Calibration of modern sedimentary δ2H plant wax-water relationships in Greenland lakes

Sedimentary plant wax distributions and isotopic compositions are powerful, widely applied paleoenvironmental proxies. However, there is conflicting evidence on the behavior of these proxies at high latitude sites, where extreme climate and light conditions may uniquely influence plant physiology and growth. Here, we present modern sedimentary n-alkane and n-alkanoic acid abundances and compound-specific (delta H-2 and delta C-13) isotope values from a 22-lake transect extending from northwest to southernmost Greenland, covering a large latitudinal and climatic gradient. Sedimentary plant waxes are similar in abundance and carbon isotopic composition across the transect, suggesting no major differences in biologic sources. There are strong correlations (r = 0.8-0.9) between delta H-2 values of many long-chain sedimentary waxes and those of modelled precipitation, with n-alkanes more tightly correlated to precipitation than n-alkanoic acids. Data presented here also demonstrate that delta H-2 values of mid-chain sedimentary waxes do not strongly correlate to the delta H-2 values of lake water when it decouples isotopically from precipitation (i.e. in glacier-fed and evaporatively-enriched lakes). This calls into question the common interpretation that mid-chain sedimentary waxes can be ascribed to aquatic plants. We contextualize our Greenland data with an updated global dataset of delta H-2 values of modern sedimentary waxes and precipitation. This update adds 100 + lakes from recently published literature to the seminal review presented by Sachse et al. (2012). This large new compilation suggests a global average apparent fractionation including Arctic data between n-C-28 alkanoic acids and annual precipitation (epsilon(C28/ANN)) of -99 parts per thousand, and between n-C-29 alkanes and annual precipitation (epsilon(C29/ANN)) of -121 parts per thousand. The latter value is remarkably consistent with the value first reported by Sachse et al. (2012). (C) 2019 Elsevier Ltd. All rights reserved.