ANSTO :: Browsing by Author "Treble, PC"

Browsing by Author "Treble, PC"

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A 1,000 year rainfall record for SE Australia using speleothem hydrological proxies
(Geological Society of Australia, 2010-07-04) McDonald, J; Drysdale, RN; Hodge, E; Hua, Q; Fischer, MJ; Treble, PC; Greig, A; Hellstrom, JC
Cave drip water studies at Wombeyan Caves (34°19’S, 149°59’E) demonstrated a marked hydrochemical response to wet/dry (McDonald et al., 2004; 2007). Three 20th Century coeval active speleothems (WM4, WM6 and WM20) were geochemically analysed and changes in trace element and stable isotope values were related to the instrumental record. These climate‐geochemical relationships were interpolated to two longrecord speleothems (WM7 and WM9) which grew deeper within the same cave system. Two major difficulties were encountered. Unlike other sub‐annual/annual climate records derived from speleothems using trace elements (Treble et al., 2003; Johnson et al., 2006); stable isotopes (Treble et al., 2005; Johnson et al., 2006) and annual laminae (Borsato et al., 2007) where annual cycles were shown to be consistent, at Wombeyan frequent droughts perturb predicted rainfall patterns and rainfall variability is high. Here, droughts can span several years, or extend over winter, diminishing or obliterating the expected winter recharge signal. Alternatively, wet summers can sustain ‘unseasonal’ high discharge and lessen the expected prior calcite precipitation (PCP) signal. Thus an annual wet/dry geochemical signal is often absent. Secondly, due to the young age of the speleothems and very low uranium concentrations (~10 ppb) the use of U‐series disequilibrium dating was ineffective to produce a robust chronology. Trace element cycle counting only gave the minimum age due to the non‐expression of many cycles. The 14C bomb pulse was successfully defined in two modern stalagmites (WM4 and WM6) and maximum 14‐C activity was around 134 per cent modern carbon (pMC) for both speleothems, indicating rapid transfer of 14‐C from atmosphere, to soil, to drip water during the bomb‐pulse period. A dampened 14C bomb pulse was detected in WM7 (where pMCmax was 112 per cent modern carbon) reflecting the greater degree of mixing within the thicker bedrock. Carbon‐14 AMS analyses were utilised together with trace element cycle counting to obtain preliminary chronological control. Despite these difficulties, palaeohydrological records using multiple proxies: Mg/Ca (aridity), P and Y (wet), δ18O (dominant air mass and rainfall amount signals), and based on 14C ages were constructed for the longerrecord, slower growing stalagmites. Over the last 1,000 years there have been several sustained episodes of wet/arid or highly variable phases. A sustained wet phase occurred ~ 900–1300 AD and followed by ~ 200 years of highly variable wet/dry conditions. From ~ 1500 to 1800 AD a dry phase is indicated. The last 150 years support a drying phase, but the negative IPO (1944–1978 [wettest period in 20thC]) is not indicated by a negative anomaly and further, sustained positive δ18O anomalies in this period suggest that other factors maybe influencing this part of the record (temperature?). The δ18O record indicates changing frequency from ~ centennial to pentadecadal time‐scales in the longer‐time scale oscillations. Within the longer‐time scale oscillations, higher resolution (~ 2–5 years) variability is evident replicating the trend shown by modern annually resolved stalagmites at this site.
