A new approach to experimental charcoal analyses: Implications for the Cretaceous and other greenhouse climate intervals

Abstract

Earth's climate has historically oscillated between different states, with greenhouse climate periods offering valuable analogs for future climate projections. The Cretaceous Period, frequently characterized by high atmospheric CO₂ levels and the absence of polar ice caps (among other changes), provides potential insights into potential ecological and environmental responses to anthropogenic climate change. This study presents new experimental data to inform the use of sedimentary charcoal as a paleofire and paleoecological proxy during the Cretaceous, supplementing the limitations of traditional palynological and fossil perspectives. Our experimental analysis includes 23 broadly sampled plant taxa, focusing on charcoal morphological classifications and a novel set of the following morphometric parameters: aspect ratio (L:W), rectangularity, circularity, and feret diameter. We also conducted novel dissections of plant tissue components (e.g., leaf vein, leaf petiole, etc.) to a finer scale than previous studies. Our results reveal significant differences in charcoal morphometrics at the tissue (e.g., leaf, petiole) and component (e.g., vein, blade) levels, challenging the assumption that larger plant tissues produce relatively uniform charcoal particles. This emphasizes the need for refined morphometric techniques that consider plant tissues as an assemblage of their respective components. Our findings provide a nuanced framework that will improve the accuracy of future charcoal-based paleofire and paleoecology studies, particularly in pre-Holocene contexts, aiding predictions of future ecological dynamics under changing climate conditions.