Browsing by Author "Cuthbert, MO"
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- ItemCave monitoring to constrain the paleoclimate interpretation of δ18O proxy in speleothems from semi-arid areas(University of New South Wales and Australian Nuclear Science and Technology Organisation, 2015-07-09) Markowska, M; Baker, AA; Andersen, MS; Jex, CN; Cuthbert, MO; Rau, GC; Graham, PW; Rutlidge, H; Mariethoz, G; Marjo, CE; Treble, PC; Edwards, NNot supplied to the ANSTO Library.
- ItemCave stalagmites as records of past recharge frequency in semi-arid Australia(National Centre for Groundwater Research And Training, 2015-11-03) Markowska, M; Baker, AA; Andersen, MS; Rutlidge, H; Jex, CN; Cuthbert, MO; Rau, GC; Adler, L; Graham, PW; Mariethoz, G; Marjo, CE; Treble, PCUnderstanding past variability in groundwater recharge over recent time scales (0 – 10 ka) in Australia is essential for future sustainable groundwater management in a changing climate. Currently, there are limited data about past infiltration rates and their relationship to environmental controls that dominate recharge variability. Speleothem (cave precipitates) records may provide a new approach to understanding past infiltration (i.e. recharge rates), in addition to traditional interpretations of connectivity between climate and the hydrological cycle, in drier parts of Australia. In this study we used Cathedral Cave, (SE Australia) located in a temperate semi-arid climate, as a natural laboratory to investigate cave infiltration rates and the climate-karst-cave interactions driving the isotopic (δ18O) and chemical variability in modern drip water. These findings were then used to interpret the δ18O stalagmite record from two modern speleothems growing during the last ~50 years. Modern drip water results showed that the δ18O composition was enriched by up to 2.77 ‰ relative to annually weighted mean rainfall. Isotopically lighter δ18O occurred during infiltration events, followed by subsequent isotopic enrichment as evaporation in the unsaturated zone fractionated δ18O of stored water. Drip rate monitoring revealed that larger events leading to infiltration were infrequent (0 – 3 a-1) and the ‘effectiveness’ of these infiltration events was controlled by antecedent moisture conditions in the soil zone. In drier climatic zones, evaporation drives the enrichment of δ18O in the unsaturated zone, allowing periods of infiltration to be identified from the stable isotopic composition of drip waters. Our findings are important for interpreting speleothem records from regions with infrequent recharge and high evaporation rates. Such records are likely to contain evidence of past infiltration events moderated by an evaporation signal, allowing records of paleo-recharge to be reconstructed for drier climate regions of Australia.
- ItemClimate and groundwater recharge: the story from Australian caves(National Centre for Groundwater Research And Training, 2017-07-11) Baker, AA; Treble, PC; Markowska, M; Andersen, MS; Wang, ZYO; Mahmud, K; Cuthbert, MO; Coleborn, K; Rau, GCQuantifying the timing and extent of diffuse groundwater recharge is crucial for our understanding of groundwater recharge processes. However, diffuse recharge is notably difficult to measure directly. Caves can be used as natural observatories of ongoing diffuse recharge processes, and speleothems (cave carbonate deposits such as stalagmites) as archives of past recharge. Cave records can improve our understanding of diffuse recharge in the context of climate change and past climate variability. A long-term, national monitoring program of infiltration into caves has been undertaken since 2010 using a network of over 200 automated loggers. This has been supplemented by artificial irrigation experiments at one semi-arid site. The timing of past recharge can be determined from the periods of past stalagmite growth. Recharge characteristics can be elucidated from oxygen isotope composition, with increased 18O likely caused by evaporative fractionation and increased 16O from high intensity/magnitude rainfall events. Automated logger data identify the diffuse recharge thresholds that vary with climate and geology. Both the logged data of natural events and the artificial irrigation experiments identify significant spatial heterogeneity in recharge in these karstified systems. Water infiltrating into the karst is often depleted in the lighter oxygen isotope due to soil and shallow subsurface evaporative fractionation. Speleothem deposition is more frequent during glacial periods, presumably because recharge thresholds are lower, and their isotopic composition provides evidence of the characteristics of the recharge process. Caves provide direct access into the unsaturated zone. Direct observation of groundwater recharge can be used to complement data from the saturated zone (boreholes) and models. The heterogeneity of recharge in karst aquifers can be directly observed and quantified. Speleothems preserve a record of groundwater recharge that can extend back for hundreds of thousands of years, providing a long-term view on the timing and variability of groundwater recharge in Australia.
