Browsing by Author "Duan, WH"

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    Global analysis reveals climatic controls on the oxygen isotope composition of cave drip water
    (Springer Nature, 2019-07-05) Baker, AA; Hartmann, A; Duan, WH; Hankin, SI; Comas-Bru, L; Cuthbert, MO; Treble, PC; Banner, J; Genty, D; Baldini, LM; Bartolomé, M; Moreno, A; Pérez-Mejías, C; Werner, M
    The oxygen isotope composition of speleothems is a widely used proxy for past climate change. Robust use of this proxy depends on understanding the relationship between precipitation and cave drip water δ18O. Here, we present the first global analysis, based on data from 163 drip sites, from 39 caves on five continents, showing that drip water δ18O is most similar to the amount-weighted precipitation δ18O where mean annual temperature (MAT) is < 10 °C. By contrast, for seasonal climates with MAT > 10 °C and < 16 °C, drip water δ18O records the recharge-weighted δ18O. This implies that the δ18O of speleothems (formed in near isotopic equilibrium) are most likely to directly reflect meteoric precipitation in cool climates only. In warmer and drier environments, speleothems will have a seasonal bias toward the precipitation δ18O of recharge periods and, in some cases, the extent of evaporative fractionation of stored karst water. © 2019, The Author(s)
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    Global distribution and controls on cave drip water oxygen isotope composition
    (Australasian Quaternary Association Inc, 2018-12-10) Baker, AA; Hartmann, A; Duan, WH; Hankin, SI; Comas-Bru, L; Cuthbert, MO; Treble, PC; Banner, J; Genty, D; Baldini, LM; Bartolomé, M; Moreno, A; Pérez-Mejías, C
    The oxygen isotope composition of speleothems is a widely utilised paleoclimate proxy that is responsible for the current state-of-knowledge of past Asian monsoon dynamics, the timing of glacial-interglacial cycles, and the insolation control on inter-tropical convergence zone position, among other climate processes. Because speleothems are deposited by cave drip water, and this is derived from meteoric precipitation, it is critical to understand the empirical relationship between precipitation and cave drip water d18O. Here, we present the first global analysis, based on data from 148 drip sites, 38 caves, and five continents. Globally, drip water d18O is most similar to the amount-weighted precipitation d18O where mean annual temperature (MAT) is < 10 °C. For seasonal climates with MAT > 10 °C and < 16 °C, we demonstrate that drip water d18O records the recharge-weighted d18O. Our analysis implies that speleothems (formed in near isotopic equilibrium) are most likely to have d18O that directly reflect meteoric precipitation only in cool climates. In warmer and drier environments, speleothems will have a seasonal bias toward the precipitation d18O of recharge periods and, in some cases, the extent of evaporative fractionation of stored karst water. We highlight the implications of our analysis for the interpretation of oxygen isotope records in Australasian speleothems. © The Authors
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    Global distribution and controls on cave drip water oxygen isotope composition
    (International Union for Quaternary Research (INQUA), 2019-07-30) Baker, AA; Comas-Bru, L; Hartmann, A; Duan, WH; Hankin, SI; Cuthbert, MO; Treble, PC; Banner, J; Gentry, D; Baldini, LM; Bartolomé, M; Moreno, A; Pérez-Mejías, C
    The oxygen isotope composition of speleothems is a widely utilised paleoclimate proxy that is responsible for the current state-of-knowledge of past Asian monsoon dynamics, the timing of glacial-interglacial cycles, and the insolation control on inter-tropical convergence zone position, among other climate processes. Because speleothems are deposited by cave drip water, and this is derived from meteoric precipitation, it is critical to understand the empirical relationship between precipitation and cave drip water δ18O. Here, we present the first global analysis, based on data from 148 drip sites, 38 caves, and five continents. Globally, drip water δ18O is most similar to the amount-weighted precipitation δ18O where mean annual temperature (MAT) is < 10 °C. For seasonal climates with MAT > 10 °C and < 16 °C, we demonstrate that drip water δ18O records the recharge-weighted δ18O. Our analysis implies that speleothems (formed in near isotopic equilibrium) are most likely to have δ18O that directly reflect meteoric precipitation only in cool climates. In warmer and drier environments, speleothems will have a seasonal bias toward the precipitation δ18O of recharge periods and, in some cases, the extent of evaporative fractionation of stored karst water.
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    Hydrological and geochemical responses of fire in a shallow cave system
    (2019-04-20) Bian, F; Coleborn, K; Flemons, I; Baker, AA; Treble, PC; Hughes, CE; Baker, AC; Andersen, MS; Tozer, MG; Duan, WH; Fogwill, CJ; Fairchild, IJ
    The influence of wildfire on surface soil and hydrology has been widely investigated, while its impact on the karst vadose zone is still poorly understood. A moderate to severe experimental fire was conducted on a plot (10 m × 10 m) above the shallow Wildman's Cave at Wombeyan Caves, New South Wales, Australia in May 2016. Continuous sampling of water stable isotopes, inorganic geochemistry and drip rates were conducted from Dec 2014 to May 2017. After the fire, drip discharge patterns were significantly altered, which is interpreted as the result of increased preferential flows and decreased diffuse flows in the soil. Post-fire drip water δ18O decreased by 6.3‰ in the first month relative to the average pre-fire isotopic composition. Post-fire monitoring showed an increase in drip water δ18O in the following six months. Bedrock related solutes (calcium, magnesium, strontium) decreased rapidly after the fire due to reduced limestone dissolution time and potentially reduced soil CO2. Soil- and ash-derived solutes (boron, lead, potassium, sodium, silicon, iodine and iron) all decreased after the fire due to volatilisation at high temperatures, except for SO42−. This is the first study to understand the hydrological impact from severe fires conducted on a karst system. It provides new insights on the cave recharge process, with a potential explanation for the decreased d18O in speleothem-based fire study, and also utilise the decreased bedrock solutes to assess the wildfire impacts both in short and long time scales. Open access © 2021 Elsevier B.V