An isotopic and modelling study of recharge to the Tamala Limestone, SW Australia: implications for speleothem paleoclimate records

Treble, PC; Bradley, C; Fairchild, IJ; Baker, AA; Jex, CN; Azcurra, CS; Wood, A

An isotopic and modelling study of recharge to the Tamala Limestone, SW Australia: implications for speleothem paleoclimate records

Date

2013-09-20

Authors

Publisher

International Association of Hydrogeologists

Abstract

We present a modern calibration of recharge pathways in the vadose zone of Quaternary dune calcarenite (Tamala Limestone in the Margaret River region, SW Western Australia. This study aimed to i. better understand groundwater recharge in these calcarenites, which has wider relevance to SW WA calcarenites and their use as a groundwater source; and to ii. interpret the O isotopic composition of these waters in order to assess the suitability of Golgotha Cave for reconstructing records of paleoclimate using speleothems. We present six years of data from our monitored site at Golgotha Cave (Treble et al. 2013). A lumped parameter hydrological model is developed to describe water fluxes and dripwater O isotopic composition. Comparison of observed data and model output allow us to assess the critical non-climatic karst hydrological processes that modify the precipitation isotopic signal and discuss the implications for speleothem records from this cave and those with a similar karst setting. Our findings include evidence of multiple reservoirs, characterised by distinct isotopic values and recharge responses ('low’ and ‘high’ flow sites). Dripwaters exhibit isotopic variations in wet versus dry years at low-flow sites receiving diffuse seepage from the epikarst with an attenuated isotopic composition that approximates mean rainfall. Recharge from high-magnitude rain events is stored <1%o lower in a secondary reservoir which is associated with high-flow dripwater that is 1%o lower than our monitored low-ow sites. One drip site is characterised by mixed-flow behaviour and exhibits a non-linear threshold response after the cessation of drainage from a secondary reservoir following a record dry year (2006). We show that ow to our monitored sites is dominated by diffuse ow with inferred transit times of less than one year. Diffuse flow appears to follow vertical preferential paths through the limestone reflecting differences in permeability and deep recharge into the host rock. Reference Treble et al. (Z013). An isotopic and modelling study of flow paths and storage in Quaternary calcarenite, SW Australia: implications for speleothem paleoclimate records, Quaternary Science Reviews 64; 90-103.

Keywords

Isotopes, Simulation, Limestone, Western Australia, Groundwater recharge, Australia, Caves, Water

Citation

Treble, P., Bradley, C., Fairchild, I. J., Baker, A., Jex, C. N., Azcurra, C., & Wood, A. (2013). An isotopic and modelling study of recharge to the Tamala Limestone, SW Australia: implications for speleothem paleoclimate records. Paper presented to the IAH 2013 Perth Australia : "solving the groundwater challenges of the 21st century", International Association of Hydrogeologists 40th International Conference, Perth, Western Australia, 15-20 September 2013, (pp. 203).