- ItemDrip water isotopes in semi-arid karst: implications for speleothem paleoclimatology(Elsevier Science BV, 2014-06-01) Cuthbert, MO; Baker, AA; Jex, CN; Graham, PW; Treble, PC; Andersen, MS; Acworth, RIWe report the results of the first multi-year monitoring and modelling study of the isotopic composition of drip waters in a semi-arid karst terrane. High temporal resolution drip rate monitoring combined with monthly isotope drip water and rainfall sampling at Cathedral Cave, Australia, demonstrates that drip water discharge to the cave occurs irregularly, and only after occasional long duration and high volume rainfall events, where the soil moisture deficit and evapotranspiration is overcome. All drip waters have a water isotopic composition that is heavier than the weighted mean annual precipitation, some fall along the local meteoric water line, others trend towards an evaporation water line. It is hypothesised that, in addition to the initial rainfall composition, evaporation of unsaturated zone water, as well as the time between infiltration events, are the dominant processes that determine infiltration water isotopic composition. We test this hypothesis using a soil moisture balance and isotope model. Our research reports, for the first time, the potential role of sub-surface evaporation in altering drip water isotopic composition, and its implications for the interpretation of speleothem delta O-18 records from arid and semi-arid regions. © 2014, Elsevier Ltd.
- ItemDripwater organic matter and trace element geochemistry in a semi-arid karst environment: Implications for speleothem paleoclimatology(Elsevier, 2014-06-15) Rutlidge, H; Baker, AA; Marjo, CE; Andersen, MS; Graham, PW; Cuthbert, MO; Jex, CN; Rau, GC; Roshan, H; Markowska, M; Mariethoz, GA series of four short-term infiltration experiments which revealed hydrochemical responses relevant to semi-arid karst environments were carried out above Cathedral Cave, Wellington, New South Wales (NSW), Australia. Dripwater samples were collected at two sites for trace element and organic matter analysis. Organic matter was characterised using fluorescence and interpreted using a PARAFAC model. Three components were isolated that represented unprocessed, soil-derived humic-like and fulvic-like material, processed humic/fulvic-like material and tryptophan-like fluorescence. Principal Component Analysis (PCA) performed on the entire dataset comprising trace element concentrations and PARAFAC scores revealed two dominant components that were identified as soil and limestone bedrock. The soil component was assigned based on significant contributions from the PARAFAC scores and additionally included Ba, Cu, Ni and Mg. The bedrock component included the expected elements of Ca, Mg and Sr as well as Si. The same elemental behaviour was observed in recent stalagmite growth collected from the site. Our experiments demonstrate that existing paleoclimate interpretations of speleothem Mg and Sr, developed in regions of positive water balance, are not readily applicable to water limited environments. We provide a new interpretation of trace element signatures unique to speleothems from water limited karst environments. © 2014, Elsevier Ltd.
- ItemEvaporative cooling of speleothem drip water(Nature Publishing Group, 2014-06-04) Cuthbert, MO; Rau, GC; Andersen, MS; Roshan, H; Rutlidge, H; Marjo, CE; Markowska, M; Jex, CN; Graham, PW; Mariethoz, G; Acworth, RI; Baker, AAThis study describes the first use of concurrent high-precision temperature and drip rate monitoring to explore what controls the temperature of speleothem forming drip water. Two contrasting sites, one with fast transient and one with slow constant dripping, in a temperate semi-arid location (Wellington, NSW, Australia), exhibit drip water temperatures which deviate significantly from the cave air temperature. We confirm the hypothesis that evaporative cooling is the dominant, but so far unattributed, control causing significant disequilibrium between drip water and host rock/air temperatures. The amount of cooling is dependent on the drip rate, relative humidity and ventilation. Our results have implications for the interpretation of temperature-sensitive, speleothem climate proxies such as delta O-18, cave microecology and the use of heat as a tracer in karst. Understanding the processes controlling the temperature of speleothem-forming cave drip waters is vital for assessing the reliability of such deposits as archives of climate change. © 2014, Nature Publishing Group.
- ItemGlobal 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, MThe 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)
- ItemGlobal 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, CThe 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.
- ItemGlobal 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, CThe 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
- ItemA groundwater recharge experiment in krast - Wellington Caves, NSW(International Association of Hydrogeologists, 2013-09-16) Andersen, MS; Baker, AA; Graham, PW; Rutlidge, H; Mariethoz, G; Roshan, H; Rau, GC; Markowska, M; Cuthbert, MOGroundwater recharge is a process which is inherently difficult to measure directly due to soil and sediment heterogeneity and the tendency for this to cause preferential flow. This often leads to groundwater recharge being estimated by indirect methods, such as remotely or by differences in the water balance, which frequently causes huge uncertainties in the estimates. Karst terrains with cave features, although notoriously heterogeneous, offer a rare opportunity to physically enter the subsurface and make direct observations. Cathedral Cave at Wellington Caves in NSW, Australia was used for a multiple tracer experiment to look a recharge processes as well as physical and chemical processes affecting speleothems formation. On four consecutive days, four water releases were applied to a 3 x 7 m soil patch 2-3 m above the cave ceiling. The applications varying from 800 to 1500 L corresponds to natural precipitation events of 40 to 70 mm, events which have been known to cause recharge into the caves in the past. The four different events were variably modified by adding deuterium (2H), a fluorescing tracer and ice to reduce the temperature. Inside the caves onset of recharge was measured by automatic drip rate monitoring and temperature loggers. In addition, discrete water samples were collected and analysed for stable water isotope composition, fluorescence and dissolved trace elements. A preliminary assessment of the cave observations suggest that. although ow was preferentially along fractures, considerable interaction with pore water in the rock matrix must have taken place to significantly dilute the tracer content of water sampled in the cave. To our knowledge this is the first time that is has been directly shown that water sampled during a recharge event is only fractionally water from that particular event. For the location of this study the result is surprising considering the short distance of 2-3 m between the soil surface and the cave ceiling. The results have significant implications for our understanding of karst hydrology as well as reconstruction of past recharge and climate conditions from cave speleothems.
- ItemInsights 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, SISince 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.
- ItemSemi-arid zone caves: evaporation and hydrological controls on δ18O drip water composition and implications for speleothem paleoclimate reconstructions(Elsevier B.V., 2016-01-01) Markowska, M; Baker, AA; Andersen, MS; Jex, CN; Cuthbert, MO; Rau, GC; Graham, PW; Rutlidge, H; Mariethoz, G; Marjo, CE; Treble, PC; Edwards, NOxygen isotope ratios in speleothems may be affected by external processes that are independent of climate, such as karst hydrology and kinetic fractionation. Consequently, there has been a shift towards characterising and understanding these processes through cave monitoring studies, particularly focussing on temperate zones where precipitation exceeds evapotranspiration. Here, we investigate oxygen isotope systematics at Wellington Caves in semi-arid, SE Australia, where evapotranspiration exceeds precipitation. We use a novel D2O isotopic tracer in a series of artificial irrigations, supplemented by pre-irrigation data comprised four years of drip monitoring and three years of stable isotope analysis of both drip waters and rainfall. This study reveals that: (1) evaporative processes in the unsaturated zone dominate the isotopic composition of drip waters; (2) significant soil zone ‘wetting up’ is required to overcome soil moisture deficits in order to achieve infiltration, which is highly dependent on antecedent hydro-climatic conditions; (3) lateral flow, preferential flow and sorption in the soil zone are important in redistributing subsurface zone water; (4) isotopic breakthrough curves suggest clear evidence of piston-flow at some drip sites where an older front of water discharged prior to artificial irrigation water; and (5) water residence times in a shallow vadose zone (<2 m) are highly variable and can exceed six months. Oxygen isotope speleothem records from semi-arid regions are therefore more likely to contain archives of alternating paleo-aridity and paleo-recharge, rather than paleo-rainfall e.g. the amount effect or mean annual. Speleothem-forming drip waters will be dominated by evaporative enrichment, up to ∼3‰ in the context of this study, relative to precipitation-weighted mean annual rainfall. The oxygen isotope variability of such coeval records may further be influenced by flow path and storage in the unsaturated zone that is not only drip specific but also influenced by internal cave climatic conditions, which may vary spatially in the cave.© 2015, Elsevier Ltd.
