Browsing by Author "McDonald, J"
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- ItemA 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, JCCave 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.
- ItemA 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, JCCave 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.
- Item129 Holocene records of environment and freshwater availability from tufa archives: implications for human occupation at Murujuga, NW WA(Australasian Quaternary Association, 2022-12-06) Mather, C; Tucker, M; Leopold, M; Levchenko, VA; O'Leary, M; Morrison, P; McDonald, JMurujuga in NW Western Australia is the world’s largest rock art province, with over 1 million engravings. The art and other archaeological evidence in this landscape are an important record of human response to the changing climate following the last ice-age. 130 m of sea level rise following Last Glacial Maximum (LGM ~22 kya) transformed Murujuga from an inland range to a coastal archipelago. We discuss the potential of freshwater tufa as multi-proxy archives to inform on the local environmental and climatic change that impacted this region during the Holocene. Tufa, which are calcium carbonate deposits that form from freshwater springs and seeps in river channels, provide a proxy of past freshwater availability. Establishing the age and rate of tufa formation will enhance our understanding of the presence and permanence of water holes that would have been important for human occupation. Outcomes of this work will provide context to the extraordinary archaeological record documented in Murujuga rock art.
- ItemENSO–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, JSpeleothems (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.
- ItemHolocene records of environment and freshwater availability from tufa archives: implications for human occupation at Murujuga, NW WA(Australasian Quaternary Association Inc., 2022-12-06) Mather, C; Tucker, M; Leopold, MD; Levchenko, VA; O'Leary, M; Morrison, P; McDonald, JMurujuga in NW Western Australia is the world’s largest rock art province, with over 1 million engravings. The art and other archaeological evidence in this landscape are an important record of human response to the changing climate following the last ice-age. 130 m of sea level rise following Last Glacial Maximum (LGM ~22 kya) transformed Murujuga from an inland range to a coastal archipelago. We discuss the potential of freshwater tufa as multi-proxy archives to inform on the local environmental and climatic change that impacted this region during the Holocene. Tufa, which are calcium carbonate deposits that form from freshwater springs and seeps in river channels, provide a proxy of past freshwater availability. Establishing the age and rate of tufa formation will enhance our understanding of the presence and permanence of water holes that would have been important for human occupation. Outcomes of this work will provide context to the extraordinary archaeological record documented in Murujuga rock art.
- ItemThe hydrochemical response of cave drip waters to sub-annual and inter-annual climate variability, Wombeyan Caves, SE Australia(Elsevier, 2007-10-15) McDonald, J; Drysdale, RN; Hill, DE; Chisari, R; Wong, HKYA thorough understanding of cave seepage waters is necessary to interpret geochemical variations in speleothem calcite in terms of changing surface climatic conditions at a particular site. Here we present the hydrochemistry of ten cave drip waters from a karst system in SE Australia based on up to 5.5 years of monitoring. Discharge was continuously measured at six sites and manually at the other sites. Dripwater samples were analysed for pH, electrical conductivity, cations and anions at all sites at monthly or more frequent intervals. Each drip possesses a unique chemistry, and not all drip waters responded to antecedent short-term hydrological variations. For example, the hydrochemical behaviour of three adjacent drips at a bedrock depth of 45 m was completely different to that of shallower sites, and was apparently un-related to surface hydrology throughout the investigation. Based on modelled calcite precipitation vectors, prior calcite precipitation was demonstrated at several sites but can only be linked directly to changes in surface recharge at the shallowest sites. At extremely low flow, shallow drip waters accessed a high Mg, Sr and Ba source, thought to be the overlying soil. High-frequency sample collection allows for the calculation of predicted Mg/Ca-calcite and Sr/ Ca-calcite values, highlighting that the sites with the greatest potential to record high-resolution palaeohydrological records are those situated at shallow depth. Longer temporal-resolution palaeohydrological records may be recorded at deeper sites but longer-term monitoring is required to identify probable time scales. Inherent system non-linearities, dissolution of secondary calcite in pore spaces of the aquifer, changes in the source of trace elements, and the presence of multiple reservoirs confirm the need for the use of multiple speleothems and a multi-proxy approach to gain accurate palaeohydrological records from this site. © 2007, Elsevier Ltd.
