HR: 0800h
AN: B21D-0906    [Abstracts]
TI: Hydrogen Isotope Fractation Between Water and Algal Lipids of Three Strains of {\it Botryococcus braunii} Under Controlled Conidtions
AU: * Zhang, Z
EM: zhaohui@mit.edu
AF: Dept. of Earth, Atmospheric and Planetary Sciences, MIT, E34-166, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Sachs, J P
EM: jsachs@mit.edu
AF: Dept. of Earth, Atmospheric and Planetary Sciences, MIT, E34-166, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AB: Understanding of precipitation anomaly variations is essential to the reconstruction of paleo-El Nino at the low latitudes. In enclosed lakes, where lake level is affected by the balance between precipitation and evaporation only, water $\delta$D reflects precipitation patterns. Freshwater algae, which utilize lake water for photosynthesis, should incorporate such signal in the hydrogen isotopes of their tissues. However, a fundamental question still exits: do algal lipid biomarkers truly record lake water hydrogen isotopic ratios? We have measured hydrogen isotope fractionation by freshwater algae Botryococcus braunii (3 strains) grown under controlled conditions in the lab. In order to establish a good relationship between lipid $\delta$D and water $\delta$D, for each strain we set up cultures in five waters with different $\delta$D. $\delta$D of alkadienes and botryococcenes of Botryococcus brauni measured on GCIRMS showed strong positive linear relation with water $\delta$D (R$^{2}$=0.99). Hydrogen isotopic ratios in the algal hydrocarbons are about 165 $\permil$ more negative compared to the water at the start while they are 270 $\permil$ more negative compared to water $\delta$D at harvest. Such linear relationships establish a foundation for reconstructing lake water level and thus precipitation anomaly by analyzing $\delta$D of algal lipids preserved in lake sediments.
DE: 9810 New fields (not classifiable under other headings)
DE: 4840 Microbiology
DE: 4870 Stable isotopes
DE: 1055 Organic geochemistry
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting