Molecular Distributions and D/H Ratios of Marine Archaea Lipids: Evaluating their Potential as Paleosalinity Proxies

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ABSTRACTOCE-0327347The Archaea constitute a significant portion of pelagic marine microbiota, with members of the Euryarchaeota and Crenarchaeota abundant and widespread in the world's oceans. The membranes of these organisms are composed of ether-linked isoprenoid lipids, which are relatively recalcitrant and therefore well preserved in sedimentary records. Recent investigations of these compounds reveal important environmental information is recorded by their structures and their relative abundances, including surface-water temperatures. Lipid membranes comprise the interface between cellular life and its physical environment, and it is likely that other environmental properties, especially salinity, are associated with changes in the properties of membrane structures. Further, these structures are potentially useful recorders of the hydrogen isotopic composition of water in their growth environment, providing an independent measure of salinity.On this project, researchers at the Pennsylvania State University will evaluate H isotopic fractionation between waters and lipids, as well as lipid structures and their distributions in order to determine relationships between these properties and those of waters in the growth environment. They will survey lipids extracted from suspended particulate matter collected at multiple depths and times from oceanic and coastal waters. They will collect samples from the Chincoteague Bay, a relatively pristine estuary, with waters that range spatially and seasonally from fresh to marine and will also employ samples collected during scheduled cruises to the Black Sea, the Mediterranean and to waters near Bermuda. They have previously collected and archived samples from hypersaline basins in a salt-manufacturing site on the coast of Sicily. The samples studied will range from fresh to hypersaline conditions. Field studies will be complemented by controlled experiments using selected Archaea taxa, grown under a range of temperatures and salinities and using isotopically constrained substrates. The utility of this dual-property approach will be evaluated by analysis of lipids in ODP samples associated with the late-Miocene Messinian Salinity Crisis. A supporting MS thesis project will be developed to investigate the lipid record associated with the marine incursion event in the Black Sea using sediment records from the past 8,000 years