Betrayed by Ancient Algae

More lasting than it looks. Whale bones used in Thule Inuit houses (a reconstruction is shown here) had a lasting impact on local ponds.

About 1000 years ago, Thule Inuit whalers abandoned Alaska for Canadian coasts above the Arctic Circle. Now, a team of scientists has found a record of their presence and departure in altered ponds near their ancient settlements. The technique could help better date the history of Arctic occupation.

In their coastal settlements, the Thule hunted whales and seals and built houses from whale bones, boulders, seal skin, and peat moss. Their whaling activities left a lasting imprint on the landscape: Archaeologists often locate ancient Thule settlements from the air by looking for regions of rich vegetation that suggest fertilization by decomposing whale bones.

Thule settlements are notoriously hard to date, says archaeologist Robert McGhee of the Archaeological Survey of Canada in Gatineau, Quebec, because the complex chemical interactions of carbon-14 in the ocean make it difficult to date discarded bones and refuse from sea mammals and because of the settlements themselves, which are permeated with sea-mammal oil the people ate and burned. Another way to date the sites would therefore be welcome, he says.

A new technique now comes from a trio of limnologists and an archaeologist from four Canadian universities. They report that whale bones around a settlement on Somerset Island has permanently altered nearby ponds. The team, led by Marianne Douglas, a limnologist at the University of Toronto, describes ponds with three times the normal Arctic levels of phosphorus as well as elevated levels of a nitrogen isotope associated with marine life. The changes could also be tracked back in time. By estimating how quickly sediment piled up in the pond over time, the team was able to date the first spike in pond chemistry--an indication of the Inuit's arrival--to about 1200 C.E., which agrees with carbon-14 dating from antlers found at the site.

But chemistry wasn't the only change, the team reports in a paper published online this week in the Proceeding of the National Academy of Sciences. The constant influx of whale nutrients altered the pond's biology too, allowing new algae species to grow. Their history is recorded in pond mud. Then, around 1600 C.E., nutrients began a slow decline, and the algae species shifted mostly back to the pond's original inhabitants, suggesting that the Inuits had left.

Related sites
A reconstructed Thule house
Douglas home page

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