Browsing by Author "Campbell, M"

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    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
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    Evidence of wet-dry cycles and mega-droughts in the Eemian climate of southeast Australia
    (Springer Nature, 2020-10-22) McGowan, HA; Campbell, M; Callow, JN; Lowry, A; Wong, HKY
    Understanding past climate variability is critical to informing debate of likely impacts of global warming on weather and climate, and water resources. Here we present a near annual resolution reconstruction of climate developed from a speleothem that spans the Eemian [Marine Isotope Stage 5e (MIS 5e)] from 117,500 to 123,500 years BP—the most recent period in the Earth’s history when temperatures were similar to those of today. Using 25 Mg, 88Sr, and 137Ba as proxies, we show the first indication of solar and teleconnection cyclic forcing of Eemian climate in southeast Australia, a region at present often affected by severe drought and bushfires. We find evidence for multi-centennial dry periods interpreted as mega-droughts, and highlight the importance of understanding the causes of these in the context of a rapidly warming world, where temperatures are now, or projected to exceed those of the Eemian. © The Author(s) 2020
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    Fire-induced shifts in stalagmite organic matter mapped using synchrotron infrared microspectroscopy
    (Elsevier, 2024-09) McDonough, LK; Campbell, M; Treble, PC; Marjo, CE; Frisia, S; Vongsvivut, JP; Klein, AR; Kovacs-Kis, V; Baker, AA
    Understanding organic matter (OM) in cave mineral deposits (speleothems) is essential for interpreting land use and climatic changes, and the incorporation of trace elements associated with organic compounds. However, the sources and composition of OM in speleothems are poorly understood due to challenges associated with measuring OM at low concentrations and the destructive nature of most speleothem OM analysis techniques. Synchrotron Fourier-transform infrared (FTIR) microspectroscopy is a promising non-destructive technique that can be used to investigate stalagmite OM composition. We use FTIR to analyse vegetation, soil, calcium carbonate and ash end-members and demonstrate the use of Synchrotron infrared microspectroscopy (IRM) mapping to detect temporal changes in the OM composition of a stalagmite from a shallow cave in south-west Western Australia. Our analysis reveals predominant FTIR peaks in the stalagmite linked to amides and CH2 groups, suggesting potential microbial contributions, with smaller proportions of aromatic, CH3 and Cdouble bondO groups. High-resolution transmission electron microscopy revealed that this OM is likely hosted in sets of nanopores spaced hundreds of nanometers apart, aligned along calcite crystallographic orientations. Furthermore, we assess the impact of known wildfire events as discrete short term environmental changes on the stalagmite’s OM composition. The temporal variability in OM functional group composition after fires implies complex fire-soil-vegetation-microbial interactions. This research demonstrates the effectiveness of Synchrotron IRM mapping in providing insights into the short and long-term environmental influences on stalagmite OM composition. Expanding this research to other regions and climates could further enhance the interpretation of OM changes in speleothem-based palaeoclimate reconstructions. © Crown Copyright © 2024 Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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    Past fires and post-fire impacts reconstructed from a southwest Australian stalagmite
    (American Geophysical Union (AGU), 2021-12-17) McDonough, LK; Treble, PC; Baker, AA; Borsato, A; Frisia, S; Campbell, M; Nagra, G; Coleborn, K; Gagan, MK; Paterson, DJ
    Stalagmites provide records of past changes in climate, vegetation, and surface events, with cave dripwaters shown to respond to fires. It is, therefore, most likely that these cave mineral deposits capture the environmental effects of palaeo-wildfires in their chemical and physical properties, as well as the climate conditions antecedent to palaeo-fire events. We analysed multiple proxies in stalagmite (YD-S2) from a shallow cave in south-west Western Australia. Principal Component Analysis revealed that short term peaks in combinations of phosphorus, copper, aluminium, lead and zinc in the stalagmite correspond to the timing of documented fire events occurring in the modern portion of the record. One particularly significant fire event is identified at 1897 ± 5 CE and shows a clear peak in P interpreted to be derived from ash, and a peak in 𝛿18O interpreted to indicate evaporation of sub-surface water during the heat of the fire. A post-fire threshold rise in organic matter content and a shift in calcite fabric associated with higher and more variable drip rates are consistent with a post-fire changes in surface-cave hydrology resulting from heat-induced deformation of the shallow karst bedrock brought about by the intensity of this fire. The combination of climate and fire sensitive proxies in YD-S2 indicates that the 1897 ± 5 CE wildfire was preceded by a multi-decadal dry period. We also identify lower and less variable peak phosphorus concentrations in the pre-European period that are consistent with low-intensity cultural burning by Indigenous Australians. The YD-S2 record shows the potential of stalagmites in capturing the climate-fire relationship and the effects of land-management practices on wildfire frequency and intensity. Plain-language Summary Fires have the potential to be recorded in stalagmites as pulses of ash-derived elements that leach intro dripwater above the cave. These ash-derived elements can then be incorporated into stalagmites as they grow. We analysed a stalagmite from a shallow cave in south-west Western Australia which revealed increases in phosphorus and metals including copper, lead, aluminium and zinc during years when fires are documented to have occurred over the cave. We use peaks in these elements to extend the fire record back to the 1760’s and identify a particularly large fire event in 1897 ± 5. This fire event was intense enough to cause not only an increase in ash-derived elements, but also an increase in the transmission of rainfall between the surface and the cave due to fracturing of the limestone as a result of intense heating and cooling. This event occurred at the end of a known drought period and was likely enhanced by the dry conditions. We also identify evidence for lower-intensity cultural burning by Indigenous Australians in the pre-European period compared to the post-European period, suggesting that changes in land management may also be recorded in stalagmites.
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    Quantifiying 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, DL
    Speleothems 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.
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    A review of speleothems as archives for paleofire proxies, with Australian case studies
    (American Geophysical Union, 2023-03-22) Campbell, M; McDonough, LK; Treble, PC; Baker, AA; Kosarac, N; Coleborn, K; Wynn, PM; Schmitt, AK
    Wildfires affect 40% of the earth's terrestrial biome, but much of our knowledge of wildfire activity is limited to the satellite era. Improved understanding of past fires is necessary to better forecast how fire regimes might change with future climate change, to understand ecosystem resilience to fire, and to improve data-model comparisons. Environmental proxy archives can extend our knowledge of past fire activity. Speleothems, naturally occurring cave formations, are widely used in paleoenvironmental research as they are absolutely dateable, occur on every ice-free continent, and include multiple proxies. Recently, speleothems have been shown to record past fire events (Argiriadis et al., 2019, https://doi.org/10.1021/acs.analchem.9b00767; McDonough et al., 2022, https://doi.org/10.1016/j.gca.2022.03.020; Homann et al., 2022, https://doi.org/10.1038/s41467-022-34950-x). Here we present a review of this emerging application in speleothem paleoenvironmental science. We give a concise overview of fire regimes and common paleofire proxies, describe past attempts to use stalagmites to investigate paleofire, and describe the physical basis through which speleothems can record past fires. We then describe the ideal speleothem sample for paleofire research and offer a summary of applicable laboratory and statistical methods. Finally, we present four case studies from southwest Australia which: (a) explore the geochemistry of ash leachates, (b) detail how sulfate isotopes may be a proxy for post fire ecological recovery, (c) demonstrate how a catastrophic paleofire was linked to changes in climate and land management, and (d) investigate whether deep caves can record past fire events. We conclude the paper by outlining future research directions for paleofire applications. © 2023 The Authors. Open Access CC-By-NC Licence
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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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    Speleothems as palaeofire archives – a synthesis and meta-analysis of data and methods
    (American Geophysical Union (AGU), 2021-12-18) Campbell, M; Treble, PC; McDonough, LK; Baker, AA; Kosarac, N
