M. D. Kravchishina

On the elemental composition of suspended matter of the Severnaya Dvina River (White Sea region)

New data on the elemental composition of the Severnaya Dvina River, the largest one in the White Sea region, are presented. The elemental composition of the river water in May, the period of the snowmelt flood, is similar to the upper layer of the Earth’s continental crust due to the active erosion of the earth material in the catchment area. In August, the period of the summer low water, the impact of biogenic components increases and elevated concentrations of Cd, Sb, Mn, Zn, Pb, and Cu are observed. At other times, no significant pollution by heavy and rare-earth elements is registered.

Transformation of particulate organic matter at the water-bottom boundary in the Russian Arctic seas: Evidence from isotope and radioisotope data

Complex biogeochemical studies including the determination of isotopic composition of Corg in both suspended particulate matter and surface horizon (0–1 cm) of sediments (more than 260 determinations of δ13C-Corg) were carried out for five Arctic shelf seas: White, Barents, Kara, East Siberian, and Chukchi. The aim of this study is to elucidate causes that change the isotopic composition of particulate organic carbon at the water-sediment boundary. It is shown that the isotopic composition of Corg in sediments from seas with a high river runoff (White, Kara, and East Siberian) does not inherit the isotopic composition of Corg in particles precipitating from the water column, but is enriched in heavy 13C. Seas with a low river runoff (Barents and Chukchi) show insignificant difference between the value of δ13C-Corg in both suspended load and sediment because of a low content of the isotopically light allochthonous organic matter (OM) in particulates. Complex biogeochemical studies with radioisotope tracers (14CO2, 35S, and 14CH4) revealed the existence of specific microbial filter formed from heterotrophic and autotrophic organisms at the water-sediment boundary. This filter prevents the mass influx of products of OM decomposition into water column, as well as reduces the influx of a part of OM contained in the suspended particulate matter from water into sediment.

Transformation of suspended particulate matter into sediment in the Kara Sea in September of 2011

The biogeochemical processes participating in the transformation of the particulate matter into sediment along the Yenisei River-St. Anna Trough (Kara Sea) meridional profile were studied using hydrochemical, geochemical, microbiological, radioisotope, and isotope methods. The water-sediment contact zone consists of three subzones: the suprabottom water, the fluffy layer, and the surface sediment. The total number, biomass, and integral activity of the microorganisms (dark 14CO2 assimilation) in the fluffy layer are usually higher than in the suprabottom water and sediment. The fluffy layer shows a decrease in the oxygen content and the growth of the dissolved biogenic elements. It was provided by the particulate organic matter supporting the vital activity of the heterotrophs from the overlying water column and by the flux of reduced compounds (NH4, H2S, CH4, Fe2+, Mn2+, and others) from the underlying sediments. The Corg isotopic composition of the fluffy layer and the sediments is 2–4 ‰ heavier than that of the particulate matter and sediment due to the presence of the isotopically heavy biomass of microorganisms. A change in the isotopic composition of the Corg in the fluffy layer and surface sediment as compared to the Corg of the particulate matter is a widespread phenomenon in the Arctic shelf seas and proves the leading role of microorganisms in the transformation of the particulate matter into sediment.

The distribution of the suspended matter concentration in the Kara Sea in September 2007 based on ship and satellite data

The distribution of the suspended particulate matter concentration in the Kara Sea is analyzed based on ship and satellite data. The statistical relationships between the suspended matter concentration and the optical characteristics were revealed. Charts of the distribution of the suspended matter concentration in the Kara Sea were plotted, which confirmed that the application of optical methods for analyzing the spatial distribution of the suspended matter is effective. The most turbid waters were observed in the Ob Gulf, Yenisei Bay, the Baidaratskaya Gulf, and the adjacent regions. The smallest concentrations of suspended matter were observed in the central and western parts of the Kara Sea.

Dispersed organic matter and its fluxes in oceans and seas from the example of the White Sea: Results of a 12-year study

Annual and long-term quantitative estimations of the vertical fluxes of sedimentary matter in the White Sea are the basis for direct calculations of the gain of chemical components and minerals and diverse pollution of the surface layer of the bottom sediments. The White Sea, one of six Russian Arctic seas, may be considered as a megapolygon for further modern study using the new mechanisms of Arctic sedimentogenesis discovered. This work is directed at elaboration of new technologies of complex study of seas using submarine sedimentation and regular vessel observatories. The first priority task is year-round monitoring along the Northern Sea route.

Isotopic Markers of Organic Matter Transformation at the Water-Sediment Geochemical Boundary

83 The main transformations of energy and matter occur at the boundary zones of the ocean. The “water column–bottom sediment” boundary is related to those areas studied insignificantly because of the diffi� culty of its direct investigation. Suspension and com� ponents dissolved in seawater come onto this bound� ary from the top fixing the end of the sedimentation stage, and dissolved and gaseous compounds formed in the upper sedimentary horizons on the stage of early diagenesis are removed from the bottom. Organic matter (OM) from suspension and reduced compounds coming from sediments play the role of an energy source for biogeochemical processes at the water–sediment boundary.

Grain-size composition of the suspended particulate matter in the marginal filter of the Severnaya Dvina River

The quantitative distribution and grain-size composition of the suspended particulate matter (SPM) in the marginal filter of the Severnaya Dvina River during the summer low-water periods of 2001–2005 were first analyzed in seawater on board of the vessel immediately after its sampling (without preliminary treatment) using a Coulter counter. This analysis revealed the main regularities in the transformation of the grain-size spectra at successive salinity steps of the marginal filter as well as the boundaries between these steps based on the data obtained by direct complex studies of the SPM dispersion. It is established that the water salinity is the main factor that controls the changes in the grain-size distribution and the composition of the particulate matter in the marginal filter. The concentrations of the pelitic fraction and the salinity demonstrate negative correlations between each other. It is shown that the areas characterized by the mass development of phytoplankton are located along the outer boundary of the marginal filter (at the biological step), where the salinity amounts to 23–24 psu. The content of the suspended forms of some chemical (lithogenic) elements and the Corg indicating the SPM’s genetic composition and their relations with the grain-size composition of the latter and the environments are studied.

Composition of the suspended particulate matter at the Severnaya Dvina River mouth (White Sea) during the spring flood period

The grain-size and mineral composition of the suspended particulate matter (SPM) of the Severnaya Dvina River mouth is studied, as well as the content of several lithogenic elements in the SPM during the spring flood in May 2004. The data published on the composition of the riverine SPM in the White Sea basin are very poor. The spring flood period when more than half of the annual runoff is supplied from the river to the sea in a short time is understood more poorly. The report considers the comparison results for the grain-size compositions of the SPM and the bottom sediments. The data of laser and hydraulic techniques of the grain-size analysis are compared. The short-period variations of the SPM concentration and composition representing two diurnal peaks of the tide level are studied. It is found that the SPM is mainly transferred during the spring flood as mineral aggregates up to 40 μm diameter. The sandysilty fraction of the riverine SPM settles in the delta branches and channels, and the bulk of the fine pelitic matter is supplied to the sea. The mineral and chemical composition of the Severnaya Dvina River SPM is determined by the supply of substances from the drainage basin. This substance is subjected to intense mechanic separation during the transfer to the sea. The key regularities of the formation of the mineral composition of the SPM during the flood time are revealed. The effect of the grain-size composition of the SPM on the distribution of the minerals and elements studied in the dynamic system of the river mouth are characterized.

The biogeochemistry of some heavy metals and metalloids in the Ob River estuary-Kara Sea section

The biogeochemical behavior of the group of heavy metals and metalloids in the water (including their dissolved and suspended particulate forms), bottom sediments, and zoobenthos was studied in the Ob River estuary-Kara Sea section on the basis of the data obtained during cruise 54 of the R/V Akademik Mstislav Keldysh in September–October 2007. The changes in the ratios of the dissolved and suspended particulate forms of Fe, Mn, Zn, Cu, Pb, Cd, and As were shown, as well as the growth of the fraction of adsorbed forms in the near-bottom suspended particulate matter under the mixing of the riverine and marine waters. The features of the metals’ accumulation in the typical benthic organisms of the Ob River estuary and the Kara Sea were revealed, and their concentrating factors were calculated based on the specific conditions of the environment. It was shown that the shells of the bivalves possessing a higher biomass compared to the other groups of organisms in the Ob River estuary play an important role in the deposition of heavy metals. The mollusks of the Ob River estuary accumulate Cd and Pb at the background level, whereas the Cu and Zn contents appear to be over the background level.

Studying the biogenic and abiogenic parts of suspended particulate matter in the Volga delta during spring flood of May 2008

Multidisciplinary studies of the dispersed sedimentary matter (suspended particulate matter) were carried out in the Volga delta during spring flood in two areas of the Astrakhan State Biosphere Reserve (Obzhorovskii and Damchikskii), allowing the authors to reveal some regularities in sedimentation conditions. Considerable differences were found to exist in the supply of sedimentary material into the sea through the branches and arms of the eastern and western parts of the river delta. Typical of the eastern part are appreciably higher concentrations of suspended particulate matter, biogenic components, and phytopigments, as well as greater phytoplankton abundance and biomass, and sedimentary material fluxes. A relationship was found to exist between the concentration of suspended particulate matter and the phytopigments under consideration. In May, almost entire chlorophyll “a” in suspended particulate matter was concentrated in the cells of small diatom algae, where it was distributed in proportion to diatom biomass. Overall, the suspended matter of the delta is mostly represented by mineral detrital particles (quartz and carbonates) with a relatively small share of clay materials against the background of a huge amount of diatom cells and biogenic detritus.