Abstract

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 skilful. Here, we analyse 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 CO2) and physiological tree responses to increasing atmospheric CO2 concentrations considering a range of published discrimination factors. The calibration of δ13CLM chronologies against instrumental data reveals 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.Sep–Aug = 0.18 (p > 0.05). The new δ13CLM chronologies were finally compared with previously produced δ2HLM values of the same trees to evaluate the additional gain of assessing past climate variability using a dual-isotope approach. Compared to δ13CLM, δ2HLM values correlates substantially stronger with large-scale temperatures averaged over western Europe (rprev.Sep–Aug = 0.69), whereas only weak and mainly insignificant correlations are obtained between precipitation and both isotope chronologies (δ13CLM and δ2HLM values). Our results indicate 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.

Highlights

  • Trees are a powerful archive in global climate research (Esper et al, 2016, 2018; Ljungqvist et al, 2020) as they endure for 30 centuries in widespread temperate climate zones and form yearly growth rings that can be used to analyze factors influencing wood formation (Stoffel and Bollschweiler, 2008)

  • Initial δ13CLM values were corrected for the Suess effect and physiological tree responses to increasing atmospheric CO2 concentrations considering a range of published discrimination factors

  • We found a correlation of r = 0.58 with local ‘shifted’ annual temperatures (Fig. 9), which is slightly higher than the observation of Anhäuser et al (2020)

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Summary

Introduction

Trees are a powerful archive in global climate research (Esper et al, 2016, 2018; Ljungqvist et al, 2020) as they endure for 30 centuries in widespread temperate climate zones and form yearly growth rings that can be used to analyze factors influencing wood formation (Stoffel and Bollschweiler, 2008). In addition Greule et al (2019) and Keppler et al (2007) showed that stable hydrogen and carbon isotope ratios of wood lignin methoxy groups (δ2HLM and δ13CLM values) have great potential to be applied for paleoclimate reconstructions. Most previous methoxy based research have applied δ2HLM values for climate studies (Anhäuser et al, 2017a, 2017b, 2020; Greule et al, 2021; Keppler et al, 2007; Riechelmann et al, 2017; Wang et al, 2020). To evaluate the potential of reconstructing past climate variability using dual-isotope approach, we revisit the δ2HLM values of the same trees provided by Anhäuser et al (2020) These previous data were corrected according to new constraints regarding analytical issues of the isotope measurements of methoxy groups (Greule et al, 2021). The dual isotope methoxy measurements of Hohenpeißenberg tree rings were used to critically evaluate their potential as a 100 proxy for regional to sub-continental scale temperature patterns

Material and Methods
Correction of δ13CLM values for non-climatic environmental factors
Correction of δ2HLM values considering new reference material
Climate data and statistics
Results
Discussion
Climate sensitivity of δ13CLM values
Findings
Conclusion
Full Text
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