A 1,500 year south Australian rainfall record based on speleothem hydrological proxies
(AMOS National Conference, 2013-02-11) McDonald, J; Drysdale, RN; Hua, Q; Hodge, E; Treble, PC; Greig, A; Fallon, SJ; Lee, S; Hellstrom, JC
Cave drip water studies at Wombeyan Caves (34°19’S, 149°59’E) demonstrated a marked hydrochemical response to wet/dry phases (McDonald Et al. 2004; 2007). Geochemical Variations in three 20th Century coeval active Speleothems were able to be linked to the instrumental record. Subsequently geochemical relationships were investigated in a long record speleothem(WM7) which grew deeper within the same cave system. Obtaining a robust chronology proved to be challenging, due to the young age of the speleothem and very low uranium concentrations (~10 ppb) the use of U‚Aeseries disequilibrium dating was ineffective to produce a robust chronology. Chronology for WM7 was based on a dense sequence of DCF corrected ages using three different age-‐depth models: Clam (Classical method), and Bacon and OxCal (Bayesian statistical approach) (Hua et al. 2012).The new chronology indicated that WM7 began growth around 4400 cal BP(171 mm). However, since sampling from 0-‐50mm was most intensive, the model is based on this part of the stalagmite and indicates that the top 50 mm of WM7 grew during the past 1360 and 1740 years. An aridity index based on Sr,P, Y, La, and Ba shows that over the last 1,500 years several sustained episodes of wet/arid and otherwise variable phases have occurred. Two sustained wet phases ~ 700-‐880 AD and ~ 900-‐ 1250 AD were followed by ~ 400 years of variable wet/dry conditions, although from ~1300 to 1600 AD a drying trend is indicated, but punctuated by several wetter episodes. The last 200 years indicate sustained drying phases. The OE￥13C record is anomalous from ~ 1880 to present and attributed to the stalagmite’s recording of increasing contribution of fossil fuel to CO2 concentrations. Within the longer-‐time scale oscillations, higher resolution (~ 2-‐5 years) variability is evident, replicating the trend shown by modern annually resolved stalagmites at this site.
A 35 ka record of groundwater recharge in south-west Australia using stable water isotopes
(Elsevier B. V., 2020-05-15) Priestley, SC; Meredith, KT; Treble, PC; Cendón, DI; Griffiths, AD; Hollins, SE; Baker, AA; Pigois, JP
The isotopic composition of groundwater can be a useful indicator of recharge conditions and may be used as an archive to infer past climate variability. Groundwater from two largely confined aquifers in south-west Australia, recharged at the northernmost extent of the westerly wind belt, can help constrain the palaeoclimate record in this region. We demonstrate that radiocarbon age measurements of dissolved inorganic carbon are appropriate for dating groundwater from the Leederville aquifer and Yarragadee aquifer within the Perth Basin. Variations in groundwater δ18O values with mean residence time were examined using regional and flow line data sets, which were compared. The trends in the regional groundwater data are consistent with the groundwater flow line data supporting the hypothesis that groundwater δ18O is a robust proxy for palaeo-recharge in the Perth Basin. A comparison between modern groundwater and rainfall water isotopes indicates that recharge is biased to months with high volume and/or intense rainfall from the westerly wind circulation and that this has been the case for the last 35 ka. Lower stable water isotope values are interpreted to represent recharge from higher volume and/or more intense rainfall from 35 ka through the Last Glacial Maximum period although potentially modulated by changes in recharge thresholds. The Southern Perth Basin groundwater isotopic record also indicates a trend towards higher volume and/or intense rainfall during the Mid- to Late Holocene. The long-term stable water isotope record provides an understanding of groundwater palaeo-recharge. Knowledge of recharge dynamics over long time scales can be used to improve current water sharing plans and future groundwater model predictions. © Crown Copyright 2019
A 35 ka record of groundwater recharge using stable water isotopes for Perth Basin in south-west Australia
(National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-25) Priestley, SC; Meredith, KT; Treble, PC; Cendón, DI; Griffiths, AD; Hollins, SE; Baker, AA; Pigois, JP
