A new study of lake sediment cores from Sanak Island in the western Gulf of Alaska has suggested that deglaciation there from the last Ice Age took place as much as 1,500 to 2,000 years earlier than previously thought.
The study that appears in the journal Quaternary Science Reviews has also concluded that the maximum thickness of the ice sheet in the Sanak Island region during the last glacial maximum was 70 m – or about half that previously projected – suggesting that deglaciation could have happened more rapidly than earlier models predicted.
The study is important because it suggests that the possible coastal migration of people from Asia into North America and South America – popularly known as “First Americans” studies – could have begun as much as two millennia earlier than the generally accepted date of ice retreat in this area, which was 15,000 years before present.
Well-established archaeology sites at Monte Verde, Chile, and Huaca Prieta, Peru, date back 14,000 to 14,200 years ago, giving little time for expansion if humans had not come to the Americas until 15,000 years before present – as many models suggest.
The massive ice sheets that covered this part of the Earth during the last Ice Age would have prevented widespread migration into the Americas, most archaeologists believe.
“It is important to note that we did not find any archaeological evidence documenting earlier entrance into the continent,” said lead author Dr Nicole Misarti of Oregon State University. “But we did collect cores from widespread places on the island and determined the lake’s age of origin based on 22 radiocarbon dates that clearly document that the retreat of the Alaska Peninsula Glacier Complex was earlier than previously thought.”
“Glaciers would have retreated sufficiently so as to not hinder the movement of humans along the southern edge of the Bering land bridge as early as almost 17,000 years ago,” Dr Misarti added.
Interestingly, the study began as a way to examine the abundance of ancient salmon runs in the region. As the researchers began examining core samples from Sanak Island lakes looking for evidence of salmon remains, however, they began getting radiocarbon dates much earlier than they had expected. These dates were based on the organic material in the sediments, which was from terrestrial plant macrofossils indicating the region was ice-free earlier than believed.
The researchers were surprised to find the lakes ranged in age from 16,500 to 17,000 years ago.
“A third factor influencing the find came from pollen,” Dr Misarti said. “We found a full contingent of pollen that indicated dry tundra vegetation by 16,300 years ago. That would have been a viable landscape for people to survive on, or move through. It wasn’t just bare ice and rock.”
Bibliographic information: Misarti N et al. 2012. Early retreat of the Alaska Peninsula Glacier Complex and the implications for coastal migrations of First Americans. Quaternary Science Reviews 48, 10 August 2012, pages 1–6; doi: 10.1016/j.quascirev.2012.05.014