Cave stalagmites as records of past recharge frequency in semi-arid Australia
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Date
2015-11-03
Journal Title
Journal ISSN
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Publisher
National Centre for Groundwater Research And Training
Abstract
Understanding past variability in groundwater recharge over recent time scales (0 – 10 ka) in
Australia is essential for future sustainable groundwater management in a changing climate.
Currently, there are limited data about past infiltration rates and their relationship to
environmental controls that dominate recharge variability. Speleothem (cave precipitates) records
may provide a new approach to understanding past infiltration (i.e. recharge rates), in addition to
traditional interpretations of connectivity between climate and the hydrological cycle, in drier parts
of Australia. In this study we used Cathedral Cave, (SE Australia) located in a temperate semi-arid
climate, as a natural laboratory to investigate cave infiltration rates and the climate-karst-cave
interactions driving the isotopic (δ18O) and chemical variability in modern drip water. These
findings were then used to interpret the δ18O stalagmite record from two modern speleothems
growing during the last ~50 years. Modern drip water results showed that the δ18O composition
was enriched by up to 2.77 ‰ relative to annually weighted mean rainfall. Isotopically lighter δ18O
occurred during infiltration events, followed by subsequent isotopic enrichment as evaporation in
the unsaturated zone fractionated δ18O of stored water. Drip rate monitoring revealed that larger
events leading to infiltration were infrequent (0 – 3 a-1) and the ‘effectiveness’ of these infiltration
events was controlled by antecedent moisture conditions in the soil zone. In drier climatic zones,
evaporation drives the enrichment of δ18O in the unsaturated zone, allowing periods of infiltration
to be identified from the stable isotopic composition of drip waters. Our findings are important for
interpreting speleothem records from regions with infrequent recharge and high evaporation rates.
Such records are likely to contain evidence of past infiltration events moderated by an evaporation
signal, allowing records of paleo-recharge to be reconstructed for drier climate regions of Australia.
Description
Keywords
Caves, Arid lands, Australia, Groundwater recharge, Climatic change, Records management, Data, Water
Citation
Markowska, M., Baker, A., Andersen, M. S., Rutlidge, H, Jex, C. N., Cuthbert, M. O., Rau, G. C., Adler, L., Graham, P. W., Mariethoz, G., Marjo, C. E., & Treble, P. C. (2015). Cave stalagmites as records of past recharge frequency in semi-arid Australia. Paper presented at the Australian Groundwater Conference, 3-5 November 2015, The Shine Dome, Canberra, Australia, (pp. 170). Retrieved from: https://www.groundwater.com.au/media/W1siZiIsIjIwMTgvMDcvMzEvMDNfNDNfMDBfNzk5X0FHQzIwMTVfQWJzdHJhY3RfYm9va2xldC5wZGYiXV0/AGC2015%20Abstract%20booklet.pdf