Gulf Of Ob Research Articles

Исследование нерастворимых частиц в снежном покрове Западной Сибири на профиле от Томска до эстуария Оби

Исследование нерастворимых частиц в снежном покрове Западной Сибири на профиле от Томска до эстуария Оби

Population structure and condition of Siberian sturgeon stock: Acipenser baeri Brandt in the River Basin of the Ob

This paper summarises materials from various sources and the author’s research on the biology of the Siberian sturgeon in the Ob basin. The paper evaluates the significance of various parts of this river system for habitation and formation of sturgeon stock. It has been possible to distinguish semi-diadromous sturgeon and four local (indigenous) schools, according to the difference in morphological characteristics and peculiarities of the Ob basin ecology. Semi-diadromous sturgeon spends most of their life in the lower reach of the Ob and in the Gulf of Ob and migrates to spawn to the upper Ob. These spawning migrations cover a distance of 2500 km or more. Spawners from local schools do not make such long spawning migrations. It is noted that at least two isolated schools have been formed higher up the dams of the hydroelectric power stations on the Ob and the Irtysh. Today, the stock of semi-diadromous sturgeon is extremely low, but this school used to be the most abundant. The population of young fish in the middle-Ob school is of high density. But it has an extremely high mortality rate. The Chulym school of Ob sturgeon is in the best condition. Its population increases from the waters of two sturgeon and nelma reserves.

Distribution of beluga whales (Delphinapterus leucas) in the Russian Arctic seas according to the results of expedition aboard RV Mikhail Somov, September–November 2010

Data on the distribution of marine mammals, including beluga whales (Delphinapterus leucas Pallas, 1766), in the Arctic are scarce because of various causes and conditions, including the vast expanses of the region, its poor accessibility, severe climate, long polar night, and high cost of research. Nevertheless, the results of aerial observations during ice reconnaissance and onboard observations during sea voyages (Kleinenberg et al., 1964; Geptner et al., 1976; Belikov, Boltunov, and Gorbunov, 2002; Belikov and Boltunov, 2002; Ezhov, 2005; Matishov and Ognetov, 2006; Biologiya i okeanografiya…, 2007; Lukin and Ognetov, 2009) have provided a general idea of the distribution pattern of beluga whales in the Russian Arctic seas. More detailed data concern the distribution of these whales in the White Sea, where aerial surveys of the water area were performed previously and have been resumed in recent years (Nazarenko et al., 2008; Glazov et al., 2010, 2011). The relevant data on the Barents, Kara, Laptev, and East Siberian seas are much poorer. In the summer (ice-free) period, beluga whales concentrate in coastal waters. They have been recorded most frequently off Franz Josef Land, Novaya Zemlya, Vaygach Island, and in Czech Bay in the Barents Sea; in Baydaratskaya Bay, Gulf of Ob, and Yenisei Gulf in the Kara Sea; off the northeastern coast of Taimyr and in estuaries of the Anabar, Olenyok, and Lena rivers in the Laptev Sea; and in the estuaries of the Indigirka (where the whales come from the west) and the Kolyma and Ked’ma rivers (where they come from the east) in the East Siberian Sea. The amount of information obtained in other seasons is very limited. In autumn, mass migration of beluga whales from the Kara Sea to the Barents Sea have been recorded in the Karskie Vorota Strait and off Cape Zhelaniya in the north of Novaya Zemlya. In winter, almost no records of these whales have been made in the Kara, Laptev, and East Siberian seas. These data are based on previous observations and have practically not been complemented in recent years.

