Circulation in the southwestern part of the Kara Sea in September 2007

During cruise 54 of the R/V Akademik Mstislav Keldysh to the southwestern Kara Sea (September 6 to October 7, 2007), a large amount of hydrophysical data with unique spatial resolution was obtained on the basis of measurements using different instruments. The analysis of the data gave us the possibility to study the dynamics and hydrological structure of the southwestern Kara Sea basin. The main elements of the general circulation are the following: the Yamal Current, the Eastern Novaya Zemlya Current, and the St. Anna Trough Current. All these currents are topographically controlled; they flow over the bottom slopes along the isobaths. The Yamal Current begins at the Kara Gates Strait and turns to the east as part of the cyclonic circulation. Then, it turns to the north and propagates along the Yamal coast over the 100-m isobath. The Eastern Novaya Zemlya Current (its core is located over the eastern slope of the Novaya Zemlya Trough) flows to the northeast. Near the northern edge of Novaya Zemlya, it encounters the St. Anna Trough Current, separates from the coast, and flows practically to the east merging with the continuation of the Yamal Current. A strong frontal zone is formed in the region where the two currents merge above the threshold that separates the St. Anna Trough from the Novaya Zemlya Trough and divides the warm and saline Arctic waters from the cooler and fresher waters of the southwestern part of the Kara Sea. This threshold, whose depth does not exceed 100–150 m, is a barrier that prevents the spreading of the Barents Sea and Arctic waters to the southwestern part of the Kara Sea basin through the St. Anna Trough.     

Hydrochemical features of the Kara Sea aquatic area in summer 2015

During cruise 65 of the R/V Akademik Mstislav Keldysh in the Kara Sea, three transects were executed: one eastwards from the Novaya Zemlya Archipelago and two in the St. Anna and Voronin troughs. It was noted that the continental runoff affected the entire surveyed aquatic area, even at the northern extremity of the Novaya Zemlya Archipelago. The transect along the St. Anna Trough showed the presence of a slope frontal zone overlaid at the surface by a desalinated layer. The Voronin Trough was characterized by sliding of slope waters. The hydrochemical parameters show that the surveys were carried out during a recession of biological activity of the waters and that the peak bloom was over by that time. The hydrochemical structure of waters conformed to early autumn conditions, but before the beginning of intense cooling of surface waters.     

Ecosystems of Siberian Arctic Seas–2020: The Kara Sea (Cruise 81 of the R/V Akademik Mstislav Keldysh)

Cruise 81 of the R/V Akademik Mstislav Keldysh was organized by Shirshov Institute of Oceanology and took place from August 27 to September 25, 2020 under the Program “Marine Ecosystems of the Siberian Arctic.” Participants included 76 scientists from the institutes of Russian Academy of Sciences, Moscow State University, VNIRO, and the NRC Kurchatov Institute and specialists from the Emergency Situations Ministry. Coordinated hydrophysical, hydrochemical, biooceanological, geochemical, and radioecological research was carried out over the Kara Sea, on the shelf near the St. Anna Trough, the continental slope, the Novaya Zemlya depression, and bays of the eastern coast of Novaya Zemlya. The condition of disposed radioactive waste in bays of the archipelago was assessed.

     

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.     

Methane in Water and Bottom Sediments in Three Sections in the Kara and Laptev Seas

The methane content in water and bottom sediments was measured in vertical sections: Lena River Delta–continental slope (the Laptev Sea), Taimyr Peninsula–Voronin Trough, and along the Novaya Zemlya Archipelago. The methane concentrations varied from 2.5 to 70 nmol/L and from 590 to 2600 nmol/L in the water column and sediments, respectively. Most of the surface water samples showed oversaturation in methane (up to 19-fold, fourfold on average), which determined the water–atmosphere direction of methane fluxes, which amounted to 1–400 mol/km² day (52 mol/km² day on average).     

Fluorescence of dissolved organic matter as a marker for distribution of desalinated waters in the Kara Sea and bays of Novaya Zemlya archipelago

The optical properties and distribution of dissolved organic matter in the surface waters of the Kara Sea and bays of Novaya Zemlya archipelago were studied during the 63th cruise of the R/V Akademik Mstislav Keldysh. The fluorescence of dissolved organic matter has been studied over wide excitation (230–550 nm) and emission (240–650 nm) wavelength ranges. Based on the results of fluorescence measurements, we propose a simple technique for estimating the relative content of humic compounds entering the Kara Sea shelf region with Ob and Yenisei river runoff. We have found that the blue shift parameters of the DOM fluorescence are Δ_270–310 = 28 ± 2 nm and Δ_355–310 = 29 ± 2 nm. The highest contents of humic compounds in surface waters were measured on the transect across the desalinated layer of the Kara Sea, near the continental slope on the transect along the St. Anna Trough, and in the area of Sedova, Oga and Tsivol’ki bays. Traces of labile terrigenous organic matter were found in the region of the Voronin Trough, in the bays of the Severny Island of Novaya Zemlya, as well as in some freshwater reservoirs and ice samples of the archipelago. We established a conservative distribution of dissolved organic matter, whose content in water varied from 1.25 to 8.55 mg/L.     