    Speleothems, mineral deposits found in caves, have recently been developed as a suitable archive to reconstruct palaeofires. Speleothems are excellent candidates for palaeoenvironmental research as they can be absolutely dated using radiometric methods and annual lamina, they incorporate a large range of chemical and physical proxies, and many are resolvable at the seasonal to annual scale. Large databases such as the Speleothem Isotope Synthesis and Analysis V2 may be used to identify and access suitable samples (Figure 1). Here, we present a meta-analysis and synthesis of published research and unpublished data to provide a toolbox for the use of speleothems as proxies of past fire. Drawing on our data from monitored caves and modern speleothems that overlap with recorded fire history, we will outline the approaches that we have adopted and identify which proxies have been validated as fire sensitive in the speleothem record. Fire sensitive proxies include ash-derived elements, in particular P and some transition metals, and proxies which reflect changes in soil productivity, hydrology, and evapotranspiration (e.g. δ18O, growth rate, organic matter, fabric). However, the success of these proxies as fire sensitive signals can differ between events recorded in speleothems. We discuss the complexities and demonstrate that an understanding of local surface-cave hydrological connectivity is required for the correct interpretation of the palaeofire signal. Improved understanding of palaeofire is necessary to characterize pre-industrial fire regimes, especially in colonised countries, where the landscape management systems of Indigenous people was disrupted. This will be of interest to the palaeoclimate community, land managers and traditional owners. Plain-language Summary Stalagmites (natural formations found in caves) have been used to reconstruct past fire events. These formations are useful for reconstructing past environments because we can find out when they grew, how quickly they grew, and so any change in chemicals included in them can be used to describe the environment that they grew in. Here, we analysed published reconstructions of past fires and unpublished data, and demonstrate which methods are best for analysing stalagmites, and which chemicals (and combinations of chemicals) best indicate that a fire occurred. The chemicals included in stalagmites include some from the ash left after a fire (especially phosphorous), and some which can change due to changes in the soil and limestone over the cave (such as the ‘type’ of oxygen included in infiltrating rainwater). How these chemicals react to a fire changes between caves, and between fire events. We need to understand past fire patterns so that we can better manage the landscape. This is especially true in colonised countries where Indigenous land management was stopped by colonialism. This research will interest land managers, traditional owners, and other scientists who research past environments.
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    Towards the development of fire proxies in speleothems using geochemical signatures in ashes from bushfires
    (Australasian Quaternary Association Inc., 2022-12-06) Campbell, M; McDonough, LK; Naeher, S; Treble, PC; Grierson, P; Sinclair, D; Howard, DL; Baker, AA
    Our knowledge of past fire regimes is limited by short observational records. Proxy archives (such as sediment cores, ice cores, speleothems, and tree scars) are used to extend these records and develop a better understanding of past fire regimes. Recently, stalagmites (i.e., cave deposits), have been shown to record past fire events, and it is possible that they include other attributes of the fire regime (e.g. burn severity). Stalagmite fire proxies are both chemical (e.g. oxygen isotope composition of calcite, and nutrient and trace metal concentrations), and physical (e.g. growth rate, fabric). Trace metals and nutrients are leached from ash and subsequently transported to the stalagmite via hydrological pathways. We collected ash from four Australian karst sites which experienced fires in recent years (2019 and 2022). Ash chemical composition was determined by analysis of leachates (inorganic chemistry) and by analysis of the ash itself (organic biomarker concentrations of a subset of the ash dataset). The concentrations of inorganic components (e.g. of trace metals strontium and magnesium) show a clear difference between more- and less-combusted materials, as inferred by ash colour. Common fire biomarker concentrations (e.g. polycyclic aromatic hydrocarbons and levoglucosan) showed no clear relationship with inferred burn severity. Together, this has implications for the use of both organic and inorganic fire proxies in stalagmites and other sedimentary proxy archives. Inorganic ash geochemistry results will be used to contextualise changes in stalagmite geochemistry from Western Australian stalagmites (as measured by LA-ICP-MS and Synchrotron micro-XFM) which experienced bushfires during the satellite era. We aim to determine whether stalagmite chemistry can be used as a proxy for burn severity.