Phytoplankton of the surface desalted lens of the Kara Sea

The phytoplankton of a surface strongly desalinated water lens was investigated on the basis of materials collected during the 57th cruise of the R/V Akademik Mstislav Keldish in September of 2007. The lens with a salinity of <18 psu had area of approximately 19 thousand square kilometers and was located in the northwestern part of the Kara Sea near the eastern coast of Novaya Zemlya. It was a specific biotope that had been isolated from the surrounding waters for more than three months. In the investigated area, 66 algae species were identified. The maximal species diversity was found in the upper layers of the desalinated lens, where the species number was 1.5 to 3 times higher than in other parts of the water column. The phytoplankton numbers in the upper layers of the lens were 1.5 to 4.5 times higher than in its lower part and generally higher than below the picnocline. Diatoms were the most abundant group in the upper layers of the lens, while flagellates dominated in numbers in the subpicnocline part of the water column. The maximal values of the phytoplankton biomass were observed everywhere in the upper layers of the lens, where they were 1.2 to 3.7 times higher than in the lower part of the lens and 1.3 to 7.2 times higher than in the layer below the picnocline. Dinoflagellates generally gave the most contribution to the total phytoplankton biomass. The phytoplankton of the desalinated surface lens in the northwestern part of the Kara Sea by its composition and quantitative parameters had the nearest resemblance to a phytocenosis that we observed two weeks later at a shallow desalinated shelf closely adjacent to the Ob estuary.

The Bazhenovo formation as a source of economic oils and rich gases in the Tithonian-Neocomian section of the South Kara Region

The main gas reservoir in the South Kara region that comprises Arctic areas of the West Siberia petroliferous basin and adjacent shelf is represented by the Aptian-Cenomanian productive sequence, which encloses unique and large gas and gas condensate fields discovered at depths up to 2.5 km: Urengoiskoe, Yamburgskoe, Medvezh'e, Zapolyarnoe, Novopor� tovskoe, Rusanovskoe, Leningradskoe, and others. In recent decades, large fields were discovered in the same sequence in the Ob and Taz estuaries region: Kamennomysskoemore, SeveroKamenomysskoe, Chugor'yakhinskoe, and others. At the same time, resources of cheap dry gas in easily accessible accumu� lations are not inexhaustible, and in the near future, mankind should purposefully develop deeper forma� tions, which contain, in the opinion of many research� ers, accumulations of rich gas and gas condensate with potential fringes of light oils. In the context of this problem, of interest are the results of the geochemical analysis of the Bazhenovo Formation (Tithonian-lower Berriasian), which is characterized by very high concentrations of plankto� nogenic organic matter and represents a main genera� tor of oils in the central and western parts of the West Siberian petroliferous basin. The unique enrichment of this unit with organic matter should also be charac� teristic of high latitude areas, since similar highcar� bonaceous sediments associated with frequently global anoxic events were deposited in the terminal Late Jurassic epoch through many petroliferous basins (North Sea, West Norwegian, Barents Sea, West Sibe� rian, Northern slope of Alaska, Mackenzie, Sverdrup, Jenna D'Arcy), where similar sequences became sources of the economic oil potential. The Bazhenovo Formation is composed of carbon� ate-siliceous-clayey bituminous sediments with high concentrations of planktonogenic organic matter (average Corg contents 5.1% and up to 30% in some layers) (1). By analogy with domanikites, these sedi� ments are called bazhenovites. They are distributed practically throughout the entire basin, where average Corg and bitumoid concentrations increase from 1 to 11% and from 0.3 to >1.0%, respectively, from its periphery toward the inner deepwater parts. The comparison of the lithological-mineralogical characteristics of rocks and the concentrations and composition of enclosed organic matter with the data obtained by the standard and radioactive logging (SL and GL) revealed certain correlations between terrig� enous, biogenic-terrigenous, and biogenic compo� nents of the Bazhenovo Formation, on the one hand, and the SL and GL values, on the other (2). The defined correlation between these parameters served as a basis for classification of bazhenovite sections and their largescale mapping. The sections with members of highresistance siliceous, carbonate, and siliceous- carbonate sapropelic-clayey rocks confined to depressions and slopes of uplifts are considered to be most favorable for the formation of oil pools. In such sections, organic matter is almost entirely represented by colloalgenite and contains 7.0-8.5% of hydrogen, while microcavities in rocks are frequently filled with oil. Perrozio and Predtechenskii (2) proposed in 1985 the notion "radiolarian paleoabundance," which des� ignates the sum of their visible remains concentrated in the form of small lenses and laminae or present as single skeletons as well as residual cavities through the whole rock volume after their dissolution. It was estab� lished that the radiolarian paleoabundance of

