Browsing by Author "Markowska, M"

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    Cave 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, N
    Not supplied to the ANSTO Library.
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    Cave 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, PC
    Understanding 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.
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    Caves: observatories of Australia’s diffuse groundwater recharge history
    (National Centre for Groundwater Research And Training, 2015-11-03) Baker, AA; Treble, PC; Andersen, MS; Markowska, M; Coleborn, K; Flemons, I; Kempsey Speleological Society
    Quantifying the timing and extent of diffuse groundwater recharge is crucial for our understanding of groundwater recharge processes. However, diffuse recharge is notably difficult to quantify. Our novel approach is to use caves as natural observatories of the diffuse recharge process, with the aim of improving our understanding of diffuse recharge in the context of climate change and climate variability. Since 2010, funded by the NCRIS Groundwater Infrastructure project, researchers from UNSW and ANSTO have established a long-term, national monitoring program of infiltration into caves using automated loggers. Five karst regions, in semi-arid, temperate, subtropical and montane climates from southwest WA to the mid- north coast of NSW, have been instrumented with automatic infiltration loggers. Over 200 loggers (between 10 and 40 per cave) have collected data on the timing and amount of diffuse recharge, from sites of contrasting limestone geology, starting in 2010. We present empirical data on the timing and relative amounts of diffuse recharge from 2010 to present. Caves with a range of depths from 0-40m show decreasing frequency of diffuse recharge events with depth below ground surface. Event-based rainfall intensity is confirmed to be the primary driver of diffuse groundwater recharge at all fractured rock sites, whereas annual rainfall amount is the primary driver at a site with high primary porosity. Inter-annual variability in the frequency and relative amount of recharge is compared to climate forcing variables such as the ENSO and surface temperature. Groundwater recharge is via both direct (river recharge) and diffuse processes. With anthropogenic global warming, increased temperatures will increase evaporation, and will likely change ENSO patterns, both of which will affect diffuse groundwater recharge. Our cave observatory system helps improve our understanding of the diffuse recharge process and provides a baseline monitoring network during a period of climate change.
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    Climate 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, Z; Mahmud, K; Cuthbert, MO; Coleborn, K; Rau, GC
    Quantifying 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.
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    Distribution and temporal variations in palaeo-groundwater on the Australian continent
    (International Association of Hydrogeologists in Canada, 2012-09-16) Cendón, DI; Markowska, M; Chen, JY; Van der Ley, M; Hughes, CE; Larsen, JR
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    Drip hydrology monitoring in caves to inform stalagmite palaeoclimate records, Yarrangobilly, NSW
    (Australasian Quaternary Association Inc, 2014-01-01) Markowska, M; Treble, PC; Baker, AA; Andersen, MS; Hankin, SI
    Palaeoclimate research using speleothems has significantly increased over the last decade, owing to their potential to provide multi-proxy high resolution (sub-annual) terrestrial records of past climate variability. A crucial step in using these archives as high resolution proxies is understanding the connectivity between the surface climate and the signal transferred to the speleothem. This study investigates the modern karst hydrology at Yarrangobilly Caves, in the Snowy Mountains NSW. A high-frequency, spatially-dense drip water monitoring campaign in Harrie Wood Cave, was conducted over a 13 month period to characterise the hydrology of 14 sites within the same cave. By utilising the cave as a natural observatory we can determine 1) vadose-zone flow regimes, and 2) thresholds of recharge at the site. Using a statistical approach (PCA and AHC) 5 main drip hydrological regimes were established. Depth was found to have a moderate relationship (r2 = 0.4) with discharge, whereby increasing depth was associated with a dampening of flow and drip response. However, depth could not account for all the variability observed in the drip hydrology, suggesting complex controls unrelated to depth, such as unsaturated zone storage and mixing, appear to have a significant impact on vadose-zone flow regimes. As a speleothem is a function of the infiltrating drip water, we suggest that stalagmites fed by different drip types may thus contain different parts of the climate record i.e. smoothed mean annual vs. an extreme event record. These findings will be used to assess three suitable stalagmites for palaeoclimate reconstruction, fed by drip waters with different hydrological regimes and the preliminary results presented here. © Australasian Quaternary Association Inc.
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    Dripwater 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, G
    A 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.
