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Study (open access): The Bering Strait was flooded 10,000 years before the Last Glacial Maximum

>Significance

>The Bering Strait was a land bridge during the peak of the last ice age (the Last Glacial Maximum, LGM), when sea level was ~130 m lower than today. This study reconstructs the history of sea level at the Bering Strait by tracing the influence of Pacific waters in the Arctic Ocean. We find that the Bering Strait was open from at least 46,000 until 35,700 y ago, thus dating the last formation of the land bridge to within 10,000 y of the LGM. This history requires that ice volume increased rapidly into the LGM. In addition, it appears that humans migrated to the Americas as soon as the formation of the land bridge allowed for their passage.

>Abstract

>The cyclic growth and decay of continental ice sheets can be reconstructed from the history of global sea level. 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 / −2.4 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.

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This study shows the land bridge was open from ~36 ka to ~11 ka which fits with our current, non controversial, understanding and timing for crossing Beringia and travelling south by coastal routes (the Ice Free Corridor didn't open until later). Scientists have traditionally agreed that the earliest dates that humans were found in North America is somewhere between 14,000 to 16,000 years ago, which is supported by recent findings, give or take:

The oldest stemmed points (pre-Clovis) in North America have been dated to ~16,000 cal yr B.P. and are in Cooper's Ferry Idaho. These findings are not controversial and have been widely accepted: Dating of a large tool assemblage at the Cooper’s Ferry site (Idaho, USA) to ~15,785 cal yr B.P. extends the age of stemmed points in the Americas

Other findings, such as the oldest foot prints, located in White Sands National Park in New Mexico, date back to between 23,000 and 21,000 years ago. However, these dates are highly controversial and several authors have called for improved methods to date them: A critical assessment of claims that human footprints in the Lake Otero basin, New Mexico date to the Last Glacial Maximum

The tiny seeds of an aquatic plant (Ruppia cirrhosa) were used to age the footprints last year are at the center of the timeframe debate. Ruppia cirrhosa, grows underwater and gets a lot of its carbon for photosynthesis from dissolved carbon atoms in water. It's possible that carbon in the water came from a much older reservoir than when the foot prints were made:

>"The dating of those footprints is crucial in interpretations of when humans first came to North America from Asia, but the ages have larger uncertainties than has been reported. Some of that uncertainty is related to the possibility of a radiocarbon reservoir in the water in which the dated propagules of Ruppia cirrhosa grew. As a test of that possibility, Ruppia specimens collected in 1947 from nearby Malpais Spring returned a radiocarbon age of ca. 7400 cal yr BP. We think it would be appropriate to devise and implement independent means for dating the footprints, thus lowering the uncertainty in the proposed age of the footprints and leading to a better understanding of when humans first arrived in the Americas."

Other sites such as those at Bluefish Caves (controversial) and Old Crow river basin (was controversial not sure if it still is) fit with the timing of the land bridge being exposed and flooded. While other foot prints found on Calvert Island along the coast of British Columbia date to 13,000 years old: Terminal Pleistocene epoch human footprints from the Pacific coast of Canada

What's rather surprising here is the rapid growth of the ice sheets, and the resulting drop in sea level, occurring surprisingly quickly and much later in the glacial cycle than previous studies had suggested.

If you build it THEY will come

Makes sense that it appears not to have formed until shortly before discovered indications of human migration to the Americas.

>>>>remained flooded until around 35,700 years ago, not long before humans began migrating into the Americas

Good thing they waited for the bridge to open up. Couldn't they have started when the gap was small, they may have had kayaks or other boats?

They may have started before it opened up entirely. There is the Kelp Highway Hypothesis that suggests a migration via water occurred

​

The Kelp Highway Hypothesis: Marine Ecology, the Coastal Migration Theory, and the Peopling of the Americas

https://www.tandfonline.com/doi/abs/10.1080/15564890701628612

That's not really what your linked article says. From the article:

>By about 16,000 years ago, the North Pacific Coast offered a linear migration route, essentially unobstructed and entirely at sea level, from northeast Asia into the Americas. Recent reconstructions suggest that rising sea levels early in the postglacial created a highly convoluted and island-rich coast along Beringia's southern shore, conditions highly favorable to maritime hunter-gatherers... With reduced wave energy, holdfasts for boats, and productive fishing, these linear kelp forest ecosystems may have provided a kind of “kelp highway” for early maritime peoples colonizing the New World.

If you examine some maps for the coastal migration / kelp highway you'll notice Beringia is fully exposed with a large tongue from the Cordilleran ice sheet extending north along the Alaska and Aleutian Ranges. The oldest footprints along the Pacific coast of Canada date to 13,000 years ago on Calvert Island: Terminal Pleistocene epoch human footprints from the Pacific coast of Canada

They asked "Couldn't they have started when the gap was small, they may have had kayaks or other boats"

I simply responded to the notion that yes, they could have. If the idea of migrating thousands of miles via boat 10k years later is plausible then so too is traveling short distances 10k years prior. You have to assume that the formation of the land bridge didnt happen overnight and instead included a network of bergs, bays, ice sheets that allowed for migration via the sea vs land.

I don't have a chart, but the gap now is a little over 50 miles. I it had narrowed to 10 they would have been able to see land on the other side and been curious. Little Diomede would have been evident earlier, unless it rose through volcanic activity after that period.