- ItemWhat controls the cave drip water temperature? Analysis and implications for paleoclimate reconstruction from speleothems(National Centre for Groundwater Research And Training, 2015-11-03) Rau, GC; Cuthbert, MO; Andersen, MS; Baker, AA; Rutlidge, H; Markowska, M; Roshan, H; Marjo, CE; Graham, PW; Ackworth, RICave drip water temperature influences cave hydrobiochemical processes and also speleothem based paleoclimate signals (e.g. biomarkers, isotopes, etc). Yet very little is known about what controls cave drip water temperature. This experimental investigation reveals the dominant heat transfer mechanisms. Design and Methodology: A shallow cave drip water flow path along a flowstone was instrumented with a number of high resolution temperature sensors and drip loggers. Cave and surface climate parameters: Pressure, Relative Humidity (RH) and Temperature were monitored with high frequency. Three separate land surface irrigation experiments were conducted comprising of multiple applications of water at the surface above the cave. One of the irrigation batched was enriched with deuterium (610% VSMOW) as a conservative tracer. The cave drip water temperature measurements clearly reveal the presence of all common heat transport mechanisms (e.g. conduction, convection, latent heat exchange). In general, the cave drip water has the same temperature as the subsurface conduction profile of the rock at that depth. However, at fast flow rates the warmer/colder signal during summer/winter is being washed down convectively leading to temperature anomalies of up 1.5 °C. Importantly, daily cave venting reduces the cave RH thus leading to evaporative cooling of drip water of up -2.5 °C. Cave drip water temperature is mainly controlled by the subsurface heat conduction profile as well as the cave climate. This, however, depends on the drip rate and length of flow path exposed to the cave air. Paleoclimate reconstruction requires depth-dependent deconvolution of the subsurface conduction signal as well as consideration of past or present cave venting and evaporative cooling.
- ItemWhere is the water going: an irrigation experiment using a natural isotopic tracer in karst SE, Australia(European Geosciences Union, 2014-05) Markowska, M; Baker, AA; Andersen, MS; Cuthbert, MO; Rau, GC; Jex, CN; Rutlidge, H; Marjo, CE; Roshan, H; Treble, PCThe karst unsaturated zone is a fractured rock environment associated with very heterogeneous water movement; spatial variability in the subsurface water storage; and fast preferential flow through fractures and fissures. These factors dominate the way in which water moves within the unsaturated zone in these environments, giving rise to flow path complexities less common in homogenous media. Currently there is limited research regarding karst infiltration/storage processes and potential evaporation in the unsaturated zone. Such processes may have the potential to alter the stable isotopic composition of groundwater. Caves provide a unique environment within which to examine exfiltration variability and flow dynamics in situ. In semi-arid environments evaporative processes in the unsaturated zone have been shown to directly alter the isotopic δ18O composition of cave drip waters, fractionating them towards heavier ratios, by a magnitude of 1-3 per mil relative to mean annual rainfall (Bar Matthews et al., 1996; Cuthbert et al., 2014). Here we present a novel isotopic drip water study from an artificial infiltration experiment at Wellington Caves, SE Australia. A series of four artificial infiltration events were initiated directly over Cathedral Cave, Wellington over as many days. The first event was spiked with a deuterium tracer and the subsurface response was monitored during several sampling campaigns over the following year. The infiltration study revealed: (1) isotopic break-through curves suggest a front of older water from the unsaturated zone storage arrived ahead of the infiltration water, (2) water residence times in the unsaturated zone were found to be longer than 6 months and, (3) large spatial heterogeneities existed in the proportion of exfiltrated deuterium tracer at different drip sites in the cave suggesting unique pathways and sources of water in the unsaturated zone. Implications from this study include the interpretation of paleo-climate speleothem records from semi-arid to arid environments. © Author(s) 2014.