Niggemann, Jutta
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Niggemann, Jutta
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Niggemann, Jutta
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Item-typ:Veröffentlichung, Molecular evidence for abiotic sulfurization of dissolved organic matter in marine shallow hydrothermal systems(Elsevier Science, 2016-10-01); ; ; ; Shallow submarine hydrothermal systems are extreme environments with strong redox gradients at the interface of hot, reduced fluids and cold, oxygenated seawater. Hydrothermal fluids are often depleted in sulfate when compared to surrounding seawater and can contain high concentrations of hydrogen sulfide (H2S). It is well known that sulfur in its various oxidation states plays an important role in processing and transformation of organic matter. However, the formation and the reactivity of dissolved organic sulfur (DOS) in the water column at hydrothermal systems are so far not well understood. We investigated DOS dynamics and its relation to the physicochemical environment by studying the molecular composition of dissolved organic matter (DOM) in three contrasting shallow hydrothermal systems off Milos (Eastern Mediterranean), Dominica (Caribbean Sea) and Iceland (North Atlantic). We used ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to characterize the DOM on a molecular level. The molecular information was complemented with general geochemical data, quantitative dissolved organic carbon (DOC) and DOS analyses as well as isotopic measurements (δ2H, δ18O and F14C). In contrast to the predominantly meteoric fluids from Dominica and Iceland, hydrothermal fluids from Milos were mainly fed by recirculating seawater. The hydrothermal fluids from Milos were enriched in H2S and DOS, as indicated by high DOS/DOC ratios and by the fact that >90% of all assigned DOM formulas that were exclusively present in the fluids contained sulfur. In all three systems, DOS from hydrothermal fluids had on average lower O/C ratios (0.26–0.34) than surrounding surface seawater DOS (0.45–0.52), suggesting shallow hydrothermal systems as a source of reduced DOS, which will likely get oxidized upon contact with oxygenated seawater. Evaluation of hypothetical sulfurization reactions suggests DOM reduction and sulfurization during seawater recirculation in Milos seafloor. The four most effective potential sulfurization reactions were those exchanging an O atom by one S atom in the formula or the equivalent + H2S reaction, correspondingly exchanging H2O, H2 and/or O2 by a H2S molecule. Our study reveals novel insights into DOS dynamics in marine hydrothermal environments and provides a conceptual framework for molecular-scale mechanisms in organic sulfur geochemistry.Wissenschaftlicher ArtikelBand:190105 106 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Composition and degradation of organic matter in sediments from the Peru-Chile upwelling region(2005-08-26); ; ; The biogeochemistry of surface sediments from the shelf and continental slope off Peru and Chile was studied in order to characterize factors and processes that control rates and extent of remineralization and burial of organic carbon in marine sediments. Elemental, isotopic, and molecular organic geochemical compositions showed that the sedimentary organic matter was predominantly derived from the highly productive surface waters in this region. Both established and newly evolved quality indicators were applied to assess organic matter freshness. Microbial degradation rates were related to organic matter freshness, providing evidence for a strong control of bioavailability on early diagenetic degradation processes. The presence of individual bacterial species could be traced by the identification of specific biomarker compounds. Abundance and distribution of bacterial cell wall constituents showed that bacteria were an important source of sedimentary organic matter and that remnants of bacteria persist in the sediments after the cell death.Dissertation298 144