The influence of salinity on D/H fractionation in dinosterol and brassicasterol from globally distributed saline and hypersaline lakes

Abstract

Salinity, growth rate, growth stage, nutrient limitation and temperature have all been shown to influence the magnitude of D/H fractionation in algal lipids through laboratory and field studies. Of these factors, salinity has been studied most extensively in the field, but to date all such investigations have focused on transect studies within specific and isolated environments. Here we test the relationship between salinity and the magnitude of D/H fractionation in algal lipids through paired analyses of sedimentary and particulate lipid and water hydrogen isotope values at a wide range of continental and coastal lake sites spanning salinities from 0 to 117ppt. Our results demonstrate broad consistency between D/H fractionations in dinosterol and brassicasterol with those obtained from previous work, with salinity changes of 1ppt resulting in lipid δD changes of 0.7–1‰. Although our results also show variability in D/H fractionation between sites that is not related to salinity, the fact that any relationship emerges above the influences of other factors suggests that the salinity effect is dominant for some lipids in the majority of saline to hypersaline environments. This improved understanding of D/H fractionation in dinosterol and brassicasterol synthesis supports the use of these compounds as paleohydrologic indicators. When combined with D/H measurements from a second lipid or oxygen isotope measurements from carbonate, quantitative reconstructions of salinity and lake water isotope changes are possible. Extending the number of algal lipids within which a consistent relationship between D/H fractionation and salinity has been identified also supports the notion that the relationship is widespread among unicellular photoautotrophs.