STALACTITES are formed by the drip, drip of water, right? Not entirely. The way caves 鈥渂reathe鈥� is the true controller, a finding which pours doubt on ancient climate records derived from these structures.
of Florida State University in Tallahassee and colleagues recorded air circulation in the Hollow Ridge cave near Marianna by measuring airborne radon, a naturally occurring radioactive gas. They found that levels were lowest in the winter, when cold, moist air at higher pressure rushes into the cave and flushes out stale, radon-rich air (Earth and Planetary Science Letters, ).
The team suggest that stagnant summer air is hindering the precipitation of calcium carbonate from groundwater. That鈥檚 because carbon dioxide is given off during the reaction, and if C02 levels in the surrounding air get too high, precipitation ceases. 鈥淚f caves don鈥檛 breathe they don鈥檛 produce stalagmites,鈥� says Froelich.
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Some records of ancient rainfall may be skewed, as estimates based on stalactite formation assume year-round mineral deposition.