Objectives: As most large groundwater basins can contain ‘old’ groundwater where extraction exceeds groundwater recharge, knowledge of the past conditions and timing under which groundwater was recharged is needed to sustainably manage groundwater resources. Moreover, the isotopic composition of groundwater can be a useful indicator of rainfall isotope compositions and help to determine the drivers and impacts of rainfall and climate change. Applying isotopic tools to groundwater contained in regional aquifer systems can provide low-resolution information on recharge intensity, recharge source and past climatic conditions for the region. Design and Methodology: A dataset containing groundwater ages (14CDIC) and stable isotopes of water (δ18O and δ2H) from two regional groundwater systems within the Perth Basin, the Leederville Formation and Yarragadee Formation, were compiled to create a low-resolution palaeo-archive of groundwater recharge. Original data and results: The trends in stable isotopes of water over time in the regional groundwater data are consistent with groundwater flow line data supporting our hypothesis that groundwater stable isotopes are a proxy for palaeo-recharge. A comparison between modern groundwater and rainfall water isotopes indicates that recharge is biased to months with high volume and/or intense rainfall from the westerly wind circulation and that this has been the case for the last 35 ka. Lower stable water isotope values are interpreted to represent recharge from higher volume and/or more intense rainfall from 35 ka through the Last Glacial Maximum period although potentially modulated by changes in recharge thresholds. Conclusion: The groundwater isotope record is interpreted to be a low-resolution archive of recharge driven by changes in the relative intensity of past rainfall and recharge thresholds. This long-term stable isotopic recharge record provides a greater understanding of groundwater palaeo-recharge, and the connection between recharge and climate in the past. © The Authors
Calibrating climate-δ18O regression models for the interpretation of high-resolution speleothem δ18O time series
(American Geophysical Union, 2008-09-03) Fischer, MJ; Treble, PC
Providing estimates of past climate changes on interannual - millenial timescales requires suitable regression models between climate and climate proxies. Many proxies appear to show relationships with climate that are timescale dependent. Any proxy-climate model should be able to replicate the major patterns that are observed at multiple timescales. Here we develop a new climate-isotope regression model for speleothems from a middle latitude site. In the low to middle latitudes, daily variation in precipitation isotopes (within individual months) is largely negatively correlated with daily rainfall amount. On interdecadal timescales, though, this relationship appears to be nonstationary. These two points provide a theoretical basis for a new climate-isotope regression model in which the slope and the intercept of a δ O-18(day) - P-day line for a given month are modulated by organized patterns of climate variability, such as the extratropical zonal waves (including the annular modes). In constructing this new regression model, we show how daily precipitation - δ O-18 relationships can be estimated using only monthly δ O-18 data and daily rainfall amounts. The new regression model provides a consistent picture of O-18 variability over a range of timescales, and this has not been the case with any previous climate-isotope regression model. © 2008, American Geophysical Union
Cave drip water solutes in south-eastern Australia: constraining sources, sinks and processes
(Elsevier, 2019-02-15) Tadros, CV; Treble, PC; Baker, AA; Hankin, SI; Roach, R
Constraining sources and site-specific processes of trace elements in speleothem geochemical records is key to an informed interpretation. This paper examines a 10-year data set of drip water solutes from Harrie Wood Cave, south-eastern Australia, and identifies the processes that control their response to El Niño-Southern Oscillation events which varies the site water balance. The contributions of aerosol and bedrock end-members are quantified via hydrochemical mass balance modelling. The parent bedrock is the main source for the drip water solutes: Mg, Sr, K and trace elements (Ba, Al, V, Cr, Mn, Ni, Co, Cu, Pb and U), while atmospheric aerosol inputs also contribute significantly to drip water trace elements and Na, K and Zn. A laboratory investigation evaluating water-soluble fractions of metals in soil samples and soil enrichment factors provided a basis for understanding metal retainment and release to solution and transport from the soil zone. These results identified the role of the soil as a sink for: trace metals, Na and K, and a secondary source for Zn. Further, soil processes including: cation exchange, K-fixation, metal adsorption to colloids and the release of Zn associated with organic matter degradation further modify the chemical composition of the resultant drip waters. This research is significant for the south-eastern Australian region, as well as other sites in a karst setting with clay-rich soil. In particular these results reveal that the response of drip water chemistry to hydroclimatic forcing is non-linear, with the greatest response observed when the long-term gradient in the cumulative water balance reverses. This longer-term drip water monitoring dataset is significant because it provides the pivotal framework required to reliably identify suitable trace element proxies for interpretation in geochemical speleothem records on multi-decadal timescales. © 2018 Crown Copyright © 2018 Published by Elsevier B.V.
