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

During the last ice age, modern-day Siberia and Alaska were connected by a single landmass, allowing animals and ancient humans to migrate across what is now the Bering Sea. While scientists have long believed that the now-submerged terrain resembles the Ice Age landscapes of both regions, recent research paints a more complicated picture.

Geologists believe that between 36,000 and 11,000 years ago, Beringia may not have been an arid grassland but a swamp ecosystem crisscrossed by rivers. This complicates scientists’ understanding of how this iconic landmass and its landscapes facilitate or impede the spread of different species. The scientists presented their work last week at the annual meeting of the American Geophysical Union (AGU).

“We’ve been looking for clues on land to try to reconstruct what happened underwater,” Jenna Hill of the USGS, who participated in the study, told AGU. statement. “But that doesn’t really tell you what’s out there now submerged on the land between Alaska and Siberia.”

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

In 2023, Hill and her colleagues took sonar readings and extracted sediment cores from an area of ​​the Bering seafloor where previous research suggested prehistoric lakes may have existed.

“We’re looking at several large lakes,” said Sarah Falwell, a paleogeologist at the University of Alaska Fairbanks who also participated in the study. “What we actually found was evidence of many small lakes and river channels.”

In addition to highlighting the rapid change from freshwater to marine sediments, the cores revealed DNA left behind in prehistoric lake sediments, fossils, pollen and sediments. Specifically, pollen indicates the presence of woody trees, while fossils hint at the presence of widespread fresh water on Beringia.

“Watery, wet landscapes can act as barriers to certain species, or serve as conduits for species that actually spread through water,” Hill said. “That’s how it fits into the larger picture.” As the researchers note , this swampy landscape can make travel easier or more difficult for different species. While one might think that aquatic ecosystems would prevent large animals from migrating, the team also detected mammoth DNA, meaning they must have had more solid paths to follow.

“This may be a swamp, but we still see evidence of mammoths,” Falwell explains. “Even though it’s mostly floodplains and ponds, herbivores are around, just uphill in higher, drier areas.”

Ultimately, geologists believe Beringia may have looked more like the modern Yukon-Kuskokwim Delta in western Alaska than the arid grasslands. It remains to be seen how future research will continue to shape our understanding of the continent that brought ancient humans to North America.