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    ENSO–cave drip water hydrochemical relationship: a 7-year dataset from south-eastern Australia
    (2020-05-26) Tadros, CV; Treble, PC; Baker, AA; Fairchild, IJ; Hankin, SI; Roach, R; Markowska, M; McDonald, J
    Speleothems (cave deposits), used for palaeoenvironmental reconstructions, are deposited from cave drip water. Differentiating climate and karst processes within a drip-water signal is fundamental for the correct identification of palaeoenvironmental proxies and ultimately their interpretation within speleothem records. We investigate the potential use of trace element and stable oxygen-isotope (δ18O) variations in cave drip water as palaeorainfall proxies in an Australian alpine karst site. This paper presents the first extensive hydrochemical and δ18O dataset from Harrie Wood Cave, in the Snowy Mountains, south-eastern (SE) Australia. Using a 7-year long rainfall δ18O and drip-water Ca, Cl, Mg / Ca, Sr / Ca and δ18O datasets from three drip sites, we determined that the processes of mixing, dilution, flow path change, carbonate mineral dissolution and prior calcite precipitation (PCP) accounted for the observed variations in the drip-water geochemical composition. We identify that the three monitored drip sites are fed by fracture flow from a well-mixed epikarst storage reservoir, supplied by variable concentrations of dissolved ions from soil and bedrock dissolution. We constrained the influence of multiple processes and controls on drip-water composition in a region dominated by El Niño–Southern Oscillation (ENSO). During the El Niño and dry periods, enhanced PCP, a flow path change and dissolution due to increased soil CO2 production occurred in response to warmer than average temperatures in contrast to the La Niña phase, where dilution dominated and reduced PCP were observed. We present a conceptual model, illustrating the key processes impacting the drip-water chemistry. We identified a robust relationship between ENSO and drip-water trace element concentrations and propose that variations in speleothem Mg / Ca and Sr / Ca ratios may be interpreted to reflect palaeorainfall conditions. These findings inform palaeorainfall reconstruction from speleothems regionally and provide a basis for palaeoclimate studies globally, in regions where there is intermittent recharge variability. © Author(s) 2016.
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    Evaporative 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, AA
    This 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.
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    Groundwater in southeast Australia: links to recharge variations and past climates
    (International Association of Hydrogeologists, 2013-01-20) Cendón, DI; Meredith, KT; Hughes, CE; Hollins, SE; Currell, MJ; Markowska, M
    Palaeogroundwater from many locations around the world contains water stable isotope trends that are linked to climatic and therefore recharge variations through the last ~30 ka. Some examples are the variations observed in the Sahara-Sahel region where humidity sources can be differentiated (Edmunds et al. 2004) and or the markedly depleted values associated with glacial activity in many basins of northern part of Europe and America (Baidla et al. 2009). ln Australia with the lack of extensive glaciation, it is anticipated that water stable isotope trends do not show major variations through time. However, in the South East of Australia, particularly in the Sydney Basin (NSW) and also across the continent in the Perth Basin (WA), deuterium excess (d-excess) show high values with an average of 15%o (n=135) in the case of the Sydney Basin. The high values are not only found in modern precipitation and groundwater but also in groundwater with residence times exceeding 20 ka for the Sydney Basin. Water stable isotopes from several locations around the Sydney Basin are presented showing regional variations and localised changes due to orography. The chronological framework is determined from 14C DlC in the same groundwater samples. The dominant siliciclastic nature of most of the aquifers in the region minimises major 14C dilution and the combination of general hydrogeochemistry and 87Sr/86Sr results are used to constrain processes such as the dissolution of dispersed carbonates when estimating groundwater residence times. These records will be, where possible, compared to higher resolution records such as pollen, where parallelisms and differences will be discussed.
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    A 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, MO
    Groundwater 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.
