Imagine not a white polar, but a green arctic, with woody bushes as far north as 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 interglacial period I found new research from the University of Colorado Boulder.
Researchers analyzed plant DNA over 100,000 years old recovered from lake sediments in the Arctic (the oldest DNA in lake sediments has been analyzed in a publication to date) and found evidence of a shrub native to northern Canada ecosystems 250 miles (400 Km) farther north from its current range.
As the Arctic is warming faster than anywhere on the planet in response to climate change, findings published this week in Proceedings of the National Academy of Sciences, It may not be just a glimpse into the past but a glimpse into our possible future.
“We have this really rare view of a certain warm period in the past that is arguably the most recent time it was much warmer than it was in the Arctic,” said Sarah Cramp, who directed the work as a PhD student in Geosciences and then a postdoctoral researcher at the Arctic Research Institute. Northern and Alpine (INSTAAR), this makes them a really useful analogue of what we might expect in the future.
To get this glimpse in the past, not only did the researchers analyze DNA samples, they first had to travel to a remote area in the Arctic with an automated transport vehicle (ATV) and snowmobile to collect and return them.
Dwarf birch is a major type of low arctic tundra, where shrubs can grow slightly taller (up to a person’s knees) in a cool, inhospitable environment. But dwarf birch does not currently live beyond the southern portion of Baffin Island in the Canadian Arctic. However, researchers found DNA of this plant in ancient lake sediments, indicating that it was growing further north.
“It’s a very big difference from the distribution of tundra plants today,” said Crump, who is currently a postdoctoral fellow in the Paleogenomics Laboratory at the University of California Santa Cruz.
While there are many potential environmental impacts of the dwarf birch’s encroachment further north, Kramp and colleagues examined climate reactions related to these shrubs covering more of the Arctic. Many climate models do not include these types of changes in vegetation, yet these taller shrubs can protrude over snow in spring and fall, making the Earth’s surface dark green instead of white – absorbing more heat from the sun.
“It’s a temperature retrograde similar to the loss of sea ice,” Kramp said.
During the period between the last ice ages, between 116,000 and 125,000 years, these plants had thousands of years to adapt and move in response to warmer temperatures. With today’s rapid rate of warming, vegetation will likely not keep pace, but that doesn’t mean it won’t play a significant role in influencing everything from melting permafrost to melting glaciers and rising sea levels.
“When we think about how to balance the landscape with current warming, it is really important to take into account how these plant ranges will change,” said Crump.
Since the Arctic could easily see an increase of 9 degrees Fahrenheit (5 degrees Celsius) above pre-industrial levels by 2100, the same temperature it was in between the last ice ages, these results can help us understand Better for how our landscapes change with climate change. The Arctic is on track to reach once again these ancient temperatures by the end of the century.
Clay as a microscope
To get the ancient DNA they wanted, the researchers couldn’t look at the ocean or the land – they had to look at a lake.
Baffin Island is located on the northeastern side of the Arctic of Canada, in the cat-corner to Greenland, in the Nunavut Territory and the Qikiqtaani Inuit Territories. It is the largest island in Canada and the fifth largest in the world, with a mountain range that stretches along its northeastern edge. But these scholars were interested in a small lake after the mountains and near the coast.
Above the Arctic Circle, the area around this lake is typical of high Arctic tundra, with average annual temperatures below 15 ° F (9.5 ° C). In this harsh climate, the soil is thin and not much of anything grows.
But the DNA stored in the bottoms of the lake below tells a completely different story.
To access this valuable resource, Cramp and her fellow researchers carefully balanced inexpensive inflatable boats in the summer – the only ships light enough to carry them – and watched polar bears from the lake’s ice in the winter. They penetrated thick clay up to 30 feet (10 meters) below its surface with long cylindrical tubes, pushing them deep into the sediments.
What is the point of this feat? To carefully pull out the vertical history of ancient plant material and then travel outside and back to the lab.
While some of the mud was analyzed in a modern organic geochemistry lab at the Sustainability, Energy and Environment Society (SEEC) at CU Boulder, it also needed access to a private lab dedicated to decoding ancient DNA, at Curtin University of Perth.
To share their secrets, these clay cores had to travel halfway across the world from the Arctic to Australia.
Once inside the laboratory, the scientists had to dress like astronauts and check the mud in an ultra-clean space to ensure that their DNA did not contaminate any of their hard-earned samples.
It was a race against time.
“Your best thing is to get fresh mud,” said Crump. “Once it gets out of the lake, the DNA will start to degrade.”
This is why old lake bottom samples in cold storage don’t exactly do the trick.
While other researchers have also collected and analyzed older DNA samples from Arctic permafrost (which acts like a natural underground freezer), lake sediments remain cool, but not frozen. With succulent clay and healthy DNA, scientists can get a clearer, more detailed picture of plants that once grew in that vicinity.
Historical vegetation reconstructions are commonly performed using fossil pollen records, which are well preserved in sediments. But pollen tends to show only the big picture, as it is easy to be blown off by the wind and not kept in one place.
The new technology that Cramp and her colleagues used allowed them to extract plant DNA directly from the sediments, sequence the DNA and infer what species of plants were living there at the time. Instead of a regional picture, analysis of sedimentary DNA 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 older than 100,000 years, the possibilities for the future are many.
“This tool will be really useful on these longer timelines,” said Crump.
This research also planted seeds to study more than just plants. In DNA samples from lake sediments, there are signals from a whole host of organisms that lived in and around the lake.
“We are just starting to scratch the surface of what we can see in these past ecosystems,” said Kramp. “We can see the past existence of everything from microbes to mammals, and we can start to get a much broader picture of how past ecosystems looked and how they functioned.”
Additional authors on this study include Jonathan H. Raburg, Julio Sepulveda, and Gifford H. Miller at the University of Colorado Boulder. Gregory de Witt of the University of Colorado Boulder and Smith College; Sam Cutler from the University of California. Beth Shapiro from the University of California and Howard Hughes Medical Institute; Bianca Freshet from the University of Quebec in Montreal; Matthew Bauer from Curtin University. Michael Pons from Curtin University and New Zealand Environmental Protection Agency; Martha K. Reynolds from the University of Alaska Fairbanks; Jason B. Brenner and Elizabeth K. Thomas of the University of Buffalo.