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Physical Chemistry

Cave dripwater may contain fire evidence

Heightened water evaporation rates leaves its mark on oxygen isotope ratio

by Elizabeth K. Wilson
July 25, 2016 | APPEARED IN VOLUME 94, ISSUE 30

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Credit: Andy Baker/U. New South Wales
Drip water in Yonderup Cave contains evidence of an aboveground fire.
Credit: Andy Baker/U. New South Wales
Drip water in Yonderup Cave contains evidence of an aboveground fire.

Water that drips from aboveground into caves to form stalactites and stalagmites carries with it paleoclimate signatures in isotopic ratios. Now, researchers say this geochemical record may be altered by fires, which could add complexity to paleoclimate interpretations (Hydrol. Earth Syst. Sci. 2016, DOI: 10.5194/hess-20-2745-2016). From 2005 to 2011, a team led by Andy Baker, Gurinder Nagra, and Pauline C. Treble of the University of New South Wales measured 18O/16O ratios in drip water at two sites in Yonderup Cave beneath a forest in southwestern Australia. Because 18O is heavier than 16O, it evaporates more slowly, and its enrichment in water, therefore, can be a marker for changing temperatures. But the authors found that the drip water at one site in Yonderup Cave was highly enriched in 18O compared with ratios predicted by models. In addition, oxygen isotope ratios at nearby Golgotha Cave showed no such enrichment, even though both caves are in the same arid environment. However, an intense wildfire in 2005 led to the loss of a giant tree directly over the 18O-enriched area in Yonderup Cave. The increased evaporation could explain the isotope findings. The authors say such isotopic changes could persist for five to 10 years.

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