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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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    Monitoring infiltration water at Yarrangobilly Caves, NSW: implications for past recharge and speleothem paleoclimate reconstructions
    (International Association of Hydrogeologists, 2013-09-20) Markowska, M; Treble, PC; Baker, AA; Andersen, MS
    The Snowy Mountains region in New South Wales Australia is an area of national significance as it provides critical head waters for many important water courses, such as ~29% of the Murray River. Recently, this area has been identified as vulnerable to future climate change (Australian Alps National Parks, 2012), thus a better understanding of past recharge and baseline climate variability is highly desirable. This study presents an investigation of the modern karst hydrology at Yarrangobilly Caves, ~70 km from Tumut, NSW. Utilising caves as a natural observatory we can determine 1) vadose-zone flow regimes, and 2) when recharge occurs at Yarrangobilly. This information can improve our understanding of recharge at the site, and also serve as a means of identifying suitable speleothems in caves to reconstruct past climate and recharge variability, at least over the last few thousand years of similar mean climate state. A high-frequency, spatially-dense drip water monitoring campaign in Harrie Wood Cave, Yarrangobilly, was conducted over an 11 month period to characterise the flow regimes of 14 sites within the cave. Sites were monitored using acoustic drip loggers and temperature sensors recording at 15 minute intervals. This monitoring study revealed a moderate relationship between decreasing drip rates and increasing depth (r2 = 0.40), however discharge was still highly variable between sites. Complex controls unrelated to depth, such as unsaturated zone storage and mixing, appear to have a significant impact on vadose-zone flow regimes. This was evident in a hydrograph analysis comparing the drip response between sites to specific effective rainfall events, revealing differences in base flows, lag times and response magnitude. These findings may be applicable to other karst areas with mature limestones of low primary porosity and may also have important implications for the choice of speleothem material used for reconstructing past climate.
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    Past hydroclimatic variability from southwest Australian speleothems during the last millennium
    (Australiasian Quaternary Association Inc., 2018-12-10) Treble, PC; Baker, AA; Griffiths, AD; Hellstrom, JC; Bajo, P; Abram, NJ; Fairchild, IJ; Borsato, A; Markowska, M; Gagan, MK
    Speleothems from Golgotha Cave in SW Western Australia have been investigated to extend our knowledge of past climate variability for this region during the last millennium. O isotopic datasets, the primary paleoclimate proxy used for speleothems, were constructed for four stalagmites. A challenge in their interpretation has been the disagreement between these records, despite representing coeval growth from within the same cave. Resolving this conundrum has necessitated the characterisation of the hydrology, hydrochemistry, rainfall isotopes7 and development of proxy system forward models1,8 for Golgotha Cave. The findings of these studies will be summarised as a conceptual model in order to present the main karst hydrological features that give rise to each stalagmite’s isotopic response to hydroclimatic forcing. The paleoclimate interpretation will focus on the two continuous stalagmite records that were fed predominately by diffuse flow. This will be supported by evidence from the two stalagmites predominantly fed by fracture flow, which has resulted in a non-linear response to hydroclimatic forcing.
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    Recharge variability in Australia's southeast alpine region derived from cave monitoring and modern stalagmite δ18O records
    (Elsevier, 2022-11-01) Tadros, CV; Markowska, M; Treble, PC; Baker, AA; Frisia, S; Adler, L.; Drysdale, RN
    Oxygen isotopic (δ18O) variations in stalagmite records have the potential to provide new insights about past climates beyond the instrumental record. This paper presents the first high-resolution oxygen isotope time series of three coeval stalagmite records from the alpine region of south-eastern Australia covering the period 1922–2006 CE. We use extended surface and cave monitoring datasets, petrographic investigation, modelled recharge time series and farmed calcite precipitates to assess the controls on speleothem δ18O and investigate the coherence between three records from Harrie Wood Cave. The drip water response to recent interannual rainfall variability shows that cave drip water Cl−, δ18O and drip rate display a clear response to an increase in rainfall recharge. It is demonstrated that stalagmites from the same drip sites also record variability in interannual recharge, where an increase in δ18O values is observed with lower recharge, while a decrease in δ18O values correspond to higher recharge amounts. The three stalagmite δ18O records are in broad agreement, showing common responses to relatively higher recharge between 1945 and 1995 CE and the low recharge periods between 1937 and 1945 CE (World War II drought) and late 1996 to 2006 CE (beginning of the Millennium Drought). However, differences in the magnitude of the relative response of each stalagmite δ18O record varies. Based on evidence from our cave monitoring study and farmed calcites, we conclude that the differences between the three stalagmite records is attributed to variability in the contribution of preferential flows during recharge events and the store reservoir volume supplying the drip site. When the δ18O decreases in response to enhanced recharge, the speleothem δ13C also decreases, and this is interpreted to reflect a soil respiration response to changes in soil moisture availability due to recharge. Hence, stalagmite δ18O from the Australian alpine region can be applied to reconstruct periods of relatively higher and lower rainfall recharge and thus extend our knowledge of the timing and relative magnitude of droughts as well as past periods of higher recharge in this region. Crown Copyright © 2022 Published by Elsevier Ltd.
