Browsing by Author "Wynn, PM"
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- ItemA 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, AKWildfires 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
- ItemRoles of forest bioproductivity, transpiration and fire in a nine-year record of cave dripwater chemistry from southwest Australia(Elsevier, 2016-07-01) Treble, PC; Fairchild, IJ; Baker, AA; Meredith, KT; Andersen, MS; Salmon, SU; Bradley, C; Wynn, PM; Hankin, SI; Wood, A; McGuire, EForest biomass has the potential to significantly impact the chemistry and volume of diffuse recharge to cave dripwater via the processes of nutrient uptake, transpiration and forest fire. Yet to-date, this role has been under-appreciated in the interpretation of speleothem trace element records from forested catchments. In this study, the impact of vegetation is examined and quantified in a long-term monitoring program from Golgotha Cave, SW Australia. The contribution of salts from rain and dry-deposition of aerosols and dissolved elements from soil mineral and bedrock dissolution to dripwater chemistry are also examined. This study is an essential pre-requisite for the future interpretation of trace element data from SW Australian stalagmite records, whose record of past environmental change will include alterations in these biogeochemical fluxes. Solute concentrations in dripwater vary spatially, supporting the existence of distinct flow paths governed by varying amounts of transpiration as well as nutrient uptake by deeply-rooted biomass. Applying principal components analysis, we identify a common pattern of variation in dripwater Cl, Mg, K, Ca, Sr and Si, interpreted as reflecting increasing transpiration, due to forest growth. Mass-balance calculations show that increasing elemental sequestration into biomass has the largest impact on SO4, providing an explanation for the overall falling dripwater SO4 concentrations through time, in contrast to the transpiration-driven rising trend dominating other ions. The long-term rise in transpiration and nutrient uptake driven by increased forest bioproductivity and its impact on our dripwater chemistry is attributed to (i) the post-fire recovery of the forest understorey after fire impacted the site in 2006 CE; (ii) and/or increased water and nutrient demand as trees in the overlying forest mature. The impact of climate-driven changes on the water balance is also examined. Finally, the implications for interpreting SW Australian speleothem trace element records are discussed. © Crown Copyright Published by Elsevier B.V.
- ItemUsing speleothem SO4 isotopes to elucidate S cycling in a fire prone region(Copernicus GmbH, 2019-04-11) Coleborn, K; Baker, AA; Treble, PC; Wynn, PMWildfires are a global hazard that can have catastrophic impacts on communities and ecosystems. A speleothem based wildfire record will allow us to determine long-term natural fire regimes and better understand the relationship between wildfires and climate. Recent research has demonstrated the potential of using S as a speleothem paleofire proxy1 but a full characterisation of S in a fire-prone environment is lacking. Firstly, we used modern monitoring to quantify the relative contributions of S sources in a cave environment with overlying post-fire forest regrowth. Sulphate concentration and isotopic values (δ34S- SO4 and δ18O-SO4) for rainfall (+18.8hand +8.1h respectively), cave drip water (+20.3hand +3.2h), bedrock (+21.7hand +10.6h) vegetation (δ34S- SO4 +22.1h) and soil (δ34S- SO4 +19.5h) were characterised. Results showed the SO4 rainfall input was from a marine source. A 1-2h fractionation of drip water δ34S- SO4 compared to rainfall δ34S- SO4 revealed there was assimilation of SO4 into vegetation above the cave. δ18O- SO4 indicated biogeochemical cycling of S by mineralisation of organic S compounds to sulphate within the soil. These results demonstrate the necessity of dual isotope analysis of δ34S- SO4 and δ18O- SO4 to correctly identify S sources and biogeochemical cycling prior to incorporation of SO4 into a speleothem. Secondly, the S isotope proxy was applied to a 2-12 ka speleothem record from the same region and forest cover. More than fifty 200 mg samples from a flowstone were analysed for δ34S- SO4 and δ18O- SO4:Mean speleothem δ34S- SO4 was enriched in 34S by >2 h compared to modern rainfall, indicative of vegetation fractionation. LGM mean δ34S- SO4 was more negative than Holocene (+22.1hand +23.2h respectively). Fast growth periods at δ10 and 7ka provided multi-annual resolution and 1.5h variability in δ34S- SO4 was observed over decadal timescales, indicative of changes in vegetation cycling of S, which we interpret as a possible fire record.