First Human Migration From Asia to North America Helped by Warm Oceans

North Pacific Currents

The Pacific Ocean’s currents support a diverse ecosystem, seen here from space with green indicating blooms of photosynthesizing plankton. Warmer currents during the ice age may also have supported early human settlements. Credit: NASA/Goddard Space Flight Center, The SeaWiFS Project and GeoEye, Scientific Visualization Studio

New research reveals significant changes to the circulation of the North Pacific and its impact on the initial migration of humans from Asia to North America.

The international study, led by the University of St. Andrews in Scotland and published on December 9, 2020, in Science Advances, provides a new picture of the circulation and climate of the North Pacific at the end of the last ice age, with implications for early human migration.

The Pacific Ocean contains around half the water in Earth’s oceans and is a vast reservoir of heat and carbon dioxide. However, at present, the sluggish circulation of the North Pacific restricts the movement of this heat and carbon dioxide, limiting its impact on climate.

The international team of scientists used sediment cores from the deep sea to reconstruct the circulation and climate of the North Pacific during the peak of the last ice age, roughly 21,000 years ago. Their results reveal a dramatically different circulation in the ice age Pacific, with vigorous ocean currents creating a relatively warm region around the modern Bering Sea.

“Our data shows that the Pacific had a warm current system during the last ice age, similar to the modern Atlantic Ocean currents that help to support a mild climate in Northern Europe,” said lead author James Rae, a faculty member at the University of St. Andrews.

The warming from these ocean currents created conditions more favorable for early human habitation, helping address a long-standing mystery about the earliest inhabitants of North America.

“According to genetic studies, the first people to populate the Americas lived in an isolated population for several thousand years during the peak of the last ice age, before spreading out into the American continents,” said co-author Ben Fitzhugh, a professor of anthropology at the University of Washington who studies early communities in the North Pacific.

This hypothesis has been termed the “Beringian Standstill,” and a significant question is where this population lived after separation from their Asian relatives before the deglaciation of the massive ice sheet covering the northern third of North America allowed them to reach and spread throughout the Americas. The new research suggests that these early Americans may have lived in a relatively warm refugium, or habitable refuge, in southern Beringia, on the now-submerged land beneath the Bering Sea. Due to the extremely cold climate that dominated other parts of this region during the ice age, it has been unclear, until now, how habitable conditions could have been maintained.

“Our work shows how dynamic Earth’s climate system is. Changes in the circulation of the ocean and atmosphere can have major impacts on how effectively humans may inhabit different environments, which is also relevant for understanding how different regions will be affected by future climate change,” said third author Robert Jnglin Wills, a postdoctoral researcher in atmospheric sciences at the University of Washington.

Wills researches the overturning circulation in the North Pacific, and did climate modeling work to help understand what the paleoclimate data — compiled by researchers at the University of St. Andrews and the University of California, Irvine — would mean for the region’s climate.

“The warm currents revealed by our data would have created a much more pleasant climate in this region than we might have previously thought,” said second author William Gray, a research scientist at the Laboratory for Sciences of Climate and Environment in France.

“This would have created milder climates in the coastal regions of the North Pacific, that would have supported more temperate terrestrial and marine ecosystems and made it possible for humans to survive the ice age in an otherwise harsh climatic period.”

Reference: “Overturning circulation, nutrient limitation, and warming in the Glacial North Pacific” by J. W. B. Rae, W. R. Gray, R. C. J. Wills, I. Eisenman4, B. Fitzhugh, M. Fotheringham, E. F. M. Littley, P. A. Rafter, R. Rees-Owen1, A. Ridgwell, B. Taylor and A. Burke, 9 December 2020, Science Advances.
DOI: 10.1126/sciadv.abd1654

The research was funded by the U.S. National Science Foundation and the U.K. Natural Environment Research Council. Other co-authors are from Scripps Institution of Oceanography; the University of California, Irvine; and the University of California, Riverside.

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