Within the EU-Project ISONET (co-ordinator: G. Schleser, http://www.isonet-online.de), 16 partner institutions collaborate to develop the first large-scale network of stable isotopes (C, O and H), integrating 25 European tree sites reaching from the Iberian Peninsula and southern Italy to Fennoscandia. Key species are oak and pine. The sampling design considers not only ecologically "extreme" sites, with a single climate factor predominantly determining tree growth, as required for ring width and wood density analyses (Bräuning and Mantwill 2005, Briffa et al. 2001, 2002, Frank and Esper 2005a, b), but also temperate regions with diffuse climate signals recorded in the 'traditional' tree ring parameters. This may enable expanding climatic reconstructions into regions not yet well covered.
In this project we aim to estimate temperature, humidity and precipitation variations with annual resolution, to reconstruct local to European scale climate variability over the last 400 years. Climate variability is addressed on three timescales, namely decade-century, inter-annual and intra-annual. This strategy allows understanding of both, high frequency (high resolution exploration of seasonality signals, and extreme events) and longer-term trends (source water/air mass dominance, baseline variability) in site specific and synoptic climate across Europe. Here we present results from initial network analyses considering first data of carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes, to evaluate (a) common patterns in these networks and (b) their potential for detailed climate reconstruction beyond the information commonly achieved from ring width and density analyses.