Using isotopes to reconstruct life histories within the transatlantic slave trade

Anthropologist Vicky Oelze uses strontium isotope analysis to match human skeletal remains to their place of origin

Vicky Oelze

"We know villages were destroyed and people were being taken," says Vicky Oelze. "We want to put numbers on it. I'm interested in individual histories." (Photo by Fred Deakin)


Map of equatorial Africa showing strontium isotope sampling sites

This geological map of equatorial Africa shows strontium isotope sampling locations Oelze's team will use to create the first-ever strontium isotope map of the region, a tool researchers will use to help trace the origins of Africans who were abducted during the transatlantic slave trade. (Map courtesy of Vicky Oelze)

Vicky Oelze, an assistant professor of anthropology, should introduce herself as a detective. Who else would attempt to fill in the gaps of the transatlantic slave trade by gathering clues from cemeteries in South Carolina and the shores of West Africa?

Four hundred years after the forced displacement of millions of Africans began, Oelze wants to use isotope biogeochemistry to trace back and identify the origins of individuals who were abducted and perished in the Americas.

Skeletal remains of slaves hold the clues that Oelze will use to identify where in Africa individuals were born and raised—information that has been lost to history.

"The narrative we have now is based on log books written by people who were deporting hundreds of Africans on ships," said Oelze. "They documented only the numbers—how many left and how many arrived in the respective harbors. There was no recordkeeping of where people were actually from."

Archaeologists have had great success in parts of the developed Western world using strontium isotopes to identify the geological origin of prehistoric people, matching data to detailed strontium isotope maps researchers have developed. This type of map does not exist for tropical Africa, a gap Oelze will fill with over 400 environmental samples from 40 field sites that cover most major geological formations in tropical Africa. The principle is simple: Vegetation takes up a specific isotopic makeup of the trace element strontium from bedrock, and, in tiny quantities, that isotopic "signature" becomes locked in the teeth of people and animals that consume it. Oelze will use samples of African flora and fauna to build a strontium isotope map to match the signatures in skeletal remains of slaves to specific regions in Africa.

With support from the Helen and Will Webster Foundation, Oelze is hiring a postdoctoral researcher for two years to work in partnership with collaborators at the Max Planck Institute for Evolutionary Anthropology in Germany. In a second step, the team will start examining human remains from the Americas for their strontium isotope values. Strontium isotope analysis is particularly valuable when deterioration of skeletal material has ruled out genetic analyses as an option, and it is a much more precise way to assess human mobility on an individual, rather than population, level, said Oelze. The team will also analyze human remains from urban centers of the West African slave trade in collaboration with UCSC archaeologist Cameron Monroe.

"We know villages were destroyed and people were being taken," said Oelze. "We want to put numbers on it. I'm interested in individual histories."

The remains of millions of slaves are buried in designated slave cemeteries and near slave trade centers in the Caribbean and the Americas, as well as in informal burial plots that have been lost to history, noted Oelze. "It is imperative to include descendant communities in the process,” she said. “Many have a genuine interest in their ancestors. It's important to them, which is why so many are turning to 23andMe."

However, genetics from Africa are postcolonial and therefore flawed, said Oelze. As people were displaced by the pressures of slave raids, they effectively erased their geographic origins; strontium isotope analysis holds the promise of retracing movements from the past, she said.

Oelze's results will also aid wildlife conservation. "Trafficking of endangered animals is of growing concern to conservation, and this map of strontium isotopes in tropical Africa will help identify hotspots of illegal poaching activity," said Oelze, who plans to share her data internationally in open-access publications. She is also eager to use the findings to spark interest in STEM fields among students from Historically Black Colleges and from high schools with diverse student populations. 

A hub of excellence

UC Santa Cruz has the potential to lead the field in tracing the histories, geographies, and molecular archaeology of the slave trade, according to Katharyne Mitchell, dean of the Division of Social Sciences. In Anthropology, Lars Fehren-Schmitz brings expertise in the analysis of ancient DNA, and Monroe has conducted extensive research in Bénin and Togo on the transformation of West African communities during the slave trade, as well as related archaeological research in the Caribbean. In History, Professor Greg O'Malley has done pathbreaking work on the transatlantic slave trade.

"This cohort of brilliant scholars is doing transformational work," said Mitchell. "Vicky is a powerhouse, and I'm delighted the Webster family wanted to support her research. I see great things emerging from this."

Oelze, who joined the faculty in 2016 from the Max Planck Institute for Evolutionary Anthropology, will organize a symposium on campus on the molecular forensics of the transatlantic slave trade, drawing historians, archaeologists, isotope geochemists, and geneticists to campus.