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.
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.
Caves demonstrate decrease in rainfall recharge of southwest Australian groundwater is unprecedented for the last 800 years
(Springer Nature, 2023-06-09) Priestley, SC; Treble, PC; Griffiths, AD; Baker, AA; Abram, NJ; Meredith, KT
Billions of people worldwide rely on groundwater. As rainfall in many regions in the future is projected to decrease, it is critical to understand the impacts of climate change on groundwater recharge. The groundwater recharge response to a sustained decrease in rainfall across southwest Australia that began in the late 1960s was examined in seven modern speleothems and drip waters from four caves. These show a pronounced increase or uptick in regional drip water and speleothem oxygen isotopic composition (δ18O) that is not driven by a change in rainfall δ18O values, but is in response to the shallow karst aquifers becoming disconnected from rainfall recharge due to regional drying. Our findings imply that rainfall recharge to groundwater may no longer be reliably occurring in this region, which is highly dependent on groundwater resources. Examination of the longer speleothem record shows that this situation is unprecedented over the last 800 years. © The Authors - Open Access licensed under a Creative Commons Attribution 4.0 International Licence.
Caves provide early warning of unprecedented decrease in rainfall recharge of groundwater
(Research Square, 2022-05-02) Priestley, SC; Treble, PC; Griffiths, AD; Baker, AA; Abram, NJ; Meredith, KT
Billions of people worldwide rely on groundwater. As rainfall in many regions in the future is projected to decrease, it is critical to understand the impacts of climate change on groundwater recharge. In this study, five caves record a consistent response to a sustained decrease in rainfall across southwest Australia that began in the late 1960s, characterised by a pronounced increase or ’uptick’ in dripwater and speleothem oxygen isotopic composition (δ18O). It is demonstrated that the uptick is in response to the shallow karst aquifers becoming disconnected from recharge due to regional drying. Our findings imply that rainfall recharge to groundwater across this region is no longer reliably occurring. Examination of the longer speleothem record shows that this is unprecedented over at least the last 800 years. A global network of cave dripwater monitoring would serve as an early warning of reduced groundwater recharge elsewhere, while evidence for upticks in speleothem paleoclimate records would provide a longer-term context to evaluate if current groundwater recharge changes are outside the range of natural variability. This study also validates speleothems as recorders of past hydroclimate via amplification of the δ18O signal by karst hydrology highlighting that speleothem δ18O are records of recharge, rather than a direct proxy for rainfall. © 2022 The Authors
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.
