On the circulation, water mass distribution, and nutrient concentrations of the western Chukchi Sea

Substantial amounts of nutrients and carbon enter the Arctic Ocean from the Pacific Ocean through the Bering Strait, distributed over three main pathways. Water with low salinities and nutrient concentrations takes an eastern route along the Alaskan coast, as Alaskan Coastal Water. A central pathway exhibits intermediate salinity and nutrient concentrations, while the most nutrient-rich water enters the Bering Strait on its western side. Towards the Arctic Ocean, the flow of these water masses is subject to strong topographic steering within the Chukchi Sea with volume transport modulated by the wind field. In this contribution, we use data from several sections crossing Herald Canyon collected in 2008 and 2014 together with numerical modelling to investigate the circulation and transport in the western part of the Chukchi Sea. We find that a substantial fraction of water from the Chukchi Sea enters the East Siberian Sea south of Wrangel Island and circulates in an anticyclonic direction around the island. This water then contributes to the high-nutrient waters of Herald Canyon. The bottom of the canyon has the highest nutrient concentrations, likely as a result of addition from the degradation of organic matter at the sediment surface in the East Siberian Sea. The flux of nutrients (nitrate, phosphate, and silicate) and dissolved inorganic carbon in Bering Summer Water and Winter Water is computed by combining hydrographic and nutrient observations with geostrophic transport referenced to lowered acoustic Doppler current profiler (LADCP) and surface drift data. Even if there are some general similarities between the years, there are differences in both the temperature–salinity and nutrient characteristics. To assess these differences, and also to get a wider temporal and spatial view, numerical modelling results are applied. According to model results, high-frequency variability dominates the flow in Herald Canyon. This leads us to conclude that this region needs to be monitored over a longer time frame to deduce the temporal variability and potential trends.

Bryozoa of the Laptev and East Siberian seas: modern research

The new data about bryozoan fauna of the Siberian seas (Laptev Sea and East Siberian Sea) are obtained. 48 species of Bryozoa were identified in the samples, collected in the MMBI RAS expedition (2014) at 50 stations: 45 – in the Laptev Sea and 16 – in the East Siberian Sea. The taxonomic and biogeographic composition, the features of distribution of Bryozoa are analyzed. A comparative analysis of the studies of the end of the 20th century (1986, 1987 and 1993–1998) based on literature data is carried out (Gontar, 1990, 1994, 2004, 2015а,б, 2016). There was a significant increase 60 in the share of boreal-arctic species due to a significant decrease of arctic species (by almost a third), which probably reflects the climate change towards warming , observed at the beginning of the 21st century.

Two rare species of Danielsseniinae (Copepoda: Harpacticoida: Pseudotachidiidae) from the Kara and East Siberian Seas, with description of their previously unknown sexes

The previously unknown females of Danielssenia spitsbergensis Gee & Huys, 1994 and males of Mucrosenia kendalli Gee & Huys, 1994 (Pseudotachidiidae, Danielsseniinae) are described based on specimens collected in the Kara and East Siberian Seas. Females of D. spitsbergensis exhibit the main diagnostic features of the genus Danielssenia Boeck, 1873 (antennule four-segmented; proximal segment of antennary exopod with one seta; structure of all the mouthparts; absence of an inner seta on exopod-1 of P2–P4; P5 not fused medially and with distinct exopod and baseoendopod, the latter with five setae; genital field with small copulatory pore and short copulatory duct leading to seminal receptacle with paired anterior chambers). At the same time, these specimens also exhibit some distinctive features which are unique for the species but disagree with the generic diagnosis. These peculiarities validate the placing of D. spitsbergensis as species incertae sedis within Danielssenia and point out the necessity of examination of other ‘Danielssenia-like’ forms before the true taxonomic position of this species can be elucidated. Both males and females of M. kendalli exhibit the autapomorphies of the genus, viz. P2 endopod-2 with a mucroniform process reaching almost to end of endopod-3 (this sexually dimorphic character is more pronounced in the males but also present in females); P2 endopod-2 without inner seta; posterior displacement of caudal ramus seta II; presence of tuft of long setules at inner distal corner of caudal ramus; P2 endopod shorter than exopod; P2–P4 exopod-1 without inner seta. Furthermore, some particular features (anal somite and pseudoperculum morphology; female P1 endopod distinctly longer than exopod; P5 exopod with distinct suture on dorsal surface separating it from the baseoendopod; prominent mucroniform process on P2 endopod-2) of the Kara and East Siberian Sea specimens conform fully with the original description of M. kendalli but apparently differ from M. kliei (Smirnov, 1946), the single female of which was collected from the same region and depth. Therefore, the validity and definite status of the specimen described by Smirnov is still a matter of conjecture pending additional findings and, particularly, the discovery of the male.

Spatial distribution of Icelus bicornis (Reinhardt, 1840) and Icelus spatula Gilbert & Burke, 1912 in the russian Arctic seas

This article provides data on distribution of two circumpolar species – twohorn sculpin Icelus bicornis and spatulate sculpin Icelus spatula in the Russian Arctic seas (Barents Sea, Kara Sea, Laptev Sea, East Siberian Sea) in the period from 2014 to 2019. The abundance of the twohorn sculpin varied from 2 to 18 ind/km2, and the biomass varied within 0.002–0.089 kg/km2. For the spatulate sculpin, these parameters were 2–21 ind/km2 and 0.002–0.699 kg/km2. The maximum and minimum values of these parameters for Icelus bicornis were recorded in the Laptev Sea, and for Icelus spatula in the East Siberian Sea. Information on the vertical spatial distribution of these species is also given, confirming the information given earlier that the spatulate sculpin occurs at shallower depths in contrast to the twohorn sculpin.

Age and Palynological Characteristics of Floodplain Deposits of the Kolyma Lowland (North-East Siberia)

River floodplains, reaching several kilometers in width, are one of the main landscape features of the Kolyma Lowland. Their relationship with other forms of relief - yedoma, alasses, and fragments of river terraces - is seen clearly in the Bolshaya Kuropatoch'ya River basin, which is located in the Lowland between 156°30' E and 157°15' E. The first radiocarbon dating of the floodplain deposits of the Kolyma Lowland was undertaken in a study of an outcrop on the left bank of the Bolshaya Kuropatoch'ya River (71°40' N, 156°45' E). Here floodplain sediments, represented by the alternating layers of alluvial silt and peat with a total thickness of 5 m, were exposed along a steep bank of an oxbow lake. The radiocarbon results show that the formation of the modern floodplain of the Bolshaya Kuropatoch'ya River began at the end of the Middle Holocene and continued during the Late Holocene to the present. Since the vegetation cover of arctic and subarctic regions is characterized by low pollen productivity, the spore-pollen spectra of modern and fossil plant communities often include an increased amount of pollen from plant species exotic to the Arctic, brought to the site by long-distance wind transport. For a more reliable interpretation of the spore- pollen spectra of the floodplain sediments, an analysis of the modern vegetation in the Bolshaya Kuropatoch'ya River basin and in a coastal area bordering the East Siberian Sea (about 71°05' N) was carried out, accompanied by an herbarium collection. The radiocarbon-dated palynological data indicate the development of the modern Betula-Salix shrub-herbaceous tundra during the second half of the Holocene. The establishment of this vegetation community reflects the replacement of an earlier Betula forest-tundra, which had prevailed in the northern regions of Western Beringia during the Early Holocene and included Duschekia fruticosa and large shrub species of Salix. Such dramatic changes in the vegetation cover were associated with the rise in sea level about 7.000-6.000 years ago, when seas approached modern levels. This change, in turn, led to a decrease in the contrast of summer and winter temperatures and, thus, to a decrease in the continentality of the climate and a significant reduction in the growing season in the coastal regions of the East Siberian Sea.

The effect of estuarine system on the meiofauna and nematodes in the East Siberian Sea

Arctic meiofauna and nematodes were examined at 12 stations in the East Siberian Sea, covering a depth range of 13–59 m and an estuarine-shelf system from the Indigirka and Kolyma rivers to the adjacent shelf. Our data reveal the low diversity of the meiofauna at the East Siberian Sea shelf. The meiobenthos abundance was influenced by river run-off and the sea bottom landscape. The samples comprised a total of 28 families and 72 genera, and the number of genera per station ranged from 15 to 32. The Comesomatidae was the dominant family with genus Sabatieria. Among all factors, depth, water temperature and the total organic carbon appeared to be important variables explaining spatial variations in meiofauna and nematodes abundance. Depth and river run-off were defining in controlling the density of nematodes in the study area.

Peculiarities of Tertiary petroleum systems evolution under prograding shelf environment on the continental margin of the East Siberian Sea

The upper part of the sedimentary cover within the East Siberian Sea shelf comprises Cenozoic clinoform deposits, which accumulated in passive continental margin settings. In the Eastern Arctic, the productivity of clinoform deposits has been proved on the Alaska North Slope and in the Beaufort–Mackenzie Basin. Considering that Cenozoic clinoform deposits are widely represented in the Russian part of the Eastern Arctic, they undoubtedly attract considerable interest from the standpoint of hydrocarbons prospecting. However, despite increasingly closer attention to this interval of the sedimentary section, it is still poorly understood due to its complicated geology. The lack of drilled wells in the region imposes a considerable limitation on an understanding of sedimentary basins development. In this situation, geophysical data become the primary source of information for building geologic models in the Russian sector of the Eastern Arctic. An assessment of hypothetical Cenozoic petroleum systems of the East Siberian Sea is the main objective of this paper. It is to be said research performed under high uncertainty of input data. The results obtained from basin analysis and numerical modeling indicate the possibility that an active petroleum system may exist in the Cenozoic sedimentary wedge of the East Siberian Sea. The outlook for the clinoform complex largely depends on the source rock maturity, i.e., higher prospects should be expected in areas where the prograding wedge has maximum thickness. Considering all factors (reservoir quality prediction, proximity to a hydrocarbon kitchen, timing), the Eocene–Oligocene part of the sedimentary section appears to offer the greatest promise within the study area. Here, predominantly oil accumulations may be expected at a depth of 2.5–3.5 km below sea bottom.