Cave detectives ferret out climate change clues

Australian humorists describe speleotherms as cavers who are lost, hot, and bothered (Aust. Cav. 1998, 143, 7–8). Maybe so, but speleotherms are also features, such as stalagmites and stalactites, that form on cave walls, ceilings, and floors as calcite is dissolved from limestone above a cave when acidic water percolates downward through soil.

Speleotherms form at varying rates, depending on factors such as outside temperature, water acidity, and rainfall amounts. Analyzing their structure and composition can tell us a lot about how climate has changed during their formation period. In particular, say a team of Irish and English scientists, knowledge of the Holocene period (approximately 11,000 years ago to today) submillennial variability of oxygen isotopes in speleotherms provides important clues about how natural climate oscillations may influence future anthropogenic warming.

On analyzing oxygen isotopes in a stalagmite taken from a cave in Ireland, researchers Frank McDermott, David Mattay, and Chris Hawkesworth found multicentury oscillations that correlate well with those in the Greenland ice cores. The latter represent one of the few available records of Holocene period climate change in the north Atlantic region.

The researchers’ findings suggest that the relatively rapid climate cycles over the Holocene period were regional, rather than local phenomena. McDermott and co-workers suggest that the rapid climate cycling could be due to changes in ocean circulation during this time period. Periodic ice rafting, another naturally occurring event during the Holocene period, seems to have been of lesser importance in influencing oxygen isotope levels, they note. (Science, 2001, 294, 1328–1330) —WALTER SHAUB