Growth phase dependent hydrogen isotopic fractionation in alkenone-producing haptophytes

TitleGrowth phase dependent hydrogen isotopic fractionation in alkenone-producing haptophytes
Publication TypeJournal Article
Year of Publication2009
AuthorsWolhowe MD, Prahl FG, Probert I, Maldonado M
Keywords2009, rcc, RCC1300, SBR$_\textrmP$hyto$_\textrmE$PPO

Recent works have investigated use of the hydrogen isotopic composition Of C-37 alkenones (delta D-K37s), lipid biomarkers of certain haptophyte microalgae, as an independent paleosalinity proxy. We discuss herein the factors impeding the success of such an application and identify the potential alternative use of delta D-K37s measurements as a proxy for non-thermal, physiological stress impacts on the U-37(K') paleotemperature index. Batch-culture experiments with the haptophyte Emiliania huxleyi (CCMP 1742) were conducted to determine the magnitude and variability of the isotopic contrasts between individual C-37 alkenones. Further experiments were conducted with Emiliania huxleyi (CCMP 1742) and Gephyrocapsa oceanica (PZ3-1) to determine whether, and to what extent, delta D-K37s varies between the physiological extremes of nutrient-replete exponential growth and nutrient-depleted senescence. Emiliania huxleyi was observed to exhibit an isotopic contrast between di- and tri-unsaturated C-37 alkenones (alpha(K37:3-K37:2)approximate to 0.97) that is nearly identical to that reported recently by others for environmental samples. Furthermore, this contrast appears to be constant with growth stage. The consistency of the offset across different growth stages suggests that a single, well-defined value for alpha(K37:3-K37:2) may exist and that its use in an isotope mass-balance will allow accurate determination of delta D values for individual alkenones without having to rely on time- and labor-intensive chemical separations. The isotopic fractionation between growth medium and C-37 alkenones was observed to increase dramatically upon the onset of nutrient-depletion-induced senescence, suggesting that delta D-K37s, may serve as an objective tool for recognizing and potentially correcting, at least semi-quantitatively, for the effects of nutrient stress on U-37(K') temperature records.