North America's first people may have arrived by sea ice highway as early as 24,000 years ago

How and when humans originally came to North America is one of the most hotly debated topics in archaeology. The conventional view among archaeologists is that around 13,000 years ago, a transient opening between ice sheets allowed humans to pass via a corridor free of ice.

However, an increasing amount of genetic and archeological evidence, such as human footprints discovered in New Mexico that date to around 23,000 years ago, indicates that humans arrived on the continent far earlier. These early Americans most likely came from Beringia, the land bridge that connects Asia and North America and developed during the last glacial maximum, when ice sheets held up vast quantities of water, lowering sea levels. They journeyed down the Pacific coastline.

Sea ice may have been one means for humans to migrate farther south, according to research that will be presented on Friday, December 15 at the American Geophysical Union Annual Meeting (AGU23) in San Francisco. Paleoclimate reconstructions of the Pacific Northwest suggest this.

It's not a novel notion that prehistoric Americans may have journeyed around the Pacific Coast. At least 16,000 years ago, much of the continent was covered by enormous ice sheets, which is presumably where people were living at the time.

Rather than the ice-free route, which would have been closed off for thousands of years prior to these early settlers, scientists suggested that people may have migrated over a "kelp highway." According to this idea, early Americans gradually migrated southward into North America on boats, pursuing the abundant resources found in coastal seas.

In western Canada, archaeologists have discovered evidence of coastal communities as early as 14,000 years ago. However, in 2020, scientists found that it could have been difficult for humans to go along the shore due to a strong current caused by freshwater from melting glaciers at the time.

Over hazardous water, an ice highway

In order to obtain a more comprehensive understanding of the oceanic conditions throughout these significant periods of human migration, Summer Praetorius and her colleagues examined climate proxies found in coastal ocean sediment. Tiny, petrified plankton provided the majority of the data. These species' chemistry and abundance aid in the reconstruction of sea ice cover, salinity, and ocean temperatures.

At AGU23, Praetorious will be speaking as part of a session on the geology and climatic history of Beringia and the North Pacific during the Pleistocene, or modern ice age. This year, the week-long conference united 3,000 online attendees and attracted 24,000 professionals from many fields in Earth and space sciences to San Francisco.

Using climate models, Praetorious' team discovered that, at the height of the last glacial maximum, some 20,000 years ago, ocean currents were more than twice as strong as they are now because of glacial winds and lower sea levels. These circumstances would have made boat passage extremely difficult, if not impossible to paddle against, according to Praetorius.

But the data also revealed that until around 15,000 years ago, a large portion of the region was covered in sea ice throughout the winter. Praetorius speculated that since they were a cold-adapted tribe, "perhaps they were using the sea ice as a platform rather than having to paddle against this horrible glacial current."

These days, people in the Arctic use dog sleds and snowmobiles to traverse the sea ice. According to Praetorius, early Americans could have traveled along the "sea ice highway" to hunt marine animals and gradually make their way into North America. The climatic data indicate that between 24,500 and 22,000 years ago and 16,400–14,800 years ago, the coastal route may have supported migration, maybe with the help of winter sea ice.

The proposal offers a fresh framework for understanding how humans may have arrived in North America without the need for an easy way over the ocean or a land bridge, even if it will be difficult to prove that people were utilizing sea ice for transportation given that the majority of the archeological sites are underwater.

Furthermore, according to Praetorius, the sea ice corridor doesn't preclude future human migrations. According to the team's models, 14,000 years ago the Alaskan current had subsided, facilitating simpler boat passage down the coast.

She declared, "Nothing is off the table." "We will always be surprised by ancient human ingenuity."