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Stable hydrogen and carbon isotope ratios of wood lignin methoxy groups (δ13CLM and δ2HLM values) have been shown to be reliable proxies of past temperature variations. Previous studies showed that δ2HLM values even work in temperate environments where classical tree-ring width and maximum latewood density measurements are less successful for climate reconstructions. Here, we analyse the annually resolved δ13CLM values from 1916–2015 of four beech trees (Fagus sylvatica) from a temperate site near Hohenpeißenberg in southern Germany and compare these data with regional- to continental-scale climate observations. Initial δ13CLM values were corrected for the Suess effect (a decrease of δ13C in atmospheric CO 2) and physiological tree responses to increasing atmospheric CO 2 concentrations considering a range of published discrimination factors. The calibration of δ13CLM chronologies against instrumental data reveals the highest correlations with regional summer (r=0.68) and mean annual temperatures (r=0.66), as well as previous-year September to current-year August temperatures (r=0.61), all calculated from 1916–2015 and reaching p<0.001. Additional calibration trials using detrended δ13CLM values and climate data (to constrain effects of autocorrelation on significance levels) returned rsummer=0.46 (p<0.001), rannual=0.25 (p<0.05) and rprev.September-August=0.18 (p>0.05). The new δ13CLM chronologies were finally compared with the previously produced δ2HLM values of the same trees in order to evaluate the additional gain of assessing past climate variability using a dual-isotope approach. Compared to δ13CLM , δ2HLM values correlate substantially more strongly with large-scale temperatures averaged over western Europe (rprev.September-August=0.69), whereas only weak and mainly insignificant correlations are obtained between precipitation and both isotope chronologies (δ13CLM and δ2HLM values). Our results indicate the great potential of using δ13CLM values from temperate environments as a proxy for local temperatures and, in combination with δ2HLM values, to assess regional- to sub-continental scale temperature patterns. [ABSTRACT FROM AUTHOR]

Stable hydrogen isotope values of wood lignin methoxy groups (δ 2H LM) are increasingly applied to reconstruct the stable hydrogen isotope composition of precipitation (δ 2H precip) and mean annual temperatures (MAT) of mid latitudes regions. Recently, the analytical procedure for measuring δ 2H LM values was considerably improved by the availability of new reference materials that are in full accordance with the requirements of normalising stable isotope measurements. Using this improved procedure we determined the δ 2H LM values of tree rings from 40 geographical locations. Using these values, we present a revised relationship between δ 2H LM and δ 2H precip which is: δ 2H precip [mUr] = (δ 2H LM [mUr] + 206 mUr)/0.67. In addition, a new equation for reconstructions of MAT is: MAT [°C] = (δ 2H LM [mUr] + 272 mUr)/3.04 [mUr/°C]. We provide a simple numerical model that explains the observed biosynthetic isotope fraction pattern between δ 2H LM and δ 2H precip. Finally, we applied the new equations to a previous data set for wood samples collected close to the Hohenpeißenberg Meteorological Observatory in Germany. The data set included a 100-year-chronology (1916–2015) from nine tree ring cores removed from four beech trees. The MAT from δ 2H LM values reconstructed for this geographical location was 7.96 ± 2.17 °C and in very good agreement with the observed mean MAT of 7.82 ± 0.75 °C during this time period. Therefore, we conclude that the revised relationships between δ 2H LM , δ 2H precip and MAT provide the basis for reliable application for paleoclimate reconstructions. [Display omitted] • New measurements and evaluation of δ 2H LM values of tree ring data. • Revised relationship between δ 2H LM values and tree source water. • Biosynthetic pathway to explain the isotope fractionation between precipitation and methoxy groups. • Equation for calculation of precipitation: δ 2H Precip [mUr] = (δ 2H LM [mUr] + 205 mUr)/0.67 • Equation for mean annual temperature: MAT [°C] = (δ 2H LM [mUr] + 272 mUr)/3.04 [mUr/°C]. [ABSTRACT FROM AUTHOR]