‘Evidence of wild boars, deer, bears and aurochs’: ancient DNA reveals sunken area Doggerland had habitable forests during the last Ice Age

The sunken continent that connected Britain to mainland Europe until thousands of years ago may have been an excellent refuge for plants and animals, including humans, during the last Ice Age, a new study has found.

16,000 years ago, temperate forests existed in parts of Doggerland that are now submerged in the North Sea. That was long before such forests recolonized Britain and northwestern Europe after the final retreat of the glaciers about 11,700 years ago.

Doggerland is named after a large sandbar in the North Sea called Dogger Bank. It is named after a type of medieval Dutch fishing boat called a dogger.

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In southern Doggerland, where the new study was conducted, oak (Quercus), elm (Ulmus) and hazel (Corylus) trees flourished for thousands of years before the continent disappeared. Previous estimates had suggested that Doggerland was completely flooded by 7,000 years ago, but new results show this may have happened nearly 6,000 years ago. Researchers used DNA preserved in ocean floor soil for thousands of years, known as ancient sedimentary DNA, to reconstruct the region’s long-lost terrestrial ecosystem.

“We have evidence for wild boars, deer, bears and aurochs,” study lead author Robin Araby, an evolutionary geneticist and professor of genomics at the University of Warwick in the UK, told Live Science. “To my knowledge, this is the largest sedimentary DNA study ever done.”

Alabi and colleagues analyzed 252 samples from 41 cores drilled from the North Sea seabed off the coast of England. Specifically, the researchers took cores along the prehistoric 20-mile-long (30-kilometer) Southern River that once ran south of Doggerland.

Researchers have long known that Doggerland was covered in forest before it was flooded by the North Sea. However, the age of these forests was unknown, leading scientists to infer that they appeared around the same time as the British forests. Before this new study, Araby said, the consensus was that 16,000 years ago, southern Doggerland was tundra (dry, treeless plains) rather than forest. At that time, the ice sheet reached what is now the border between Scotland and England.

The researchers analyzed the sediments in the cores and classified them into two categories: safe and unsafe. The safe deposits were fine silts and clays that contained ancient DNA from species that lived in the area where the cores were taken. The unstable deposits were coarse sand and gravel containing ancient DNA that had been washed away far from where the cores were extracted. This means that this DNA was not useful in rebuilding the local ecosystem.

“DNA doesn’t survive long in water, so that makes perfect sense,” Alabi said. Sediments are typically carried and deposited in fluids, with slow-moving water picking up only fine sediments and fast-moving, high-energy water displacing coarser sediments. In slow-flowing water, sediment carrying DNA can only be carried a short distance before it is rapidly degraded. Fast-flowing water, on the other hand, can carry DNA-containing sediments much farther before breaking down.

This means that when researchers found microscopic deposits containing ancient DNA in the core, that DNA was likely shed locally. The DNA in the coarse sediment likely came from an upstream ecosystem. Therefore, “we were able to draw samples that we couldn’t believe were talking about the local environment,” Alabi said.

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Ancient DNA in the safe deposits showed that temperate trees and forest animals lived around the Southern River from around 16,000 years ago, when much of northwestern Europe and Britain was still covered in tundra. Remarkably, the researchers identified DNA from a close relative of the walnut (Pterocarya) that was thought to have become extinct in the region 400,000 years ago. The researchers also found evidence of warmth-loving lime trees (tilia), suggesting that southern Doggerland was calmer than surrounding areas during the last ice age.

“In the end, our knowledge turned out to be highly inaccurate,” Alabi says. “This is not pure tundra. There is enough environment here to sustain something like a forest.”

The results, published March 10 in the journal PNAS, show that Stone Age people were “well able to survive” in southern Doggerland after the ice sheet retreated from the area about 21,000 years ago, Alabi said. “We can predict where the best places to settle will be, and river estuaries are usually the best places because they’re close to resources.”

The discovery could also help resolve Reed’s paradox, which explains the discrepancy between seed dispersal rates and how quickly trees like oaks recolonized northern regions from the far south after the last ice age, the researchers said. Nearby regions, such as southern Doggerland and northern France, may have been glacial “microshelters” for temperate trees. This allowed the species to spread north much faster than it would have if it had survived only on the Iberian Peninsula, for example.

Finally, the study showed that the North Sea completely submerged southern Doggerland about 6,000 years ago. This is at least 1,000 years earlier than previous estimates of when the continent was flooded.

“This is another highlight that shows that our knowledge of this landscape is inaccurate,” Alabi said. “It really is the frontier.”