Summer moisture balance from peatland water table reconstructions for the last 1100 years from North America and Europe

The last millennium may have been characterized by strong regional variations in precipitation, as evidenced by the megadrought of south west North America during the Medieval Climate Anomaly (MCA), for example. Here we present the first large regional scale peatland hydrology reconstruction for eastern North America and western Europe reflecting warm-season moisture balance for the last 1100 years. We use testate amoebae analysis of forty-three mires distributed over Europe and central and eastern North America to reconstruct changes in water table during the last 1100 years. The chronology of each peat profile was determined individually by radiocarbon and other dating techniques and then reconstructions were combined with all other cores. The regional palaeohydrology reconstructions were assembled using a novel method to include both chronological uncertainties derived from the radiocarbon age-depth model and uncertainties linked to the quantification of the proxies. We present hydrological trends for each region separately and overall with associated uncertainties. We compare these with climate model outputs in the form of soil moisture, warm-season precipitation and reconstructed PDSI from tree rings for Northern America. The hydrological reconstructions suggests that it was relatively dry during the MCA and became wetter during the Little Ice Age (LIA) in both Europe and central-eastern North America. The MCA drying in North America was more extreme and shows greater centennial scale variability than in Europe. LIA wetness was probably more extreme and more hydrologically unstable in Europe. Recent (last 100 years) trends are to drier conditions in both regions and peatlands in Europe are drier than they have been at any time during the last 1100 years.