Measurements and applications of δ2H values of wood lignin methoxy groups for paleoclimatic studies

Abstract

Stable hydrogen isotope values of wood lignin methoxy groups (δ2HLM) are increasingly applied to reconstruct the stable hydrogen isotope composition of precipitation (δ2Hprecip) and mean annual temperatures (MAT) of mid latitudes regions. Recently, the analytical procedure for measuring δ2HLM 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 δ2HLM values of tree rings from 40 geographical locations. Using these values, we present a revised relationship between δ2HLM and δ2Hprecip which is: δ2Hprecip [mUr] = (δ2HLM [mUr] + 206 mUr)/0.67. In addition, a new equation for reconstructions of MAT is: MAT [°C] = (δ2HLM [mUr] + 272 mUr)/3.04 [mUr/°C]. We provide a simple numerical model that explains the observed biosynthetic isotope fraction pattern between δ2HLM and δ2Hprecip. 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 δ2HLM 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 δ2HLM, δ2Hprecip and MAT provide the basis for reliable application for paleoclimate reconstructions.