Eight-years of cave monitoring at Golgotha Cave, SW Australia: implications for speleothem paleoclimate records

Abstract

Speleothems are an important archive of paleoenvironmental information but a thorough understanding of processes are necessary for their interpretation. In order to better understand speleothem records from the climatically-sensitive southwest region of WA, we have conducted a detailed eight-year monitoring study at Golgotha Cave, southwest WA. Oxygen isotopic data demonstrated that the majority of water moved through the porous Quaternary calcarenite as matrix-flow with an inferred transit time of <1 year. A zone of high-flow dripwater is fed by high-magnitude rainfall events (Treble et al., 2013). Prior calcite precipitation (PCP) signals of increased Mg/Ca and Sr/Ca in dripwater are attributed to stalactite deposition. This signal is enhanced at low-flow sites and minimised at the high-flow site as degassing and subsequent stalactite deposition are a function of drip interval. Long-term rising trends found in most solutes are attributed via a mass-balance approach to increasing forest bioproductivity, consistent with an increase in forest understorey following a low-intensity burn in 2006. A fundamental message from this study is that individual speleothem records from within Golgotha Cave will differ, e.g. speleothem δ18O at our high-flow site is biased to recording high-magnitude rainfall events, whilst PCP will be the main driver of speleothem Mg/Ca and Sr/Ca at low-flow sites. Forest biomass appears to be modulating transpiration-sensitive ions and these may serve as an indicator of fire history.