Linked fire activity and climate whiplash in California during the early Holocene

Recent wildfire activity in semi-arid regions like western North America
exceeds the range of historical records. High-resolution paleoclimate archives
such as stalagmites could illuminate the link between hydroclimate, vegetation
change, and fire activity in pre-anthropogenic climate states beyond the
timescale of existing tree-ring records. Here we present an analysis of levoglucosan,
a combustion-sensitive anhydrosugar, and lignin oxidation products
(LOPs) in a stalagmite, reconstructing fire activity and vegetation composition
in the California Coast Range across the 8.2 kyr event. Elevated levoglucosan
concentrations suggest increased fire activity while altered LOP compositions
indicate a shift toward more woody vegetation during the event. These
changes are concurrent with increased hydroclimate volatility as shown by
carbon and calcium isotope proxies. Together, these records suggest that
climate whiplash (oscillations between extreme wetness and aridity) and fire
activity in California, both projected to increase with anthropogenic climate
change, were tightly coupled during the early Holocene.