Key points:
- A new theory, along with paleoclimate reconstructions of the Pacific Northwest, hint that sea ice may have been one way for people to move farther south.
- Using climate proxies in ocean sediment from the coast, researchers reconstructed ocean temperatures, salinity and sea ice cover.
- The study concludes Early Americans may have used the “sea ice highway” to get around and hunt marine mammals, slowly making their way into North America in the process.
One of the hottest debates in archeology is how and when humans first arrived in North America. Archaeologists have traditionally argued that people walked through an ice-free corridor that briefly opened between ice sheets an estimated 13,000 years ago.
But a growing number of archeological and genetic finds suggests that people made their way onto the continent much earlier—which would mean these early Americans traveled along the Pacific coastline when it was full of ice.
To examine this idea of an “ice highway,” researchers at the U.S. Geological Survey looked at climate proxies in ocean sediment from the coast. Most of the data came from tiny, fossilized plankton. The abundance and chemistry of these organisms help reconstruct ocean temperatures, salinity and sea ice cover.
According to the climate models, ocean currents were more than twice the strength they are today during the height of the last glacial maximum around 20,000 years ago due to glacial winds and lower sea levels. While not impossible to paddle against, these conditions would have made traveling by boat very difficult. However, the records also showed that much of the area was home to winter sea ice until around 15,000 years ago.
“As a cold-adapted people, rather than having to paddle against this horrible glacial current, maybe they were using the sea ice as a platform,” said lead researcher Summer Praetorius.
The climate data suggest conditions along the coastal route may have been conducive to migration between 24,500-22,000 years ago and 16,400-14,800 years ago, possibly aided by the presence of winter sea ice.
While proving that people were using sea ice to travel will be tricky given most of the archeological sites are underwater, the theory provides a new framework for understanding how humans may have arrived in North America without a land bridge or easy ocean travel.
And the sea ice highway isn’t mutually exclusive with other human migrations further down the line, says Praetorius. The team’s models show that the Alaskan current had calmed down by 14,000 years ago, making it easier for people to travel by boat along the coast.
“Nothing is off the table,” Praetorius said. "We will always be surprised by ancient human ingenuity."