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

The hydrogen isotopic composition of terrestrial plant waxes (delta H-2(wax)) is widely used to reconstruct past hydroclimate. delta H-2(wax) values reflect plant source water or precipitation delta H-2 (delta H-2(precip)) values, and when extracted from sediment archives, records of past delta H-2(precip) values can be generated. In order to better interpret these delta H-2(wax) 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 delta 2Hwax values and source water delta H-2 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 delta 2Hwax values on the Falkland Islands by analyzing n-alkane plant wax concentrations, delta H-2 and delta C-13 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 delta H-2(wax) and delta H-2(precip) values ((EHwax/precip)-H-2) for all plant species to be -110 +/- 17 parts per thousand (1 sigma, n = 22), which is similar to the global average (EHwax/precip)-H-2. Observed and modelled monthly delta H-2(precip) values indicate that delta H-2(wax) values can be interpreted as mean annual delta H-2(precip) values, ultimately establishing the framework for utilizing plant wax-based paleoreconstructions from the mid-latitude maritime climatic regions.

Automated summary

The hydrogen isotope composition of terrestrial plant waxes (delta H-2(wax)) is widely used to reconstruct past hydroclimate. By analyzing 11 common plant species on the Falkland Islands, it was found that the most commonly observed plants, Empetrum rubrum and Cortaderia pilosa, contribute the most to the waxes in sediment archives. The fractionation between n-C29 alkane delta H-2(wax) and delta H-2(precip) values was calculated to be similar to the global average, indicating that delta H-2(wax) values can be interpreted as mean annual delta H-2(precip) values in plant wax-based paleoreconstructions.