The influence of salinity on D/H fractionation in alkenones from saline and hypersaline lakes in continental North America

Abstract

We present a preliminary assessment of the hydrogen isotopic composition of individual alkenones (C37–39 di-, tri- and tetra-unsaturated methyl- and ethyl-ketones) purified from surface lake sediment from sites spanning a range of salinities from 20 to 133ppt. Combining these measurements with measurements of the hydrogen isotopic composition of modern lake water, we estimate the magnitude of D/H fractionation across our sample set and observe reduced sensitivity to salinity compared to observations from Emiliania huxleyi and Gephyrocapsa oceanica. This lends support to the hypothesis that D/H fractionation during biosynthesis is less sensitive to changes in salinity in alkenone producers from continental interior sites than in producers from open marine environments. We also observe stronger correlations between the tetra-unsaturated alkenone δD values with water δD values, and associated α values with salinity than we do for the di- and tri-unsaturated compounds, and suggest that this may result from increased number of lacustrine haptophyte species producing the di- and tri-unsaturated as compared to the tetra-unsaturated.