The Bering Land Bridge Was Accessible Only During Two Short Periods of Time
During these two times, the Bering Strait Land Bridge may have served as the coastal route used by the first people to reach the Americas.
According to a new study in the journal Proceedings of the National Academy of Sciences the coastal route between Asia and North America was so perilous during the last ice age, humans probably only crossed during two time windows, when the environmental conditions were more suited for the exhausting and deadly trek.
The first window lasted from 24,500 to 22,000 years ago, and the other one covered from 16,400 to 14,800 years ago. The researchers added that during these times, sea ice cover in the winter and sea ice-free summers would have likely provided these migrants with access to a varied marine buffet as well as means of traveling safely around the North Pacific coast.
There are two basic hypotheses about the origins of human migration to the New World.
According to an earlier theory, people traveled across Beringia, the land bridge that previously united Asia and North America, on foot when there wasn't much ice.
A rising collection of evidence, however, indicates that people may have utilized boats throughout the Pacific coasts of Asia, Beringia, and North America before 15,000 years ago, a time when enormous ice sheets would have made an overland journey extremely challenging.
Researchers examined how variations in temperature over the previous 45,000 years would have affected sea ice, glacier area, ocean current strength, and food availability on land and at sea in order to determine how feasible the coastal path may have been for migration at various times. Using data from previously collected soil samples from the Gulf of Alaska that contained information on surface temperatures, salinity, and debris carried on ice, the researchers created climate models based on oscillations in sea ice.
Their simulations identified two temporal windows for year-round coastal migration, the first 2,500 years and the second 1,600 years, which would have allowed a suitable coastal route when the inland route was blocked.
Summer kelp forests would have contributed to keeping tourists fed during those two windows. When frozen on the coast, sea ice can be quite level and stable, allowing ancient hunters to walk on it and catch seals, whales, and other wildlife to survive those winters. Sea ice throughout the winter during those periods may also have supported migration.
The presence of sea ice in this area may have helped rather than hindered travel and subsistence.
There is a good chance that coastal migration was less welcome at other points in the past 45,000 years. For instance, between 18,500 and 16,000 years ago, a massive pulse of meltwater from the borders of the massive ice sheet that previously covered most of northeastern North America poured into the Pacific, which would have more than doubled the average strength of the northward ocean currents along Alaska. In consequence, this would have made boat passage along the southern Pacific coast more challenging. At the time, coastal migration would have been seriously endangered by the regular calving into the ocean of enormous icebergs caused by melting glaciers.
We now have additional information regarding the ice-free corridor, including when it opened and when it was practical for people to migrate via it. To achieve the same for the coastal migration path, this article is a good first step. To better understand the resources accessible to coastal residents at various times, the researchers plan to examine how marine habitats changed in response to historical climate variations. They also want to know more about any brief warming events, lasting a few decades to millennia, that occurred around Beringia to determine whether they were associated with certain migration epochs.
With this study, we can now generally accept that prehistoric peoples crossed the coast to reach the Americas.
Praetorius, S. K., Alder, J. R., Condron, A., Mix, A. C., Walczak, M. H., Caissie, B. E., & Erlandson, J. M. (2023). Ice and ocean constraints on early human migrations into North America along the Pacific coast. Proceedings of the National Academy of Sciences of the United States of America, 120(7), e2208738120. https://doi.org/10.1073/pnas.2208738120