Integrated research on the Gulf of Ob (July to October 2010)

Integrated research on the Gulf of Ob (July to October 2010)

Microbial processes of the carbon and sulfur cycles in the Kara Sea

The results of microbiological, biogeochemical, and isotope geochemical studies in the Kara Sea are described. The samples for these studies were obtained during the 54th voyage of the research vessel Akademik Mstislav Keldysh in September 2007. The studied area covered the northern, central, and southwestern parts of the Kara Sea and the Gulf of Ob. The quantitative characteristics of the total bacterial population and the activity of the microbial processes in the water column and bottom sediments were obtained. The total population of the bacterioplankton (BP) varied from 250000 cells/ml in the northern water area to 3000000 cells/ml in the Gulf of Ob. The BP population depended on the content of the water suspension. The net BP production was minimal in the central water area, amounting to 0.15–0.2 μg C/(l day), and maximal (0.5–0.75 μg C/(l day)) in the Gulf of Ob. The organic material at the majority of the stations in the Ob transect predominantly contained light carbon isotopes (−28.0 to −30.18‰) of terrigenous origin. The methane content in the surface water layer varied from 0.18 to 2.0 μl CH4/l, and the methane oxidation rate changed in the range of 0.1–100 nl CH4/(l day). The methane concentration in the upper sediment layer varied from 30 to 300 μl CH4/dm3; the rate of the methanogenesis was 44 to 500 nl CH4/(dm3 day) and that of the methane oxidation, 30 to 2000 nl CH4/(dm3 day). The rate of the sulfate reduction varied from 4 to 184 μg S/(dm3 day).

Macrobenthos of the Ob River estuarine zone and of the adjacent regions of the Kara Sea

The composition and distribution of the macrobenthic communities in the Ob estuary and the adjacent Kara Sea shelf were studied during the 54th cruise of the R/V Akademik Mstislav Keldysh. With the transition from the Ob River’s mouth to the open parts of the sea, the gradual changes of the bottom biocenoses included changes in the leading taxa. Along with the increase in the salinity, the freshwater and brackish water taxa are replaced by related forms adapted to dwelling in seawater. The comparison of the original data with the results of the previous investigations revealed considerable spatial and temporal variations of the bottom communities in the studied area. The main environmental factors determining the fauna distribution in the estuarine zone are discussed. The extensive biocenosis dominated by Portlandia aestuariorum in the Ob estuary was found for the first time.

The role of zooplankton in the transformation of the organic matter in the Ob estuary, on the shelf, and in the deep regions of the Kara Sea

The data for the present study were collected at 20 sampling stations in the Kara Sea along the transect from the Ob estuary to the deep sea St. Anna Trough in September 2007. Based on the hydrophysical features, the distribution of the Chl a, and the primary production, we distinguished six habitats: the river, estuary, inner and outer shelf, continental slope, and trough. The impact of the small-size ( 0.5 mm) fractions of the zooplankton on the phytoplankton’s organic carbon in the different regions of the Kara Sea was estimated. The ingestion rate was assessed using the analysis of the gut fluorescence content and the gut evacuation rate. The zooplankton grazed 1–2% of the phytoplankton biomass in the river and estuary; 3.5% over the shelf; and 6 and 10% in the regions of the trough and slope, respectively. The grazing impact of the small-sized zooplankton increased from the river zone to the deep regions (from 1 to 90%) along with their share in the total zooplankton abundance (from 18 to 95%). From 72 to 86% of the primary production was grazed over the shelf and slope. The primary production did not cover the feeding requirements of the zooplankton in the estuarine regions and St. Anna Trough in the autumn. In the estuarine regions, the major portion of the organic matter settles on the bottom due to the strong inflow of the allochthonous matter and the relatively low zooplankton grazing.

