After hiking nine kilometres with a 400‑metre elevation gain and carrying heavy backpacks through very rocky terrain, the researchers spent more than 24 hours in the field and returned with sediment samples from the lake Stuptjørna.

Stuptjørna lived up to its name: the terrain was steep and at times almost impassable.

“We completely underestimated the trip, especially with the amount of equipment we had to carry. Sleep was also in short supply and people were exhausted,” says research professor Willem van der Bilt of the University of Bergen and the Bjerknes Centre, reflecting on the demanding field trip in the summer of 2022.

What is that white spot?

Alexandra Rouillard from Umeå University was also part of the crew. She was a postdoc at the time, and it was her first trip to Svalbard. What began as a scenic hike turned into a demanding expedition across steep terrain, unstable boulder fields, and long ascents carrying heavy equipment, all under the constant awareness that polar bears roam the area.

“I seriously began questioning my priorities in life. Indeed, living itself emerges as a strong contender versus science at that point”, she says.

After more than 24 hours, they returned to the shore of Wijdefjorden with their sediment cores and wet gear.

Surprising layers

The lake was chosen because of its high elevation. The goal was to gain a better understanding of past Arctic winter climate and the natural mechanisms that control it, by using this lake as an archive of winter conditions.

“The higher the lake, the longer winter lasts,” van der Bilt explains.

They collected a sediment core from the lake containing 7,000 years of climate history, and during laboratory analyses they discovered something surprising. The paper is published in Geophysical Research Letters.

“We found out that these little layers we saw already during fieldwork, were minerals that form in the lake under very specific conditions, when there is no oxygen in the water. The longer the lake is covered by ice, the less oxygen is found in the water, which is directly linked to winter climate”, van der Bilt explains.

“We all took a (much needed) cleansing swim and finally made it back to the sailboat, ferrying our equipment and people back and forth until the last of the team were on board. Pure joy. Minutes later, we noticed a white spot on the beach we just left behind,” Rouillard says. In the picture below you can see what that was.

Combining methods

Methodologically, the study married established laboratory methods with new scanning techniques. For example, medical CT scans were used to identify the (often invisible) anoxic mineral concretions, while their chemical composition was confirmed using microscopic analysis. In addition, they relied on hyperspectral imaging, a method that identifies the characteristic visible and invisible light spectra of specific materials. In this case, they used the light spectra of pigments produced by bacteria that lived in the lake when there was little oxygen.

They found that variations in winter climate track a well-known 1500-year climate cycle.

“You can think of it as the heartbeat of natural climate in this area. But we are the first to report that it also has an impact on winter climate on land,” van der Bilt says.

“So, depending on where you are in that cycle in a future also shaped by human climate warming, that cycle could either make the impacts of human climate change worse or dampen it a little bit.”

Volcanic eruptions

The second big thing is that almost every extreme winter they found in this lake appeared to happen after multiple volcanic eruptions that had occurred closely spaced in time.

Volcanic eruptions inject large clouds of particles and gases into the atmosphere, which can block incoming sunlight for years to decades.

“By combining all kinds of fancy scanning and microscope techniques, we find that these extreme volcanic winters happened throughout the past 8,000 years, regardless of the background state of climate, meaning they happened under warm and cold conditions. That means that extremely cold volcanic winters also can happen in the warmer future that the region faces”.