Comparison of δ18O in groundwater and a cave flowstone: improving the interpretation of the speleothem δ18O paleoclimate proxy
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Date
2019-07-30
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Publisher
International Union for Quaternary Research (INQUA)
Abstract
Speleothems are high-resolution records that can be used for terrestrial paleoclimate reconstruction from their oxygen and carbon isotopes (δ18O and δ13C), and whose deposition is directly related to the groundwater recharge process. Groundwater δ18O records have the potential to provide an important long-term record of past climate, but they are low-resolution records as the isotope signal can be altered during flow within the aquifer. In this study we compare measured δ18O values from both a groundwater record and speleothem record from a flowstone over the past 12,000 years for the first time from south west Western Australia.
Flowstones normally form from cave streams or fast dripping seepages and their oxygen isotope composition is sensitive to the extent of kinetic fractionation, determined by water flow rate, as well as, streams or seepages water δ18O composition. In this study comparison of δ18O values from a groundwater record and flowstone enables the source water oxygen isotopic composition to be constrained in order for a more complete interpretation of the higher resolution speleothem record, including the site specific kinetic processes and climatic changes.
The flowstone δ18O values appear consistent with millennial variability in recharge δ18O predicted using the groundwater values, although the flowstone oxygen isotopes are generally enriched in 18O compared to the regional groundwater record before ~7.4ka. This offset between the records indicates that flowstone calcite deposition was not in isotopic equilibrium with its source water likely due to low flow regimes and extensive degassing of CO2. According to a model of isotopic disequilibrium that is driven by water supply, the Holocene portion of the flowstone record contains periods of relatively lower isotopic disequilibrium indicating possible higher water supply, and periods of relatively higher isotopic disequilibrium indicating possible lower water supply consistent with local and regional archives.
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Keywords
Ground water, Caves, Aquifers, Quaternary period, Isotopes, Climates, Western Australia, Water
Citation
Adler, L., Priestley, S., Treble, P., Baker, A., Hellstrom, J., Griffiths, A., & Meredith, K. (2019). Comparison of δ18O in groundwater and a cave flowstone: improving the interpretation of the speleothem δ18O paleoclimate proxy. Paper presented to the 20th INQUA Congress 25th - 31st July 2019, Dublin, Ireland. Retrieved from: https://virtual.oxfordabstracts.com/#/event/public/574/submission/853