The climate change archive

The stalagmites and stalactites found in karst caves provide valuable information about the earth’s climate to date. Scientists use the composition of oxygen isotopes in stalagmites as a climate archive that has stored important information on past climate change. The oxygen in the stalagmites comes from the water that drips from the stalactites onto the stalagmites. This drip water originates from precipitation and provides a direct link to the surface climate. Researchers want to find out how the composition of the oxygen isotopes in drip water is related to precipitation in order to better analyze the so-called climate archive. Junior Professor Dr. Andreas Hartmann from the Chair of Hydrological Modeling and Water Resources at the University of Freiburg and a team led by Prof. Dr. Andy Baker from the University of New South Wales in Sydney, Australia have published the world’s first global analysis of drip water in karst caves in the current issue of Nature Communications.

In their study, the scientists compared the oxygen isotope composition of drip water with that of precipitation. Using statistical analysis, they identified important climatic threshold values: In cool climates, the oxygen isotope composition of drip water in caves is similar to that of precipitation, which means that stalagmite oxygen isotopes are best able to store past precipitation in these regions. In warmer and strongly seasonal climate zones, the oxygen isotope composition of the drip water resembles the groundwater formation determined on the basis of Hartmann’s large-scale karst simulation model.

The researchers thus show that in these warmer climate zones, which also include the Mediterranean region, stalagmite oxygen isotopes have stored information about the amount of groundwater formation in the past. In times of recurring heat waves in the Mediterranean region, these findings are particularly important as they allow conclusions to be drawn about the earlier groundwater formation and the associated water availability.

Original publication:
Baker, A., Hartmann, A., Duan, W., Hankin, S., Comas-bru, L., Cuthbert, M.O., Treble, P.C., Banner, J., Genty, D., Baldini, L.M., Bartolomé, M., Moreno, A., Pérez-Mejías, C., Werner, M. (2019): Global analysis reveals climatic controls on the oxygen isotope composition of cave drip water. In: Nature Communications, 10. S. 1–7. DOI: 10.1038/s41467-019-11027-w