Glacial-to-interglacial fire-vegetation-climate feedbacks during marine isotope stages 11 and 12: a multi-fire proxy study using sediments of Lake El’gygytgyn, NE Siberia

Abstract:

The ongoing spread of forest fires in the Siberian Arctic raises concerns on how far increasing temperatures and fire occurrence lead to biome shifts from tundra to summergreen or evergreen boreal forest. Eastern Siberia displays widespread summergreen boreal forest dominated by larch on permafrost, in contrast to North America. These larch forests show a regime of frequent low-temperature surface fires in contrast to less frequent high-intensity fires in evergreen boreal forest or the scarcity of wildfires in the tundra. A change in biome and fire regime would strongly affect global biogeochemical and biophysical cycles. However, it is unknown which role internal fire-vegetation-climate feedbacks play to dampen or enlarge the ongoing amplified warming.

Here, we investigate vegetation and fire regime shifts during MIS 11 and 12, which was the last period of the Quaternary that showed multiple shifts from a glacial steppe to interglacial summergreen and evergreen boreal forest at Lake El’gygytgyn in the Russian Far East. We analyze multiple fire proxies using ICDP sediment core 5011-1A to enable a quantitative reconstruction of changes in fire intensities and the type of biomass burnt: The monosaccharide anhydrides (MAs) levoglucosan, mannosan and galactosan are specific biomass burning residues from low-temperature fires analyzed using UHPLC coupled to a high-resolution MS. Sedimentary charcoal reflects mid-to-high intensity fires and was analyzed in two size classes using classical microscopy. MA isomer ratios and charcoal morphotypes were used to reconstruct the type of biomass burnt. Together with a new pollen- and non-pollen palynomorph-based vegetation reconstruction, an independent temperature reconstruction based on diatom isotopes and existing lithological proxies, we statistically analyze the links between fire regime properties, vegetation composition, and climate change, independent from local sedimentological changes. We find internal fire-vegetation-climate feedbacks that differ during climatically more stable periods of the cold glacial and the warmer-than-Holocene interglacial compared to the transition period, potentially related to permafrost thaw. To include long-term internal feedbacks is crucial for model predictions of future high northern fire regime shifts.