Arctic was once lush and green, and could be again, new research shows

Picture this: not a white, but a green pole, with woody shrubs up to the Canadian coast of the Arctic Ocean. This is what the northernmost region of North America looked like about 125,000 years ago, during the last interglacial period, finds new research from the University of Colorado at Boulder.

Researchers analyzed plant DNA more than 100,000 years old from Arctic lake sediment (the oldest lake sediment DNA analyzed in a publication to date) and found evidence of a shrub native to Northern Canadian ecosystems, 400 km further north than its current range.

Because the Arctic is warming much faster than anywhere else in the world in response to climate change, the findings, published this week in the Proceedings of the National Academy of Sciences, is perhaps not only a glimpse of the past, but also a snapshot of our potential future.

“We have this very rare look at a particular warm period in the past, which was perhaps the most recent time it was warmer than it was in the Arctic. That makes it a very useful analog of what we might expect in the future. , said Sarah Crump, who led the work as a Ph.D. student in geological sciences and then postdoctoral researcher at the Institute of Arctic and Alpine Research (INSTAAR).

To catch this glimpse back in time, the researchers not only analyzed DNA samples, they first had to travel by ATV and snowmobile to a remote area of ​​the Arctic to collect and return them.

Dwarf birch is a key species of the low Arctic tundra, where slightly taller shrubs (reaching a person’s knees) can grow in an otherwise cold and inhospitable environment. But dwarf birch does not currently live beyond the southern part of Baffin Island in the Canadian Arctic. Still, researchers found DNA from this plant in the lake’s ancient sediment, showing that it used to grow much farther north.

“It’s quite a significant difference from the distribution of tundra plants today,” said Crump, currently a postdoctoral fellow in the Paleogenomics Lab at the University of California at Santa Cruz.

While there are many potential ecological effects of the dwarf birch creeping further north, Crump and her colleagues examined the climate feedbacks regarding these shrubs covering more of the Arctic. Many climate models do not account for these types of changes in vegetation, but these taller shrubs can rise above the snow in spring and fall, turning the Earth’s surface dark green instead of white, absorbing more heat from the sun.

“It’s a temperature feedback comparable to sea ice loss,” Crump said.

During the last interglacial period, between 116,000 and 125,000 years ago, these plants had thousands of years to adapt and move in response to warmer temperatures. With today’s rapid warming, vegetation is unlikely to keep up, but that doesn’t mean it won’t play a major role in affecting everything from thawing permafrost to melting glaciers to sea-level rise.

“As we think about how landscapes will balance with current warming, it is very important to consider how these plant series will change,” said Crump.

Since the Arctic could easily see a 9 degrees Fahrenheit (5 degrees Celsius) rise above pre-industrial levels by 2100, the same temperature as in the last interglacial period, these findings could help us better understand how our landscapes could change if the North Pole is on track to return to these ancient temperatures by the end of the century.

Mud as a microscope

To get the ancient DNA they were looking for, the researchers couldn’t look at the ocean or land – they had to look into a lake.

Baffin Island is located on the northeastern side of Arctic Canada, on the corner of Greenland, in the territory of Nunavut and the land of the Qikiqtaani Inuit. It is Canada’s largest island and the world’s fifth-largest island, with a mountain range running along its northeastern rim. But these scientists were interested in a small lake, along the mountains and near the coast.

Above the Arctic Circle, the area around this lake is typical of a high arctic tundra, with average annual temperatures below 15 ° F (? 9.5 ° C). In this inhospitable climate, the soil is thin and not much grows.

But DNA stored in the bottom of the lake below tells a completely different story.

To reach this valuable resource, Crump and her fellow researchers carefully balanced in the summer on cheap inflatables – the only ships light enough to take with them – and watched out for polar bears from the lake ice in the winter. They pierced the thick mud up to 10 meters below the surface with long, cylindrical pipes and plunged them deep into the sediment.

The purpose of this uncertain performance? To carefully withdraw a vertical history of old plant material and then travel back and take it with you to the laboratory.

While some of the mud was analyzed in a state-of-the-art organic geochemical lab at the Sustainability, Energy and Environment Community (SEEC) in CU Boulder, it also had to reach a special lab dedicated to decoding ancient DNA, in Curtin. University in Perth.

To share their secrets, these mud cores had to travel halfway around the world, from the North Pole to Australia.

A local snapshot

Once in the lab, the scientists had to dress like astronauts and examine the mud in an ultra-clean space to make sure their own DNA didn’t contaminate that of their hard-earned samples.

It was a race against time.

“Your best bet is to get some fresh mud,” Crump said. “Once it’s out of the lake, the DNA starts to break down.”

This is why older lake bottom samples in cold storage do not work completely.

While other researchers have also collected and analyzed much older DNA samples from permafrost in the Arctic (which acts like a natural underground freezer), sediments in the lake are kept cool, but not frozen. With fresher mud and more intact DNA, scientists can get a clearer and more detailed picture of the vegetation that once grew in that immediate area.

Reconstructing historical vegetation has usually been done using fossil pollen records, which are well preserved in sediment. But pollen tends to show only the big picture because it’s easily blown around by the wind and doesn’t stay in one place.

The new technique that Crump and her colleagues used allowed them to extract plant DNA directly from the sediment, sequence the DNA, and infer which plant species were living at the time. Rather than a regional picture, sedimentary DNA analysis gives researchers a local snapshot of the plant species that lived there at the time.

Now that they have shown that it is possible to extract DNA that is more than 100,000 years old, there are many future possibilities.

“This tool will be very useful on these longer timescales,” said Crump.

This research also planted the seed to study more than just plants. In the DNA samples of their lake sediment, there are signals from a whole host of organisms that lived in and around the lake.

“We’re just starting to scratch the surface of what we can see in these past ecosystems,” Crump said. “We can see the past presence of everything from microbes to mammals, and we can begin to get much broader views of what ecosystems looked like and functioned in the past.”