Speaker
Description
Forest fires in the Siberian Arctic get larger, hotter and the fire season gets longer, which raises concerns if these fires might lead to biome shifts from tundra to summergreen or evergreen boreal forest – with consequences for regional to global biophysical land properties and biogeochemical cycles. Given the short time span of instrumental observations, it is unknown if fire can initiate or support biome shifts under the ongoing amplified warming or if climate drives fire regime and biome changes independently. Lake El’gygytgyn in the Russian Far East is currently surrounded by tundra, but for example, during late marine isotope stage (MIS) 12 and “superinterglacial” MIS 11, c. 375-440 kyrs ago, pollen data suggests that biome composition changed several times – from a glacial steppe to interglacial summergreen and evergreen boreal forest. In a DFG project, we investigate fire regime shifts during previous warmer-than-present interglacials, such as MIS 5e, 11c and MIS 101-104, and ask if and which type of fire regime shifts accompanied biome shifts in the East Asian high latitudes.
To enable a quantitative reconstruction of changes in fire intensities and the type of biomass burnt, we analyzed multiple fire proxies. The monosaccharide anhydrides (MAs) are specific biomass burning residues from low-temperature fires analyzed with ultra-high-performance liquid chromatography coupled to a high-resolution mass spectrometer. Sedimentary charcoal reflects mid-to-high intensity fires and was analyzed in sieved fraction > 150 m and from pollen slides using classical microscopy. MA isomer ratios and charcoal morphotypes were used to reconstruct the type of biomass burnt. We analyzed fire proxy amounts and composition and updated existing pollen-based vegetation reconstructions for the early and late Pleistocene using sediments from ICDP sediment core 5011-1 and compare that with fire proxies in modern lake surface sediments from three, modern-analogue lakes in Eastern Siberia.
We find clear differences in sedimentary fire proxy composition over time, with modern compositions depending on source area of charcoals and MAs. Modern fire-vegetation-relationships are linkable to past interglacial proxy relationships indicating that fire regime change played a role during some, but not all biome shifts. More in-depth analyses of the multiple fire proxies with identify the background conditions for that. Overall, this new understanding of Siberian sedimentary fire proxies is crucial for a sound, i.e. quantitative reconstruction of long-term fire regime change, to assess the role of fire regime intensification in biome changes during periods of stark warming.
