The Famous Bering Land Bridge Was More Like a Swamp, Geologists Say

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During the last Ice Age, modern-day Siberia and Alaska were connected by a landmass that allowed animals—and ancient humans—to migrate across what is now the Bering Sea. While scientists have long assumed that the now-submerged topography resembled the Ice Age landscape of these two regions, recent research paints a more complex picture.

Geologists suggest that between 36,000 and 11,000 years ago, the Bering Land Bridge may have been less an arid steppe grassland and more a boggy ecosystem crisscrossed by rivers. This complicates scientists’ understanding of the iconic landmass and how its landscape would have facilitated or impeded the spread of different species. The scientists presented their work at the American Geophysical Union (AGU) Annual Meeting last week.

“We’ve been looking on land to try to reconstruct what is underwater,” Jenna Hill of the U.S. Geological Survey, who took part in the research, said in an AGU statement. “But that doesn’t really tell you what was on land that is now submerged between Alaska and Siberia.”

It’s worth noting that the name “Bering Land Bridge” is often misleading. The landscape was not a literal bridge that necessarily compelled ancient humans and animals to cross it—it was a sprawling region in its own right that allowed for species to spread between Siberia and North America when sea levels were about 400 feet (122 meters) lower than today. It was a viable habitat in its own right.

In 2023, Hill and her colleagues conducted sonar readings and extracted sediment cores from regions of the Bering Sea floor where previous research had indicated the likely presence of prehistoric lakes.

“We were looking for several large lakes,” said Sarah Fowell, a paleogeologist at the University of Alaska Fairbanks, who was also involved in the research. “What we actually found was evidence of lots of small lakes and river channels.”

In addition to highlighting the rapid change from freshwater to marine sediment, the cores revealed prehistoric lake sediments, fossils, pollen, and DNA left behind in sediments. Specifically, the pollen indicated the presence of woody trees, while the fossils hinted at widespread freshwater across the Bering Land Bridge.

“Even if it was mostly floodplains and ponds, the grazers were around, just uphill following higher, drier areas.” “The watery, wet landscape could have been a barrier for some species, or a pathway for species that actually travel by water,” Hill said. “That’s how this fits into the bigger picture.” This boggy topography, as the researchers note, would have made traveling easier or harder for different species. While one might assume that the watery ecosystem would prevent the migration of larger animals, however, the team also detected DNA from mammoths, meaning that there must have also been more solid paths for them to take.

“It may have been marshy, but we are still seeing evidence of mammoths,” Fowell explained. “Even if it was mostly floodplains and ponds, the grazers were around, just uphill following higher, drier areas.”

Ultimately, the geologists suggest that the Bering Land Bridge may have looked more like the modern-day Yukon-Kuskokwim Delta in western Alaska than its arid steppe grassland. It remains to be seen how future research will continue to shape our understanding of the landmass that brought ancient humans to North America.

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