Investigation of metal cycling in anoxic marine sediments by the application of stable isotopes

点击翻译按钮获取中文摘要

The goal of the proposed research is to better understand the cycling of iron and manganese in anoxic marine sediments and their relevance in the biogeochemical processing of carbon and sulfur. The main purpose is to explore iron and manganese pathways known under laboratory conditions but little studied in natural marine systems. Stable isotope measurements of molybdenum and iron will be emphasized. A specific objective is to study the reduction of reactive iron phases in the presence of methane-producing microorganisms, and the alteration of reactive manganese in these environments. Because manganese is mono-isotopic, processes leading to its alteration will be investigated by the application of molybdenum isotope techniques. The strong affinity between molybdenum and manganese oxides and associated fractionations are well known. Metal pathways are intimately tied to the cycling of carbon and sulfur. These relationships will also be investigated, inter alia, by the determination of sulfur isotopes on metal sulfides. Carbonate-associated sulfate and its stable isotopes will be analyzed as an integrated measure of the corresponding evolution of the sulfate reservoir during bacterial sulfate reduction. The proposed studies will be carried out on sediments from the Argentine Basin, which due to its dynamic sedimentary conditions, favors the occurrence of reactive metal oxides within methane-bearing sediments. As such, the possibility of anaerobic oxidation of methane tied syntrophically to concomitant reduction of iron, manganese and other oxide-bound metals is very real. To date, this pathway is underexplored, in part due to the limited number of easy accessible marine settings where reactive iron and manganese and abundant methane are juxtaposed in the limited presence or absence of sulfate. The sediments of the Argentine Basin are almost unique in this regard. Additionally, to investigate the importance of these pathways for the deep biosphere, we will compare the results with data of deep subsurface sediments from the Nankai Trough, Japan.