- ItemLignin degradation in a coastal groundwater aquifer: a useful tracer?(American Geophysical Union, 2014-12) Howley, EM; Jex, CN; Andersen, MS; Baker, AA; Zainuddin, NS; Meredith, KT; Wells, E; McDonald, J; Kham, S; Blyth, AJ; Spencer, RGMLignin as a biomarker in soils, peat, lakes and intertidal and marine sediment cores has been widely researched in the last four decades. The biogeochemical processes controlling their distribution and composition include fractionation due to phase changes, mineral binding, and abiotic and biotic decay. However, there appears to be no studies in the literature describing the concentration and composition of lignin in groundwater aquifers, despite lignin tracing having the potential to differentiate between types of vegetation and recharge source. In the latter case aquifers could potentially be a source of old, degradation resistant lignin. In this study, we characterise the lignin composition in groundwater samples from a coastal sand aquifer, in SE Australia. We compare these data with lignin composition of fresh vegetation samples from the study site, and with lignin data from other environments in the literature. Groundwater samples were also analysed for Dissolved Organic Carbon (DOC) and inorganic chemistry (major ions, Dissolved Inorganic Carbon (DIC) and redox sensitive species) to investigate lignin fractionation processes. To achieve this, the groundwater lignin composition was compared to the total DOC and DIC in the samples and the prevailing redox reactions. The lignin composition in groundwater was found to be unrelated to the surrounding surface vegetation, indicating significant alteration by biogeochemical processes along its flow paths. We identify potential lignin degradation zones, via determination of total OC consumed through redox reactions and microbial activity. In conclusion, this study, by closely examining the correlations of lignin phenols in groundwater with lignin in surface waters, as well as biogeochemical processes in the aquifer is shedding a new light on the ability of lignin as a biomarker in these subsurface systems. To our knowledge, this is the first attempt to assess the usefulness of lignin as a tracer in groundwater. © AGU
- ItemPaleoclimate studies and natural-resource management in the Murray-Darling Basin I: past, present and future climates(Taylor & Francis, 2013-06-19) Mills, K; Gell, PA; Hesse, PP; Jones, R; Kershaw, P; Drysdale, RN; McDonald, JThis paper provides an incisive review of paleoclimate science and its relevance to natural-resource management within the Murray-Darling Basin (MDB). The drought of 1997–2010 focussed scientific, public and media attention on intrinsic climate variability and the confounding effect of human activity, especially in terms of water-resource management. Many policy and research reviews make statements about future planning with little consideration of climate change and without useful actionable knowledge. In order to understand future climate changes, modellers need, and demand, better paleoclimate data to constrain their model projections. Here, we present an insight into a number of existing long-term paleoclimate studies relevant to the MDB. Past records of climate, in response to orbital forcing (glacial–interglacial cycles) are found within, and immediately outside, the MDB. High-resolution temperature records, spanning the last 105 years, exist from floodplains and cave speleothems, as well as evidence from lakes and their associated lunettes. More recently, historical climate records show major changes in relation to El Niño–Southern Oscillation cycles and decadal shifts in rainfall regimes. A considerable body of research currently exists on the past climates of southeastern Australia but, this has not been collated and validated over large spatial scales. It is clear that a number of knowledge gaps still exist, and there is a pressing need for the establishment of new paleoclimatic research within the MDB catchment and within adjacent, sensitive catchments if past climate science is to fulfil its potential to provide policy-relevant information to natural-resource management into the future. © 2013, Taylor & Francis.
- ItemPaleoclimate studies and natural-resource management in the Murray-Darling Basin II: unravelling human impacts and climate variability(Taylor and Francis Group, 2013-08-09) Mills, K; Gell, PA; Gergis, J; Baker, PJ; Finlayson, CM; Hesse, PP; Jones, R; Kershaw, P; Pearson, S; Treble, PC; Barr, C; Brookhouse, MT; Drysdale, RN; McDonald, J; Haberle, SG; Reid, M; Thoms, M; Tibby, JThe management of the water resources of the Murray-Darling Basin (MDB) has long been contested, and the effects of the recent Millennium drought and subsequent flooding events have generated acute contests over the appropriate allocation of water supplies to agricultural, domestic and environmental uses. This water-availability crisis has driven demand for improved knowledge of climate change trends, cycles of variability, the range of historical climates experienced by natural systems and the ecological health of the system relative to a past benchmark. A considerable volume of research on the past climates of southeastern Australia has been produced over recent decades, but much of this work has focused on longer geological time-scales, and is of low temporal resolution. Less evidence has been generated of recent climate change at the level of resolution that accesses the cycles of change relevant to management. Intra-decadal and near-annual resolution (high-resolution) records do exist and provide evidence of climate change and variability, and of human impact on systems, relevant to natural-resource management. There exist now many research groups using a range of proxy indicators of climate that will rapidly escalate our knowledge of management-relevant, climate change and variability. This review assembles available climate and catchment change research within, and in the vicinity of, the MDB and portrays the research activities that are responding to the knowledge need. It also discusses how paleoclimate scientists may better integrate their pursuits into the resource-management realm to enhance the utility of the science, the effectiveness of the management measures and the outcomes for the end users. © 2020 Informa UK Limited
