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With relatively few exceptions, dendrochronological records in Australia have been developed from conifer species. Over the last 20 years, some effort has successfully extracted records from some Eucalyptus species and Toona ciliata. However, very little attempt has been made to examine a broader range of species. There has been some success with extracting records from the African Boab species. We collected 10mm core samples from around 30 A. gregorii trees in the Kimberly and will be assessing the potential of the species by examining variability in vessel characteristics, isotopic and elemental tracers. We hope to use elemental tracers in the wood to corroborate a fire record from speleothems in the region. 

With relatively few exceptions, dendrochronological records in Australia have been developed from conifer species. Over the last 20 years, some effort has successfully extracted records from some Eucalyptus species and Toona ciliata. However, very little attempt has been made to examine a broader range of species. There has been some success with extracting records from the African Boab species. We collected 10mm core samples from around 30 A. gregorii trees in the Kimberly and will be assessing the potential of the species by examining variability in vessel characteristics, isotopic an elemental traces. We hope to use elemental traces in the wood to corroborate a fire record from speleothems in the region. 

Understanding the long-term interactions among vegetation, fire, and climate is critical for interpreting ecosystem responses to climatic perturbations. Project Prometheus investigates Holocene paleofire dynamics, vegetation shifts, and climate variability in the Mediterranean, using speleothem records from caves in Italy (Alps, Apennines, Sardinia) and the Balkans. By integrating multiple proxies, including polycyclic aromatic hydrocarbons (PAHs) as fire markers and n-alkanes as a proxy for vegetation composition and terrigenous input, this project aims to provide insights into the environmental drivers of fire activity from millennial to sub-centennial timescales, thus creating a high resolution fire history for the Mediterranean region. Speleothems offer a novel paleoenvironmental archive, and we apply an advanced hydrocarbon extraction protocol adapted from a study on Australian stalagmites1. This method, which includes slow acid dissolution in a clean-room setting to minimize contamination and maximize compound yields, has significantly improved the detection limits and expanded the range of PAHs identified2. Uranium-thorium (U-Th) dating ensures a precise chronological framework, enabling robust correlation between fire, vegetation, and climate proxies. Here we present results from the initial phase of the project, analyizing a dozen archives from Italy, Greece, and Northern Macedonia, at low resolution (millennial- and sub-millennial-scale). Preliminary results, will provide a first indication of technique effectiveness, archive quality, and regional historical variations (if any) in paleofire regimes. Comparative studies with paleofire data from lake sediments in Italy, where shifts in fire regimes have been previously documented, as well as with modern fire data derived from registries and satellite observations, will help contextualizing our findings within broader regional fire histories. This research advances our understanding of vegetation-wildfire-climate interactions in the Mediterranean by contributing high-resolution, multi-proxy reconstructions from an understudied archive. By linking past fire and vegetation responses to climatic variability, it provides critical context for assessing future ecosystem resilience and informing land management policies under changing climate conditions. 

Australia has long been recognized as one of the world’s fire hotspots, but the Black Summer of 2019-2020, when 97,000 km2 were scorched across southeastern Australia, and the larger fires of northern Australia’s savanna and desert in 2023, may indicate a shift toward a higher level of fire activity. Placing these events in context requires developing precisely-dated, high resolution records of bushfire through periods with different climate and land use mean states. We reconstructed bushfire activity for the period 1110-2009 CE using polycyclic aromatic hydrocarbons (PAH) in three precisely-dated, fast-growing, and partially overlapping aragonite stalagmites from cave KNI-51, located in the central Australian tropical savanna. PAH molecular weights are tied to combustion temperature (i.e., low molecular weights form in lower temperature fires), and thus our record preserves evidence of both the timing and intensity of bushfire over the majority of the last millennium. Comparisons of burn scar satellite imagery with temporal changes in PAH abundances in recently deposited stalagmite suggest that airfall (smoke and ash) from fires within a 5 km radius is primarily responsible for transmitting PAHs to the land surface over the cave, a finding supported by our recent controlled burn and irrigation experiment. The rapid growth rate of KNI-51 stalagmites (1-2 mm yr-1), coupled with the extremely thin soils above the cave, appear to allow for transmission and preservation of multi-annual paleofire signals. To investigate the effects of external forcing on bushfire activity over the last millennium, we applied linear mixed-effect regression to the PAH data, and also included monsoon rainfall (using oxygen isotope ratios from the same stalagmites), annual surface air temperature (using output from the CESM-Last Millennium Ensemble), antecedent fire (using the same stalagmite PAH record), and timing with respect to the arrival of European pastoralists (EP) and their cattle in the 1880s. The model reveals significant differences prior to and following the arrival of EP. Most notably, prior to the arrival of EP, rainfall was significantly correlated with low and medium intensity fires, but not high intensity ones. After the arrival of EP, the correlation between rainfall and fire activity decreased markedly, and showed no statistically significant correlation to any fire intensity. Similarly, prior to the arrival of EP, antecedent fire activity (determined as the sum of PAH within the previous 5 years) was correlated with all levels of fire intensity, but after EP arrival, only high intensity fires are correlated with such antecedent burning. Our findings thus suggest that fire activity following the arrival of EP in the eastern Kimberley has been distinct from any other extended period of the last nine centuries. 

