A Review of Speleothems as Archives for Paleofire Proxies, With Australian Case Studies

Abstract

Wildfires are a significant hazard with ∼40% of the Earth's terrestrial surface being fire prone, and ∼3% of the terrestrial surface burning each year (Chapin et al., 2011;Giglio et al., 2010). In many areas, instances of dangerous fire weather are increasing (Jones et al., 2022). In northern California and Oregon, the likelihood of extreme autumn fire weather has increased by 40% (Hawkins et al., 2022), and both the frequency and size of wildfires have increased in the western United States (Abatzoglou & Williams, 2016;Iglesias et al., 2022). A long-term increase in both extreme fire weather and fire season length has been observed in parts of Australia (BOM and CSIRO, 2020), and there has been a global increase in the frequency of compound fire weather and meteorological drought events (Richardson et al., 2022). Fire regimes are a function of climate, human activity, and land use.

Combustion Completeness and Sample Location Determine Wildfire Ash Leachate Chemistry

“…If volatilization temperature was the sole control on element concentration, we would expect to see concentrations of elements with high volatilization temperatures (e.g., Mn, Al, Zn, K, P, Cu, Mg, Ca and Na, which all volatilize at >700°C. Please see summary figures in M. Campbell et al (2023) and Bodí et al (2014)) in greater relative proportions in white ash than in black ash. This is true for Na and K, which are higher in white ash leachates than in black ash leachates, but Mn, Al, P, and Zn are higher in black ash leachates than in white ash leachates, and Cu, Mg, and Ca concentrations do not vary significantly with ash color.…”

“…These proxy archives have allowed past fire activity to be reconstructed at local (e.g., Rehn et al., 2021), continental (e.g., Zennaro et al., 2015), and global scales (e.g., Marlon et al., 2008). In recent years, speleothems (primarily stalagmites) have been developed as archives of past fire activity, with both inorganic proxies (predominantly trace metals) and pyrogenic biomarkers used to investigate past fire activity (Argiriadis et al., 2019, 2023; M. Campbell et al., 2023; Homann et al., 2022, 2023; McDonough et al., 2022). The inorganic fire proxy signal in speleothems is thought to be sourced from ashes deposited over the cave, which are subsequently leached by rainfall, transported via karst flowpaths, and deposited with speleothem calcite.…”

“…These proxy archives have allowed past fire activity to be reconstructed at local (e.g.,Rehn et al, 2021), continental (e.g.,Zennaro et al, 2015), and global scales (e.g.,Marlon et al, 2008). In recent years, speleothems (primarily stalagmites) have been developed as archives of past fire activity, with both inorganic proxies (predominantly trace metals) and pyrogenic biomarkers used to investigate past fire activity(Argiriadis et al, 2019(Argiriadis et al, , 2023M. Campbell et al, 2023;Homann et al, 2022Homann et al, , 2023McDonough et al, 2022).…”

Fire in the Earth System: Introduction to the Special Collection

“…Campbell et al. (2023) discussed the importance of understanding past fire activity for predicting future changes and improving data–model connections. Campbell et al.…”

“…Several of the papers featured in this Special Collection presented new data on fire effects across space and time, exploring the connection between paleofire history and climate. Campbell et al (2023) discussed the importance of understanding past fire activity for predicting future changes and improving data-model connections. Campbell et al reviewed the emerging applications to paleofire in speleothem paleoenvironmental science, including an overview of fire regimes and paleofire proxies, laboratory and statistical analytical methods, and presented case studies from southwestern Australia.…”