A Bug’s (Long) Life

Geologist Yarrow Axford uses millennia-old insect remains to help predict climate change

The six tents on a stone-filled Arctic beach add a splash of color to an otherwise monochromatic grey day.

For geologist Yarrow Axford, who has trekked to the Arctic’s isolated landscapes on more than a dozen expeditions and currently conducts research in Greenland, the seclusion is a large part of what makes the science work.

“Traveling to remote places allows us to control for human influence and look at landscapes in their most natural state as they respond to climate change,” says Axford, whose first wilderness expedition brought the then-undergraduate researcher to Alaska’s Denali National Park in 1996.

Today Axford, earth and planetary sciences, is interested in learning how Greenland’s climate has changed during the Holocene Epoch, a period of the past 11,000 years since the last ice age.

The travel itself is rigorous and can involve flying in a military transport plane, a small commercial jet, or a helicopter with a net full of supplies dangling from its underbelly. Once on the ground, the team must reassemble everything from tents to research equipment. At the most northerly study sites, they do this with the knowledge that there may be more polar bears nearby than people.

Arriving in the Arctic feels like a bit of a homecoming for Axford, who grew up surrounded by the spruce trees and tundra-like surroundings of rural Maine. Though she fondly recalls a seventh-grade trip to explore the glacial history of New England, it wasn’t until she was an undergraduate at Mount Holyoke College that she thought of geology as a potential career.

The difficulty in getting there is met with the reality that the Arctic is critically important to the rest of the world, says Axford, a 2015 recipient of a prestigious National Science Foundation Faculty Early Career Development (CAREER) award, adding, “In Earth’s history, whenever we’ve had a large climate shift in the Arctic, it has translated to huge changes in global climate and sea level change.”

Once on the ground in Greenland, Axford’s team heads toward a predetermined inland body of water and sets out on a small boat, with human-powered tools that will quite literally extract a historical record from the lakebed below.

Long, clear tubes pierce the lake floor and become filled with mud containing mineral grains and organic material — insects, pollen, molecular traces of plants and algae — that has accumulated year after year.

Back in a lab in Evanston, where the walk-in refrigerator for the sediment cores is 39.2 degrees Fahrenheit — the same temperature as an Arctic lakebed — the tubes of mud must be sliced lengthwise and scanned before the tedious process of dissecting can begin. The team uses the insect bodies, molecular markers, and geochemistry as climate indicators.

“Looking for chironomids — tiny insects that resemble mosquitoes — is a bit like looking for hay in a haystack,” Axford says. “They tend to be abundant, meaning you can sometimes find thousands in a small amount of mud.”

Graduate students physically pluck the remains from each core, placing the insects under a microscope to identify and sort each species. Previous research has shown how the distribution of various species is tied to the climate they lived in, meaning these little bugs offer a rare indicator of past temperatures. Axford and her students also hunt down other complementary ways to reconstruct past climate. On any given day in the lab, her students might be found outlining former glaciers on satellite imagery or extracting molecular traces of ancient organisms to assess their chemistry.

Axford’s research results are of great relevance to a scientific community concerned about global climate change and Greenland’s shrinking ice sheet — the second largest in the world and the only ice sheet outside the Antarctic. Covering three-quarters of Greenland, the ice sheet is currently losing billions of tons of ice each year.

“We are interested in understanding climate change as it unfolded over thousands of years,” says Axford. “If we are to help better predict the changes that will happen in our lifetime, we have to account for the fact that what used to occur over centuries might today occur in decades.”

One of Axford’s scientific goals is to circumnavigate Greenland to create climate reconstructions from the island’s different climate zones.

A recent study led by doctoral student Jamie McFarlin,in collaboration with Maggie Osburn, earth and planetary sciences, showed that northwestern Greenland was even warmer during the past two interglacial periods than previously thought. Today the summertime weather hovers near freezing, but due to well-documented natural causes, average temperatures in the early Holocene (8,000 to 11,000 years ago) and last interglacial (116,000 to 130,000 years ago) climbed past 50 degrees Fahrenheit.

Finding a lakebed unscathed by shifting ice for more than 100,000 years was a rare discovery and helped Axford garner support from the Institute for Sustainability and Energy at Northwestern. When the team of researchers brought these lakebed cores to the lab, the samples revealed a mix of chironomids and another insect known as the phantom midge. The mix of insects present suggests a much warmer climate during both periods.

“Just a few knobs control Earth’s climate,” says Axford. “It seems that when those knobs were turned a little bit in the past, northern Greenland changed profoundly. That means future climate change could have especially big impacts there, including on the Greenland ice sheet.”

McFarlin obtained the samples during a 2014 trip and returned to the Arctic in 2015 and 2016 to conduct fieldwork in southern Greenland. She expects to defend her dissertation in spring 2019.

This summer, a group of four researchers from Axford’s lab returned to Greenland. Postdoctoral fellow Melissa Chipman conducted fieldwork in late June for a National Geographic–funded project to reconstruct the long-term history of tundra wildfires in western Greenland. From mid-July to mid-August, Chipman, doctoral students Laura Larocca and Everett Lasher, and undergraduate earth science major Peter Puleo were in southern Greenland coring lakes to reconstruct the history of mountain glaciers. 

It typically takes a year—and sometimes several years—to move from field sampling to dating a core, then developing and publishing an illustration of what a place was like thousands of years ago.

“We have to know what happened in the past if we are to predict the future,” says Axford. “Because there aren’t a lot of researchers with boots on the ground collecting these kinds of records in Greenland, our group has a really exciting role to play in quantifying prehistoric temperature changes. That helps us understand how the Arctic climate system works, and in turn what the consequences of future climate change will be.”

By Roger AndersonSeptember 19, 2018