A hidden Arctic cave holds secrets about our past and future

A hidden Arctic cave holds secrets about our past and future

MOSELEY’S LOVE FOR caves began on a family camping trip to Cheddar, Somerset, when she was 12 years old. When an opportunity came up to take a guided tour of some local caves, she made her first foray into the dim, labyrinthine underbelly of the earth’s crust. Crawling about in the muck, she was instantly hooked: she started saving the money from her paper round so that on future holidays to Somerset she could disappear into those caves once more. “I just absolutely loved it,” Moseley says. “Other people might get the feeling if they go to Venice, and they wander around the alleyways, and want to know what’s around the corner – you know, that excitement. I get that when I’m underground.”

Years later she started a PhD in paleoclimatology, which combined her two interests: caving, and climate change. Caves are valuable in climate research, because many contain speleothems: the collective name for geological features that are made out of mineral deposits, forming the stalagmites, stalactites and flow stones that hang from the cave roofs, or rise up like anthills from the floor. Speleothems grow slowly over millennia through the gradual drip of water from the outside world through the cave’s roof. Mineral calcite deposits form the physical structure, building individual hair-thin layers over time, somewhat like tree rings. “Each drop of water brings with it a chemical signature that can tell us about the processes going on at the surface at the time it was deposited,” Moseley explains. Calcite, oxygen, carbon, even traces of soil, pollen, and vegetation captured within, collectively build up a picture of past environments: what the carbon dioxide levels were in the atmosphere, the temperature, rainfall levels, and even the cave’s surrounding habitat.

Meanwhile, the cave itself keeps this valuable record highly-preserved, making them portholes to the past. “[Caves are] well-connected to the surface environments, but also well-protected from the surface environment. What that means is that they’re sitting there beneath the surface, silently recording changes that are taking place over hundreds of thousands, even millions, of years,” Moseley says. This stable environment can generate long, detailed records of past climates that are largely intact. That’s compared to other climate archives like marine sediments which may be more vulnerable to disturbance by animals, or ice cores, which melt away when temperatures warm. “[Speleothems] really do tick many boxes, and provide some nice advantages as an archive type,” says Christopher Day, an isotope geochemist and paleoclimatologist at the University of Oxford, who is not involved in Moseley’s research.

Advances in the uranium thorium radiometric dating used to analyse speleothems now allow researchers to date individual layers down to an accuracy of roughly 20 years. Paired with the environmental information they contain, “we can say with a lot of certainty when certain things happened,” Moseley says. She’s careful to emphasise that when it comes to climate records, speleothems are just one small part of a bigger picture but because caves are spread widely across the planet, their speleothems can help fill the gaps where other archive measures don’t exist. Meanwhile, their detailed records help build a richer global portrait of past environments. “You can gradually work towards a much more global representation of what the environment looked like, but with information that is specific to individual regions,” says Day. That helps researchers detect broad climate trends, and also compare the differences and relationships between regions, he explains.

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