(Table 1) Vertical fluxes of sediment matter and organic carbon in the Kara Sea and in the Yenisey and Ob estuaries

Sedimentary particle fluxes in the Kara Sea and in the Ob and Yenisey estuaries were first estimated and particulate matter composition was studied in September 1993 during Cruise 49 of R/V Dmitry Mendeleev. Twenty three bottom stations with sediment traps were deployed, and samples were collected from 13 stations. Particle fluxes ranged from 9.0 to 62.6 mg/m**2/day to the north of the Ob and Yenisey estuaries and were 18.7 to 62.0 mg/m**2/day in the southwestern part of the Kara Sea. Fluxes were up to 1321 mg/m**2/day in the Ob estuary and up to 22156 mg/m**2/day in the Yenisey estuary. Organic matter fluxes were estimated as 0.71-3.29, 4.28-9.04, 26.7, and 368 mg/m**2/day, respectively. Particulate matter is largely represented by pellets of planktic Crustacea and by "sea snow" flakes mainly composed of diatoms. Rapidly settling particles are extensively inhabited by bacterial flora.

Sulfur and carbon in mIcrobial processes in waters and sediments of the Kara Sea in September 2007

Results of microbiological, biogeochemical and isotope geochemical studies in the Kara Sea are described. Samples for these studies were obtained during Cruise 54 of R/V Akademik Mstislav Keldysh in September 2007. The studied area covered the northern, central, and southwestern parts of the Kara Sea and the Obskaya Guba (Ob River estuary). Quantitative characteristics of total bacterial population and activity of microbial processes in the water column and bottom sediments were obtained. Total abundance of bacterioplankton (BP) varied from 250000 cells/ml in the northern Kara Sea to 3000000 cells/ml in the Obskaya Guba. BP abundance depended on concentration of suspensded matter. Net BP production was minimal in the central Kara Sea (up to 0.15-0.2 µg C/l/day) and maximal (0.5-0.75 µg C/l/day) in the Obskaya Guba. Organic material at the majority of stations at the Ob transect predominantly contained light carbon isotopes (-28.0 to -30.18 per mil) of terrigenous origin. Methane concentration in the surface water layer varied from 0.18 to 2.0 µl CH4/l, and methane oxidation rate varied from 0.1 to 100 nl CH4/l/day. Methane concentration in the upper sediment layer varied from 30 to 300 µl CH4/dm**3; rate of methane formation was varied from 44 to 500 nl CH4/dm**3/day and rate of methane oxidation - from 30 to 2000 nl CH4/dm**3/day. Rate of sulfate reduction varied from 4 to 184 µg S/dm**3/day.

Heavy metal and petroleum product concentrations in waters at the Obskaya 1 drill site

During recent years, the basins of the Kara Sea (Kamennomysskaya, Obskaya, and Chugor'yakhinskaya structures) in the Russian Federation have been considered as promising regions for oil and gas exploration and, simultaneously, as possible paths of relatively cheap pipeline and tanker transportation of hydrocarbons projected for recovery. On the other hand, exploration operations, recovery, and transportation of gas pose a considerable risk of accidents and environmental pollution, which causes a justified concern about the future state of the ecological system of the Gulf of Ob and the adjoining parts of the Kara Sea. Therefore, regular combined environmental investigations (monitoring) are the most important factor for estimating the current state and forecasting the dynamics of the development of estuary systems. The program of investigations (schedule, station network, and measured parameters) is standardized in accordance with the international practice of such work and accounts for the experience of monitoring studies of Russian and foreign researchers. Two measurement sessions were performed during ecological investigations in the region of exploration drilling: at the beginning at final stage of drilling operations and borehole testing; in addition, natural parameters were determined in various parts of the Ob estuary before the beginning of investigations. Hydrophysical and hydrochemical characteristics of the water medium were determined and bottom sediments and water were analyzed for various pollutants (petroleum products, heavy metals, and radionuclides). The forms of heavy-metal occurrence in river and sea waters were determined by the method of continuous multistep filtration, which is based on water component fractionation on membrane filters of various pore sizes. These investigations revealed environmental pollution by chemical substances during the initial stage of drilling operations, when remains of fuels, oils, and solutions could be spilled, and part of the chemical pollutants could enter the environment. Owing to horizontal and vertical turbulent diffusion, wave mixing, and the effect of the general direction of currents in the Ob estuary from south to north, areas are formed with elevated concentrations of the analyzed elements and compounds. However, the concentration levels of chemical pollutants are practically no higher than the maximum admissible concentrations, and their substantial dissipation to the average regional background contents can be expected in the near future. Our investigations allowed us to determine in detail the parameters of anthropogenic pollution in the regions affected by hydrocarbon exploration drilling in the Obskii and Kamennomysskii prospects in the Gulf of Ob and estimate their influence on the ecological state of the basin of the Ob River and the Kara Sea on the whole.

Distribution of marine invertebrate larvae in the southern Kara Sea (Russian Arctic)

Within the generally oligotroph Arctic marine environment river outlets are favoured by many planktonic and benthic organisms due to their high input of organic carbon. The retention of pelagic larvae within nursery grounds and/or the ability to return to their parental grounds prior to settlement is one important factor for the persistence of benthic communities in such river influenced areas. The southern Kara Sea is strongly controlled by high freshwater inputs from the Ob and Yenisei Rivers, which create a pronounced bi-layered pycnocline with a warm fresh/brackish water layer on top and a cold high saline marine layer below. The dispersal of five meroplanktonic species and settled juveniles (the brittle star Ophiocten sericeum, and the polychaetes Micronephtys minuta, Nereimyra aphroditoides, Phyllodoce groenlandica and Prionospio cirrifera) in relation to the adult distribution patterns was investigated. For all apart from P. cirrifera the highest densities of larvae were found in the upper brackish water layer. To assess size-at-settlement, the body sizes of larvae and newly settled juveniles were estimated and compared. Dispersal patterns ranged from virtually no adaption to river run-off as in the common, stenohaline O. sericeum and M. minuta (7 ind./m**3, 459 µm) to local retention as in N. aphroditoides (7 ind./m**3, 541 µm) and P. groenlandica (0.5 ind./m**3, 1121 µm) retained by horizontal eddies created by the outflow. Adults of P. cirrifera, which were exclusively restricted to the estuary of the Yenisei River, showed a well adapted reproductive behaviour to ensure a high retention potential of their progenies. The larvae (1.5 ind./m**3, 1513 µm) were only present in the lower water layers, most probably taking advantage of the prevailing near bottom counter current retaining them within their hatching areas.

Particle analysis in the Kara Sea

In September 1999 two short-term moorings with cylindrical sediment traps were deployed to collect sinking particles in bottom waters off the Ob and Yenisei river mouths. Samples were studied for their bulk composition, pigments, phytoplankton, microzooplankton, fecal material, amino acids, hexosamines, fatty acids and sterols and compared to suspended matter and surface sediments in order to collect information about the nature and cycling of particulate matter in the water column. Results of all measured components in sinking particles point to an ongoing seasonality in the pelagic system from blooming diatoms in the first phase to a more retention system in the second half of trap deployment. Due to a phytoplankton bloom observed north of the Ob estuary, flux rates were generally higher in the trap deployed off the Ob than off the Yenisei. The Ob trap collected fresh surface-derived particulate matter. Particles from the Yenisei trap were more degraded and resembled deep water suspension. This material may partly have been derived from resuspended sediments.