982 was a wake-up call. Northern Peru was hit with a dramatic warming of coastal waters, torrential rains and flooding. Houses and irrigation structures were washed away. The globally significant anchovy fishery crashed. Even in southern Peru, where the impact was weaker, the temporary warming eliminated cold-water clams from areas where they had thrived.

The clam species Sandweiss discovered required a warm, stable environment, not the stormy temper tantrum brought on by El Niño. In other words, El Niño as we know it today could not have existed. Instead, the ocean system must have been bringing warm water from the tropics. Ancient people in northern Peru may have lived in a grassland savanna with shrubs and trees instead of a barren desert. That is, until ocean currents changed, allowing cold water to stretch farther north.

Such a climate change would have created cold-water conditions like those found off the Peruvian coast today. The clams Sandweiss discovered are indicators of the climate change, which included El Niño.

In 1986, with Rollins as the lead author, Sandweiss and his colleagues presented their views in a new scientific journal, Geoarchaeology. They suggested that about 5,800 years ago, rising sea level and a shift in ocean currents led to a major environmental change along the northern Peruvian coast in a short 500-year period.

"The clams we found were in living position in a bay which had uplifted or dried catastrophically," Sandweiss says. "They were not imported by people. It was a reproducing, stable population that indicated very different conditions.
"My problem," he says, "was how to go about proving it."

After Sandweiss joined The University of Maine faculty in 1993, he and his colleagues worked with Dan Belknap and Kirk Maasch of UMaine's Department of Geological Sciences and Institute for Quaternary and Climate Studies, and Elizabeth Reitz, a University of Georgia scientist who specializes in the identification of fish bones in archeological sites.

Their subsequent research strengthened the climate change theory and gave it a global context. The 5,800-year-old story could now be told by shells and fish bones in other Peruvian middens, pollen in Australia, and molluscs in the Sea of Japan and off the coast of Greenland.

In 1996, the researchers' story was published in Science, one of the world's top scientific journals. The article generated media headlines around the world and caught the attention of scientists studying climate change from South America to New England.

The climate change that gave birth to El Niño set the stage for a cultural revolution that is seen today in the ruins of cities and water control structures.

People appear to have responded to the new environment by specializing in fishing and irrigated agriculture. Trade networks grew. Systems of political control evolved to manage the labor necessary to construct elaborate buildings and feed a growing population.

Archaeologists have unearthed many structures built by people who harvested riches from the sea and cultivated cotton, gourds, beans and other plants in irrigated valleys. As long as the destructive floods did not come too often, civilization could thrive.

"After the climate shift 5,800 years ago, you get people building monuments, exhibiting signs of a more complex social organization, not just bigger, not just settled, but something else entirely — communal labor to build the pyramids and temples.

"I don't think climate drives culture," Sandweiss adds, "but climate creates opportunities and necessities. It gives some people entrepreneurial opportunities to garner power and control."

Knowing how El Niño got started and how people responded is important if we want to understand how environmental changes affect people today, says Sandweiss. "Archaeology has a lot to say about what the natural world was like in the past and how people have adapted."

In the past 20 years, Sandweiss has excavated sites older and younger than those in the Chimbote area. On flat ground above a river in southern Peru, at a place called Quebrada Jaguay, he led teams of Peruvian and UMaine archaeologists that found evidence of human activity dating back about 13,000 years. No one knows if the people were seasonal visitors or residents, but it's clear they knew what they were doing.

"This was a targeted fishing site. They were drying fish and molluscs, which was an excellent source of protein. This is the oldest dated fishing site in the New World," says Sandweiss.

Charcoal, shells and knotted reeds found in layers of debris suggest that Quebrada Jaguay was occupied intermittently for thousands of years. Remarkably, the pattern of postholes and the shape of the reed knots are nearly identical to those used in that area today. It appears that people retained cultural habits over a span of more than 12,000 years.

The story of ancient Peruvians, their use of the seas and their struggles with environmental changes is far from complete. This summer, Sandweiss is headed to the mountains east of Quebrada Jaguay, some more than 10,000 feet above sea level, to study the places where ancient people mined black obsidian rock to make tools.

Like the clams at Chimbote, the rock is expected to provide another window on the earliest chapters of human civilization in a country where cultures arose out of the struggle between humans and their environment.

by Nick Houtman
Summer 2002

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