Credit: alaskapublic.org
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Princeton scientists found that the Bering Land Bridge, the strip of land that once connected Asia to Alaska, emerged far later during the last ice age than previously thought,
says Eurekalert.
The unexpected findings shorten the window of time that humans could have first migrated from Asia to the Americas across the Bering Land Bridge.
The findings also indicate that there may be a less direct relationship between climate and global ice volume than scientists had thought, casting into doubt some explanations for the chain of events that causes ice age cycles.
The study was published on December 27 in the Proceedings of the National Academy of Sciences.
“This result came totally out of left field,” said Jesse Farmer, postdoctoral researcher at Princeton University and co-lead author on the study. “As it turns out, our research into sediments from the bottom of the Arctic Ocean told us not only about past climate change but also one of the great migrations in human history.”
Insight into ice age cycles
During the periodic ice ages over Earth’s history, global sea levels drop as more and more of Earth’s water becomes locked up in massive ice sheets.
At the end of each ice age, as temperatures increase, ice sheets melt and sea levels rise. These ice age cycles repeat throughout the last 3 million years of Earth’s history, but their causes have been hard to pin down.
By reconstructing the history of the Arctic Ocean over the last 50,000 years, the researchers revealed that the growth of the ice sheets — and the resulting drop in sea level — occurred surprisingly quickly and much later in the last glacial cycle than previous studies had suggested.
“One implication is that ice sheets can change more rapidly than previously thought,” Farmer said.
During the last ice age’s peak of the last ice age, known as the Last Glacial Maximum, the low sea levels exposed a vast land area that extended between Siberia and Alaska known as Beringia, which included the Bering Land Bridge. In its place today is a passage of water known as the Bering Strait, which connects the Pacific and Arctic Oceans.
Based on records of estimated global temperature and sea level, scientists thought the Bering Land Bridge emerged around 70,000 years ago, long before the Last Glacial Maximum.
But the new data show that sea levels became low enough for the land bridge to appear only 35,700 years ago. This finding was particularly surprising because global temperatures were relatively stable at the time of the fall in sea level, raising questions about the correlation between temperature, sea level and ice volume.
“Remarkably, the data suggest that the ice sheets can change in response to more than just global climate,” Farmer said. For example, the change in ice volume may have been the direct result of changes in the intensity of sunlight that struck the ice surface over the summer.
“These findings appear to poke a hole in our current understanding of how past ice sheets interacted with the rest of the climate system, including the greenhouse effect,” said Daniel Sigman, Dusenbury Professor of Geological and Geophysical Sciences at Princeton University and Farmer’s postdoctoral advisor.
“Our next goal is to extend this record further back in time to see if the same tendencies apply to other major ice sheet changes. The scientific community will be hungry for confirmation.”
Full article here.
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Study: The Bering Strait was flooded 10,000 years before the Last Glacial Maximum
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