Genesis and Nd Isotope Composition of Ferromanganese Deposits of the Sea of Okhotsk and the Kuril Island Arc

—The Nd isotope composition of ferromanganese deposits (FMD) from the central part of the Sea of Okhotsk and the Kuril island arc has been studied. The results showed that diagenetic samples from the Deryugin Basin have a heterogeneous Nd isotope composition. The positive εNd values here might be both due to the input of a terrigenous impurity and due to diffuse endogenetic element supply. The FMD samples from the Sonne underwater ridge show a εNd value specific to seawater (–3.2). The εNd value of hydrogenetic FMD from Volcano 7.14 is –3.4, which corresponds to the εNd value of the Pacific water. The FMD samples from Volcano 5.5 are characterized by εNd = –2.0. The higher εNd value might be due to a moderate dilution of the hydrothermal fluid by seawater and might also indicate the presence of volcanic fragments in the FMD samples. The highest εNd value (+4.4) has been established for volcaniclastic sandstone saturated with Fe and Mn hydroxides. It points to a mixing of volcanomictic and hydrothermal materials.

Peculiarities of anomalous gas-geochemical fields in the East Deryugin graben of the Sea of Okhotsk

This paper presents the research data on methane distribution in the area of the most noticeable gas discharges in the Deryugin Basin of the Sea of Okhotsk. In the East Deryugin graben, a unique methane seep is known, which spatially coincides with the local authigenic barite-carbonate mineralization. The question of the source nature, which is associated with the methane emission in the studied area, is considered.

Bioaccumulation of Trace Elements in the Organisms of Benthic Communities in the Reducing Environments of the Sea of Okhotsk

A comparative study of the bioaccumulation of trace elements in benthic organisms inhabiting the area of methane seeps in the Deryugin Basin and nearby the Paramushir Island (Sea of Okhotsk) has been performed. The data pertain to both essential elements (Fe, Mn, Ni, Co, Cr, and Cu), which are necessary in certain concentrations for the metabolism of organisms, and nonessential heavy metals (Cd, Pb, and Hg), as well as As, a toxic metalloid. Dominating representatives of the bottom fauna from the Deryugin Basin (sea anemones, clams) were characterized by high bioaccumulation coefficients of most of the elements (≥ n103), regardless of their biochemical properties. The use of the coefficient K, which characterizes the accumulation of trace elements in the soft tissues of bivalves relative to their shells, allowed us to detect differences in the bioaccumulation character. Symbiotrophic bivalves of the family Vesicomyidae from the Deryugin Basin were characterized by the accumulation of all of the trace elements mostly in soft tissues (gills, primarily) compared to the carbonate shells (coefficient K > 1). We suppose that different effect of abiotic (biological availability of elements and water turbidity) and biotic (throphic strategy) factors of the habitats may probably be a reason of such phenomenon.