Meiobenthos and nematode community in Yenisei Bay and adjacent parts of the Kara Sea shelf

Material is collected on a meridional profile from Yenisei Bay to adjacent parts of the Kara Sea shelf. The length of the profile is 550 km; 13 to 62 m depths. A multiple corer and Niemistö corer are used as sampling tools. The meiobenthos is represented by 13 taxa. Nematodes are the most abundant taxon, and harpacticoid copepods (Harpacticoida) are subdominant. The abundance and taxonomic diversity of meiobenthos and nematodes increases from the freshwater part of Yenisei Bay towards the Kara Sea shelf. Three types of taxocene are distinguished: freshwater, brackish-water, and marine. The taxocene of the estuary is not distinguished by any specific set of species and consists of species characteristic of the nematode community both in the freshwater and marine zones. The trophic structure of the taxocene of nematodes in Yenisei Bay is dominated by nematodes with well-defined stoma and are differently armed. The estuary and shelf are dominated by selective and nonselective deposit feeders.     

A contemporary sediment and organic carbon budget for the Kara Sea shelf (Siberia)

It has recently been realized that the Arctic undergoes drastic changes, probably resulting from global change induced processes. This acts on the cycling of matter and on biogenic elements in the Arctic Ocean having feedback mechanisms with the global climate, for example by interacting with atmospheric trace gas concentration. A contemporary budget for biogenic elements as well as suspended matter for the Arctic Ocean as a baseline for comparison with effects of further global change is, thus, needed. Available budgets are based on the late Holocene sedimentary record and are therefore quiet different from the present which has already been affected by the intense anthropogenic activity of the last centuries.

We calculated a contemporary suspended matter and organic carbon budget for the Kara Sea utilizing the numerous available data from the recent literature as well as our own data from Russian-German SIRRO (Siberian River Run-off) expeditions. For calculation of the budgets we used a multi-box model to simplify the Kara Sea shelf and estuary system: input was assumed to comprise riverine and eolian input as well as coastal erosion, output was assumed to consist of sedimentation and export to the Arctic Ocean. Exchange with the adjacent seas was considered in our budget, and primary production as well as recycling of organic material was taken into account. According to our calculations, about 18.5 × 10⁶ t yr^− 1 of sediments and 0.37 × 10⁶ t yr^− 1 of organic carbon are buried in the estuaries, whereas 20.9 × 10⁶ t yr^− 1 sediment and 0.31 × 10⁶ t yr^− 1 organic carbon are buried on the shelf. Most sources and sinks of our organic carbon budget of the Kara Sea are in the same order of magnitude, making it a region very sensitive to further changes.     

Virio- and bacterioplankton in the estuary zone of the Ob River and adjacent regions of the Kara Sea shelf

The distribution of structural and functional characteristics of virioplankton in the north of the Ob River estuary and the adjacent Kara Sea shelf (between latitudes 71°44′44″ N and 73°45′24″ N) was studied with consideration of the spatial variations in the number (N _B) and productivity (P _B) of bacteria and water properties (temperature, salinity, density) by analyzing samples taken in September 2013. The number of plankton viruses (N _V), the occurrence of visible infected bacteria cells, virus-induced mortality of bacteria, and virioplankton production in the studied region varied within (214?2917) × 10³ particles/mL, 0.3?5.6% of NB, 2.2?64.4% of P _B, and (6?17248) × 10³ particles/(mL day), respectively. These parameters were the highest in water layers with a temperature of +7.3–7.5°C, salinity of 3.75?5.41 psu, and conventional density (στ) of 2.846?4.144. The number of bacterioplankton was (614?822) × 10³ cells/mL, and the N _V/N _B ratio was 1.1?4.5. A large amount of virus particles were attached to bacterial cells and suspended matter. The data testify to the considerable role of viruses in controlling the number and production of heterotrophic bacterioplankton in the interaction zone of river and sea waters.     

Structure of the phytoplankton communities and primary production in the Ob River estuary and over the adjacent Kara Sea shelf

The material was collected in the Ob River estuary and over the adjacent shallow Kara Sea shelf between 71°14′0 and 75°33′0N at the end of September 2007. Latitudinal zoning in the phytoplankton distribution was demonstrated; this zoning was determined by the changes in the salinity and concentration of nutrients. Characteristic of the phytocenosis in the southern desalinated zone composed of freshwater species of diatom and green algae were the high population density (1.5 × 10⁶ cells/l), biomass (210 μgC/l), chlorophyll concentration (4.5 μg/l), and uniform distribution in the water column. High primary production (∼40 μgC/l/day) was recorded in the upper 1.5-m layer. The estuarine frontal zone located to the north contained a halocline at a depth of 3–5 m. Freshwater species with low population density (2.5 × 10⁵ cells/l), biomass (24 μgC/l), and chlorophyll concentration (1.5 μg/l) dominated above the halocline. Marine diatom algae, dinoflagellates, and autotrophic flagellates formed a considerable part of the phytocenosis below the halocline; the community characteristics were twofold lower as compared with the upper layer. The maximal values of the primary production (∼10 μgC/l per day) were recorded in the upper 1.5-m layer. The phytocenosis in the seaward zone was formed by marine alga species and was considerably poorer as compared with the frontal zone. The assimilation numbers at the end of the vegetation season in the overall studied area were low, amounting to 0.4–1.0 μgC/μgChl/h in the upper layer and 0.03–0.1 μgC/μgChl/h under the pycnocline.     

Phytoplankton of the south-western part of the Kara Sea

The research was performed along a transect from the Yamal Peninsula coast towards the outer shelf of the southwestern part of the Kara Sea in September 2007. 130 phytoplankton species have been identified, among which 63 were found in the area for the first time. The total phytoplankton numbers varied within the range of 0.2 to 11.3 × 10⁹ cells/m², while biomass within the range of 43 to 1057 mgC/m². A well pronounced cross-shelf zoning in the phytoplankton communities was ascertained. The inner shelf zone about 30 km wide with depths down to 30 meters was characterized by the predominance of diatoms (up to 80% of the total algae numbers and biomass). The second group by value was dinoflagellates. Seaward in the area of the depth increase from 30 to 140 m, the zone of the Yamal Current was located, which was 40 km wide and notable for its active water dynamics. The total cell numbers in the zone reached a maximum for the entire investigated area: up to 11.3 × 10⁹ cells/m². The leading group in the phytoplankton was autotrophic flagellates, whose share in the total numbers reached 56–82%. Further than 70 km from the shore, the outer shelf zone was found with the water column rigidly stratified. The highest for the whole area phytoplankton biomass was identified here (up to 1.06 gC/m⁹), 80% of which was concentrated above the halocline. Diatoms dominated in the phytoplankton numbers (up to 92%) and biomass (up to 90%), which was related to the mass development of two species: Chaetoceros diadema and Leptocylindrus danicus.     

Estimation of Annual Kara Sea Primary Production

Primary production of phytoplankton and ice and under-ice flora of the Kara Sea and regions thereof has been assessed using region-specific models and MODIS-Aqua satellite data for 2002–2015. Average annual primary production of phytoplankton calculated for the growing season (April–October) amounted to 165 mg С m^–2 day^–1. Annual primary production of phytoplankton was 35 g C/m². Annual primary production of phytoplankton in the entire Kara Sea was 13 × 10¹² g C. Annual primary production of ice and underice flora calculated using an integrated biophysical model was 1.7 × 10¹² g C, or 12% of total primary production of the Kara Sea; the ice cover dynamics and published data were taken into account for the calculations. The results have been compared to earlier primary production estimates for the Kara Sea. The extent of the increase in sea productivity during warming of the Arctic and the decrease in ice cover area are discussed.     

Phosphatized calcareous conglomerate from the Kara Sea floor

Trawling of the bottom in the northeastern Kara Sea during cruise 125 of the R/V Professor Shtokman in 2013 recovered a block of cavernous, partly phosphatized carbonate rock consisting of biogenic carbonate material and partly crystallized diagenetic calcite. The fauna remains are mainly Oligocene–Pliocene planktonic and benthic foraminifers, with less common Oligocene–Miocene coccoliths and single wormlike organisms. Part of the phosphatized material in caverns is impregnated by manganese and iron oxides and enriched in heavy and trace metals. According to the oxygen isotopic composition, this rock formed under moderate temperature conditions. In terms of morphology, mineralogy, and the abundance of organic remains, the block is comparable to methanogenic carbonates found in other parts of the ocean, but shows no isotopically light carbon signatures typical of methane activity. This indicates the diversity of the carbon isotope composition of the Arctic carbonates.     

The upper desalinated layer in the Kara Sea

An area of about 40000 km² of desalinated upper layer waters with a salinity of less than 25 psu was found during cruise 54 of the R/V Akademik Mstislav Keldysh in the southwestern part of the Kara Sea (September 2007). Close to the boundary of this region located near the eastern coast of Novaya Zemlya, the salinity was less than 16 psu. The thickness of the desalinated layer was about 10 m. The results of the chemical analysis revealed that the observed desalination of the sea water was produced, first of all, by the Yenisei River, while the contribution of the Ob River’s waters was secondary. However, the most desalinated region near the eastern coast of Novaya Zemlya was separated from the Ob-Yenisei estuary and corresponded to a quasi-isolated lens. It is likely that the formation of this lens, as well as the major part of the desalinated upper layer waters, occurred in June when the flood of the Yenisei was maximal, while the further drift of the desalinated waters to the west of the Ob-Yenisei estuary was forced by the prevailing northern wind. The additional desalination (by 2–3 psu and even more) of the upper layer waters near the eastern coast of Novaya Zemlya might be related to the melting of the Novozemelskiy ice massif. The regularities of the temporal evolution of the upper desalinated layer, as well as the influence of this layer on the hydrological structure and dynamics of the southwestern Kara Sea, are discussed.     

Structure of the macrozoobenthic communities in the southwestern Kara Sea

The structure and distribution of the macrobenthic communities were studied in the southwestern Kara Sea. The material was collected in Baidaratskaya Bay in July 2007 and in a section running westward of the Yamal Peninsula in September 2007. The depths of the sampling stations ranged from 5 to 25 m in the Baidaratskaya Bay area and between 16 and 46 m in the Yamal section. A total of 212 benthic invertebrate species were recorded. In both areas, Bivalvia was the group with the highest biomass (54.88 g/m² in the Yamal section and 59.71 g/m² in the Baidaratskaya Bay area), while polychaetes were the group with the highest number of species (45 in the Yamal section and 64 the Baidaratskaya Bay area). Three major macrozoobenthic communities were recognized: the Astarte borealis community (20–46 m, the deepest sampling stations in both areas); the “medium-depth” community (10–20 m, extremely mosaic, usually dominated by Serripes groenlandicus); and the Nephtys longosetosa community (depth smaller than 10 m, characterized by low biomass and the absence of large bivalves and echinoderms). The western Yamal shallow-water communities were shown to be generally similar to those of Baidaratskaya Bay. The comparison of these results with those of the benthos censuses performed in 1927–1945, 1975, and 1993 showed that the benthic communities in the southwestern Kara Sea remained relatively stable during the second half of the 20th century and the early 21st century.     

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.     

Features of the continental runoff distribution over the Kara Sea

This paper considers different types of the continental runoff distribution over the Kara Sea depending on hydrological and meteorological processes based on 1993–2014 expedition data of the Shirshov Institute of Oceanology. The results of calculating the relative contribution of fresh water from several sources (the Ob and Yenisei rivers and melted ice) using hydrochemical parameters are also given.     

Warm-Water Planktonic Foraminifera in Kara Sea Sediments

Oceanology - The article is devoted to research of warm-water planktonic foraminifera species in the Arctic. The fauna of planktonic and benthic foraminifera in the surface and subsurface layer of...     

Genesis of organic matter in the Kara Sea bottom sediments

Based on simultaneous use of organic and geochemical indicators (δ¹³C, C/N, and n-alkanes), the genesis of organic matter (OM) in recent bottom sediments of the Kara Sea was characterized. Maps for percentages and absolute masses of marine and terrigenous OM were drawn. The masses of buried marine and terrigenous OM were compared to its supply to the sea and onto the sea bottom.     

