Temperature reconstructions for the last 140 years at Hohenpeißenberg using stable isotopes of wood lignin methoxyl groups

• Applicant: Professor Dr. Frank Keppler
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2009 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 148522579

Tree rings are widely used climate archives providing annual resolutions on centennial to millennial timescales. Lignin is a major wood component (up to one third) and contains up to 20% methoxyl groups. Recently it was suggested that these lignin methoxyl groups were an ideal target moiety for the investigation of stable hydrogen isotopes in climate archives such as tree rings. Indeed the stable hydrogen isotope ratio of wood lignin methoxyl groups has been shown to mirror the stable hydrogen isotope ratio of precipitation which is mainly controlled by climatic factors such as temperature. Moreover, we recently investigated stable hydrogen isotopes of lignin methoxyl groups of tree rings from various species collected along a ~3500 km north-south transect across Europe with mean annual temperatures (MAT) ranging from -4 to +17°C. We found a strong linar relationship between the MAT and stable hydrogen isotopes of wood lignin methoxyl groups. We used this relationship to predict MAT from randomly collected wood samples and found general agreement between predicted and observed MATs for the mid-latitudes on a global scale. Thus we suggested that stable hydrogen isotopes of lignin methoxyl groups might be used as a paleothermometer to reconstruct mid-latitude temperatures of the Holocene. However, further calibration studies are now required to more accurately access the influence of temperature on the stable hydrogen isotopes of lignin methoxyl groups for a lower range of MAT. The goal of this project is to reconstruct mean annual temperatures at Hohenpeißenberg (Germany) for the last 140 years using a high resolution stable hydrogen isotope chronology of lignin methoxyl groups in European beech trees (Fagus sylvatica). Hohenpeißenberg is considered an ideal sampling site since nearby is a weather station of the Deutsche Wetterdienst which provides a continuous record of climate data (full record dates back to 1782 AD). Since records began, the mean annual temperatures at Hohenpeißenberg show substantial variations ranging from 4.5 to 8.7°C and also show a significant correlation with stable hydrogen isotope values of precipitation (monitored since 1971). In the proposed project we will investigate trees with a minimum age of 120 to 140 years. We will sample 15 to 20 European beech trees (three cores per tree) and measure the tree ring width (TRW) to validate cross-dating and assess the climate controls of European beech growth in the region. For stable hydrogen isotope measurements three individual European beech trees will be selected to avoid potential site-specific influences. With the obtained samples it should be possible to assess the potential drought (TRW) and temperature influences (stable hydrogen isotopes) on wood formation in the close vicinity of weather station records from southern Germany. Consequently, this study would likely provide a valuable temperature calibration for further applications in the field of paleoclimatology.

• DFG Programme: Research Grants
• Cooperation Partners: Professor Dr. Jan Esper; Dr. Claudia Hartl; Dr. Werner Thomas