Over the last three years, 16 European isotope labs collaborated in the EU project ISONET (co-ordinator: G. Schleser, http//www.isonet-online.de) on developing the first large-scale δ¹³C, δ¹⁸O δ²H in from oak, pine and cedar tree-rings, covering sites from Fennoscandia to the Mediterranean region. The sampling design considered not only ecologically "extreme" sites, with a single climate factor predominantly determining tree growth, as required for ring width and wood density analyses (Bräuning & Mantwill 2005, Briffa et al. 2001, 2002, Frank & Esper 2005a, b), but also temperate regions with diffuse climate signals recorded in the 'traditional' tree ring parameters. This strategy, however, may enable expanding climatic reconstructions into regions not yet well covered. As reported earlier (Treydte et al. 2005), the aim is 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 intra-annual to century timescales. This strategy should allow understanding both, high frequency variations including the exploration of seasonality signals and extreme events, and longer-term trends including source water/air mass changes and baseline variability across Europe.
Here we present first climate calibration results for the 20^th century, using δ¹³C and δ¹⁸C data from up to 25 sites currently available in the network. We discuss (i) relationships of each parameter to summer conditions expressed by maximum temperatures, precipitation and drought, (ii) strength of the climate signal within the networks and (iii) similarities/differences of climate response between the networks. Finally we provide some ideas for further investigations of this unique dataset to fully exploit its potential for detailed European climate reconstruction beyond the information commonly achieved from ring width and density analyses.