HR: 08:30h
AN: PP51D-03    [Abstracts]
TI: Towards a paleo-salinity proxy: Decreasing D/H fractionation in algal and bacterial lipids with increasing salinity in Christmas Island saline ponds
AU: * Sachse, D
EM: dsachse@u.washington.edu
AF: University of Washington, School of Oceanography, Box 355351, Seattle, WA 98195-5351, United States
AU: Sachs, J P
EM: jsachs@u.washington.edu
AF: University of Washington, School of Oceanography, Box 355351, Seattle, WA 98195-5351, United States
AB: We investigated the effect of a wide range of salinities (13 -149 PSU) on the D/H ratio of lipids in microbial mat sediments from hypersaline ponds on Christmas Island. The hydrogen isotope ratios (expressed as δD values) of total lipid extracts, and the individual hydrocarbons heptadecane, heptadecene, octadecane, octadecene, diploptene and phytene from algae and bacteria, became increasingly enriched in deuterium as salinity increased, spanning a range of 100‰ while lake water δD values spanned a range of just 12‰. D/H fractionation between lipids and source water thus decreased as salinity increased. Isotope fractionation factors (α_lipid-water) were strongly correlated with salinity and increased in all compound classes studied. The apparent isotope fractionation (ε_lipid-water) decreased by 0.8 to 1.1‰ per PSU increase in salinity. Differences in the hydrogen isotopic composition of lipids derived from three biosynthetic pathways (acetogenic, MVA and DOXP/MEP) remained similar irrespective of the salinity, suggesting that the mechanism responsible for the observed α_lipid-water – salinity relationship originates prior to the last common biosynthetic branching point, the Calvin Cycle. These findings imply that caution must be exercised when attempting to reconstruct source water δD values using lipid δD values from aquatic environments that may have experienced salinity variations of ~3 PSU or more (based on a 1‰ per PSU response of D/H fractionation to salinity changes, and a lipid δD measurement precision of 3‰). On the other hand our results can be used to establish a paleo-salinity proxy based on algal and bacterial lipid δD values if salinity variations exceeded ~3 PSU and/or if additional constraints on source water δD values can be made.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1055 Organic and biogenic geochemistry
DE: 4870 Stable isotopes (0454, 1041)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting