Climate signals in stable carbon and hydrogen isotopes of lignin methoxy groups: assessing the potential for temperature reconstructions at different spatial and temporal scales

Stable hydrogen and carbon isotope ratios of wood lignin methoxy groups (δ¹³C_LM and δ²H_LM values) have been shown to be reliable proxies of past temperature variability. Recent studies revealed δ²H_LM values even work in temperate environments where classical tree-ring width and maximum latewood density data are less skilful. In this presentation, we report 100 years of annually resolved δ¹³C_LM values of four beech trees (Fagus sylvatica) from a temperate site near Hohenpeißenberg in southern Germany. The series are compared with regional to continental scale climate observations to assess their potential for paleoclimate reconstruction. The δ¹³C_LM values were corrected for both the Suess effect to mitigate the effect of decreasing δ¹³C in atmospheric CO₂ and the physiological tree response to increasing atmospheric CO₂ concentrations using different factors for possible changes in discrimination. The calibration of δ¹³C_LM chronologies against regional instrumental data reveals highest temperature sensitivity with mean summer, annual, and previous-year September to current-year August temperatures.

We additionally compared the new δ¹³C_LM chronology with the previously produced δ²H_LM series of the same trees to evaluate the additional gain of assessing past climate variability using a dual-isotope approach. The δ²H_LM values predominantly reflect large-scale temperatures since highest correlations were found with western European temperatures. Weak and mainly non-significant correlations were found between precipitation and both isotopic chronologies (δ¹³C_LM and δ²H_LM values). Our findings described for the first time the great potential of using δ¹³C_LM values from temperate, low elevation environments as a proxy for local temperatures, whereas the combination of both proxies supports the reconstruction of temperature variations at different spatial and temporal scales.