Chemical characterisation and source identification of atmospheric aerosols in the Snowy Mountains, south-eastern Australia
(Elsevier, 2018-07-15) Tadros, CV; Crawford, J; Treble, PC; Baker, AA; Cohen, DD; Atanacio, AJ; Hankin, SI; Roach, R
Characterisation of atmospheric aerosols is of major importance for: climate, the hydrological cycle, human health and policymaking, biogeochemical and palaeo-climatological studies. In this study, the chemical composition and source apportionment of PM2.5 (particulate matter with aerodynamic diameters less than 2.5 μm) at Yarrangobilly, in the Snowy Mountains, SE Australia are examined and quantified. A new aerosol monitoring network was deployed in June 2013 and aerosol samples collected during the period July 2013 to July 2017 were analysed for 22 trace elements and black carbon by ion beam analysis techniques. Positive matrix factorisation and back trajectory analysis and trajectory clustering methods were employed for source apportionment and to isolate source areas and air mass travel pathways, respectively. This study identified the mean atmospheric PM2.5 mass concentration for the study period was (3.3 ± 2.5) μg m−3. It is shown that automobile (44.9 ± 0.8)%, secondary sulfate (21.4 ± 0.9)%, smoke (12.3 ± 0.6)%, soil (11.3 ± 0.5)% and aged sea salt (10.1 ± 0.4)% were the five PM2.5 source types, each with its own distinctive trends. The automobile and smoke sources were ascribed to a significant local influence from the road network and bushfire and hazard reduction burns, respectively. Long-range transport are the dominant sources for secondary sulfate from coal-fired power stations, windblown soil from the inland saline regions of the Lake Eyre and Murray-Darling Basins, and aged sea salt from the Southern Ocean to the remote alpine study site. The impact of recent climate change was recognised, as elevated smoke and windblown soil events correlated with drought and El Niño periods. Finally, the overall implications including potential aerosol derived proxies for interpreting palaeo-archives are discussed. To our knowledge, this is the first long-term detailed temporal and spatial characterisation of PM2.5 aerosols for the region and provides a crucial dataset for a range of multidisciplinary research. Crown Copyright © 2018 Published by Elsevier B.V.
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.
Climatic, hydrological and karst geological controls on groundwater recharge: the view from an Australian vadose zone cave observatory
(American Geophysical Union (AGU), 2021-12-18) Baker, AA; Berthelin, R; Hartmann, AJ; Treble, PC
In water-limited environments, quantifying the timing and frequency of erratic rainfall recharge events and its climate forcing is of critical importance for groundwater resource management. In temperate semi-arid New South Wales, SE Australia (precipitation: 615 mm/year, pan evaporation: 1679 mm/year), since 2010 we have been using a limestone cave situated at 20 m below land surface, and just above the water table, as a vadose zone observatory of potential recharge approximated by drip rate observations. Complimented since 2018 by a soil moisture probe network and using the VarKarst karst-specialized recharge model, we investigate the climatic, hydrological and karst geological controls on recharge dynamics. We observe nineteen recharge events (07.2010 to 01.2021). They cluster into two periods (1) seven events between 08.2010 and 12.2010 during a La Niña (enhanced spring rainfall is typical in eastern Australia) and (2) seven events between 06.2016 and 10.2016 associated with a negative Indian Ocean Dipole (which is associated with wet winters and springs in southern Australia). Comparison with antecedent rainfall indicates a minimum of 40 mm rainfall over 14-days is required for recharge in winter, and >120 mm rainfall over 14-days in summer. We will use the karst recharge model to simulate the observed recharge events and to quantify the threshold behavior of the soil and vadose zone above the cave. Two recharge events have occurred since the establishment of the soil moisture network (03.05.2020, 29.07.2020). For those, we can analyze the influence of antecedent soil storage on the initiation of recharge and use this understanding for an evaluation of the simulated internal fluxes and storages of karst recharge model. Providing realistic results of both recharge and soil moisture observations, the model can be used as tool to predict the impact of past and future climate changes on groundwater renewal. Plain-language Summary Many arid and semi-arid regions rely on groundwater for water supply. Rainfall replenishes this groundwater resource, but how do we know when this replenishment (technically called recharge) occurs? We report the results from a unique Australian observatory – a cave situated in limestone and located just above the water table in a semi-arid climate region. Water percolating into the cave has been measured for over ten years, and we observe nineteen recharge events, most of which occur in wet climate phases of the climate phenomena La Niña or the Indian Ocean Dipole. Combined with measurements of climate and soil moisture, and a computational model of recharge, we quantify fluxes and storages of the unsaturated zone above the cave to better understand which conditions favor or hinder groundwater renewal. That way, we can estimate how potential future climate changes will affect future groundwater availability.
