Speleothems as palaeofire archives a synthesis and meta-analysis of data and methods

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 Here, we present a meta-analysis and synthesis of published research and unpublished data to provide a toolbox for the use of speleothems as proxies of past fire.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. 18O, 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.