δ¹⁸O of tree rings of beech (Fagus silvatica) as a record of δ¹⁸O of the growing season precipitation

Abstract

The measurement of δ¹⁸O in cellulose of tree rings is a potential means to reconstruct δ¹⁸O variations of precipitation and climate. We present δ¹⁸O data from cellulose of 3 beech trees (Fagus silvatica) growing on a relatively dry site in Switzerland where the roots do not have access to ground water, as well as data of 2 other groups of 4 beech trees each, one from a dry site and the other from a semi-dry site, respectively. The measurements cover the time period from 1934 to 1987 in 3-year-groups for the 1st site and 1965 to 1992 with a 1-year resolution for the other 2 sites. We find a high degree of common variance (61%) between the δ18O variations of the 3 trees from the 1st location suggesting a common external cause. The comparison with climate data indicates that spring temperature (April/May/June) is the main influence for the long-term isotope variations, with a temperature coefficient of 0.33‰ per °C, whereas the short-term variations are mainly influenced by the relative humidity, with a coefficient of –0.13‰ per %. This latter value is about ⅓ of the expected model value which points to leaf water pools with different δ¹⁸O values influencing the isotopic composition of synthesised carbohydrates or to oxygen exchange with stem water. Tree ring δ¹⁸O is correlated with δ¹⁸O in precipitation, and the slope of the linear regression for different months most probably yield information about the growth rate function of the particular tree group. Our results confirm the potential of δ¹⁸O measurements in tree ring cellulose for climate reconstruction, in particular information about δ¹⁸O in precipitation can be gained.