Combustion completeness and sample location determine wildfire ash leachate chemistry
(American Geophysical Union, 2024-05-21) Campbell, M; Treble, PC; McDonough, LK; Naeher, S; Baker, AA; Grierson, PF; Wong, HKY; Andersen, MS
Understanding past fire regimes and how they vary with climate, human activity, and vegetation patterns is fundamental to the mitigation and management of changing fire regimes as anthropogenic climate change progresses. Ash‐derived trace elements and pyrogenic biomarkers from speleothems have recently been shown to record past fire activity in speleothems from both Australia and North America. This calls for an empirical study of ash geochemistry to aid the interpretation of speleothem palaeofire proxy records. Here we present analyses of leached ashes collected following fires in southwest and southeast Australia. We include a suite of inorganic elemental data from the water‐soluble fraction of ash as well as a selection of organic analytes (pyrogenic lipid biomarkers). We also present elemental data from leachates of soils collected from sites in southwest Australia. We demonstrate that the water‐soluble fraction of ash differs from the water‐soluble fraction of soils, with trace and minor element concentrations in ash leachates varying with combustion completeness (burn severity) and sample location. Changes in some lipid biomarker concentrations extracted from ashes may reflect burn severity. Our results contribute to building a process‐based understanding of how speleothem geochemistry may record fire frequency and severity, and suggest that more research is needed to understand the transport pathways for the inclusion of pyrogenic biomarkers in speleothems. Our results also demonstrate that potential contaminant loads from ashes are much higher than from soils, with implications for the management of karst catchments, which are a critical water resource. © 2024 The Author(s). Geochemistry,Geophysics, Geosystems published by Wiley Periodicals LLC on behalf of American Geophysical Union. This is an open access article under the terms of the Creative Commons Attribution License, which permits use,distribution and reproduction in any medium, provided the original work is properly cited
Comparison of oxygen isotope records from radiocarbon dated groundwater and U-Th dated flowstone
(20th International Mass Spectroscopy Conference, 2014-08-24) Adler, L; Treble, PC; Meredith, KT; Baker, AA; Hellstrom, JC
Not available.
Comparison of δ18O in groundwater and a cave flowstone: improving the interpretation of the speleothem δ18O paleoclimate proxy
(International Union for Quaternary Research (INQUA), 2019-07-30) Adler, L; Priestley, SC; Treble, PC; Baker, AA; Hellstrom, JC; Griffiths, AD; Meredith, KT
Speleothems are high-resolution records that can be used for terrestrial paleoclimate reconstruction from their oxygen and carbon isotopes (δ18O and δ13C), and whose deposition is directly related to the groundwater recharge process. Groundwater δ18O records have the potential to provide an important long-term record of past climate, but they are low-resolution records as the isotope signal can be altered during flow within the aquifer. In this study we compare measured δ18O values from both a groundwater record and speleothem record from a flowstone over the past 12,000 years for the first time from south west Western Australia. Flowstones normally form from cave streams or fast dripping seepages and their oxygen isotope composition is sensitive to the extent of kinetic fractionation, determined by water flow rate, as well as, streams or seepages water δ18O composition. In this study comparison of δ18O values from a groundwater record and flowstone enables the source water oxygen isotopic composition to be constrained in order for a more complete interpretation of the higher resolution speleothem record, including the site specific kinetic processes and climatic changes. The flowstone δ18O values appear consistent with millennial variability in recharge δ18O predicted using the groundwater values, although the flowstone oxygen isotopes are generally enriched in 18O compared to the regional groundwater record before ~7.4ka. This offset between the records indicates that flowstone calcite deposition was not in isotopic equilibrium with its source water likely due to low flow regimes and extensive degassing of CO2. According to a model of isotopic disequilibrium that is driven by water supply, the Holocene portion of the flowstone record contains periods of relatively lower isotopic disequilibrium indicating possible higher water supply, and periods of relatively higher isotopic disequilibrium indicating possible lower water supply consistent with local and regional archives.
