D/H ratios of methoxyl groups of the sedimentary organic matter of Lake Holzmaar (Eifel, Germany): A potential palaeoclimate/-hydrology proxy

Stable hydrogen isotope ratios (delta D values) of methoxyl groups in lignin and pectin from a variety of plant types from different locations have been shown to mirror delta D values of precipitation, with a mean uniform isotopic fractionation. Since delta D in precipitation is mainly influenced by climatic conditions, including temperature, evaporation and precipitation amount, methoxyl groups of organic matter have been proposed as a potential palaeoclimate proxy. Here, we measured the delta D values of the methoxyl groups of sedimentary organic matter derived from sediment core segments of Lake Holzmaar (Eifel, Germany). The sediment core covers the entire Holocene and part of the Late Glacial (until 13,650 years BP). Since the sedimentary organic matter was indicated by organic source proxies of predominantly phytoplanktonic origin, we considered the delta D values of the methoxyl groups as a proxy for the delta D value of the lake water. Presently and probably during most of the Holocene, the delta D value of precipitation was primarily controlled by temperature (2-4.5 parts per thousand/degrees C) as well as in isotopic equilibrium with the delta D value of the lake water. We used these modern temperature sensitivities of the Eifel region together with the measured delta D values of the methoxyl groups of the sedimentary organic matter to evaluate temperature changes recorded for the Holocene. The resulting mean temperature variance was found to be consistently less than 1.8-4 degrees C and is broadly in line with that reported from the NGRIP ice core for the same period. The transition from the Holocene to the Late Glacial period was accompanied with more negative delta D values of the methoxyl groups (similar to 13 parts per thousand/for the Younger Dryas). Besides the association with temperature we assumed a higher susceptibility of the delta D value of Lake Holzmaar to evaporative enrichment during the Younger Dryas which could serve as an explanation for discrepancies reported for existing palaeoclimate/-hydrology records of the Eifel region. Our findings indicate that the delta D values of methoxyl groups have great potential for assisting with palaeoclimate and palaeohydrology, particularly when the organic matter is well characterized and of uniform origin. (C) 2014 Elsevier Ltd. All rights reserved

Mean annual temperatures of mid-latitude regions derived from δ² H values of wood lignin methoxyl groups and its implications for paleoclimate studies

Tree-rings are widely used climate archives providing annual resolutions on centennial to millennial timescales. Stable isotope ratios of tree-rings have been applied to assist with the delineation of climate parameters such as temperature and precipitation. Here, we investigated stable hydrogen isotope ratios (expressed as δ2H values) of lignin methoxyl groups of wood from various tree 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 linear relationship between MATs and δ2H values of wood lignin methoxyl groups. We used this relationship to predict MATs from randomly collected wood samples and found general agreement between predicted and observed MATs for the mid-latitudes on a global scale. Our results are discussed in context of their paleoclimate relevance and suggest that δ2H values of lignin methoxyl groups might have the potential to reconstruct MATs when applied on mid-latitudinal tree-ring chronologies of the Late Holocene

Warm season precipitation signal in δ2H values of wood lignin methoxyl groups from high elevation larch trees in Switzerland

Rationale In this study, we tested stable hydrogen isotope ratios of wood lignin methoxyl groups (δ2Hmethoxyl values) as a palaeoclimate proxy in dendrochronology. This is a quite new method in the field of dendrochronology and the sample preparation is much simpler than the methods used before to measure δ2H values from wood. Methods We measured δ2Hmethoxyl values in high elevation larch trees (Larix decidua Mill.) from Simplon Valley (southern Switzerland). Thirty-seven larch trees were sampled and five individuals analysed for their δ2Hmethoxyl values at annual (1971–2009) and pentadal resolution (1746–2009). The δ2Hmethoxyl values were measured as CH3I released upon treatment of the dried wood samples with hydroiodic acid. 10–90 μL from the head-space were injected into the gas chromatography/high-temperature conversion/isotope ratio mass spectrometry (GC/HTC-IRMS) system. Results Testing the climate response of the δ2Hmethoxyl values, the annually resolved series show a positive correlation of r = 0.60 with June/July precipitation. The pentadally resolved δ2Hmethoxyl series do not show any significant correlation to climate parameters. Conclusions Increased precipitation during June and July, which are on average warm and relatively dry months, results in higher δ2H values of the xylem water and, therefore, higher δ2H values in the lignin methoxyl groups. Therefore, we suggest that δ2Hmethoxyl values of high elevation larch trees might serve as a summer precipitation proxy

Perfluorinated Acenes Crystalline Phases, Polymorph Selective Growth, and Optoelectronic Properties

The emerging field of organic electronics triggers the search for new molecular semiconductors and fluorophores. Since optoelectronic properties of molecular solids also depend crucially on molecular packing motifs, it is not sufficient to only consider single-molecule properties, but also to gain precise knowledge of the crystalline phases to understand structure–property relationships. Here, we analyze and compare structural and optoelectronic properties of perfluorinated acenes ranging from perfluoro­naphthalene (PFN) via perfluoro­anthracene (PFA) and perfluoro­tetracene (PFT) to perfluoro­pentacene (PFP), while previous studies, due to the lack of availability of PFA and PFT, were limited to PFN and PFP, which exhibit rather different crystal structures. Applying various crystallization techniques such as gradient sublimation, solution growth, and liquid-assisted organic molecular beam deposition, we identified different crystalline phases that allow closing this structural gap. A comparison of all known phases reveals clear trends in the molecular packing motifs, which are rationalized by corresponding Hirshfeld analyses. Using UV/vis and X-ray absorption spectroscopy, also optoelectronic solid state properties of the various compounds were analyzed, and from a comparison with the corresponding solution spectra, the exciton binding energies are estimated. In addition, we demonstrate that like PFP PFT also exhibits a π-stacked polymorph in films grown on graphene, where molecules are flat lying and adopt a slip-stacked packing. This interface-mediated phase is found to be stable only for PFP and PFT, while it is unstable for the smaller PFA. Finally, we demonstrate for the case of PFT that the different packing motifs occurring in the various phases have a strong influence on the photoluminescence spectra