Reconstruction of the natural variability of precipitation in the Netherlands and North Germany for the last 8000 years using ultra-long tree-ring chronologies of oak.

Project outline:The aim of this study is to use the existing ultra-long Europan oak chronologies to derive reconstructions of precipitation for The Netherlands and North Germany on annual to centennial timescales. Until now climate reconstructions almost exclusively concern summer temperature (e.g. Briffa et al. 1995). These are based on pine and larch chronologies from high latitudes, where summer temperature limits tree growth. The Dutch and northern German oak data that will be used, represent both living and subfossil oak from moisture-dominated sites. They are expected to contain a strong precipitation signal, possibly also a temperature signal. The oak chronologies span the time intervals 6069 BC to AD 928 and AD 1850 to present (Leuschner 1992; Jansma 1995; 1996; Jansma unpubl). At present there is a gap in the timeseries, because natural wet forests disappeared after ca. AD 1000 due to increased human activity.The proposed research has four elements: (1) calibration of the relationship between climate and the growth of oak on two low-fenland sites in the Netherlands and on two wet sites in adjacent Germany; vessel area will be included as a new climate-sensitive variable in addition to the classical variable of tree-ring width; (2) extension of the Dutch and German bog-oak chronologies at least into the Upper Midde Ages (AD 1200) by including archaeological/historical time series with a similar signal, which is assumed to be climate related; (3) projection of the models resulting from (1) on the extended chronologies; (4) analyses of the temporal characteristics of precipitation for the last eight millennia on annual to centennial timescales.