Continental aridification and the vanishing of Australia's megalakes
(Geological Society of America, 2011-02) Cohen, TJ; Nanson, GC; Jansen, JD; Jones, BG; Jacobs, Z; Treble, PC; Price, DM; May, JH; Smith, AM; Ayliffe, LK; Hellstrom, JC
The nature of the Australian climate at about the time of rapid megafaunal extinctions and humans arriving in Australia is poorly understood and is an important element in the contentious debate as to whether humans or climate caused the extinctions. Here we present a new paleoshoreline chronology that extends over the past 100 k.y. for Lake Mega-Frome, the coalescence of Lakes Frome, Blanche, Callabonna and Gregory, in the southern latitudes of central Australia. We show that Lake Mega-Frome was connected for the last time to adjacent Lake Eyre at 50–47 ka, forming the largest remaining interconnected system of paleolakes on the Australian continent. The final disconnection and a progressive drop in the level of Lake Mega-Frome represents a major climate shift to aridification that coincided with the arrival of humans and the demise of the megafauna. The supply of moisture to the Australian continent at various times in the Quaternary has commonly been ascribed to an enhanced monsoon. This study, in combination with other paleoclimate data, provides reliable evidence for periods of enhanced tropical and enhanced Southern Ocean sources of water filling these lakes at different times during the last full glacial cycle. © 2011, Geological Society of America
Dissolved organic matter in the unsaturated zone: the view from the cave
(American Geophysical Union (AGU), 2017-12-14) Baker, AA; Duan, W; Rutlidge, H; McDonough, LK; Oudone, PP; Meredith, KT; Andersen, MS; O'Carroll, DM; Coleborn, K; Treble, PC
Soil organic matter content is typically a few percent of the total soil composition. Diffuse recharge can mobilise some of this soil-derived organic matter. While soil pore water dissolved organic matter (DOM) concentrations are up to 100 ppm, the resulting groundwater dissolved organic matter concentration is typically less than 2ppm. Dissolved organic matter transported from the soil can be both biodegraded and sorbed to minerals, and the relative importance of these two processes in the unsaturated zone is poorly understood. Caves in karstified limestone uniquely provide direct access to water percolating from the soil to the groundwater. Cave percolation waters can be analysed for their DOM concentration and character. This provides insights into the extent and type of biological and chemical processing of DOM during transport from the soil to the groundwater. We determine the concentration and characteristics of DOM in cave percolation waters using liquid chromatography (LC-OCD) and optical spectrophotometry (fluorescence and absorbance). We sample DOM from multiple caves in SE Australia (Cathedral Cave, Wellington; South Glory and Harrie Wood Caves, Yarrangobilly), permitting comparison of unsaturated zone DOM properties at different depths (up to 30m below land surface) and different climate zones (montane and temperate). We use caves with long-term hydrological monitoring programs so that DOM in waters of contrasting residence times can be compared. Additionally, we compare these cave percolation water DOM characteristics to those from local and regional groundwater, sampled from nearby wells. Our results will help improve our understanding of how DOM is processed from soil to groundwater, and is also relevant to speleothem scientists interested in using organic matter preserved in speleothems as a paleoclimate or paleoenvironmental proxy. Plain Language Summary When plants die, they break down to organic matter, which forms part of the soil. When this organic matter is washed out of the soil and into the subsurface, we know very little about what happens next. Partly it is because we can't see and measure what is happening. There is a solution. We can use caves as observatories. We can collect the organic matter in the water which enters the caves, and analyse it back in the laboratory. There, we can determine not only the cocntration of organic matter, but also its chemical composition. Why is this important? There's lot of organic matter in soil. But only one or two organic molecues per million water molecules are present in groundwater. Where does it all go? One idea is that it is used as food by subterranean microbes. Another is that is sorbed to minerals. By measuring the chemical composition of organic matter in cave drip waters, we can work out which is more important, and help understand why there is so little organic matter in groundwater.
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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