Carbon, nitrogen and their stable isotope (δ13C and δ15N) records in two peat deposits of Central Siberia: raised bog of middle taiga and palsa of forest-tundra ecotone

Abstract

The peatlands in the northern hemisphere accumulated substantially more atmospheric carbon (C) during the Holocene than other terrestrial ecosystems. In this study we applied a multi-proxy record to distinguish variations in dynamics of two peatlands in the boreal belt (raised bog) and the forest-tundra ecotone (palsa mire) in Central Siberia. Carbon and nitrogen content in peatland soils and their stable isotope composition δ13C and δ15Μ) were used to trace likely changes of hydrothermal regimes, vegetation shifts and diagenetic alteration of accumulated peat. Several inter-related allogenic and autogenic forcings have influenced the changes in macroelement content and stable isotope composition of peat with depth. In particular, there were climate-induced and succession-driven vegetation community shifts in domination of plants characterized by specific nutrient requirements, nutrient stoichiometry and fractionation of stable isotope values. The climate and permafrost-mediated processes like hummock uplift affected 13C uptake by Sphagnum mosses in wet and dry periods and changing hydrothermal conditions in peat profiles resulted in perturbations of the nitrogen cycle inducing N loss and enrichment 15N abundance, as well as enhanced decomposition was responsible for enrichment of organic matter in the heavier isotopes. These findings confirm the hypothesis that combined use of elemental and stable isotope composition provide meaningful insights in tracing the hydrothermal conditions and the functional state of peatbogs for paleoecological and paleoclimate reconstructions.