Bering Land Bridge Formed Surprisingly Late During Last Ice Age – Zoo House News
A new study reconstructing the history of sea level along the Bering Strait shows that the Bering Land Bridge, which connects Asia to North America, only formed about 35,700 years ago, less than 10,000 years before the peak of the last Ice Age (known as the Last Ice Age). glacial maximum).
The new findings, published the week of December 26 in the Proceedings of the National Academy of Sciences, indicate that the growth of the ice sheets — and the resulting decline in sea levels — occurred surprisingly quickly and much later in the glacial cycle than previous studies had suggested.
“That means more than 50 percent of the global ice volume increased at the last glacial maximum 46,000 years ago,” said Tamara Pico, assistant professor of Earth and Planetary Sciences at UC Santa Cruz and corresponding author of the paper. “This is important for understanding the climate-ice sheet feedbacks because it implies that there was a significant lag in ice sheet development after global temperatures fell.”
Global sea levels drop during ice ages as more and more of the Earth’s water becomes trapped in massive ice sheets, but the timing of these processes has been difficult to pinpoint. Ice sheets covered much of North America during the last glacial maximum, which lasted about 26,500 to 19,000 years ago. Dramatically lower sea levels uncovered a vast tract of land called Beringia, stretching from Siberia to Alaska and home to herds of horses, mammoths, and other Pleistocene fauna. When the ice sheets melted, the Bering Strait flooded again about 13,000 to 11,000 years ago.
The new findings are interesting in relation to human migration because they shorten the time between the opening of the land bridge and the arrival of people in America. The timing of human migration to North America remains unresolved, but some studies suggest that humans may have lived in Beringia during the peak of the Ice Age.
“People may have started crossing the bridge as soon as the land bridge formed,” Pico said.
The new study used an analysis of nitrogen isotopes in seafloor sediments to determine when in the past 46,000 years the Bering Strait flooded, allowing water to flow from the Pacific Ocean into the Arctic Ocean. First author Jesse Farmer of Princeton University led the isotope analysis and measured nitrogen isotope ratios in marine plankton remains preserved in sediment cores collected from the seafloor at three locations in the western Arctic Ocean. Because of differences in the nitrogen composition of Pacific and Arctic waters, Farmer was able to identify a nitrogen isotope signature that indicates when Pacific waters flowed into the Arctic.
Pico, whose expertise lies in sea-level modeling, then compared Farmer’s results to sea-level models based on different ice sheet growth scenarios.
“What’s exciting to me is that this represents a completely independent limitation of global sea level over this time period,” Pico said. “Some of the proposed ice sheet histories differ significantly, and we were able to look at what the predicted sea level would be at the Bering Strait and see which ones matched the nitrogen data.”
The findings support recent studies suggesting that global sea levels before the Last Glacial Maximum were much higher than previous estimates suggested, she said. The average global sea level during the Last Glacial Maximum was about 130 meters (425 feet) lower than it is today. However, the actual sea level at a given location like the Bering Strait depends on factors such as the deformation of the Earth’s crust by the weight of the ice sheets.
“It’s like hitting bread dough — the crust sinks under the ice and rises at the edges,” Pico said. “Also, the ice sheets are so massive that they have gravitational effects on the water. I model these processes to see how sea levels would vary around the world, and in this case, to look at the Bering Strait.”
The findings imply an intricate relationship between climate and global ice volume, and suggest new ways to study the mechanisms underlying glacial cycles.
In addition to Pico and Farmer, co-authors include Ona Underwood and Daniel Sigman of Princeton University; Rebecca Cleveland-Stout from the University of Washington; Julie Granger at the University of Connecticut; Thomas Cronin of the US Geological Survey; and François Fripiat, Alfredo Martinez-Garcia, and Gerald Haug at the Max Planck Institute for Chemistry in Germany. This work was supported by the National Science Foundation.