Beneath New England's Lakes, Hints of What an Arctic Thaw May Look Like

Near the end of Earth's last ice age, about 12,000 years ago, northern New England looked a lot like the Arctic. Herds of caribou roamed an open terrain of ice, snow, and scattered spruce and shrubs. Then, in the geological blink of an eye, the climate warmed and it all changed.
 
In less than a thousand years, pine forests and lakes filled in the tundra, and the caribou herds dispersed into smaller groups. New England's newly settled hunter gatherers may have also altered their lifestyle. In the archeological record, a new tool-making style emerged in this warmer world, about 10,000 years ago. Smaller, less sophisticated tools made of volcanic rhyolite replaced arrowheads and scrapers chipped from shiny chert.
 
These cruder toolkits appeared more frequently near rivers, close to the places where they were quarried, leading some archeologists to wonder if humans became less nomadic when the climate warmed. Instead of chasing caribou across an open, ice-packed landscape, they may have chosen to settle near water, where fish could have provided a steadier source of food.
 
"The rapid warming caused a profound ecological shift, and that almost certainly impacted the people living here," says Nathaniel Kitchel, a research associate in the Department of Anthropology. "We want to understand how New England's environment changed then, and what this can tell us about the shifts happening at higher latitudes today."

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Research associate Nathaniel Kitchel and professor Meredith Kelly

Thanks to a $1.1 million grant from the National Science Foundation, Kitchel will join Professor of Earth Sciences Meredith Kelly and colleagues at Emerson College and Northwestern University in reconstructing temperatures at this time to understand how plants, animals, and even humans in New England and Quebec responded. They will spend the next four years extracting pollen and fossilized midge larvae from lake sediment cores, and reanalyzing archeological sites to get a fuller picture of how abrupt climate change reshaped the region.

Taking New England's temperature
 
Most of what we know about climate change in New England comes from ice cores extracted from the Greenland Ice Sheet more than 2,000 miles away. The cores provide an excellent record for Greenland, where temperatures warmed by as much as 27 degrees Fahrenheit at the end of the last ice age. But in New England, the picture is fuzzier. Evidence from lake sediments suggest a less severe warming of 5-9 degrees, but the records are sparse, and the dates imprecise.

For a more detailed look at what happened, researchers are drilling into lakes across Vermont, New Hampshire, and Maine for sediments from which scientists can infer temperatures over the last 12,000 years. On a humid morning this summer, Kelly led students on a coring mission to Sky Pond, an hour from Hanover and west of Lake Winnipesaukee. 

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Joining them was Greg Stott, an eighth-grade Hanover science teacher making a documentary film about the last ice age. Stott had long been struck by how much glaciers had shaped the New England we see today, from the kettle ponds to Lebanon's airfield built on a delta formed in an ancient glacial lake.
 
From a canoe, Stott and his video director filmed as Kelly and her crew hoisted tubes of mud aboard their anchored pontoon boat. As the color and texture of the sediments changed, he could envision the movement of past glaciers; brown mud turning to gray clay as the students drilled down, clay giving way to sand and gravel marking the glaciers' last retreat.
 
Initially, Stott had planned to focus on just the glaciers, but after learning about the NSF project, he decided to widen the scope of his film. "I didn't even think about the human element," he says. "But yes, there were people here!"
 
Pollen, leaves, and a type of tiny fly known as a midge are buried in the sediments, too. From these biological remnants, scientists can reconstruct the various plants and trees that covered the landscape, along with summer temperatures going back thousands of years. Kelly's cores will be shipped to Northwestern, where students will extract the heads of midge larvae under a microscope, and from their distinctive mouth parts, identify each species. The cores will also be analyzed for pollen and other material by Wyatt Oswald, a professor at Emerson College.
 
"It's a bit like trying to guess who people are based only on their smiles — it works but it's kind of a challenge," says Yarrow Axford, an earth sciences professor at Northwestern. "Sometimes you can find hundreds of these heads in about a half teaspoon of mud – which gives you a sense for how abundant midges are in the environments where they live."
 
Midges are probably familiar to anyone who has gone fly fishing and tried to tie a lure. Climate scientists like midges because of how finicky they are about temperature. Each species varies distinctly by climate, allowing scientists to infer what summer air temperatures were like when the fly was alive.
 
Estimates of New England's past climate come largely from Greenland ice cores, which provide a high-resolution snapshot of temperature changes at the end of the last ice age. These records show that climate warmed dramatically, "within a human lifespan," says Kelly. However, it's unclear if the changes in New England were as intense and followed the same pattern.
 
A mysterious gap
 
By gathering and analyzing lake sediments across northern New England, the researchers hope to develop a more precise climate record for the region and establish a timeline for the glacial retreat and other landscape changes. In parallel, Kitchel will retrace the footsteps of New England's ancient people, using radiocarbon dating to reanalyze archeological sites last visited decades ago.
 
One mystery the researchers hope to resolve is the absence of archeological sites from about 11,700 years ago, when the climate warmed abruptly, until about 10,200 years ago. It could be that archeologists haven't looked hard enough, says Kitchel. Or it could be that humans visited the region infrequently during that 1,500-year stretch.
 
"People are very resilient and adaptable," he says. "If climate change largely pushed people out of the area for a few hundred years, that's pretty profound."
 
The last ice age ended in New England as Earth's orientation toward the Sun shifted. This time, though, it's humans and a carbon-based economy that are warming the climate. This summer, many parts of the world faced record wildfires, heat waves, and drought, while in the Arctic, summer sea ice continued to retreat.
 
By digging into the past, researchers hope to catch a glimpse of the future. "We don't really know how fast those transitions happened, or exactly how much temperature change it took to cause them," says Axford. "That's what we're delving into. Together, we hope to say more about how a past rapid, big warming affected people who had been living in Arctic-like ecosystems."