Early oceans （〉520 Ma） were characterized by widespread water-column anoxia, stratification, and limited oxidant availability which are comparable to the chemical characteristics of modern marine sedimentary pore-w...Early oceans （〉520 Ma） were characterized by widespread water-column anoxia, stratification, and limited oxidant availability which are comparable to the chemical characteristics of modern marine sedimentary pore-waters in productive continental margins. Based on this similarity and our current understanding of the formation mechanism of early Earth ocean chemistry, we propose an idealized chemical zonation model for early oceans that includes the following redox zones （from shallow nearshore to deep offshore regions）： oxic, nitrogenous （NO3^-NO2^-enriched）, manganous-ferruginous （Mn^2＋ or Fe^2＋-enriched）, sulfidic （H2S-enriched）, methanic （CH4-enriched）, and ferruginous （Fe^2＋-enriched）. These zones were dynamically maintained by a combination of processes including surface-water oxygenation by atmospheric free oxygen, nitrate reduction beneath the chemocline, nearshore manganese-iron reduction, sulfate reduction, methanogenesis, and hydrothennal Fe^2＋ inputs from the deep ocean. Our modified ＂euxinic wedge＂ model expands on previous versions of this model, providing a more complete theoretical framework for the chemical zonation of early Earth oceans that helps to explain observations of unusual Mo-S-C isotope patterns. This model may provide a useful foundation for future studies of ocean chemistry evolution and elemental biogeochemical cycles in early Earth history.展开更多
基金supported by the National Basic Research Program of China(Grant No.2013CB955704)National Natural Science Foundation of China(Grant No.41172030)support from the U.S.National Science Foundation,the NASA Exobiology Program,and the China University of Geosciences(Wuhan)(SKL-GPMR program GPMR201301,and SKL-BGEG program BGL21407)
文摘Early oceans （〉520 Ma） were characterized by widespread water-column anoxia, stratification, and limited oxidant availability which are comparable to the chemical characteristics of modern marine sedimentary pore-waters in productive continental margins. Based on this similarity and our current understanding of the formation mechanism of early Earth ocean chemistry, we propose an idealized chemical zonation model for early oceans that includes the following redox zones （from shallow nearshore to deep offshore regions）： oxic, nitrogenous （NO3^-NO2^-enriched）, manganous-ferruginous （Mn^2＋ or Fe^2＋-enriched）, sulfidic （H2S-enriched）, methanic （CH4-enriched）, and ferruginous （Fe^2＋-enriched）. These zones were dynamically maintained by a combination of processes including surface-water oxygenation by atmospheric free oxygen, nitrate reduction beneath the chemocline, nearshore manganese-iron reduction, sulfate reduction, methanogenesis, and hydrothennal Fe^2＋ inputs from the deep ocean. Our modified ＂euxinic wedge＂ model expands on previous versions of this model, providing a more complete theoretical framework for the chemical zonation of early Earth oceans that helps to explain observations of unusual Mo-S-C isotope patterns. This model may provide a useful foundation for future studies of ocean chemistry evolution and elemental biogeochemical cycles in early Earth history.
