Postglacial spatiotemporal peatland formation dynamics in Europe and North-America

Peatlands are important ecosystems in the northern hemisphere where they cover vast areas. Their important role in global biogeochemical processes is acknowledged and accordingly increasing interest to understand peatland dynamics - past, modern and future - is rising. However, chronological and geographical data of peatland initiation has been scattered hampering the establishment of a reliable view of postglacial spatial and temporal peatland development patterns. Comprehensive information of initiation dynamics is of importance because of possible links to climate. Essential questions are: shall future climate conditions result in accelerated peatland initiation and what would the geographical pattern be? Here we present, for the first time, a comprehensive broad-scale spatiotemporal account of the initiation and development histories of peatlands in northern Europe and North-America since the last deglaciation. We used a data set of 1400 basal peat ages from 700 peatlands and literature-based sediment type interpretations to investigate peatland formation pathways. Based on the examined data the prevailing conception of relative proportions of different initiation processes (primary mire formation, terrestrialization and paludification) changed. Moreover, the data indicate that in the past all peatland initiation pathways widely co-occurred. In Europe paludification seemed to have a link to Holocene climate variations while in northern America the link could not be depicted. The data however clearly show that later peatland expansion (secondary paludification) that accelerated ca. 5000 years ago in both continents had a strong link to climate. This process strongly contributed to the late Holocene atmospheric methane rise.