Stalagmites are excellent archives of past climate change. They can grow continuously for tens of thousands of years, be precisely dated, and record a wide range of climate variables through their chemistry. In the last quarter century, numerous studies have focused on (sub)tropical hydroclimate variability, particularly from South Asia, the Maritime Continent, and northern Australia. This talk will discuss how stalagmite paleoclimate research is conducted and what important findings have resulted from this work. 

Stalagmites serve as valuable archives that significantly enhance our understanding of past climate and environmental changes. The trace element records preserved within stalagmites have been used to reconstruct past rainfall patterns at regional scale [1]. However, interpreting these geochemical proxies is challenging, as the functioning of the cave system, within its specific climatological and geological context, must be taken into account. Comparing instrumental climate measurements with these proxies from stalagmites that grew during the 20th century provides an opportunity to investigate how stalagmite geochemistry responds to variations in rainfall.In this study, we present results from a stalagmite collected from cave KNI-51, located in the Kimberley region of northeast Western Australia. Previous uranium–thorium disequilibrium dating of the stalagmite has yielded a high-precision age model (2 sd errors of ±1–2 years over much of the last century) and revealed rapid growth (1–2 mm/yr) [2], allowing for nearly annual resolution of geochemical records. We examined trace element variations related to historical annual rainfall fluctuations, retrieved from five stations near the cave area between 1915 and 2007. Comprehensive statistical analyses, accounting for stationarity and autocorrelation in the time series data, revealed significant correlations when comparing certain trace elements to both total annual rainfall and the rainfall recorded during the monsoon season (December to March). Notably, some trace elements exhibited a stronger response to rainfall occurring during the monsoon period. Furthermore, we applied rolling window correlation to assess the evolution and stability of these correlations over time, identifying intervals where the relationship between the time series appeared weaker or stronger.The multi-annual calibration provided critical insights into how the stalagmite recorded rainfall variability through trace elements fluctuations and represents a key step in defining the response times of the cave and stalagmite recording systems to changes in climate and water balance in the Kimberley region. The disclosed correspondence between the instrumental rainfall record and the trace element signals encoded in the stalagmite demonstrates that rainfall time series can be successfully reconstructed from stalagmites. This marks an important milestone in the development of a calibrated trace element–rainfall transfer function, which can be applied to past stalagmite geochemical records.[1]         S. F. Warken et al., “Reconstruction of late Holocene autumn/winter precipitation variability in SW Romania from a high-resolution speleothem trace element record,” Earth Planet. Sci. Lett., vol. 499, pp. 122–133, 2018, doi: https://doi.org/10.1016/j.epsl.2018.07.027.[2]         R. F. Denniston et al., “Expansion and contraction of the indo-pacific tropical rain belt over the last three millennia,” Sci. Rep., vol. 6, pp. 1–9, 2016, doi: 10.1038/srep34485. 

Pyrogenic compounds, such as polycyclic aromatic hydrocarbons (PAHs), can track the type and intensity of fires and are preserved in many environmental matrices including speleothems. We recently reported on a stalagmite record of PAH abundance distributions from cave KNI-51, located among the eucalypt savanna in the Ningbing range of tropical Western Australia. In order to better understand the manner by which PAHs from local bushfires are deposited on the land surface and transported into caves, we performed a controlled burn and irrigation experiment at cave KNI-140, located near to and in the same bedrock as cave KNI-51. Samples of soil, vegetation, ash, and air were collected prior to and immediately succeeding the prescribed burn. The fire, which burned predominantly grasses, was ignited by matches (no accelerants were used) and covered approximately 30,000 square meters upwind from the cave. The land surface above the cave was irrigated prior to and immediately succeeding the burn with resulting dripwater collected for analysis. Next, ash samples were deposited directly above the cave and then similarly irrigated, with the drip water also collected. The PAHs present in these samples were measured via gas chromatography-mass spectrometry at Ca’ Foscari University, Venice. Our results reveal that low molecular weight PAHs were the most abundant species of PAH in the drip water and heavier PAHs were substantially less abundant. This result is likely due to the low combustion temperature of the burn, with abundances increasing through each of the three stages of sample collection, demonstrating that deposition from smoke and cinders produces identifiable signals in dripwater (and thus stalagmite) PAHs, supporting the contention that KNI-51 stalagmites record fire activity occurring not just above the cave but within km of the cave. On-going analyses of soil, vegetation, and ash samples will further clarify the role of fire on production and transmission of PAHs at this site, and thus how these organic compounds preserved in speleothems can help delineate the fire history in the region. 