Benthic fauna of Blagopoluchiya Bay (Novaya Zemlya Archipelago,Kara Sea)

The benthic fauna was studied in the Blagopoluchiya Bay (Kara Sea, Novaya Zemlya Archipelago) during an expedition of the R/V Professor Shtokman in autumn 2013. The inner basin of the bay, with depths of around 150 m, is separated from the outer slope of Novaya Zemlya by a shoal 30 m in depth. Six macrobenthic communities were described at nine stations (25 bottom grab samples) taken along a transect from the inner part of the bay to the outer part of the slope. The depths, position on the transect axis and sediment types were the major factors influencing the distribution of the communities. The benthic abundance and biomass in the inner and outer parts of the bay did not differ significantly. The diversity of macrobenthic organisms (α-diversity as the number of species in the sample and β-diversity as the rate of increase in species number in the area) was lower in the inner part of the bay. The intertidal zone (littoral) has been described. The littoral fauna was very poor; it comprised only the amphipods Gammarus setosus inhabiting the near-surface area.     

Atlantic Water flow through the Barents and Kara Seas

The pathway and transformation of water from the Norwegian Sea across the Barents Sea and through the St. Anna Trough are documented from hydrographic and current measurements of the 1990s. The transport through an array of moorings in the north-eastern Barents Sea was between 0.6 Sv in summer and 2.6 Sv in winter towards the Kara Sea and between zero and 0.3 Sv towards the Barents Sea with a record mean net flow of 1.5 Sv. The westward flow originates in the Fram Strait branch of Atlantic Water at the Eurasian continental slope, while the eastward flow constitutes the Barents Sea branch, continuing from the western Barents Sea opening.About 75% of the eastward flow was colder than 0°C. The flow was strongly sheared, with the highest velocities close to the bottom. A deep layer with almost constant temperature of about −0.5°C throughout the year formed about 50% of the flow to the Kara Sea. This water was a mixture between warm saline Atlantic Water and cold, brine-enriched water generated through freezing and convection in polynyas west of Novaya Zemlya, and possibly also at the Central Bank. Its salinity is lower than that of the Atlantic Water at its entrance to the Barents Sea, because the ice formation occurs in a low salinity surface layer. The released brine increases the salinity and density of the surface layer sufficiently for it to convect, but not necessarily above the salinity of the Atlantic Water. The freshwater west of Novaya Zemlya primarily stems from continental runoff and at the Central Bank probably from ice melt. The amount of fresh water compares to about 22% of the terrestrial freshwater supply to the western Barents Sea. The deep layer continues to the Kara Sea without further change and enters the Nansen Basin at or below the core depth of the warm, saline Fram Strait branch. Because it is colder than 0°C it will not be addressed as Atlantic Water in the Arctic Ocean.In earlier decades, the Atlantic Water advected from Fram Strait was colder by almost 2 K as compared to the 1990s, while the dense Barents Sea water was colder by up to 1 K only in a thin layer at the bottom and the salinity varied significantly. However, also with the resulting higher densities, deep Eurasian Basin water properties were met only in the 1970s. The very low salinities of the Great Salinity Anomaly in 1980 were not discovered in the outflow data. We conclude that the thermal variability of inflowing Atlantic water is damped in the Barents Sea, while the salinity variation is strongly modified through the freshwater conditions and ice growth in the convective area off Novaya Zemlya.     

Benthic fauna of Tsivolki Bay (Novaya Zemlya Archipelago,Kara Sea)

Benthic fauna in Tsivolki Bay (Novaya Zemlya Archipelago, Kara Sea) has been studied during the voyage of the R/V Professor Shtokman in 2013 and 2014. A peculiar feature of the bay is the presence of the Serp i Molot glacier in its inner part, which determines the extremely high content of suspended particles in the water column. The bay is divided into three parts: the inner part (close to the glacier), the middle basin, and the outer slope. These parts are separated from each other by several rises. Benthic communities changed gradually from the inner part of the bay towards the outer slope. Three communities were described from the data of nine grab stations (26 samples). The apex of the bay is occupied by the depleted community dominated by the isopod Saduria sabini and the bivalve Yoldiella lenticula, which can successfully survive the increased mineral sedimentation. In the middle basin, it is replaced by the transitional community with Ennucula tenuis and Portlandia arctica being the main dominants. Finally, the outer slope is inhabited by the community typical for the open parts of the Kara Sea. It is dominated by ^{Astarte crenata, Ophiacantha bidentata}, and Ophiopleura borealis. The main reason for macrobenthic distribution in the studied region is the content of mineral particles in the water column and bottom layers.     

The structure and distribution of the phytoplankton community in the deep region of the Northern Kara Sea

The phytoplankton community and its distribution were investigated in the eastern branch of the St. Anna Trough and over the adjacent Kara Sea shelf in September 2011 and in August 2014. The spatial and seasonal differences in the phytoplankton structure were analyzed in connection with ice melting and changes in the temperature, salinity, and biogenic regime. Four 4 zones were defined: the Kara Sea shelf, the upper part of the St. Anna Trough slope, the lower part of the St. Anna Trough slope, and its deep part. It was shown that over the Kara Sea shelf where riverine runoff influence was observed, the phytoplankton community differs from the community of the St. Anna Trough in both investigated periods: in September and August. Rearrangement of the phytoplankton community was observed in the frontal zone associated with the upper part of the slope in September of 2011. The main features of this rearrangement were a change in dominant species composition and a 1.5–2-fold increase in the number and biomass of algae. Over the lower part of the slope and deep area of the St. Anna Trough in August 2014 and September 2011, the phytoplankton community was at different successive stages: in August, at the late spring and summer stage, and in September, at the summer–autumn stage.     

Zooplankton in Bays of the Novaya Zemlya Archipelago: Composition,Distribution, and Role in Phytoplankton Grazing and Biosedimentation

Oceanology - The zooplankton community in two bays of the eastern coast of the Novaya Zemlya archipelago (Blagopoluchiya Bay and Tsivolki Bay) has been studied for the first time. Copepods of the...     

Ichthyofauna of the Eastern Coast Bays of the Novaya Zemlya Archipelago

Based on 2014–2016 studies and published data on the ichthyofauna composition near the eastern coast of Novaya Zemlya, a revised list of fish fauna has been compiled. It includes 30 species from 23 genera and 13 families. The taxonomic diversity of ichthyofauna, its characteristics in respect to geographic range and biotopic groups of fish are considered. In general, ichthyological communities in bays off the eastern coast are similar in the species ratio to the communities in the open Kara Sea, and do not demonstrate any essential features of isolation.     

The surface runoff of nutrients from the coasts of Blagopoluchiya bay of the Novaya Zemlya Archipelago

Resulting from the surveys in the Blagopoluchiya and Techenii bays at the Novaya Zemlya Archipelago during cruise 54 of the R/V Akademik Mstislav Keldysh in September of 2007, it was shown that the waters supplied from the archipelago coasts contained considerable amounts of dissolved nitrogen and phosphorus. The pH values and total alkalinities were also considerably increased. The laboratory experiments confirmed that the rocks forming the coasts of the surveyed bays might be sources of nitrogen and phosphorus. The effect of the Novaya Zemlya runoff upon the hydrochemical structure of the upper 10-m layer of the seawaters was traced for 16–20 km from the coast during the period of the surveys.     

Characteristics of short-period internal waves in the Kara Sea inferred from satellite SAR data

In this paper we present the results of short-period internal wave (SIW) observations in the Kara Sea on the basis of satellite ENVISAT ASAR data between July and October 2007. Altogether, 248 internal wave (IW) packets and solitons are identified in 89 SAR images. Detailed spatial statistics of IW signatures and their properties in the Kara Sea is presented. The primary regions of IW activity are the areas near the Kara Gates Strait, the southeastern part of the Novaya Zemlya Trough, and in the vicinity of Cape Zhelaniya. We identify the regions where large IW packets are observed with wavelengths up to 2–3 km and the front length exceeding 200 km. The mean interpacket distance for observed IWs is about 20 km, but it may reach 50–60 km. Consequent IW packets are observed to travel up to 500 km from the presumed generation points. The results of satellite observations are compared with results of previous studies.     

Elemental composition of zooplankton in the Kara Sea and the bays on the eastern side of Novaya Zemlya

The chemical composition of zooplankton in the Kara Sea Basin has been studied. Independent samplings of the open sea and the Blagopoluchie and Tsivol’ki bays of Novaya Zemlya testify to the similarity of the distribution pattern of all the studied elements. The chemical composition of samples is predominated by organic carbon (49.5 ± 4.8% of dry weight). The other most important constituent elements are Na, P, S, K, Mg, and Ca. Their average total concentrations are 4.82 ± 0.1%. From an analysis of the composition of major and trace elements of zooplankton in the Kara Sea and the bays of Novaya Zemlya, three groups of elements have been specified: with similar (С_org, K, S, P, Al, Ti, Sc, Cd, Se, Cs, and Rb), lower (Na, Ca, Mg, Fe, Mn, Zn, Sr, Ba, B, Cu, Pb, Cr, Ni, V, Co, Sb, Mo, Ag, Be, Ga, and Hg), and higher (Li, As, and U) contents compared to their mean concentrations in ocean zooplankton.     

Changes in the Quantitative Characteristics of Macro- and Meiobenthos in the Blagopoluchiya Bay from 2013 to 2020 (Novaya Zemlya,the Kara Sea)

Oceanology - Macro- and meiobenthos of the Blagopoluchiya Bay (Novaya Zemlya, Kara Sea) have undergone significant changes in their quantitative distribution from 2013 to 2020. During this period,...     

Radioecological investigations on the Northern Novaya Zemlya Archipelago

Multidisciplinary investigations carried out in the Cape Zhelaniya area and on the Severny ice dome of Severny Island in the Novaya Zemlya Archipelago during cruise 63 of the R/V Akademik Mstislav Keldysh in September 2015 included a study of the environmental radiation level. The landscape?geochemical and radiation?glaciological data show that the Severny ice dome serves as a secondary source of radionuclides on the surface of the ice sheet; this source originated from past nuclear weapons testing in the atmosphere over the Severnaya Zemlya test site. Some samples taken from the periglacial zone near the edge of the Severny ice dome yielded specific activity levels of radioactive cesium of 450–650 Bq/kg. The study of ice cores obtained by shallow (up to 5.4 m) drilling of three boreholes revealed no significant activity values. At the same time, glaciological investigations made it possible to obtain the first data on the previously unexamined glacier, which indicate that the radioactively contaminated layer is located at a depth of 15?20 m at the boundary of the glacier alimentation zone. No similar investigations had been conducted earlier either by Russian or international scientific teams.     

冲绳海槽中部表层沉积物中的放射虫

1992年7月“向阳红16号”海洋调查船利用大洋50型抓斗在冲绳海槽中部（25°30’－30°N,125°－129°E）区域内获取表层沉积物样品88个。表层沉积物中的放射虫定量分析结果表明;愈近海槽放射虫的数量及属、种丰度值愈高,西侧槽坡离开槽区越远,放射虫数量及属种越渐少。而东侧槽被放射虫数量则表现了高、低值成点状分布的格局。表层沉积物中两大类放射虫的百分含量分别为泡沫虫约占87％,罩笼虫约占13％。另外根据分析结果,把本区分为3个小的沉积区：陆坡上部沉积区;陆被下部沉积区;海槽底部沉积区。     

Benthic Fauna of Oga Bay (Novaya Zemlya,Kara Sea)

Oceanology - The benthic fauna of Oga Bay (Kara Sea, Novaya Zemlya archipelago) was studied in 2015–2016 during the R/V Akademik Mstislav Keldysh expeditions. Five grab stations at depths of...     

NotesBenthic foraminiferal distribution in surface sediments along continental slope of the southern Okinawa Trough: dependance on water masses and food supply

Benthic foraminiferal analysis of 29 samples in surface sediments from the southern Okinawa Trough is carried out. The results indicate that benthic foraminiferal abundance decreases rapidly with increasing water depth. Percentage frequencies of agglutinated foraminifera further confirm the modern shallow carbonate lysocline in the southern Okinawa Trough. From continental shelf edge to the bottom of Okinawa Trough, benthic foraminiferal fauna in the surface sediments can be divided into 5 assemblages: (1) Continental shelf break assemblage, dominated by Cibicides pseudoungerianus, corresponds to subsurface water mass of the Kuroshio Current; (2) upper continental slope assemblage, dominated by Cassidulina carinata , Globocassidulina subglobosa, corresponds to intermediate water mass of the Kuroshio Current; (3) intermediate continental slope assemblage, dominated by Uvigerina hispi-da, corresponds to the Okinawa Trough deep water mass above the carbonate lysocline; (4) lower continental slope- trough b