26 May 2025 The Future is the Product of the Past

A Scientific Surprise: Bering Land Bridge formed surprisingly late during last ice age

A new study shows 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.

Princeton scientists found that the Bering Land Bridge was flooded until 35,700 years ago, with its full emergence occurring only shortly before the migration of humans into the Americas.

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 study was published on December 27 in the Proceedings of the National Academy of Sciences.

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.

“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.

The samples used in this study were collected on the U.S. Coast Guard icebreaker Polar Sea on an ambitious trans-Arctic expedition in 1994. Photo by U.S. Coast Guard
The samples used in this study were collected on the U.S. Coast Guard icebreaker Polar Sea on an ambitious trans-Arctic expedition in 1994. Photo by U.S. Coast Guard

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.”

New context for human migration

The timing of human migration into North America from Asia remains unresolved, but genetic studies tell us that ancestral Native American populations diverged from Asian populations about 36,000 years ago, the same time that Farmer and colleagues found that the Bering Land Bridge emerged.

“It’s generally believed that the land bridge was open for a while, and then humans crossed it at some point,” Sigman said. “But our new data suggest that the land bridge was not open, and as soon as it opened up, human populations made their way into North America.”

The finding raises questions about why humans decided to migrate as soon as the land bridge opened, and how humans made their way across the land bridge with no previous knowledge of the landscape.

During 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. Image by National Park Service
During 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. Image by National Park Service

The researchers noted that they need to be cautious when considering these implications, as the interpretation requires combining very different types of information, including the new data and the information of human geneticists and paleoanthropologists. They look forward to seeing how their results are built upon by these other scientific communities.

A window to the past

To reconstruct the history of the Bering Strait, Farmer and Sigman sought an ocean chemical fingerprint.

Pacific waters carry high concentrations of nitrogen molecules that have a distinct chemical composition, known as an isotope ratio. Today, waters from the Pacific Ocean travel northwards across the Bering Strait into the Arctic Ocean, carrying a traceable nitrogen isotope ratio.

By measuring nitrogen isotopes in sediments at the bottom of the Arctic Ocean, Farmer found that the fingerprint of Pacific Ocean nitrogen disappeared when the Bering Strait was closed during the peak of the last ice age, as expected.

But when Farmer continued his analyses further back in time – to about 50,000 years ago – he found that the Pacific nitrogen fingerprint returned far more recently than researchers had thought possible.

“When Jesse showed me his data, he didn’t need to explain to me what had happened,” Sigman said. “It was too large of a change to be anything other than a previous opening of the Bering Strait.”

To understand the implications for global sea level, Farmer and Sigman collaborated with Tamara Pico, a sea level expert and professor of Earth and Planetary Sciences at UC Santa Cruz, Princeton undergraduate Class of 2014, and co-lead author on the paper. Pico compared Farmer’s results with sea level models based on different scenarios for the growth of the ice sheets.

“When Jesse contacted me I was so excited,” Pico said. “A large part of my PhD thesis was focused on how fast global ice sheets grew leading into the Last Glacial Maximum, and much of my work suggests that they might have grown faster than previously thought.”

Farmer’s nitrogen analyses provided a new set of evidence to back up Pico’s research about sea levels during the last ice age.

“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.”

“This study brought together experts in the Arctic Ocean, nitrogen cycling, and global sea level. And the outcome has consequences not only for climate and sea level but also for human prehistory,” Farmer said. “One of the thrilling aspects of paleoclimate research is the opportunity to collaborate across such a broad range of subjects.”

DOI: 10.1073/pnas.2206742119

Princeton University

Cover Photo: Cape Espenberg, the northern tip of the Seward Peninsula, Bering Land Bridge National Preserve, western Alaska, U.S. Photo: Michael J. Thompson/U.S. National Park Service

Related Articles

4 Aztec child burials unearthed in Mexico and dated to the Early Colonial period may be indicators of Aztec resistance

6 July 2022

6 July 2022

During an archaeological rescue effort in Mexico City’s historic central district of La Lagunilla, the remains of an Aztec house...

Europe’s oldest grave of a newborn girl found in İtaly

15 December 2021

15 December 2021

An international team of researchers has found Europe’s oldest tomb of a newborn girl, dating back 10,000 years, in Liguria....

New studies confirm that there was indeed a shipyard at Lothal, the commercial center of the Harappan civilization and world’s oldest port

6 September 2024

6 September 2024

Since the discovery of Harappan sites at Lothal, located about 30 kilometers inland from the coast of the Gulf of...

New research reveals that Baltic amber was transported to the most westerly region of the continent more than 5,000 years ago

21 October 2023

21 October 2023

A team of scientists has identified the oldest pieces of Baltic amber ever found on the Iberian Peninsula, revealing that...

Anthropologists say humans have been using personal ornaments to communicate about themselves without the fuss of conversation – for millennia

24 September 2021

24 September 2021

Anthropologists believe that for millennia, individuals have used personal decorations to communicate about themselves without the hassle of dialogue. They...

“One of the outstanding discoveries of recent decades”: Gold coin reveals unknown British King

20 October 2023

20 October 2023

New light has been shed on a little-known part of British history thanks to the extraordinary discovery of a coin...

World’s Oldest Place Name Signs

4 February 2021

4 February 2021

Throughout the history of the world, our interest and curiosity in ancient cultures and lives continue to increase day by...

Large Roman Complex found in Swiss Gravel Quarry

30 August 2023

30 August 2023

Archaeologists have discovered the remains of walls of a Roman building complex built nearly 2,000 years ago in the Äbnetwald...

Three Roman Graves Uncovered in Portugal

17 April 2024

17 April 2024

Three burials dating to the 5th or 6th century AD have been unearthed in the ancient Roman city of Ossónoba...

A 3,400-year-old Pyramid from the Scythian-Saka period found in Karaganda region of Kazakhstan

2 November 2023

2 November 2023

A pyramid belonging to the Scythian-Saka period was found in the Karaganda region of Kazakhstan. Experts announced that the Karajartas...

In Russia, archaeologists 2100-Year-Old Medallion of Goddess Aphrodite and a warrior tomb unearthed

30 October 2022

30 October 2022

Archaeologists have unearthed a silver medallion depicting the Greek goddess Aphrodite (Roma Venüs) in a 2100-year-old grave of a priestess...

Homo Bodoensis may be the ancestor of modern humans

28 October 2021

28 October 2021

Although modern humans are the only surviving human lineages, their kinship with other human species that roamed the world is...

New insight into the history of human presence in Paveh county, Kermanshah province, which is located in western Iran

22 August 2021

22 August 2021

Stone tools and animal bones unearthed recently have thrown new insight into the history of human presence in Paveh county,...

Lidar Technology Reveals a 3,000-year-old Secret Mayan City with Full of Pyramids and Plazas

30 October 2024

30 October 2024

Tulane University researchers used laser-guided imaging to uncover vast unexplored Maya settlements in Campeche, Mexico, revealing more than 6,500 pre-Hispanic...

Study Reveals Córdoba’s Advanced Sanitation System: A Medieval Model Unmatched in Europe for Centuries

25 April 2025

25 April 2025

Recent research has unveiled the impressive sanitation systems of medieval Córdoba, revealing that the city’s infrastructure was so advanced that...