Slicing open stalagmites to reveal climate secrets

[xchrom]

http://grist.org/climate-energy/slicing-open-stalagmites-to-reveal-climate-secrets/

?w=470&h=266
Stacy Carolin collects samples in a Borneo cave last fall.

If you’ve ever visited a cave, you know the rules: Stay on the path, and keep your greasy paws off the formations. So Stacy Carolin was a bit taken aback the first time she headed into a cave not as a tourist, but as a scientist, and took a step off the beaten path. “I was a city girl back then,” she recalls. “It was very muddy and slippery … and also completely pitch black.” Not exactly the setting you’d expect for cutting-edge climate change research.

A few years later, Carolin, a PhD student at Georgia Tech, is breaking ground in the field of paleoclimatology, the study of ancient climates, using an unconventional but increasingly prevalent tool: “speleothems,” a catchall term for cave formations that includes stalagmites (remember the mnemonic: those that “mite” reach the ceiling from the floor) and stalactites (those that hold “tite” to the ceiling).

In a study released Thursday in the journal Science, Carolin and her colleagues outline 100,000-year-old rainfall conditions in Borneo, mapped from chemical clues in cave formations there. Like most historic climate reconstructions, the goal is to compile real-life data against which to test predictive models; if scientists know how much rainfall there was in the tropics in the past, they can see how well their models are able to replicate those conditions, and tweak accordingly. But the most commonly used “proxies” for ancient climates, including tree rings and ice cores, are notoriously inadequate in the tropics, leaving holes in scientists’ geographic picture of the past and making it difficult to measure historic changes in tropical weather systems, like monsoons, which can themselves have major impacts on global climate.

Deep inside caves in Mexico, Southeast Asia, China, and other limestone-rich locales worldwide, scientists have found rich troves of data in speleothems. Researchers look for formations that have already fallen over or broken off, so as not to damage the cave, haul these back to the lab, slice them open (“like a hot dog,” Carolin says), and study the ancient atoms within to discover how old they are and how much rainfall there was at different points in their past (speleothems form when rainwater drips through the limestone, picking up acid and minerals that pile up in the cave).