The barite-opal-organic carbon association in oceanic particulate matter

Abstract

Barite particles 0.5–5 μm in size are ubiquitous in the ocean and their formation, sinking and dissolution is a major part of the marine barium cycle^1,2. Barite formation appears to be caused by biological activity in the upper water column, but the exact mechanism is unknown. Analysis of 1–53 μm and >53 μm sized particles obtained by large volume in situ filtration in the Atlantic suggests that barites are formed in the >53 fxm fraction in near-surface waters and released into the 1–53 μm fraction at depths below the euphotic zone. Scanning electron microscopy and energy dispersive X-ray fluorescence analysis of both size fractions shows first, that barites are formed almost exclusively in microenvironments containing decaying organic matter and the remains of siliceous plankton, and second that barites do not appear to be actively formed by the planktonic organism sampled. This explains the origin of suspended barite, and the similarity of dissolved Si and Ba distributions in the ocean. Suspended and sedimented barite may indicate the intensity of organic matter regeneration in the water column.