How sea ice may have been a route for early Americans to reach North America

The timing and means of human migration to North America have long been debated in archaeological circles. The conventional view suggests that humans traversed an ice-free corridor around 13,000 years ago between ice sheets. However, recent archaeological and genetic discoveries, including human footprints in New Mexico dating back approximately 23,000 years, challenge this timeline, indicating an earlier arrival.

The emerging perspective proposes that early Americans may have journeyed along the Pacific coastline from Beringia, the land bridge between Asia and North America formed during the last glacial maximum. This period saw ice sheets sequester substantial water, causing a drop in sea levels.

Presenting research at the American Geophysical Union Annual Meeting in San Francisco on December 15, scientists explored paleoclimate reconstructions of the Pacific Northwest, suggesting sea ice might have facilitated southward movement.

The notion of early Americans traveling along the Pacific Coast is not new, as evidence suggests human presence south of massive ice sheets at least 16,000 years ago. With the ice-free corridor unavailable for thousands of years, the concept of a “kelp highway” gained traction. This theory posits that early Americans navigated down into North America in boats, capitalizing on coastal resources.

While archaeological finds in western Canada indicate coastal settlements dating back to 14,000 years ago, a 2020 observation raised questions about the kelp highway theory. Researchers suggested that freshwater from melting glaciers created strong currents, posing challenges for coastal travel during that time.

Ice highway over dangerous water

To gain a comprehensive understanding of ocean conditions during pivotal periods of human migration, Summer Praetorius and her colleagues at the US Geological Survey analyzed climate proxies in coastal ocean sediment. Drawing data primarily from tiny, fossilized plankton, the team reconstructed ocean temperatures, salinity, and sea ice cover, offering insights into conditions during the Pleistocene, the ongoing ice age.

Presenting at AGU23’s session on the climate history and geology of Beringia and the North Pacific, Praetorius utilized climate models, revealing that ocean currents were over twice as strong during the last glacial maximum approximately 20,000 years ago, influenced by glacial winds and lower sea levels. While challenging for boat travel, the team found evidence suggesting winter sea ice persisted in the region until around 15,000 years ago.

Proposing the concept of a ‘sea ice highway,’ Praetorius speculated that early Americans might have utilized sea ice as a platform for travel and hunting marine mammals, offering a potential explanation for migration into North America. Although proving this theory is challenging due to underwater archaeological sites, it introduces a novel framework for understanding human arrival in North America without a land bridge or easy ocean travel.

The ‘sea ice highway’ theory doesn’t exclude other migration routes. Praetorius noted that their models indicate a calmer Alaskan current by 14,000 years ago, facilitating boat travel along the coast. Emphasizing the surprises inherent in uncovering ancient human ingenuity, she concluded, “Nothing is off the table.”

Source: American Geophysical Union

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