Tracing the Sea Ice Highway: The Arrival of North America’s First Immigrants

A new study suggests that some early Americans may have traveled down the coast from Beringia 24,000 years ago on winter sea ice.

One of the hottest debates in archeology is when and how humans first arrived in North America. Archaeologists have traditionally argued that people walked through temporary ice-free passages between ice sheets an estimated 13,000 years ago.

New evidence casts doubt on traditional theory

But a growing number of archaeological and genetic discoveries, such as human footprints in New Mexico dating back some 23,000 years, suggest that humans were on the continent much earlier. These early Americans likely migrated from Beringia along the Pacific coastline. Beringia is a land bridge between Asia and North America that appeared during the last ice age maximum when ice sheets trapped large amounts of water and caused sea levels to drop.

Now, in a study presented at the American Geophysical Union Annual Meeting (AGU23) in San Francisco on Friday, December 15th, paleoclimate reconstructions of the Pacific Northwest show that sea ice has grown even further south than humans. This suggests that it may have been a means of transportation.

Coastal migration theory

The idea that early Americans may have traveled along the Pacific coast is not new. People may have been south of the giant ice sheet that once covered much of the continent by at least 16,000 years ago. Given that ice-free corridors would not open for thousands of years before these early arrivals, scientists proposed that people instead migrated along a “kelp highway.” Along this path, early Americans slowly made their way down to North America by ship. Abundant supplies found in coastal waters.

Archaeologists have discovered evidence of coastal settlements in western Canada dating back 14,000 years. But in 2020, researchers noted that freshwater from melting glaciers at the time may have created strong currents, making it difficult for people to travel along the coast.

Sea ice in Nunavut, Canada. Credit: Grid-Arendel CC-BY-NC-SA

An icy highway crossing a dangerous sea

To get a more complete picture of ocean conditions during key periods of human migration, Summer Pretorius and colleagues at the U.S. Geological Survey examined climate proxies in marine sediments along the coast. Most of the data came from small fossilized plankton. Its abundance and chemistry help scientists reconstruct ocean temperatures, salinity, and sea ice cover.

Praetorius’ presentation is part of a session at AGU23 on the climate history and geology of Beringia and the North Pacific during the Pleistocene. This year, his week-long conference brought together 24,000 of his experts from all areas of earth and space sciences in San Francisco and 3,000 online participants.

Using climate models, Praetorius’ team found that at the height of the Last Glacial Maximum, about 20,000 years ago, ocean currents were more than twice as strong as they are today due to glacial winds and falling sea levels. Pretorius said it would have been very difficult to travel by boat in these conditions, although it was not impossible to row.

However, records show that much of the region had winter sea ice until about 15,000 years ago. As a cold-adapted people, “they may have been using the sea ice as a foothold instead of having to row against this terrible glacial current,” Pretorius said.

Sea ice as a migration path

People in the Arctic now travel along the sea ice on dog sleds and snowmobiles. Pretorius said early Americans may also have used the “sea ice highway” to travel and hunt marine mammals, slowly making their way into North America in the process. Climate data suggest that conditions along the coastal route may have been favorable for migration between 24,500 and 22,000 years ago and between 16,400 and 14,800 years ago, possibly due to the presence of winter sea ice.

Integration of old and new theories

It’s difficult to prove that people used sea ice for travel, given that most ruins are underwater, but the idea is that without land bridges or easy ocean travel, humans It provides a new framework for understanding how it arrived in North America.

And the Sea Ice Highway is not mutually exclusive with other human movements beyond it, Pretorius said. The researchers’ model shows that by 14,000 years ago, the Alaska Current had calmed down, making it easier for people to travel by boat along the coast.

“There’s nothing wrong with it,” she said. “We are always amazed by the ingenuity of ancient humans.”