DOI: 10.21963/13247
title: Hydrogen isotopes of lignin-methoxy groups from Neogene sub-fossil wood in the Canadian Arctic

description: The purpose of this study was to estimate Miocene and Pliocene climate conditions at Canadian Arctic sites using the stable isotope geochemistry of sub-fossil wood. Specifically, we measured the stable hydrogen isotope composition of lignin-methoxy (d2HLM) from sub-fossil wood specimens preserved in Miocene and Pliocene aged sedimentary deposits at several sites across the Canadian Arctic Archipelago – Banks Island, Prince Patrick Island, Meighen Island, Ellesmere Island and Bylot Island. The d2HLM measurements can be used to estimate the d2H of water (precipitation) used by the trees at the time they were alive. In high latitude regions, the d2H of precipitation is sensitive to air temperature and, therefore, sub-fossil d2HLM values from Miocene-Pliocene aged trees can be used to reconstruct Miocene-Pliocene climate conditions. These sites were targeted because fossil forest beds had been documented here in previous studies. Insights from this research inform our understanding of the Arctic climate system, including its sensitivity to past (and potentially future) changes in land-ocean-atmospheric boundary conditions. Ultimately, such datasets are needed to inform climate models that are being used to predict future changes in the Arctic.
description: Sub-fossil wood samples were obtained from existing sub-fossil wood collections described in previous studies (Csank et al., 2011, 2013; Devaney et al, 1991; Fyles et al., 1990, 1994, 1998; Williams et al., 2008). The number of samples analysed varies depending on site – Banks Island Ballast Brook Formation (n = 10), Banks Island Beaufort Formation (n = 9), Prince Patrick Island (n = 5), Meighen Island (n = 5), Ellesmere Island Fyles Leaf Bed and Beaver Pond (n = 9) and Bylot Island (n = 5). Each sample represents a full or partial cross-section of a tree, with an average of 53 rings per sample. In the lab, a representative sub-sample (integrating all rings) was collected from each of the independent tree samples, and homogenised to a fine powder. The powdered wood was then placed in a crimped vial for chemical reaction with hydroiodic acid, which converts lignin-methoxy groups in the sample to gaseous methyl iodide (CH3I). The ratio of 2H/1H (d2H) of the CH3I gas in the headspace of the vials was measured by Gas Chromatography-Isotope Ratio Mass Spectrometry (GC-IRMS) at the University of Heidelberg in Germany. The d2H measurements were normalised to the Vienna Standard Mean Ocean Water scale and are reported in units of permille. All samples were analysed in quadruplicate and the average measurement precision is less than 2 permille. The site-averaged d2H lignin-methoxy values indicate precipitation d2H values were +33 to +60 permile higher than today, which is explained by a mean climate that was +8.6 to +15.6°C warmer than today assuming the modern d2Hprecip-temperature sensitivity is a reasonable assumption for the past. This research provides new information about the Neogene Arctic climate. These data be used to understand the mean climate sensitivity the Arctic (including slow feedbacks) and help to improve our ability to predict of future climate change at high latitudes. References: [1] Csank et al. 2011. Palaeogeogr. Palaeoclimatol. Palaeoecol. 308, 339–349. [2] Csank et al., 2013. Palaeogeogr. Palaeoclimatol. Palaeoecol. 369, 313–322. [3] Devaney, J., 1991. Arctic 206–216. [4] Fyles, 1990. Arctic. https://doi.org/10.2307/40510962. [5] Fyles et al. 1994. Quat. Int. 22–23, 141–171. [6] Fyles et al. 1998. Geol. Surv. Canada Bull. 512. [7] Williams et al. 2008. Palaeogeogr. Palaeoclimatol. Palaeoecol. 261, 60–176.