People may have crossed the Beringia much earlier than thought, new study claims

Bridge did not appear until roughly 35,700 years ago, fewer than 10,000 years before the last ice age peaked.
Nergis Firtina
Satellite views of Bering Strait.
Satellite views of Bering Strait.

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It is thought humans arrived in the Americas for the first time through the Bering Land Bridge. Now, researchers at the University of California Santa Cruz claim that Bering Land Bridge formed surprisingly late during the last ice age.

According to a recent study that reconstructs the history of water level at the Beringia, the Bering Land Bridge did not appear until roughly 35,700 years ago, fewer than 10,000 years before the last ice age peaked, as per the new study.

"Last Glacial Maximum grew after 46,000 years ago"

"It means that more than 50 percent of the global ice volume at the Last Glacial Maximum grew after 46,000 years ago," said Tamara Pico, assistant professor of Earth and planetary sciences at UC Santa Cruz and a corresponding author of the paper.

"This is important for understanding the feedback between climate and ice sheets because it implies that there was a substantial delay in the development of ice sheets after global temperatures dropped."

People may have crossed the Beringia much earlier than thought, new study claims
Bering Land Bridge.

Because they reduce the amount of time between the opening of the land bridge and the arrival of humans in the Americas, the new discoveries are intriguing in terms of human migration. Although the exact time of human migration into North America is still unclear, certain research indicates that people may have resided in Beringia for the duration of the last ice age, as per the university's release.

"People may have started going across as soon as the land bridge formed," Pico added.

Analysis of nitrogen isotopes

The new study determined when the Bering Land Bridge was flooded throughout the previous 46,000 years, allowing water from the Pacific Ocean to flow into the Arctic Ocean by analyzing nitrogen isotopes in bottom sediments. 

The isotope analysis was carried out by the first author Jesse Farmer of Princeton University, who determined the ratios of nitrogen isotopes in the marine plankton remnants found in sediment cores dug up from the seafloor at three different locations in the western Arctic Ocean.

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"The exciting thing to me is that this provides a completely independent constraint on global sea level during this time period," Pico said. "Some of the ice sheet histories that have been proposed differ by quite a lot, and we were able to look at what the predicted sea level would be at the Bering Strait and see which ones are consistent with the nitrogen data."

The findings are consistent with recent studies showing that global sea levels were significantly higher than previously thought before the Last Glacial Maximum. The results show a complex relationship between climate and the volume of ice on Earth and offer new directions for studying the processes that underlie glacial cycles.

The study was published in PNAS on December 26.

Study abstract:

The cyclic growth and decay of continental ice sheets can be reconstructed from the history of global sea levels. Sea level is relatively well constrained for the Last Glacial Maximum (LGM, 26,500 to 19,000 y ago, 26.5 to 19 ka) and the ensuing deglaciation. However, sea-level estimates for the period of ice-sheet growth before the LGM vary by > 60 m, an uncertainty comparable to the sea-level equivalent of the contemporary Antarctic Ice Sheet. Here, we constrain sea level prior to the LGM by reconstructing the flooding history of the shallow Bering Strait since 46 ka. Using a geochemical proxy of Pacific nutrient input to the Arctic Ocean, we find that the Bering Strait was flooded from the beginning of our records at 46 ka until 35.7+3.3−2.435.7-2.4+3.3 ka. To match this flooding history, our sea-level model requires an ice history in which over 50% of the LGM's global peak ice volume grew after 46 ka. This finding implies that global ice volume and climate were not linearly coupled during the last ice age, with implications for the controls on each. Moreover, our results shorten the time window between the opening of the Bering Land Bridge and the arrival of humans in the Americas.