2000 years of variability in hydroclimate and carbon accumulation in western Siberia and the relationship with large-scale atmospheric circulation : a multi-proxy peat record

The climate of Siberia is primarily influenced by the Siberian High (SH), although other large-scale atmospheric circulation systems, in particular North Atlantic Oscillation (NAO) storm tracks, play an important role. How variability in the relative strength and trajectory of these climatic systems has affected local to regional palaeoclimatic conditions remains little known. Here, we employ multi-proxy peat core analysis (δ13C, δ15N in Sphagnum, plant macrofossil, pollen, charcoal) from Plotnikovo Mire, part of the Great Vasyugan Mire in western Siberia (Tomsk province, Russia). We provide a high-resolution record of variations in climatic conditions and the biogeochemical fluxes of carbon and nitrogen over the past 2000 years and then discus the link between local climatic conditions and larger scale atmospheric circulation patterns. Our record shows that generally warm and dry conditions prevailed from BC 500 to 500 CE. Warm and wet episodes occurred during the early (800–950 CE) and later (1150–1300 CE) part of the Mediaeval Climate Anomaly (MCA), and were interrupted by a warm and dry mid-MCA phase (1000–1200 CE). Progressively cooler and wetter conditions established from 1400 CE, which became most marked between 1600 and 1850 CE, coincident with the Little Ice Age (LIA). Finally, drying of the mire surface reflects the warming trend of recent decades. We found that C accumulation was greater (90 g C m−2 yr−1) at times of wetter conditions and when Sphagnum was dominant, and lowest (35 g C m−2 yr−1) during periods of mixed vascular plant growth and Sphagnum under drier/unstable hydrological conditions. This peatland has been an active C sink over the past 1500 years, however, its ability to sequester carbon has decreased with recent warming and may continue to decrease with ongoing climatic warming and drying. We hypothesise that generally warm and moist conditions at the study site and over wider Siberia during the MCA could have been linked to a weakening of the Siberian High, which in turn enhanced the ingress of Atlantic moisture-carrying air masses across Siberia. Conversely, a strengthened SH overlapping negative North Atlantic Oscillation (NAO) modes during the LIA, resulted in a longer cold season with a delayed snowmelt and diminished evapotranspiration. This study shows that the interplay of moisture bearing air masses from different origins led to complex local hydroclimate and biogeochemical patterns. However, to resolve the spatio-temporal coherency of such climate variability due to the interaction of different air masses, and therefore better predict future climate changes, a denser network of palaeo-records is needed