The Bering Land Bridge, which connects Asia to North America, did not appear until roughly 35,700 years ago, or less than 10,000 years before the peak of the last ice age, according to a recent study that reconstructs the history of sea level at the Bering Strait (known as the Last Glacial Maximum).
The results show that, contrary to what earlier research had suggested, the growth of the ice sheets and the subsequent drop in sea level happened surprisingly quickly and much later in the glacial cycle.
Bering Land Bridge formed surprisingly late during the last ice age
BARBARA GINDL/APA/AFP via Getty Images
According to Tamara Pico, an assistant professor of Earth and planetary sciences at UC Santa Cruz and a corresponding author of the study, "it means that more than 50% of the global ice volume at the Last Glacial Maximum grew after 46,000 years ago," as per ScienceDaily.
This suggests that there was a significant delay in the development of ice sheets after global temperatures dropped, which is crucial for understanding the feedback between climate and ice sheets.
As more and more of the Earth's water is trapped in enormous ice sheets, global sea levels fall during ice ages, but the exact timing of these processes has been difficult to determine.
Large portions of North America were covered by ice sheets during the Last Glacial Maximum, which occurred between 26,500 and 19,000 years ago.
A vast landmass known as Beringia, which stretched from Siberia to Alaska and was home to herds of horses, mammoths, and other Pleistocene animals, was made visible by dramatically lower sea levels.
Around 13,000 to 11,000 years ago, the Bering Strait was once more flooded due to the melting of the ice sheets.
Because they reduce the amount of time between the opening of the land bridge and the arrival of humans in the Americas, the new findings are intriguing in terms of human migration.
Although the exact timing of human migration into North America is still unclear, some studies indicate that people may have lived in Beringia for the duration of the last ice age.
The new study determined when the Bering Strait was flooded during the previous 46,000 years, allowing water from the Pacific Ocean to flow into the Arctic Ocean, by analyzing nitrogen isotopes in seafloor sediments.
The isotope analysis was carried out by the first author Jesse Farmer at Princeton University, who determined the ratios of nitrogen isotopes in the marine plankton remains found in sediment cores dug up from the seafloor at three different locations in the western Arctic Ocean.
Farmer was able to determine a nitrogen isotope signature indicating when Pacific water flowed into the Arctic because of differences in the nitrogen composition of Pacific and Arctic waters.
The findings are consistent with recent research showing that global sea levels were significantly higher than previously thought before the Last Glacial Maximum, she said.
During the Last Glacial Maximum, the average global sea level was about 130 meters (425 feet) lower than it is today.
However, factors like the deformation of the Earth's crust caused by the weight of the ice sheets play a role in determining the actual sea level at a specific location, like the Bering Strait.
The Earth system has undergone a series of significant transitions over the last 25,000 years, as per Britannica.
The Last Glacial Maximum, also known as the LGM, marked the peak of the most recent glacial epoch 21,500 years ago.
The Laurentide Ice Sheet, which at the time reached as far south as Des Moines, Iowa; Cincinnati, Ohio; and New York City, covered the northern third of North America.
Much of western Canada, as well as northern Washington, Idaho, and Montana in the United States, were covered by the Cordilleran Ice Sheet.
The British Isles, Scandinavia, northeastern Europe, and north-central Siberia were all covered by the Scandinavian Ice Sheet in Europe.
In other areas, even at low latitudes in Africa and South America, montane glaciers were widespread.
The melting of the continental ice sheets first started around 20,000 years ago. Submerged fossil coral reefs can be drilled into and date to clearly show how the sea level rose as the ice melted.
Since 15,000 years ago, the melting has been the fastest.
For instance, by 10,000 years ago, the Laurentide Ice Sheet's southern limit in North America was north of the Great Lakes and St. Lawrence regions, and by 6,000 years ago, it had completely vanished.
