Hydrogen isotopes in dinosterol from the Chesapeake Bay estuary

The hydrogen isotope ratio of the dinoflagellate sterol dinosterol (4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol) was measured in suspended particles and surface sediments from the Chesapeake Bay estuary in order to evaluate the influence of salinity on hydrogen isotope fractionation. D/H fractionation was found to decrease by 0.99 ± 0.23‰ per unit increase in salinity over the salinity range 10-29 PSU, a similar decrease to that observed in a variety of lipids from hypersaline ponds on Christmas Island (Kiribati). We hypothesize that the hydrogen isotopic response to salinity may result from diminished exchange of water between algal cells and their environment, lower growth rates and/or increased production of osmolytes at high salinities. Regardless of the mechanism, the consistent sign and magnitude of dinosterol δD response to changing salinity should permit qualitative to semi-quantitative reconstructions of past salinities from sedimentary dinosterol δD values.