Comparative study of vertical suspension fluxes from the water column,rates of sedimentation,and absolute masses of the bottom sediments in the White Sea basin of the Arctic Ocean

A new approach using dispersed organic matter of the water column in sedimentation traps in comparison with the surface layer of the bottom sediments is applied for the study of marine sedimentation. This approach provides the opportunity for an in situ (by fluxes of sedimentary matter in the water column) study of modern sedimentation in the surface layers of the bottom sediments and tracing the changes in the environment and climate at a new technological level. This also allows us to choose the reverse task: to reconstruct the fluxes of the matter and chemical elements in ancient seas by the rates (or absolute masses) of sedimentation.     

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.     

Relationship between the suspended particulate matter and microorganisms in the White Sea waters

During the summer periods of 2003–2005, the spatial and vertical distributions of the suspended particulate matter and bacteria in stratified and homogeneous waters of the White Sea was studied. The results of the study of various quantitative characteristics of the suspended particulate matter (first of all, the area of the surface and the volumetric and mass concentrations) and the abundance of microorganisms in the water are discussed. A direct correlation between the value of the surface area of the suspended particulate matter and the total number of bacteria in the water is revealed. However, it was manifested only during the early summer period of the observations and was not expressed at the end of the summer. The enhanced surface area of the suspended particulate matter can indicate the higher biochemical activity of its particles. The influence of the pelitic fraction on the bacteria abundance in different parts of the sea during the summer is estimated.     

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 C_org in both suspended particulate matter and surface horizon (0–1 cm) of sediments (more than 260 determinations of δ¹³C-C_org) 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 C_org in sediments from seas with a high river runoff (White, Kara, and East Siberian) does not inherit the isotopic composition of C_org 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-C_org 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.     

Genesis of organic and carbonate carbon in sediments of the North and Middle Caspian basins inferred from the isotope data

Isotopic compositions of organic (δ¹³C-C_org) and carbonate (δ¹³C-C_carb) carbon were analyzed in the particulate matter (hereafter, particulates) and sediments from the North and Middle Caspian basins. Isotopic composition of C_org was used for assessing proportions of the allochthonous and autochthonous organic matter in the particulates. Difference between the δ¹³C-C_org values in surface sediments and particulates is explained by the aerobic and anaerobic diagenetic transformations. Isotopic composition of C_org in sediments may be used as a tool for reconstructing the Quaternary transgressive-regressive history of the Caspian Sea.     

Vertical distribution of suspended particulate matter in the Caspian Sea in early summer

The features of the vertical distribution of chlorophyll a, particulate organic carbon and its isotopic composition, total suspended particulate matter (SPM), and the structure of the phytoplankton community in the Middle and South Caspian Sea in May–June 2012 are discussed. The subsurface chlorophyll a maximum (SCM) was found everywhere at depths of ~20 to 40–60 m. The position of this layer is confined to the depth of the seasonal thermocline, which is determined by the development of a cold-water (dark) phytocenosis. The genesis of this layer was studied. The increase in chlorophyll a concentration in this layer is caused by an abundance of phytoplankton or an increased concentration of this phytopigments per algal cell. The highest values of the studied organic compounds and phytoplankton biomass are revealed as close to the seasonal thermocline extending from the southern periphery of the Derbent Depression to the Apsheron Sill, which is determined by the bottom topography. The presence of chlorophyll a at depths exceeding 300 m (up to ≥1 mg/m³) was revealed. This was supported by findings of individual algal cells containing chlorophyll a and even their accumulations in the deep water layer. The most probable mechanisms responsible for the presence of these cells at the deep water level are discussed in the paper. The vertical distribution of the values of the organic carbon isotopic composition is primarily controlled by the vertical structure of phytoplankton and chlorophyll a in the water column up to ~500 m and by biogeochemical processes at the redox barrier (~600 m layer). The relative stability of chlorophyll a and the stability of pheophytin a in anaerobic environments were verified. A significant amount of weakly transformed chlorophyll a was found close the sea bottom.     

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.     

Functional Activity of Phytoplankton and Optical Properties of Suspended Particulate Matter in Onega Bay of the White Sea

Oceanology - The phytoplankton activity was analyzed in June 2015 in Onega Bay of the White Sea. The chlorophyll a concentration, as well as cell abundance and cell biomass, were assessed in...     

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 C_org 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 C_org in the fluffy layer and surface sediment as compared to the C_org 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.