Hydrogen and carbon isotope fractionation in modern plant wax n-alkanes from the Falkland Islands

Abstract

The hydrogen isotopic composition of terrestrial plant waxes (δ2Hwax) is widely used to reconstruct past hydroclimate. δ2Hwax values reflect plant source water or precipitation δ2H (δ2Hprecip) values, and when extracted from sediment archives, records of past δ2Hprecip values can be generated. In order to better interpret these δ2Hwax records, modern calibrations between plant waxes and source water are required when vegetation and location diverge from plant calibrations in other regions. To date, no modern study has examined how δ2Hwax values and source water δ2H values relate in the southern mid- and high-latitude maritime climatic regions where the climate is affected by the Southern Hemisphere Westerly Wind Belt. We present the first modern calibration of δ2Hwax values on the Falkland Islands by analyzing n-alkane plant wax concentrations, δ2H and δ13C values from 11 of the most common plant species, one lichen species, and surface lake sediment samples from four sites on Mount Usborne on East Falkland. Based on plant wax concentrations, the most commonly observed plants on the landscape, Empetrum rubrum and Cortaderia pilosa, are contributing the most to the waxes in sediment archives. We calculate the fractionation between the n-C29 alkane δ2Hwax and δ2Hprecip values (ε2Hwax/precip) for all plant species to be –110 ± 17‰ (1σ, n = 22), which is similar to the global average ε2Hwax/precip. Observed and modelled monthly δ2Hprecip values indicate that δ2Hwax values can be interpreted as mean annual δ2Hprecip values, ultimately establishing the framework for utilizing plant wax-based paleoreconstructions from the mid-latitude maritime climatic regions.