Browsing by Subject "Euxinia"

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    Characterization of diverse bacteriohopanepolyols in a permanently stratified, hyper-euxinic lake
    (Elsevier, 2022-06) O'Beirne, Molly D.; Sparkes, Robert; Hamilton, Trinity L.; van Dongen, Bart E.; Gilhooly, William P., III; Werne, Josef P.; Earth Science, School of Science
    Bacteriohopanepolyols (BHPs) are a diverse class of bacterial lipids that hold promise as biomarkers of specific microbes, microbial processes, and environmental conditions. BHPs have been characterized in a variety of terrestrial and aquatic environments, but less is known about their distribution and abundance in extreme environmental systems. In the present study, samples taken from the water column and upper sediments of the hyper-euxinic, meromictic Mahoney Lake (Canada) were analyzed for BHPs. Analyses show distinct BHP distributions within the oxic mixolimnion, the chemocline, and the euxinic monimolimnion. Bacteriohopanetetrol (BHT) and unsaturated BHT are the dominant BHPs found in the oxic mixolimnion and at the chemocline, whereas a novel BHP (tentatively identified as diunsaturated aminotriol) dominates the euxinic monimolimnion. Along with the novel BHP structure, composite BHPs (i.e., BHT-cyclitol ether and BHT-glucosamine) were observed in the euxinic monimolimnion and sediments, indicating their production by anaerobic bacteria. Complementary metagenomic analysis of genes involved in BHP biosynthesis (i.e., shc, hpnH, hpnO, hpnP, and hpnR) further revealed that BHPs in Mahoney Lake are most likely produced by bacteria belonging to Deltaproteobacteria, Chloroflexi, Planctomycetia, and Verrucomicrobia. The combined observations of BHP distribution and metagenomic analyses additionally indicate that 2- and 3-methyl BHTs are produced within the euxinic sediments in response to low oxygen and high osmotic concentrations, as opposed to being diagnostic biomarkers of cyanobacteria and aerobic metabolisms.
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    On the Biogeochemistry of Modern Euxinia: From the Origin and Controls of Sulfurization Pathways to Trace Elements as Indicators of Environmental Changes
    (2025-05) Fouskas, Fotios; Gilhooly, William P., III; Druschel, Gregory K.; Macris, Catherine A.; Filippelli, Gabriel
    Euxinic lakes are analogues of the chemical and microbial sulfur (S) cycling that was prevalent in the anoxic conditions of ancient Earth. Mahoney Lake (Canada) and Green Lake (USA) were studied for their sulfate reducing and sulfide oxidizing bacteria that respectively produce high concentrations of sulfide and organic matter (OM) that are preserved as pyrite and organo-sulfur compounds (OSCs) in the sediments. Isotope and elemental proxies were used to evaluate the origin and controls of the sulfurization reactions that drive pyrite and OSCs burial, and the elements that influence localized environmental changes. The wide range in sulfate and sulfide concentrations make the lakes ideal settings for comparing S cycling between a hyper-euxinic (Mahoney) and a moderate (Green) end member of euxinia. The S isotope offset between dissolved sulfate and sulfide is identical (~50‰) showing that sulfate availability did not influence the isotope fractionation. The S isotopes of pyrite and OSCs in Mahoney sediments did not exhibit diagenetic effects observed in other studies. The S isotopes of these two phases are nearly identical, suggesting that pyrite and OSCs are formed within the water column. In contrast, diagenetic reactions preferentially formed pyrite in Green Lake sediments with an average 10‰ S isotope offset from OSCs. Reactive Fe and trace element patterns are consistent with euxinic conditions in both lakes. Redox sensitive trace metals (i.e., Mo) can track temporally and spatially localized changes in redox and broader climatic changes during the Holocene. These climate changes, including tephra from an eruption, might have influenced the variability of OM and ecology in Mahoney Lake. Molecular analysis of Mahoney Lake water showed a diverse stoichiometry of OSCs that suggests the sulfurization rates of iron and OM are competitive. These OM compounds can contribute to rapid rates of OSCs formation. Kinetic modelling supports our hypothesis that high concentrations of reactive OM play a significant role to competitive sulfurization reactions, which subsequently influenced the observed unconventional isotope patterns within the sedimentary record of Mahoney Lake.