Barium accumulation in the Arabian Sea: Controls on barite preservation inmarine sediments

In this study, a new sequential extraction technique is used to investigate the particulate barium (Ba) phases in sediments from the Arabian Sea to de termine the processes controlling Ba accumulation in marine sediments, The total solid-phase Ba concentration in Arabian Sea surface sediments: increa ses with water depth from similar to 200 ppm at 500 meters below sea surfac e (mbss) to similar to 1000 ppm at 3000 mbss. The sedimentary Ba compositio n consists of three major fractions barite, Ba incorporated in aluminosilic ates, and Ba associated with Mn/Fe oxides. Accumulation of barite, which is the most important Ba fraction in sediments located below 2000 mbss, incre ases gradually with watts depth. The Ba/Al ratio of the terrigenous Fractio n varies significantly across the Arabian Basin as the result of difference s in grain size and provenance of the terrigenous sediment. Ba associated w ith Mn oxides is a relatively minor fraction compared with bulk Ba concentr ations, and it only accumulates in well-oxygenated sediments below the pres ent-day oxygen minimum zone. The water-depth-dependent accumulation of bari te in the Arabian Sea is not related to the continuous formation of barite in settling organic particles or Ba scavenging by Mn oxyhydroxides but is p rimarily controlled by differences in Ba preservation upon deposition. A go od correlation between the barite saturation index and the barite accumulat ion rate in the upper 2000 m of the water column may indicate that the degr ee of barite saturation of the bottom water is the main environmental facto r regulating the burial efficiency of barite. Organic matter degradation, b ioturbation, diagenetic Mn cycling, and the crystallinity of the accumulati ng barite may play additional roles. Copyright (C) 2001 Elsevier Science Lt d.