Coastal dynamics at the Barents and Kara Sea key sites

The results of permafrost and coastal dynamics investigations at four key sites on the shores of the Kara and Barents Seas are discussed. Three ACD key sites, Marre-Sale, Shpindler, and Kolguev, characterize areas with active thermal erosion; key site Cape Bolvansky is found on a relatively stable coast. It is found that the coastal retreat rate has spatial and temporal variability, which is typical of the entire Arctic coast. Coastal deposits on the Kara and Barents Seas have a low organic carbon content. Annual input of material into the Kara Sea resulting from coastal degradation reaches 35–40 million t, including about 7.5 million t of ice, 0.35 million t of organic carbon, and 0.3 million t of soluble salts.This revised version was published online January 2005 with corrections to the title of the article.     

Submarine permafrost in the nearshore zone of the southwestern Kara Sea

The results of seismic studies in the shallow waters of the southwestern Kara Sea show the presence of a seismic unit that can be interpreted as relict submarine permafrost. The permafrost table has a strongly dissected upper surface and is located at a water depth of 5–10 m. A 3D modeling of the permafrost table suggests the presence of relict buried thermodenudational depressions (up to 2 km across) at a water depth of 5–10 m. The depressions may be considered to be paragenetic to thermocirques found at the Shpindler site. Relict thermocirques are completely filled with sediment and not exposed at the sediment surface.     

Variations in the composition of the ferromanganese concretions of the Kara Sea

It has been found when studying the distribution of 57 elements in flattened, pellet-shaped, and pipelike iron-manganese concretions of the Kara Sea, that the F₂O₃ and MnO₂ contents in them are 52.5 and 5.30%; 18.3 and 24.2%; and 13.0 and 0.44%, respectively. The pellet-shaped concretions are enriched with nonferrous metals and microelements (especially with arsenic, cobalt, molybdenum, and animony) to the highest degree relative to the sediments, the flattened concretions are enriched to a lesser degree, and the pipelike ones are enriched to the least degree. The relative enrichment with the medium elements and a negative cerium anomaly are observed in the distribution of the rare-earth elements, which is also revealed in the host sediments to a lesser degree. The low content of ore and rare elements in the iron-manganese concretions of the Kara Sea relative to oceanic concretions is related mostly to the high sedimentation rates and short exposition period of the concretions on the sea bottom.     

Depth-integrated and depth-resolved models of Kara Sea primary production

Primary production (PP) models of the Kara Sea are developed based on data collected on fall expeditions (September–October 1993, 2007, and 2011) and their precision assessment utilizes the dataset collected in September 2013. The algorithms for different model types (depth-integrated and depth-resolved) are compared. The depth-resolved model performs slightly better than the depth-integrated one (the rootmean- square-difference (RMSD) are 0.29 and 0.31, respectively). These algorithms utilize the daily assimilation number (DAN) and photosynthetic efficiency (ψ) as the model coefficients, and surface chlorophyll a (chl a) and photosynthetically active radiation (PAR) as input variables. These algorithms perform better than the models that use chl a alone. Our results suggest that an increase in the performance of the Kara Sea PP models depends on the input of the photophysiological characteristics of phytoplankton (DAN and ψ) and PAR. To a lesser extent, this concerns the advantages of the depth-resolved model over the depth-integrated one. The constructed region-specific Kara Sea PP models combined with satellite-derived chl a and PAR can be used to estimate annual values and long-term variation of PP in hydrologically and hydrochemically similar waters of the Arctic Ocean.     

Simulation of surface and internal semidiurnal tides in the Kara Sea

The problem of the dynamics of surface and internal waves M ₂ in the Kara Sea is solved within the QUODDY-4 3D finite-element hydrostatic model. It is shown that the conventional concept of surface-tide wave generation due to the interaction of two tidal waves (one arrives from the Barents Sea and the other is generated in the Arctic Ocean (AO) and propagates southward along the west coasts of Severnaya Zemlya) is only partially valid: the east branch of the tidal wave generated in the AO actually exists, but there is also a west branch that propagates along the St. Anna trough and another tidal wave that penetrates in the Kara Sea from the Laptev Sea through the Vilkitsky Strait. Simulated spatial distributions of the tidal velocities, amplitudes of internal tidal waves at the pycnocline depth, and some components of the budgets of barotropic and baroclinic tidal energy are discussed.