Climate signals in stable carbon and hydrogen isotopes of lignin methoxy groups: assessing the potential for temperature reconstructions at different spatial and temporal scales
Authors: Wieland Anna , Greule Markus , Roemer Philipp , Esper Jan , Keppler Frank 
Published: March 2022

&lt;p&gt;Stable hydrogen and carbon isotope ratios of wood lignin methoxy groups (&lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;LM&lt;/sub&gt; and &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt;H&lt;sub&gt;LM&lt;/sub&gt; values) have been shown to be reliable proxies of past temperature variability. Recent studies revealed &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt;H&lt;sub&gt;LM&lt;/sub&gt; 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 &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;LM&lt;/sub&gt; values of four beech trees (&lt;em&gt;Fagus sylvatica&lt;/em&gt;) from a temperate site near Hohenpei&amp;#223;enberg in southern Germany. The series are compared with regional to continental scale climate observations to assess their potential for paleoclimate reconstruction. The &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;LM&lt;/sub&gt; values were corrected for both the Suess effect to mitigate the effect of decreasing &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C in atmospheric CO&lt;sub&gt;2&lt;/sub&gt; and the physiological tree response to increasing atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentrations using different factors for possible changes in discrimination. The calibration of &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;LM&lt;/sub&gt; chronologies against regional instrumental data reveals highest temperature sensitivity with mean summer, annual, and previous-year September to current-year August temperatures.&lt;/p&gt;&lt;p&gt;We additionally compared the new &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;LM&lt;/sub&gt; chronology with the previously produced &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt;H&lt;sub&gt;LM&lt;/sub&gt; series of the same trees to evaluate the additional gain of assessing past climate variability using a dual-isotope approach. The &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt;H&lt;sub&gt;LM&lt;/sub&gt; 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 (&lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;LM&lt;/sub&gt; and &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt;H&lt;sub&gt;LM&lt;/sub&gt; values). Our findings described for the first time the great potential of using &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;LM&lt;/sub&gt; 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.&lt;/p&gt;