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

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 (delta H-2 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 H-2 relative to both meteoric water and whole wood. A high correlation (r(2) = 0.91) was observed between the delta H-2 values of the methoxyl groups and meteoric water, with a relatively uniform fractionation of -216 +/- 19 parts per thousand recorded with respect to meteoric water over a range of delta H-2 values from -110 in northern Norway to +20 parts per thousand in Yemen. Thus, woods from northern latitudes can be clearly distinguished from those from tropical regions. By contrast, the delta H-2 values of bulk wood were only relatively poorly correlated (r(2) = 0.47) with those of meteoric water. Measurement of the delta H-2 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.