Barium Geochemical Cycle in the Ocean

Fluid Inclusion Studies of Barite Disseminated in Hydrothermal Sediments of the Mohns Ridge

“…Barite is one of the most abundant authigenic minerals in deep ocean sediments [1] and one of a few authigenic minerals that may form in the water column during the microbial oxidation of sinking organic matter (e.g., [2,3]). Two main genetic types of barite form in the marine realm: (i) sedimentary barite-particulate crystals formed usually due to passive biogeochemical precipitation in seawater (pelagic barite) and more rarely through an active biological pathway by several planktonic organisms (biogenic barite) [4]; and (ii) diagenetic or fluid-related barite formed via diagenetic processes with the participation of pore water of sediments or reduced fluids of cold seeps and hydrothermal vents [1,5,6]. The diagenetic type, in our view, includes barites formed from the reduced solutions during their mixing with the oxidized ocean water.…”

“…Recent studies [11][12][13] indicated that barite in hydrothermal systems did not necessarily precipitate from a mixture of ambient seawater and a hydrothermal fluid, and microbial sulfate reduction is also taking place in hydrothermal environments. Hydrothermal barite crystals are also larger in size (~10-700 µm) and are typically precipitated as cross-cutting tabular crystals commonly forming rosettes (roses, druses, brooms, and others) [5,6]. One can also see barite intergrowths as compact plates, granular aggregates, and zoned nodules.…”

“…Hydrothermal barite is characterized by the Sr isotope ( 87 Sr/ 86 Sr) ratio, which often occupies an intermediate position between the modern value in seawater and the isotopic composition in pure hydrothermal fluids [15]. Furthermore, the precipitation of barite at the hydrothermal vent fields is confined to the redox barrier and related to a formation mechanism similar to that of the diagenetic pathway [6].…”