Influence of vegetation type on n-alkane composition and hydrogen isotope values from a high latitude ombrotrophic bog

摘要

The composition and hydrogen isotope values of leaf wax components can be powerful tools in reconstructing past climate and environments. However, interpretation of past environmental conditions from such components in sediments is complicated by species-specific influences and there is a need to better understand how vegetation type affects leaf wax composition and isotope ratios in modern environments. In this study we analyzed leaf wax (n-alkane) distributions and hydrogen isotope values of plants from a high latitude ombrotrophic bog in northern Norway. The isotopic analysis of surface water was also conducted on samples from 15 lakes along a ca. 150 km transect to contextualize the bog water isotopic composition and constrain fractionation factors among n-alkane homologues. We identified 14 different plant types growing on the bog surface, including mosses, graminoids and other herbs, sub-shrubs and a tree. n-Alkanes from the leaves of the modern plants had average chain lengths from 25 to 30.5, with a variety of distributions, and with the dominant compound of longer chain lengths (C-27, C-29, or C-31). SD values of n-C-25 to n-C-33 for the vegetation samples ranged from -197 parts per thousand, to -116 parts per thousand, with an average of -162 parts per thousand. The data also revealed that the SD values for the homologues for half of the vegetation types had ranges that were = 20 parts per thousand. Using the average isotopic value of bog water samples, -60%, we calculated apparent fractionation factors that ranged from -66 parts per thousand, to -134 parts per thousand (avg. -108 +/- 22 parts per thousand), similar to other sites across Europe and to a global data compilation. Our results demonstrate the range of species-specific influences on leaf wax composition and isotopic values at this site and presumably other ombrotrophic bog environments, and provide a dataset to help evaluate the influence of vegetation type on regional sedimentary leaf wax