On the eastern shore of Wijdefjorden in Svalbard, a team of scientists hauled 7,000 years of climate history out of Lake Stuptjørna—after hiking 9 kilometers with a 400-meter elevation gain through terrain so steep and rocky that one researcher found herself questioning whether science was worth living for. The brutal 2022 field expedition, which consumed more than 24 hours and left the team exhausted and operating on minimal sleep, yielded something far more valuable than survival stories: sediment cores that reveal how Arctic winters behave across millennia, and what controls them.
The lake itself was chosen deliberately. "The higher the lake, the longer winter lasts," explains research professor Willem van der Bilt of the University of Bergen and the Bjerknes Center. By studying a high-elevation alpine lake, the team could extract a detailed archive of past winter conditions written in layers of sediment. What they discovered was surprising enough to make the bruising trek worthwhile: microscopic minerals preserved in those layers form only under very specific conditions—when there is no oxygen in the water. And the longer a lake stays frozen beneath ice, the less oxygen survives in it. That anoxic signature, locked in stone, became a proxy for ancient winter length.
Alexandra Rouillard, a postdoc from Umeå University making her first journey to Svalbard, was part of the crew that hauled heavy equipment across boulder fields under the constant awareness that polar bears roam the area. Minutes after everyone reached the sailboat—and after taking a "much needed cleansing swim"—she spotted a white blur moving along the beach they had just left. It was a polar bear, a reminder of both the remoteness of their work and the living landscape they were studying.
The findings, published in Geophysical Research Letters, unite old methods with cutting-edge scanning technology. The team used medical CT scans to identify minerals otherwise invisible to the naked eye, confirmed chemical composition through microscopic analysis, and employed hyperspectral imaging to detect light signatures from bacteria that thrived in oxygen-starved water. The result: a window into natural climate cycles spanning seven millennia.
Two discoveries stand out. First, the research team found that Arctic winter climate tracks a well-known 1,500-year natural climate cycle—a "heartbeat" of sorts for the region's climate system. Van der Bilt notes this cycle has never before been shown to influence winter conditions on land, raising a crucial question for our warming future: depending on where humanity finds itself within this natural cycle, it could either amplify or dampen the impacts of human-caused climate change.
Second, nearly every extreme winter preserved in Stuptjørna's sediment appeared after multiple volcanic eruptions clustered close together in time. Volcanic particles and gases block incoming sunlight for years or decades, and the lake's layers reveal that this mechanism has shaped Arctic winters across thousands of years.
The work demonstrates how high-altitude lakes, preserved sediment, and rigorous field science can unlock the rules governing Earth's climate systems—even when the work demands everything researchers are willing to give.