Input of organic carbon as determinant of nutrient fluxes, light climate and productivity in the Ob and Yenisey estuaries

Spectral light attenuation profiles and concentrations of total and dissolved carbon (C), nutrients and chlorophyll a (Chl a) were studied along transects running from the river mouth to the Kara Sea during late summer 2003 for the Yenisey and fall 2005 for the Ob estuaries. Earth Observation data were used to generate composite images of water color and Chl a distribution over the estuaries and the Kara Sea to reveal the spatial impact of the river efflux in terms of optical properties. High levels of total nitrogen (N), total phosphorus (P), silicate (Si) and iron (Fe), but low levels of inorganic N and P and Chl a were found in the estuaries. More than 90 % of total organic C was in dissolved form (DOC). The high concentrations of DOC, mostly terrigenous, humic compounds, gave extremely high attenuation coefficients for both visible and ultraviolet light. For UV-B, Z 10% (the depth at which 10% of surface light remains) was <10 cm, while Z 10% for visible light (PAR) generally ranged between 1 and 3 m for both transects. The light attenuation rapidly decreases when the freshwater is mixed with the coastal water outside off the coast. This leads to a strong light limitation and low productivity in the inner estuaries, while the high load of N and P associated with DOC eventually could promote primary production in the Kara Sea and further upstream the coastal current in the Arctic Ocean as the organic matter becomes diluted and photooxidized. On the other hand, the high inputs of colored dissolved organic matter (CDOM) provide an efficient screening of potential harmful UV-radiation over vast areas of the Arctic Ocean. A rising trend of riverine efflux to the Arctic seas is observed, and further increases in freshwater runoff as well as eventual permafrost thawing, will accentuate the freshwater impact in the estuaries and the Kara Sea.

Natural background of hydrocarbon gases (C1–C5) in the waters of the Kara Sea

The distributions of methane and hydrocarbons (HC) C2+ throughout the vertical section of the water mass and sediments of the Kara Sea and the estuaries of the Ob and Yenisei rivers were examine during expeditions aboard the R/V “Akademik Boris Petrov” in 1997–2002. Data obtained during the expeditions and extensive information provided by the complex study of the carbon cycle in the aquatic area were used to analyze the genesis of hydrocarbon gases in marine water. The example of particulate matter was used to demonstrate that hydrocarbon gases of the composition C2–C5 contained in seawater are genetically related to aquatic organic matter (OM), regardless of seawater salinity. The hydrocarbon complex is dominated (80%) by higher C4–C5 homologues. The concentration of C4–C5 hydrocarbons in the estuarine fresh waters is comparable with the high methane concentration (2–3 μl/l), drastically decreases in the zone of water mixing, and then rapidly increases to values several times higher than the methane concentration in seawater outside the outer boundary of the sedimentation depocenter of riverine particulate matter. A direct correlation was established for the concentration of the C4 + C5 homologues with the OM of the water mass, and the leading role was demonstrated to be played by labile OM of the autochthonous biomass (marine phytoplankton) in the genesis of higher hydrocarbon gases (alkenes, alkanes, and isoalkanes) during the early diagenetic stage of OM transformations in water. Along with the biomass of phytoplankton, a significant role in the genesis of C2–C3 hydrocarbons is played by destruction products of terrigenous OM. The destruction of OM and generation of gaseous hydrocarbons, including methane, are restricted to the pycnocline and the water-sediment interface. The absolute predominance of the sum of the C4 + C5 homologues in the hydrocarbon C2+ gases and the presence of unsaturated C2–C4 hydrocarbons are typical of the natural background of hydrocarbons of the Kara Sea water mass.

Ob' River flood inundations from satellite observations: A relationship with winter snow parameters and river runoff

Using a multisatellite method, including passive microwave land surface emissivities, along with active microwave, visible and near infrared observations developed to estimate global inundated area, we examine the spatial and temporal variations of the 1993–2000 monthly inundation extents over a Boreal environment, the Ob River basin. Over the entire watershed, the mean extent of inundation during the snow‐free months is 2.6 × 105 km2, consistent with previous independent static or satellites‐derived estimates. The maximum in yearly inundation, showing propagation from south to north between April and June, exhibits strong seasonal and inter‐annual variations. The consistency of the inundation estimates is then analyzed at local or basin‐wide scale using different in situ or satellite‐derived snow and runoff parameters. The results show a strong relationship between the inundation extent and the snowmelt date, the snowpack depth at three in situ stations located in the southern part of the basin. Over the northern part, results show that flooding is more closely linked to the amount of water coming downstream from the southern part of the basin. A close systematic relationship is also found between the inundation extent and the local in situ runoff at six locations as well as with the altimeter‐derived discharge measured at the Ob estuary. This case study evaluation shows the potential of these data sets to provide consistent information about the seasonal and inter‐annual variations of inundation over a major Boreal river basin. These results also suggest new potential to improve the description of the snow‐inundation‐runoff relationship that are fundamental for climate and hydrological models.

Poles of inaccessibility: A calculation algorithm for the remotest places on earth

An algorithm is presented to calculate the point on the surface of a sphere maximising the great-circle distance to a given spherical polygon. This is used to calculate the spots furthest from the sea in major land masses, also known as Poles of Inaccessibility (PIA), a concept that has raised the interest of explorers. For the Eurasian pole of inaccessibility (EPIA), the results reveal a misplacement in previous calculations ranging from 156 to 435 km. Although in general there is only one pole for a given coastline, the present calculations show that, within the error inherent to the definition of the coastline, two locations are candidates for EPIA, one equidistant from Gulf of Ob, Gulf of Bengal and Arabian Sea, and the other equidistant from Gulf of Ob, Gulf of Bengal and Gulf of Bohai, both poles being located in the north westernmost Chinese province of Xinjiang. The distance to the sea at these locations is 2510 and 2514 km respectively, about 120 km closer than generally thought.

Biogeochemistry of the Russian Arctic. Kara Sea: Research results under the SIRRO project, 1995–2003

The Kara Sea is an area uniquely suitable for studying processes in the river-sea system. This is a shallow sea into which two great Siberian rivers, Yenisei and Ob, flow. From 1995 to 2003, the sea was studied by six international expeditions aboard the R/V Akademik Boris Petrov. This publication summarizes the results obtained, within the framework of this project, at the Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Various hydrogeochemical parameters, concentrations and isotopic composition of organic and carbonate carbon of the sediments, plankton, particulate organic matter, hydrocarbons, and dissolved CO2 were examined throughout the whole sea area at more than 200 sites. The δ13C varies from −22 and −24‰ where Atlantic waters enter the Kara Sea and in the North-eastern part of the water area to −27‰ in the Yenisei and Ob estuaries. The value of δ13C of the plankton is only weakly correlated with the δ13C of the organic matter from the sediments and is lower by as much as 3–4‰. The paper presents the results obtained from a number of meridional river-sea profiles. It was determined from the relations between the isotopic compositions of plankton and particulate matter that the riverwaters carry material consisting of 70% detrital-humus matter and 30% planktonogenic material in the river part, and the material contained in the off-shore waters consists of 30% terrigenous components, with the contribution of bioproducers amounting to 70%. The carbon isotopic composition of the plankton ranges from −29 to −35‰ in the riverine part, from −28 to −27‰ in the estuaries, and from −27.0 to −25% in the marine part. The relative lightness of the carbon isotopic composition of plankton in Arctic waters is explained by the temperature effect, elevated CO2 concentrations, and long-distance CO2 supply to the sea with riverwaters. The data obtained on the isotopic composition of CO2 in the surface waters of the Kara Sea were used to map the distribution of δ13CCO 2. The complex of hydrocarbon gases extracted from the waters included methane, C2–C5, and unsaturated C2=–C4= hydrocarbons, for which variations in the concentrations in the waters were studied along river-estuary-sea profiles. The geochemistry of hydrocarbon gases in surface fresh waters is characterized by comparable concentrations of methane (0.3–5 μl/l) and heavier hydrocarbons, including unsaturated ones. Microbiological methane with δ13C from −105 to −90‰ first occurs in the sediments at depths of 40–200 cm. The sediments practically everywhere display traces of methane oxidation in the form of a shift of the δ13C of methane toward higher values and the occurrence of autogenic carbonate material, including ikaite, enriched in the light isotope. Ikaite (δ13C from −25 to −60‰) was found and examined in several profiles. The redox conditions in the sediments varied from normal in the southern part of the sea to highly oxidized along the Novaya Zemlya Trough. Vertical sections through the sediments of the latter exemplify the complete suppression of the biochemical activity of microorganisms. Our data provide insight into the biogeochemistry of the Kara Sea and make it possible to specify the background values needed for ecological control during the future exploration operations and extraction of hydrocarbons in the Kara Sea.

Ecological and geochemical investigations in the Ob estuary at sites of hydrocarbon exploration drilling

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.

Study of the ice conditions in the Gulf of Ob

The results of theoretical studies of fracture lines in the ice floes of the Gulf of Ob as a function of the coefficient of internal sliding are presented in this paper. An estimate of the fractal dimensions of the emerging topological structures and the results of the calculation of stresses in the ice cover of the Gulf of Ob are presented as functions of different directions of external forcing caused by the joint action of winds and currents on the ice. The geographical locations of the zones of possible loads are shown, together with the estimates of the hummock sizes in the zones of the maximal compression of the ice floes in the Gulf of Ob.

Comparison between the interannual variability of snow parameters derived from SSM/I and the Ob river discharge

This paper analyses the relationship between the interannual variations of snow depth and snowmelt date and river discharge measurements in the Ob river basin. The snow parameters are derived from passive microwave remote sensing measurements by SSM/I during the time period 1989–2001. We find a significant correlation between the snowmelt date and the runoff in May (correlation coefficient R = − 0.92) and between the winter snow depth and the runoff in June ( R = 0.61) measured at the Ob estuary. These results validate the methods used to derive the interannual variability of the snow parameters, particularly the snow depth. In such vast and remote regions, this is fundamental for monitoring and predicting snow related flood events. Furthermore, the results obtained can be very useful to improve the description of the snow-runoff relationship in global hydrological models.

Holocene variability of bottom water hydrography on the Kara Sea shelf (Siberia) depicted in multiple single-valve analyses of stable isotopes in ostracods

