Oceanic molybdenum isotope fractionation:: Diagenesis and hydrothermal ridge-flank alteration -: art. no. 1078

[1] Isotopic analyses of dissolved molybdenum are presented for sediment pore waters from a reducing sedimentary basin and for fluids from a low-temperature ridge flank hydrothermal system. delta(98/95)Mo in these fluids range from 0.8 to 3.5parts per thousand (relative to a laboratory standard), demonstrating that marine sedimentary reactions significantly fractionate Mo isotopes. Within the upper 3 cm of sediment, manganese oxide dissolution produces an isotopically light fluid relative to seawater (mean of four analyses = 2.1 +/- 0.1parts per thousand versus seawater = 2.3 +/- 0.1parts per thousand). Below 6 cm depth, authigenic Mo uptake results in an isotopically heavier fluid (up to 3.5parts per thousand) indicating that reducing sediments are likely to be a net sink for isotopically light dissolved Mo. In contrast, fluid circulation within a low-temperature ridge-flank hydrothermal system is a source of isotopically light Mo to the ocean having an end-member fluid of similar to0.8parts per thousand.