A calibration of hydrogen isotope ratios of sedimentary plant waxes as a proxy for meteoric water in the Arctic

In middle to low latitudes, sedimentary compounds derived from plants are an established proxy for reconstructing precipitation trends through time; in these regions, surveys of the hydrogen isotope ratios (d²H) of sedimentary plant n-alkanes (C29) demonstrate a strong correlation with the d²H of local mean annual precipitation (Sachse et al, 2012). However, systematic examination of this proxy in high latitudes, where extreme climate and light conditions may impact both plant physiology and source water, is limited. Here, we present d²H data of modern sedimentary n-alkanes and n-alkanoic acids from a lake transect extending from northwest to southernmost Greenland. This transect includes 22 lakes and covers a large latitudinal and climatic gradient that spans from 60 to 76°N, and from +1 to -11°C in mean annual air temperature. We discuss evidence for a strong correlation between the d²H values of long-chain (C27, C29) n-alkanes and (C26,28) n-alkanoic acids and those of local summer precipitation. We also discuss significant limitations in applying mid-chain (C21, C23) n-alkanes and (C22, C24) n-alkanoic acids to reconstruct lake water d²H. We find in our dataset that there is no chain length that unambiguously records lake water. Further, we present an updated global synthesis of the hydrogen isotope composition of C28 n-alkanoic acids and C29 n-alkanes with >120 additional lakes, from our data and from the published literature, included in the calibration. We show that the apparent fractionation (e_app) between plant waxes and meteoric water is predictable in the Arctic, and that the average global offset first calibrated to mid-low latitudes of 120 per mil is remarkably consistent globally. We argue that the d²H of sedimentary long-chain n-alkanes is a reliable proxy for growth-season meteoric water d²H in the Arctic, where records of past precipitation are crucial to understanding the hydrologic balance through large past climate shifts.