HR: 14:25h
AN: PP53A-04    [Abstracts]
TI: Growth-Phase Dependence of Hydrogen Isotope Fractionation in Long-Chain Alkenones from Emiliani huxleyi
AU: * Wolhowe, M D
EM: mwolhowe@coas.oregonstate.edu
AF: Oregon State University College of Oceanic and Atmospheric Sciences, COAS Admin #104, Corvallis, OR 97331,
AU: Prahl, F G
EM: fprahl@coas.oregonstate.edu
AF: Oregon State University College of Oceanic and Atmospheric Sciences, COAS Admin #104, Corvallis, OR 97331,
AU: Mix, A C
EM: mix@coas.oregonstate.edu
AF: Oregon State University College of Oceanic and Atmospheric Sciences, COAS Admin #104, Corvallis, OR 97331,
AB: Emiliani huxleyi CCMP1742, a paleoceanographic benchmark strain, was cultured for the purpose of isolating the possible effects of growth phase on water-alkenone hydrogen isotope fractionation. Given molecular evidence that much of the geologic alkenone record derives from stressed, senescent cells (Prahl et al. 2006), cultures were sampled during both the mid-log and senescent phases to bolster previous work investigating fractionation in log-phase samples. Analysis of the δD of extracted C₃₇ alkenones via GC-TC-MS and the δD of the growth media via TCEA-MS is currently taking place. Preliminary results for the fractionation factor of senescent-phase cells (~0.772) agree well with those determined for different strains of E. huxleyi harvested during exponential growth (0.775, Englebrecht and Sachs, 2005) and at a two- to three-fold greater light saturated growth rate (0.779, Schouten et al., 2006). These results are suggestive when considered in light of recent work (D`Andrea et al., 2007) reporting significant isotopic differences between di- and tri-unsaturated C<sub>37</sub> alkenones. Given the large changes in U<sup>K`</sup>₃₇ that occurred in our isothermal (15°C) experiment between log- (~0.50) and senescent-phase (~0.30) growth, the similarity of our results to previous log-phase work may bolster D`Andrea's hypothesis that the isotopic fractionation of combined C<sub>37</sub> alkenones represents an unchanging "weighted average". D`Andrea's preferred hypothesis, that di- and tri-unsaturated C₃₇ alkenones exhibit unchanging, distinct water-alkenone fractionations, would lead us to predict a fractionation factor of 0.783 for the log-phase samples based on U^K`₃₇ measurements. This corresponds to a difference, if δD_water was calculated using alkenone values and the fractionation factor, of approximately ~14‰. The results necessary to compare log- and senescent-phase samples from the same cultures and determine which case appears to be true are now being generated and will be presented.
DE: 0424 Biosignatures and proxies
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 4855 Phytoplankton
DE: 4870 Stable isotopes (0454, 1041)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting