Browsing by Author "Leopold, M"

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    129 Holocene records of environment and freshwater availability from tufa archives: implications for human occupation at Murujuga, NW WA
    (Australasian Quaternary Association, 2022-12-06) Mather, C; Tucker, M; Leopold, M; Levchenko, VA; O'Leary, M; Morrison, P; McDonald, J
    Murujuga in NW Western Australia is the world’s largest rock art province, with over 1 million engravings. The art and other archaeological evidence in this landscape are an important record of human response to the changing climate following the last ice-age. 130 m of sea level rise following Last Glacial Maximum (LGM ~22 kya) transformed Murujuga from an inland range to a coastal archipelago. We discuss the potential of freshwater tufa as multi-proxy archives to inform on the local environmental and climatic change that impacted this region during the Holocene. Tufa, which are calcium carbonate deposits that form from freshwater springs and seeps in river channels, provide a proxy of past freshwater availability. Establishing the age and rate of tufa formation will enhance our understanding of the presence and permanence of water holes that would have been important for human occupation. Outcomes of this work will provide context to the extraordinary archaeological record documented in Murujuga rock art.
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    Insights into recharge processes and speleothem proxy archives from long-term monitoring networks of cave drip water hydrology
    (Copernicus GmbH, 2020-05-04) Baker, AA; Treble, PC; Hartmann, A; Cuthbert, MO; Markowska, M; Berthelin, R; Tadros, CV; Leopold, M; Hankin, SI
    Since 2010 we have established cave drip water hydrological monitoring networks in four contrasting climate zones (Mediterranean, montane, semi-arid and sub-tropical) across continental Australia. Deploying over one hundred automated drip loggers, we combine these long-term monitoring datasets with climate and water isotope data, lidar mapping, electrical resistivity imaging and karst hydrological modelling to provide insights into recharge processes and the impact of hydrological variability on speleothem proxy archives. We identify increases in drip discharge and compare the timing of those events to antecedent climate conditions (rainfall, evapotranspiration). We find rainfall recharge thresholds vary with climate. At our montane site, recharge occurs after 13 to 31 mm rainfall events, depending on antecedent conditions. At the semi-arid site, recharge occurs after 40 mm rainfall events, and at our sub-tropical sites, recharge occurs following all instances where > 93 mm / week of precipitation occurs, with lower precipitation thresholds (down to 33 mm / week) possible depending on antecedent conditions and at sites with limited vegetation cover. We use these recharge thresholds to constrain simple soil moisture balance models to better understand soil and karst storage volumes. Combined with electrical resistivity imaging, we can relate recharge to the caves to subsurface water flow paths and karst water stores. At our montane and Mediterranean climate sites, relatively consistent drip water isotopic composition confirms the presence of well-mixed water stores. This allows us to quantify the extent of speleothem oxygen isotope variability due to fractionation associated with changes in drip rate. We identify significant differences in long-term mean drip rates between different drip sites within a cave, and significant differences in event-based drip rate responses within a cave. Drip hydrological variability helps explain the within-cave variability of speleothem oxygen isotope composition observed at both sites, and helps identify the primary drip water oxygen isotope signal. At our semi-arid site, drip water isotopic composition is dominated by epikarst evaporation and our drip water monitoring demonstrates that recharge events are infrequent (~1.6 per year). Using both observational and modelling data, we quantify the relative importance of evaporative fractionation in the epikarst and fractionation during calcite precipitation. Using modern speleothem samples, we demonstrate that the oxygen isotope signal in this water limited environment reflects the balance between the oxygen isotope composition of recharge and its subsequent fractionation in the soil, epikarst and cave. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 Licence.
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    Time lapse electric resistivity tomography to portray infiltration and hydrologic flow paths from surface to cave
    (Elsevier, 2021-02) Leopold, M; Gupanis-Broadway, C; Baker, AA; Hankin, SI; Treble, PC
    This study provides the example of Golgotha Cave, in the south west of Western Australia, where previous long-term hydrological, geochemical and climate monitoring resulted in a theoretical hydrological model of the karst critical zone. We test this model by presenting the results of a 1.5 year monitoring program above the cave using time-lapse electric resistivity tomography (TL-ERT). Between May 2016 and January 2018 several lines up to 200 m long were monitored using a 100 multi-electrode Lipmann 4point light instrument. Various Wenner and Dipole-Dipole arrays provided information of electric resistivity changes at certain points of the year. Laboratory studies measuring volumetric water content versus electric resistivity of various rocks and soils resulted in three different ERT-hydrogeological zones. Besides the annual infiltration patterns, TL-ERT also identified previously unknown, permanent water storages as well as several areas acting as fast hydrological flow pathways most likely caused by pipe structures in the aeolianite. Specific aspects of the TL-ERT study could be correlated with the long term drip water monitoring and thus confirmed and extended the hydrogeological model of the area. A resulting conceptual model of the flow pathways derived from ERT surveys and cave water monitoring results is presented to visualise water flux from the surface to the ceiling of Golgotha Cave. This includes annual recharge to 40 m depth in less than one hydrological year, preferential flow paths to a persistent store of water, and a time lag between soil moisture saturation and seasonal connection of karst stores that indicates a narrower window for seasonal recharge than indicated by soil moisture data. © 2020 Elsevier B.V.