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    Reconstructing past environmental change at Yarrangobilly Caves
    (Sydney Speleological Society, 2016-01-01) Treble, PC; Markowska, M; Tadros, CV; Jex, CN; Coleborn, K; Dredge, J; Baker, AA; Roach, R; Spate, A
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    Semi-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, N
    Oxygen 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.
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    A snapshot of groundwater residence times and water stable isotope results across the Australian continent (2015 update)
    (Geoloogia instituut, Tallinn University of Technology, 2015-07-05) Cendón, DI; Jasechko, S; Meredith, KT; Hughes, CE; Markowska, M; Hollins, SE
    The G@GPS (Groundwater@Global Paleoclimatic Signals) was setup to explore links between paleogroundwater climate-derived observations (low resolution) and other palaeoclimate archives (higher resolution) e.g. speleothemes, palynological reconstructions, etc. Initially, an emphasis was placed in large aquifers (e.g. Baltic Aquifer Basin, etc) and intercontinental comparisons. However, the addition of smaller groundwater basins has improved paleoclimatic interpretations and allowed intracontinental interpretations. Several reasons contribute to this: 1) better geographic distribution; 2) smaller basins are more likely to contain groundwater with residence times between 0 to ~30 ka, the gap where 14CDIC can obtain best results and better matching to other paleoclimate proxy records; 3) shorter flow paths minimize intense water-interaction processes, maximising residence time estimations; and 4) small systems are more likely to record local conditions while bigger counterparts (e.g. Great Artesian Basin, Australia) represent mixtures of several regional recharge zones in some cases thousands of kilometres away from the recharge zone. During the last 5 years several new datasets have been incorporated into our snapshot of Australia groundwater (Fig 1). The need to understand inter-aquifer connectivity, particularly within coal seam gas (CSG) exploitation zones, and regulatory assessments of aquifer sustainability, have driven most of the research in Australia. In the case of CSG studies, many groundwater samples are beyond 14C capabilities and occasionally 36Cl/Cl residence times have been suggested. In order to interpret the distribution of paleo-groundwater recharge across Australia, we have assembled a continent wide database comprising over 1300 groundwater samples. Information includes geographical, geological data as well as available geochemical information. Geochemical data include mostly 14CDIC, δ13CDIC and water stable isotopes (δ18O, δ2H) with other complementary information such as 3H activity or major ion composition available in some cases. In general, 14CDIC shows a wide spread of values (0 – 140 pmC) with an average of ~51 pmC. Radiocarbon values have been filtered so all “bomb-pulse” affected samples are considered modern, prior to building a chronological framework. Due to the uncertainties associated with hydrogeochemical 14C corrections and the difference of input data for each individual study, original corrections were maintained, if provided. Any other treatment was done on individual basis when data from neighbouring basins allowed better estimates for input parameters. Interestingly, there are observable patterns and distinctions in the frequency of pmC data over the last ~30 ka. The greatest frequency of observations occurred in the range of 0 – 10 pmC, which assuming no sampling bias, would suggest important late Pleistocene recharge. There also seems to be a slight ‘dip’ in pmC frequency during the period of 20–40 pmC. This may indicate a period of less recharge and/or an enhanced dryness with a diminished water cycle, roughly coinciding with the end of the last glacial. Water stable isotopes show the meteoric origin of groundwater across the continent and reveal important evaporation processes during recharge for some basins, including: Otway Basin (SA), Murchinson River Basin (WA), West Canning Basin (WA), Murray Basin (Lake Cooper, VIC) and Murray-Darling Basin (NSW, QLD). In general groundwater isotopic trends are more depleted from the coast to the interior, particularly in northern areas where major rainfall is dominated by the Australasian monsoon. The increasing aridity in the Holocene in most of the continent suggests only large, rainfall/flooding events produced effective recharge. On a general temporal scale, modern groundwater generally appears to be more isotopically enriched.