- ItemRobust chronological reconstruction for young speleothems using radiocarbon(Elsevier Science Ltd, 2012-12-01) Hua, Q; McDonald, J; Redwood, D; Drysdale, RN; Lee, S; Fallon, SJ; Hellstrom, JCWe have studied two young speleothems, SC4 from Smiths Cave (Christmas Island, eastern Indian Ocean) and WM7 from Wollondilly Cave (Wombeyan caves, SE Australia). Attempts to date these speleothems by the Th/U method have proved unsuccessful with some age reversals for SC4 due to multiple sources of non-authigenic Th. This method has also resulted in imprecise ages for WM7 because of low U concentrations (<10 ppb) and consequently very low levels of authigenic Th-230 relative even to the very low levels of detrital Th-230 present. Here, we present an alternative method for reliable dating of these young speleothems using radiocarbon. Approximately 100 carbonate samples from SC4 and WM7 were analysed for C-14 by accelerator mass spectrometry (AMS). The AMS results indicate that bomb C-14 was evident in the youngest parts of both stalagmites. Two different approaches were used to estimate dead carbon fraction (DCF) values for these stalagmites for the pre-bomb period. For SC4, the DCF values were estimated based on the timing of C-14 dates for that period determined by high-resolution delta O-18 recorded in the speleothem, and the timing of the onset of bomb C-14. For WM7, a "maximum" range of pre-bomb DCF was determined. Chronologies of these speleothems were built 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). Good agreement between these age-depth models were observed indicating that the top 170 mm of SC4 and the top 50 mm of WM7 grew during the past 550-750 years and 1360-1740 years, respectively. © 2012, Elsevier Ltd.
- ItemRobust chronological reconstruction for your speleothems using radiocarbon(18th INQUA Congress, 2011-07-21) Hua, Q; McDonald, J; Redwood, D; Drysdale, RN; Lee, S; Fallon, SJ; Hellstrom, JCU/Th dating method is usually employed to build precise and reliable chronologies for speleothems. However, for some speleothems U-series dates may not be useful. We have studied two young speleothems, SC4 from Smiths Cave (Christmas Island, eastern Indian Ocean and WM7 from Wollondilly Cave (Wombeyan caves, SE Australia), with the aim to get a better understanding of past climate and rainfall variability beyond the instrumental records. Attempts to date SC4 by the U/Th method have proved unsuccessful with some age reversals due to multiple sources of non-authigenic Th. In addition, a sample close to the base of speleothem WM7 dated by U-series resulted in an imprecise age of ~4000 ± 500 cal BP (2?), which is due to the fact WM7 has low uranium concentrations (<10 ppb) and consequently contains very low levels of authigenic 230Th for a good U/Th age determination. In this paper, we investigate the possibility of using radiocarbon for the reconstruction of reliable chronologies for these young speleothems. Approximately 100 carbonate samples from the two stalagmites were analysed for 14C using the AMS facilities at ANSTO and ANU. The AMS results indicated that bomb 14C was evident in the youngest parts of both stalagmites. Dead carbon fraction (DCF) values for these stalagmites for the pre-bomb period were estimated based on the timing of 14C dates for that period determined by high-resolution stable isotopes recorded in the speleothems (?18O for SC4 and ?13C for WM7), and the timing of the onset of bomb 14C. Chronologies of these speleothems were built based on a dense sequence of AMS dates using 3 different age-depth models, OxCal and Bacon (Bayesian statistical approach) and Clam (non-Bayesian statistical model). The result of our radiocarbon-based chronologies and their reliability will be discussed for different DCF values including the mean DCF for the pre-bomb period and for different age-depth models. Copyright (c) 2011 INQUA 18
- ItemUsing the 14C bomb pulse to date young speleothems(University of Arizona, 2011-04-01) Hodge, E; McDonald, J; Fischer, MJ; Redwood, D; Hua, Q; Levchenko, VA; Drysdale, RN; Waring, CL; Fink, DMany factors may influence the radiocarbon age results of lacustrine sediments, among which the hardwater effect is particularly important. Daihai Lake is a closed lake located in the semi-arid region of Inner Mongolia, China. High concentrations of (HCO3)- and (CO3)2- and high pH values in the lake water imply that there is a hardwater effect when using bulk lacustrine sediment samples for 14C dating. To correct the apparent 14C age, we present a pilot study based on a series of 14C ages of lake surface sediment, lake water, submerged aquatic plant (Myriophyllum), fish bone (Cyprinus carpio), and surface soil samples from and around Daihai Lake. Assuming that the relationship between the 14C/12C ratio of DIC and of atmospheric CO2 was constant (at 0.816), the hardwater effect ages calculated for the past 8000 yr would have varied from 949 to 1788 yr. Together with the reservoir effect and soil organic matter input, the hardwater effect is a major factor causing changes in apparent age when using bulk organic matter for 14C dating. © 2011, University of Arizona.