Because traditional paleofire archives (e.g., burn scars on trees, charcoal in lake sediments) are not available in all settings, new ways of reconstructing past fire activity are needed. We focus here on polycyclic aromatic hydrocarbons (PAHs) in stalagmites. PAHs are organic molecules composed of two or more fused aromatic rings formed through incomplete combustion of organic matter, and vary in molecular weight depending on combustion conditions. Because the use of PAHs in stalagmites as a paleofire indicator is still in its infancy and because the production, deposition, and transport of PAHs into a cave is a complex and multi-faceted system, we tested the reproducibility of PAHs in two coeval and precisely-dated aragonite stalagmites – KNI-51-F and KNI-51-G - from KNI-51 (15.3°S, 128.6°E), a shallow cave located in the Kimberley region of tropical Western Australia. KNI-51-F and KNI-51-G span 1110-1620 CE and 1310-1630 CE, respectively. Each was hand-milled for analysis in continuous sections spanning approx. 2 mm-tall intervals at Ca’ Foscari University. Owing to differences in growth rate, temporal resolutions for KNI-51-F and KNI-51-G were 3±2 and 1±0.4 yr/sample, respectively. Chemical preparations and analysis methods follow those of Argiriadis et al. (2019) Analytical Chemistry, volume 91. In order to assess replication between the two stalagmites, we compared total abundances of low molecular weight (LMW: Napthalene, Acenaphthylene, Acenaphthene, Fluorene), medium molecular weight (MMW: Phenanthrene, Anthracene, Fluoranthene, Pyrene, Benzo(a)Anthracene, Chrysene, Retene), and high molecular weight (HHM: Benzo(b)Fluoranthene, Benzo(k)Fluoranthene, Benzo(e)Pyrene, Benzo(a)Pyrene, Perylene, Benzo(ghi)Perylene, Indeno(1,2,3-c,d)Pyrene, Dibenzo(A,H)Anthracene) PAHs. Total abundances of LMW, MMW, and HMW PAHs are similar (<10 ng/g) except for HMW PAHs in KNI-51-G, which are generally <1 ng/g. Total LMW and MMW abundance time series replicate well, with multiple synchronous multidecadal periods characterized by consistently low PAH abundances, suggestive of reduced bushfire activity, punctuated by intervals of high PAH abundances, likely reflecting frequent bushfire. Less coherence exists between HMW PAHs. 

Gli speleotemi sono ampiamente utilizzati come archivio paleoclimatico in ragione di alcune caratteristiche come la crescita continua e regolare, la resistenza all’alterazione, la datazione precisa e la possibilità di ottenere record ad alta risoluzione. La ricostruzione di paleofuochi dagli speleotemi è un innovativo ambito di ricerca che sta velocemente prendendo piede con lo sviluppo di tecniche analitiche dedicate e l’utilizzo di nuovi proxy geochimici. Di recente, abbiamo proposto un metodo per la determinazione di idrocarburi policiclici aromatici in tracce e n-alcani nelle stalagmiti, dimostrando la validità del metodo e dei proxy attraverso una serie di test effettuati su stalagmiti provenienti dalla grotta KNI-51, situata nella regione del Kimberley, in Australia nord-occidentale. Il sito è particolarmente adatto per questo tipo di studio, trattandosi di una zona soggetta a frequenti incendi e di una grotta poco profonda le cui stalagmiti hanno una crescita media di 1-2 mm/anno. Attualmente è in fase di completamento il record ad alta risoluzione ottenuto da tre stalagmiti che coprono l’ultimo millennio, includendo quindi la colonizzazione europea e il conseguente cambiamento del regime di fuoco dovuto alla soppressione del controllo tradizionalmente effettuato dalla popolazione aborigena e all’introduzione di animali da pascolo. Alle nostre latitudini, il fuoco sta acquisendo un’importanza crescente a livello ambientale, climatico e sociale. Comprendere la complessità coinvolta nelle interazioni tra fuoco, clima ed ecosistemi beneficia della conoscenza delle dinamiche del passato. Pertanto, nell’ottica di testare questo approccio in un contesto come quello Mediterraneo, è stato finanziato il progetto PRIN-PNRR PROMETHEUS, che prevede di testare lo stesso metodo su campioni provenienti da aree situate in Italia e in Europa meridionale e caratterizzate da diversi microclimi.