Late Neogene leaf wax and polycyclic aromatic hydrocarbon records from Lake Baikal, Russia

In the arctic and subarctic, increasingly large and frequent fires because of 21st century warming and drying have been modeled to drive a widespread shift from boreal forest ecosystems to steppe grasslands and broadleaf deciduous forests by the end of this century. This shift can transition boreal forests from net sinks to net sources of atmospheric CO2 by direct burning emissions, enhanced respiration of soil carbon, and drastically accelerated permafrost melt. The global transition of boreal forests to grasslands driven by these frequent fires would likely further enhance boreal burning due to the inherently high flammability of grassland ecosystems. However, the nature and extent of the modeled hydroclimate, ecosystem, and fire regime changes remain uncertain.

The deep drillcore from Lake Baikal covering the past 8.4 Ma provides a unique opportunity to study the geologic history of terrestrial climate and ecosystem change as an analogue and comparison to future climate change for boreal regions. In the Baikal region, modeled end of the 21st century and mid-Pliocene precipitation and temperature change are remarkably similar, providing a geologic analogue for future warming. The late Miocene is a more extreme analogue, likely comparable to additional warming in the coming centuries. Here, we present preliminary n-alkane and PAH distribution data from the 8.4 - 4.2 Ma interval of the drill core. The data indicate that the n-alkanes and PAHs from the Baikal drillcore have been minimally influenced by diagenesis or thermally mature organic matter and are primarily sourced from biological (alkanes) and pyrogenic (PAHs) sources. The n-alkane data reveal a long-term shift from dominance of the nC29 to the nC27 alkane beginning ca. 6 Ma, which may indicate an increasing proportion of alkanes contributed by leaf waxes from conifers. Meanwhile, a decreasing trend in the retene / 3-ring PAH index suggests a shift away from conifer burning.