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    Towards the development of fire proxies in speleothems using geochemical signatures in ashes from bushfires
    (Australasian Quaternary Association Inc., 2022-12-06) Campbell, M; McDonough, LK; Naeher, S; Treble, PC; Grierson, P; Sinclair, D; Howard, DL; Baker, AA
    Our knowledge of past fire regimes is limited by short observational records. Proxy archives (such as sediment cores, ice cores, speleothems, and tree scars) are used to extend these records and develop a better understanding of past fire regimes. Recently, stalagmites (i.e., cave deposits), have been shown to record past fire events, and it is possible that they include other attributes of the fire regime (e.g. burn severity). Stalagmite fire proxies are both chemical (e.g. oxygen isotope composition of calcite, and nutrient and trace metal concentrations), and physical (e.g. growth rate, fabric). Trace metals and nutrients are leached from ash and subsequently transported to the stalagmite via hydrological pathways. We collected ash from four Australian karst sites which experienced fires in recent years (2019 and 2022). Ash chemical composition was determined by analysis of leachates (inorganic chemistry) and by analysis of the ash itself (organic biomarker concentrations of a subset of the ash dataset). The concentrations of inorganic components (e.g. of trace metals strontium and magnesium) show a clear difference between more- and less-combusted materials, as inferred by ash colour. Common fire biomarker concentrations (e.g. polycyclic aromatic hydrocarbons and levoglucosan) showed no clear relationship with inferred burn severity. Together, this has implications for the use of both organic and inorganic fire proxies in stalagmites and other sedimentary proxy archives. Inorganic ash geochemistry results will be used to contextualise changes in stalagmite geochemistry from Western Australian stalagmites (as measured by LA-ICP-MS and Synchrotron micro-XFM) which experienced bushfires during the satellite era. We aim to determine whether stalagmite chemistry can be used as a proxy for burn severity.
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    Tracking down carbon inputs underground from an arid zone Australian calcrete
    (Public Library of Science (PLOS), 2020-08-28) Saccò, M; Blyth, AJ; Humphreys, WF; Middleton, JA; White, NE; Campbell, M; Mousavi-Derazmahalleh, M; Laini, A; Hua, Q; Meredith, KT; Cooper, SJB; Griebler, C; Allard, S; Grierson, P; Grice, K
    Freshwater ecosystems play a key role in shaping the global carbon cycle and maintaining the ecological balance that sustains biodiversity worldwide. Surficial water bodies are often interconnected with groundwater, forming a physical continuum, and their interaction has been reported as a crucial driver for organic matter (OM) inputs in groundwater systems. However, despite the growing concerns related to increasing anthropogenic pressure and effects of global change to groundwater environments, our understanding of the dynamics regulating subterranean carbon flows is still sparse. We traced carbon composition and transformations in an arid zone calcrete aquifer using a novel multidisciplinary approach that combined isotopic analyses of dissolved organic carbon (DOC) and inorganic carbon (DIC) (δ13CDOC, δ13CDIC, 14CDOC and 14CDIC) with fluorescence spectroscopy (Chromophoric Dissolved OM (CDOM) characterisation) and metabarcoding analyses (taxonomic and functional genomics on bacterial 16S rRNA). To compare dynamics linked to potential aquifer recharge processes, water samples were collected from two boreholes under contrasting rainfall: low rainfall ((LR), dry season) and high rainfall ((HR), wet season). Our isotopic results indicate limited changes and dominance of modern terrestrial carbon in the upper part (northeast) of the bore field, but correlation between HR and increased old and 13C-enriched DOC in the lower area (southwest). CDOM results show a shift from terrestrially to microbially derived compounds after rainfall in the same lower field bore, which was also sampled for microbial genetics. Functional genomic results showed increased genes coding for degradative pathways—dominated by those related to aromatic compound metabolisms—during HR. Our results indicate that rainfall leads to different responses in different parts of the bore field, with an increase in old carbon sources and microbial processing in the lower part of the field. We hypothesise that this may be due to increasing salinity, either due to mobilisation of Cl- from the soil, or infiltration from the downstream salt lake during HR. This study is the first to use a multi-technique assessment using stable and radioactive isotopes together with functional genomics to probe the principal organic biogeochemical pathways regulating an arid zone calcrete system. Further investigations involving extensive sampling from diverse groundwater ecosystems will allow better understanding of the microbiological pathways sustaining the ecological functioning of subterranean biota. © 2020 Saccò et al
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    Using cave formations to investigate ancient wildfires
    (American Geophysical Union, 2023-05-02) Campbell, M; McDonough, LK; Treble, PC; Baker, AA
    From sediment cores to speleothems, environmental archives are helping us to understand the history of wildfires. © 2023. The authors. CC BY-NC-ND 3.0