Ostracods secrete their valve calcite within a few hours or days, therefore, its isotopic composition records ambient environmental conditions of only a short time span. Hydrographic changes between the calcification of individuals lead to a corresponding range (max.–min.) in the isotope values when measuring several (≥5) single valves from a specific sediment sample. Analyses of living (stained) ostracods from the Kara Sea sediment surface revealed high ranges of >2‰ of δ 18O and δ 13C at low absolute levels ( δ 18O: <3‰, δ 13C: <−3‰) near the river estuaries of Ob and Yenisei and low ranges of ∼1‰ at higher absolute levels ( δ 18O: 2–5.4‰, δ 13C: −3‰ to −1.5‰) on the shelf and in submarine paleo-river channels. Comparison with a hydrographic data base and isotope measurements of bottom water samples shows that the average and the span of the ostracod-based isotope ranges closely mirror the long-term means and variabilities (standard deviation) of bottom water temperature and salinity. The bottom hydrography in the southern part of the Kara Sea shows strong response to the river discharge and its extreme seasonal and interannual variability. Less variable hydrographic conditions are indicative for deeper shelf areas to the north, but also for areas near the river estuaries along submarine paleo-river channels, which act as corridors for southward flowing cold and saline bottom water. Isotope analyses on up to five single ostracod valves per sample in the lower section (8–7 cal. ka BP) of a sediment core north of Yenisei estuary revealed δ 18O and δ 13C values which on average are lower by 0.6‰ in both, δ 18O and δ 13C, than in the upper core section (<5 cal. ka BP). The isotope shifts illustrate the decreasing influence of isotopically light river water at the bottom as a result of the southward retreat of the Yenisei river mouth from the coring site due to global sea level rise. However, the ranges (max.–min.) in the single-valve δ 18O and δ 13C data of the individual core samples are similar in the upper and in the lower core section, although a higher hydrographic variability is expected prior to 7 cal. ka BP due to river proximity. This lack of variability indicates the southward flow of cold, saline water along a submarine paleo-river channel, formerly existing at the core location. Despite shallowing of the site due to sediment filling of the channel and isostatic uplift of the area, the hydrographic variability at the core location remained low during the Late Holocene, because the shallowing proceeded synchronously with the retreat of the river mouth due to the global sea level rise.

Characterization of Siberian Arctic coastal sediments: Implications for terrestrial organic carbon export

Surface sediments were collected during the 2000 TransArctic Expedition along the Siberian Arctic coastline, including the Ob, Yenisey, Khatanga, Lena, and Indigirka estuaries. Sediments were characterized for elemental composition (total organic carbon, TOC, black carbon, BC, and total N, as well as major and trace elements), isotopic signature (δ13C, δ15N, Δ14C, εNd, 87Sr/86Sr), and organic molecular composition to better understand river export variations over the large spatial scale of the Siberian Arctic. On average, 79 ± 9% of the total C in sediments was organic while 21 ± 9% was inorganic. BC made up 9 ± 4% of the TOC pool, with a general increasing trend from west to east along the Siberian coast. The combined Nd‐ and Sr‐isotopes (εNd and 87Sr/86Sr) were used to define two distinct sediment sources between east and west Siberian regions with the Khatanga River as a boundary. Data from pyrolysis‐GC/MS of the sedimentary organic carbon (SOC) indicated an increase in the freshness of the organic matter from west to east on the Siberian Arctic coast, with increasing relative abundance of furfurals (polysaccharides) with respect to nitriles. Values for the δ13C of SOC ranged from −27.1‰ (mostly terrigenous) to −23.8‰, while δ15N increased from east to west (3.1 to 5.2‰) with a significant correlation with C/N ratio. Values for the Δ14C of SOC ranged from −805 to −279‰, with a consistent trend increasing from the east (Indigirka River) to the west (Ob River). These Δ14C values corresponded to a 14C age of 2570 ± 30 yBP in the Ob estuary and 13,050 ± 50 yBP in the Indigirka estuary. Most importantly, Δ14C values were significantly correlated with the ratio of BC/TOC (R2 = 0.91, n = 6), consistent with the distribution pattern of increasing permafrost zone from the west to the east along the Siberian coast. Together, our results suggest that older OC was derived from the release of recalcitrant BC during permafrost thawing and riverbank and coastal erosion, likely enhanced by ongoing environmental changes in the northern ecosystem.

The Role of Phytoplankton from the Ob River in Biological Productivity of the Ob–Yenisei Shoal

The program of investigations on the taxonomic composition and spatial distribution of planktonic microalgae in the Gulf of Ob and the southern Kara Sea in different seasons was carried out. Throughout the observation period, from July to October, high values of phytoplankton biomass were recorded in the Gulf of Ob and adjacent areas of the Ob–Yenisei shoal. This is evidence for a higher productivity of waters off the Ob estuary, compared to other coastal areas of the Kara Sea. The main factor responsible for this phenomenon is permanent (during the warm season) transport of living and dead organic matter by river runoff to the shelf.