Stable hydrogen isotope ratios of lignin methoxyl groups as a paleoclimate proxy and constraint of the geographical origin of wood.

Summary • Stable isotope ratios of organic compounds are valuable tools for determining the geographical origin, identity, authenticity or history of samples from a vast range of sources such as sediments, plants and animals, including humans. • Hydrogen isotope ratios (δ2H values) of methoxyl groups in lignin from wood of trees grown in different geographical areas were measured using compound-specific pyrolysis isotope ratio mass spectrometry analysis. • Lignin methoxyl groups were depleted in 2H relative to both meteoric water and whole wood. A high correlation (r2 = 0.91) was observed between the δ2H values of the methoxyl groups and meteoric water, with a relatively uniform fractionation of –216 ± 19‰ recorded with respect to meteoric water over a range of δ2H values from –110 in northern Norway to +20‰ in Yemen. Thus, woods from northern latitudes can be clearly distinguished from those from tropical regions. By contrast, the δ2H values of bulk wood were only relatively poorly correlated (r2 = 0.47) with those of meteoric water. • Measurement of the δ2H values of lignin methoxyl groups is potentially a powerful tool that could be of use not only in the constraint of the geographical origin of lignified material but also in paleoclimate, food authenticity and forensic investigations.