Late Neogene surge in sedimentary charcoal fluxes partly due to preservation biases, not fire activity

Abstract

Fire has been an important Earth System phenomenon for millions of years and our ability to understand its role in geologic history relies upon robust and unequivocal paleofire archives. Charcoal particles preserved in sedimentary deposits form the primary basis of our understanding of fire's variability on geologic timescales as well as its role in the emergence of plant physiology, ecosystems, and biogeographic configurations. An intriguing aspect of global Cenozoic fire history is the surge in fire activity that is thought to have occurred in the late Neogene (beginning ca. 7 Ma) and indicates that modern biogeography, ecology, and plant physiology was born out of the ashes of an extremely fiery period in Earth's history. The late Neogene fire surge is primarily inferred from charcoal fluxes to sediment records in the North Pacific. In this paper, we revisit these data and show that they are unlikely to reflect an increase in fire activity alone. Rather, these charcoal fluxes likely also reflect an anomalous late Neogene increase in the amount of terrigenous material (and charcoal) supplied to marine sediment records and/or an inflation of late Neogene charcoal flux measurements (and sedimentation rates) resulting from the incompleteness of older stratigraphic sections. These results highlight the importance of accounting for sediment preservation biases when interpreting long term paleoenvironmental records and suggest charcoal fluxes in the North Pacific do not provide conclusive evidence that fire activity increased in the late Neogene.