Browsing by Author "Adler, L"
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- ItemCave stalagmites as records of past recharge frequency in semi-arid Australia(National Centre for Groundwater Research And Training, 2015-11-03) Markowska, M; Baker, AA; Andersen, MS; Rutlidge, H; Jex, CN; Cuthbert, MO; Rau, GC; Adler, L; Graham, PW; Mariethoz, G; Marjo, CE; Treble, PCUnderstanding past variability in groundwater recharge over recent time scales (0 – 10 ka) in Australia is essential for future sustainable groundwater management in a changing climate. Currently, there are limited data about past infiltration rates and their relationship to environmental controls that dominate recharge variability. Speleothem (cave precipitates) records may provide a new approach to understanding past infiltration (i.e. recharge rates), in addition to traditional interpretations of connectivity between climate and the hydrological cycle, in drier parts of Australia. In this study we used Cathedral Cave, (SE Australia) located in a temperate semi-arid climate, as a natural laboratory to investigate cave infiltration rates and the climate-karst-cave interactions driving the isotopic (δ18O) and chemical variability in modern drip water. These findings were then used to interpret the δ18O stalagmite record from two modern speleothems growing during the last ~50 years. Modern drip water results showed that the δ18O composition was enriched by up to 2.77 ‰ relative to annually weighted mean rainfall. Isotopically lighter δ18O occurred during infiltration events, followed by subsequent isotopic enrichment as evaporation in the unsaturated zone fractionated δ18O of stored water. Drip rate monitoring revealed that larger events leading to infiltration were infrequent (0 – 3 a-1) and the ‘effectiveness’ of these infiltration events was controlled by antecedent moisture conditions in the soil zone. In drier climatic zones, evaporation drives the enrichment of δ18O in the unsaturated zone, allowing periods of infiltration to be identified from the stable isotopic composition of drip waters. Our findings are important for interpreting speleothem records from regions with infrequent recharge and high evaporation rates. Such records are likely to contain evidence of past infiltration events moderated by an evaporation signal, allowing records of paleo-recharge to be reconstructed for drier climate regions of Australia.
- ItemComparison 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, JCNot available.
- ItemComparison 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, KTSpeleothems 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.
- ItemQuantifiying the fire imprint in speleothem oxygen and carbon isotope records(American Geophysical Union (AGU), 2022-12-14) Baker, AA; Campbell, M; Treble, PC; Adler, L; McDonough, LK; Howard, DLSpeleothems are an emerging archive of past fires. Fires primarily leave an imprint in speleothem calcite from ash-derived water-soluble trace elements transported from the surface to the cave in percolation waters. But what about the influence of fire on speleothem oxygen and carbon isotopes? Oxygen and carbon isotopes are the most widely used speleothem geochemical proxies, generally interpreted as archives of past climatic and environmental change. The link between speleothem oxygen and carbon isotopes and fire, however, is still unclear. Field monitoring before and after recent fires provides some clues to the possible fire effect on speleothem oxygen isotope composition. Recent papers present evidence that cave percolation water can have oxygen isotope composition that is enriched in oxygen-18 post-fire, due to partial evaporation of soil water and loss of shade cover. There is also evidence indicating that post-fire, percolation waters have greater variability in oxygen-18 when there is complete evaporation of soil water. To better understand the influence of fire on speleothem oxygen and carbon isotopes, we have sampled ~10 mm from the tops of actively-depositing stalagmites from cave systems at Yanchep, Western Australia. The sampled material contains calcite that has formed over the last ~50 years, during which numerous fires have occurred at the site. The data spans the period of satellite monitoring, allowing fire size and intensity to be determined. We use synchrotron x-ray fluorescence imaging to map the trace element composition of the stalagmites, and use this to identify the fire imprint of the ash-derived water-soluble elements in the stalagmite calcite. Using this as a time marker of the fires, we quantify the magnitude and duration of any post-fire changes in stalagmite oxygen and carbon stable isotope composition. We identify whether changes in oxygen or carbon isotopes are replicated between stalagmites and between fire events, and compare the extent to which the post-fire imprint in stalagmite oxygen and carbon isotopes is significant compared to climatic and hydrological controls on these isotopes. This information will inform paleoclimate studies where shifts in speleothem oxygen and carbon isotopes due to fires may be misinterpreted to result from changes in climate and hydrology. Full Abstract Are wildfires increasing in number, intensity or spatial extent compared to the past? Before the era of satellite imaging, we have to rely on geological and biological archives of past fires. One such archive is cave stalagmites. However, they are normally used as an archive of past climate through the analysis of oxygen isotopes contained within their calcite. And wildfire can affect the oxygen isotope composition of the water percolating from the surface to the cave through the burnt environment. To what extent does wildfire affect the stalagmite climate archive? Here, we compare stalagmite records from caves in a region in Western Australia that has burnt many times in recent decades. We identify the fire imprint in the stalagmite calcite using synchrotron mapping of ash-derived elements. And we line these fire events up with the stable isotope record in the same sample. That way we can quantify the fire imprint in the stalagmite oxygen isotope record for the first time. This will allow future researchers to take this into consideration when interpretating stalagmite oxygen isotope records from fire-prone regions.
- ItemReconstructing a fire and climate history using a stalagmite from Crystal Cave, south-west Western Australia(Australasian Quaternary Association (AQUA), 2021-07-08) Kosarac, N; Treble, PC; McDonough, LK; Paterson, DJ; Adler, L; Baker, AABushfires are a major natural hazard, with a growing impact on communities and ecosystems in Australia and worldwide. However, our understanding of long-term past fire intervals and behaviour is limited by low temporal resolution. Cave stalagmites offer a novel opportunity to reconstruct long, high-resolution datasets of past fire and climate with a precise chronology. CRY-S1 is a cave stalagmite from Crystal Cave, Margaret River, south-west Western Australia. Monitoring has shown that speleothems from shallow caves are more likely to record fire events as pulses of ash-derived elements and evaporative enrichment of δ18O. However, Crystal Cave is located approximately 30 m below the surface, indicating that past fire events can also be recorded in a deep cave system. This may be on account of the cave’s fracture flow contribution enabling a more direct connection with the surface, or the catchment morphology. This Honours project aims to compile and analyse fire and climate data over 300 years using new and existing datasets for stalagmite CRY-S1. We assess 18O and 13C isotope data, as well as a suite of trace elements. Past studies have determined that fire events can be identified through ash-derived elements in stalagmite laminae. Elements of interest include phosphorous, strontium and zinc. Results from 14C analyses will be used to test a hypothesis that large fires will eliminate young carbon in soils, altering the stalagmite 14C/12C ratio. An age depth model was obtained using annual lamina counts from Sr synchrotron mapping. Studying trace elements and isotope signals in this context increases our understanding of how past fire and climatic changes can be interpreted through stalagmite geochemistry. This Honours project will contribute to a world first project which uses stalagmites to construct annually-resolved records of fire frequency and intensity.