7 February 2023 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

Banner
Related Post

The 890-million-year-old sponge fossil may be the oldest animal yet discovered

1 August 2021

1 August 2021

890-million-year-old fossil sponges found in the “Little Dal” limestones of northwest Canada may be the oldest animal ever found. According...

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....

Egyptian archaeologists discovered 16 meters long ancient papyrus with spells from the Book of the Dead

19 January 2023

19 January 2023

Archaeologists working in Egypt’s Saqqara region have unearthed a 16-meter-long ancient papyrus for the first time in a century. Saqqara...

Archaeologists have unearthed two early Aksumite Churches in Africa

11 December 2022

11 December 2022

New discoveries in the port city of Adulis on Eritrea’s Red Sea coast show that two ancient churches discovered more...

Return of a 4,250-year-old Hattian golden beak-spouted ewer to Turkey

27 October 2021

27 October 2021

The 4,250-year-old golden beak-spouted ewer was returned to the Anatolian Civilizations Museum by the Gilbert Art Foundation. Culture and Tourism...

Researchers may have found 3,000-year-old evidence of Yue (Amputation), one of the five punishments practiced in ancient China

4 May 2022

4 May 2022

According to the South China Morning Post, researchers in China believe a skeleton discovered in a tomb in the country’s...

Researchers have found in miniature ceramic bottles evidence of the oldest known use of cosmetics in the Balkans

14 July 2021

14 July 2021

In miniature ceramic bottles from excavations ascribed to the Lasinja Culture in the Southeast Prealps and the Vinča Culture in...

Peru finds perfectly preserved a wooden figure in the Americas’ largest mud-brick city

29 June 2022

29 June 2022

A perfectly preserved wooden figure has been discovered at the Chan Chan archaeological site, in northern Peru, the Ministry of...

Archaeologists uncovered a second mosaic in Rutland Roman villa in England

29 November 2022

29 November 2022

Archaeologists report they have uncovered a second mosaic at the site of the 2020 mosaic discovery at the Roman villa...

25 Qing Dynasty tombs found in China’s Hunan

25 May 2022

25 May 2022

25 graves dating from the Qing Dynasty (A.D. 1644–1912) have been uncovered in the Houbeishan tomb complex in southern China,...

New research reveals the true function of Bronze Age daggers

30 April 2022

30 April 2022

A new study led by Newcastle University has revealed that the analysis of Bronze Age daggers has shown that they...

Xujiayao hominid’s brain in China had the biggest known brain of the time

17 January 2022

17 January 2022

A study showed that the ancient relatives of modern humans in northern China may have had an “Einstein’s brain” at...

Turkey to Present 12 Historic Artifacts to Istanbul Patriarch

10 August 2021

10 August 2021

The government said on Monday that Turkey will deliver stolen icons from ancient local churches to Istanbul’s Fener Greek Patriarch...

Archaeologists unearth 128 ancient urn burial tombs for children in north China

22 November 2021

22 November 2021

Archaeologists have uncovered urn burial chambers containing the remains of 128 infants among the ruins of an ancient city of...

A 7,500-year-old settlement has been discovered in Turkey’s Domuztepe Mound

11 September 2021

11 September 2021

During the most recent excavations at Domuztepe Mound in the Türkoğlu district of southern Turkey’s Kahramanmaraş province, a settlement and...

Comments
Leave a Reply

Your email address will not be published. Required fields are marked *