Multiproxy Records of Holocene Peatland Dynamics in Finland and European Russia

Northern (mid to high latitude) peatlands contain 90% of the global peatland carbon stock, yet the persistence of their carbon sequestration is uncertain in the face of a rapidly changing climate. Rising atmospheric temperatures and shifting precipitation patterns threaten to deepen peatland water tables, exposing peatland organic matter to prolonged oxygenation, increased microbial decomposition, and greater fire risk. Yet, alleviations of limitations on ecosystem productivity may increase peatland accumulation in the colder high latitudes and propel the northwards expansion of Sphagnum. In boreal northeastern Europe, Finland and European Russia contain vast peatland expanses, but questions remain concerning their long-term dynamics in response to climate. This is particularly true for European Russia, which remains severely understudied for multiproxy, palaeoecological investigations. However, gaps in our knowledge still remain for peatlands in Finland, particularly concerning their sensitivity to past climates and their long-term fire dynamics. This study aims to rectify these knowledge gaps through a multiproxy, palaeoecological approach that investigates three representative mire types for the boreal region; a high latitude fen (Apatity) on the Kola peninsula, a continental raised bog (Koporskiy Mokh) in European Russia, and a southern boreal bog (Kaurastensuo) in southern Finland. To achieve this, a suite of established (plant macrofossils, testate amoebae, pollen, Cladocera, charcoal, decomposition indices) and emergent (Raman spectroscopy, testate amoebae functional traits) palaeoecological techniques were combined with well-resolved, 14C-derived Bayesian age-depth models.The high-latitude fen record from Apatity showed greatly reduced carbon sequestration in colder regional climate periods, with a transition to Sphagnum dominance over recent centuries promoting rapid peat accumulation. Novel applications of Raman spectroscopy in tandem with multiproxy records revealed the severe impact of fire on continental bogs at Koporskiy Mokh, resulting in greatly reduced carbon stocks over an 8000-year period through persistence of a bog pool. Hydrological reconstructions at Kaurastensuo displayed clear identification of a solar forcing-induced prolonged and pronounced wet shift at 2.8 cal. yr. BP, mirroring records from northwestern Europe. In this true raised bog, any deviations to surface-level water tables, or towards slight drying, both appear to exhibit clear reductions in rates of carbon sequestration. These results suggest support for an increased high-latitude carbon sink with warming, but provide concern for the impact of deepening water tables on southern boreal bogs, and for heightened fire risk in the more continental peatlands of European Russia.