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    Speleothem 14C is unlikely to be impacted by wildfire – case studies from Western Australia and Tasmania
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Campbell, M; McDonough, LK; Kosarac, N; Treble, PC; Markowska, M; Baker, AA; Hua, Q
    Accelerator Mass Spectrometry (AMS) can be used to measure ¹⁴ C in speleothems (cave formations). AMS derived ¹⁴ C measurements offer an alternative geochronological method to U-series dating for recently formed speleothems with low U concentrations and insufficient ²³⁰ Th ingrowth, and where speleothems are impacted by allogenic thorium. However, using ¹⁴ C for dating speleothems is complicated by variable ¹⁴ C sources and dilution by ¹⁴ C-depleted parent rock (dead carbon). Old carbon may be mobilised from soil and decaying organic matter, which can mix with new carbon from root respiration in the vadose zone. These processes and their incorporation in speleothems are non-stationary in time and can be difficult to correct for. While variable dead carbon is a complication for dating speleothems, hypothetically, a sudden decline in ¹⁴ C, indicating an influx of old carbon, could be expected to occur after a bushfire. This could be because old carbon previously sequestered in soil and biomass may be mobilised, or there could be a decline in the previous oversupply of biological CO₂ while root respiration is in recovery following tree death. Using speleothems as proxy archives for past fire is an emerging field, and recent research has shown multiple proxies are needed to accurately characterise a fire event. To test the hypothesis that ¹⁴ C may serve as a proxy for palaeofire, we chose four sites which have experienced bushfires; Crystal, Golgotha, and Yonderup Caves in Western Australia, and Frankcombe Cave in central Tasmania. We used the AMS facilities at the Australian Nuclear Science and Technology Organisation to quantify the ¹⁴ C content along growth axes for the speleothems from Western Australia. Previously published AMS ¹⁴ C data for the Tasmanian speleothem were measured at the Australian National University. Crystal and Yonderup Cave speleothems had additional age-constraints of annual laminations. The Crystal Cave speleothem shows no decline in ¹⁴ C after an historical fire event. The Yonderup Cave speleothem does show a decline in ¹⁴ C after a reconstructed fire event, but the decrease is within analytical uncertainty. The Golgotha speleothem ¹⁴ C shows no change after a documented fire. The Tasmanian speleothem does show a significant decline in ¹⁴ C during a period where the region experienced successive large bushfires, as recorded in the historical record, but the temporal uncertainty of the measurements is so high (± 15 years), that the decline cannot reliably be attributed to the bushfires. These case studies provide only limited evidence to support our hypothesis that ¹⁴ C in speleothems may be a proxy for past fire events. This may be because the response is too short to be observed, sampling resolution is insufficient, or the carbon flux associated with a bushfire is too small relative to the total CO₂ flux in the vadose zone. While this is discouraging for palaeofire researchers, results offer relief to those who use ¹⁴ C dates to create speleothem chronologies, as it is one less source of uncertainty to consider when correcting ¹⁴ C ages. Our results may also serve to elucidate the importance of CO₂ source on ¹⁴ C, and by extension, on δ¹³C. © The Authors
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    Ubiquitous karst hydrological control on speleothem oxygen isotope variability in a global study
    (Springer Nature, 2022-02-15) Treble, PC; Baker, AA; Abram, NJ; Hellstrom, JC; Crawford, J; Gagan, MK; Borsato, A; Griffiths, AD; Bajo, P; Markowska, M; Priestley, SC; Hankin, SI; Paterson, DJ
    Speleothem oxygen isotopic (δ18O) records are used to reconstruct past hydroclimate yet records from the same cave do not always replicate. We use a global database of speleothem δ18O to quantify the replicability of records to show that disagreement is common worldwide, occurs across timescales and is unrelated to climate, depth or lithology. Our global analysis demonstrates that within-cave differences in mean speleothem δ18O values are consistent with those of dripwater, supporting a ubiquitous influence of flowpaths. We present a case study of four new stalagmite records from Golgotha Cave, southwest Australia, where the isotopic differences between them are informed by cave monitoring. It is demonstrated that karst hydrology is a major driver of within-cave speleothem and dripwater δ18O variability, primarily due to the influence of fractures on flowpaths. Applying our understanding of water movement through fractures assists in quantitative reconstruction of past climate variability from speleothem δ18O records. © The Authors - Open Access under a Creative Commons Attribution 4.0 International License.