Anna Trough Research Articles

The Origin of the Chionoecetes Opilio Snow Crab Larvae in the Kara Sea

Most likely, the non-indigenous snow crab opilio, Chionoecetes opilio, entered the Kara Sea from the Barents Sea, both due to the migration of adults and with currents at the larval stage. At the moment, all bottom stages, including mature individuals and a large number of pelagic larvae are present in the Kara Sea. However, the origin of the larvae has not yet been clarified. The larvae that hatched in the Kara Sea should be at an earlier stage of development compared to the Barents Sea larvae that got here due, to later development of phytoplankton and, accordingly, later hatching. The larvae of the snow crab Chionoecetes opilio and the spider crab H. araneus were collected in the central and southwestern parts of the Kara Sea in July — early August 2019 by the Bongo zooplankton net 60 cm in diameter. It was established that the larvae were unevenly distributed across the Kara Sea. The main concentrations were found on the border with the Barents Sea in the St. Anna Trough (up to 860 ind./m2), and relatively high concentrations of larvae were noted in the southwestern part, where their abundance at the stations varied from 18 to 302 ind./m2. In the zone of the Ob-Yenisei plume, crab larvae were absent or their abundance was minimal. Using molecular genetic methods, the species identity of 361 larvae (344 C. opilio and 17 H. araneus) was reliably determined, and measurements of a number of morphological structures were made for 401 larvae. Significant differences in size at the zoea stage II between C. opilio and H. araneus were established. In most of the Kara Sea in July 2019, in zooplankton samples, crab larvae were represented by zoea I C. opilio with rare specimens of zoea I H. araneus of the Kara Sea origin. Only in the southwestern part, on the border with the Barents Sea, the presence of zoea II C. opilio and H. araneus was observed in samples with an increase in the proportion of the latter species in catches, which probably originate from the Barents Sea.

Bacterioplankton of the Western Part of the Kara Sea

Data on the structural and production characteristics of bacterioplankton in the western part of the Kara Sea at the beginning and in the middle of summer are presented. In the region of the St. Anna Trough slope, the average abundance of prokaryotes for the water column was (594–708) × 103 cells/ml (26.4–36.5 mgC/m3) in June and (247–517) × 103 cells/ml (12–28 mgC/m3) at the beginning of August. On the transect along Novaya Zemlya, the average abundance of bacterioplankton in the water column was (186–554) × 103 cells/mL (8.5–30 mgC/m3) within a week after the seasonal ice and (169–443) × 103 cells/mL (8–21 mgC/m3) in the midsummer. Bacterial specific growth rate did not exceed 1.28 day–1; its high values were observed in the upper warm water layer, above the halocline, and also at the near-bottom depths. At the beginning of summer, the production of bacterioplankton tended to decrease in the northeast direction. The distribution of prokaryotes abundance was determined by temperature and water saturation with oxygen, possibly as an indirect indicator of past phytoplankton “bloom”.

Vertical distribution of chlorophyll a in the western part of the Kara Sea in autumn 2020

The aim of the work was to study the distribution of chlorophyll a (Chl-a) in the deepest part of the western Kara Sea — the Novaya Zemlya Trough and in St. Anna Trough. Materials: field studies of Chl-a, macronutrients, dissolved oxygen and physical parameters were held in September 2020 during the 81st cruise of R/V «Akademik Mstislav Keldysh».The results showed that Chl-a concentration within the upper 100 m layer ranged from 0.01 to 1.37 mg/m3 (median value of 0.23 mg/m3). The maximum concentrations of Chl-a in the Novaya Zemlya Trough (0.39–1.18 mg/m3) were observed at depths of 10–35 m, in the St. Anna Trough (0.25–1.37 mg/m3) — in the upper 15-meter layer. In the vertical distribution of Chl-a the subsurface chlorophyll maximum (SCM) was noted at depths of 10–42 m. In the southern part of the St. Anna Trough, the maximum concentrations of Chl-a were observed in the surface horizon. SCM existence depended on the runoff water distribution: well-pronounced SCM was observed at stations with high surface salinity which were characterized by a deeper euphotic depth, and a low concentration of Chl-a at the surface. In regions affected by river runoff, which had low salinity and high nutrient content in the upper layer as well as shallow depth of the photic layer, the maximum concentrations of Chl-a were observed at the surface. The share of pheophytin varied from 18 to 73% (median value of 41%) with minimum values in the layer of chlorophyll maximum. Integrated Chl-a concentration ranged from 5.75 to 24.54 mg/m2 (median value of 9.51 mg/m2), the highest values were observed in regions with deeper euphotic layer and pronounced SCM.Practical value: the data on the vertical distribution of Chl-a concentration allow to expand understanding of the conditions of organic matter formation and productivity of the Kara Sea.

The Impact of Sea Ice Loss on Benthic Communities of the Makarov Strait (Northeastern Barents Sea).

The continental shelf of the northeastern Barents Sea is presently experiencing a weak influx of Atlantic water from the west. In recent times, warming in Arctic regions has led to an increase in extended ice-free periods in this area, instead of significantly elevating water temperatures. The implications of this phenomenon on the structure and functioning of benthic communities were investigated during the autumn of 2019 within the Makarov Strait, located in the southwestern part of the St. Anna Trough. The macrozoobenthic communities exhibited a clear connection with the duration of ice-free periods. This variable influenced a vertical carbon flux, which subsequently served as the primary predictor for faunal abundance and diversity, as demonstrated by redundancy and correlation analyses. Two faunal groups were identified, corresponding to short and long open-water periods. Both groups had similar alpha diversity (65 ± 6 and 61 ± 9 species per station) and biomasses (39 ± 13 and 47 ± 13 g m-2) but displayed differing abundances (1140 ± 100 vs. 4070 ± 790 ind. m-2) and other diversity indices. We observed a decline in the proportion of polychaetes, accompanied by an increase in the proportion and diversity of bivalves, as well as a rise in the abundance of infaunal species, sub-surface deposit feeders, and mobile suspension feeders, in response to the increasing vertical carbon flux. The potential increase in anthropogenic pressures related to oil development in the northeastern Barents Sea highlights the importance of our study for conservation and monitoring efforts in the region.

Pulses of Cold Atlantic Water in the Arctic Ocean From an Ocean Model Simulation

AbstractThe intrusion of the warm and saline Atlantic Water (AW) has significant implications and feedback on the dynamics and thermodynamics of the Arctic Ocean. The AW enters the Arctic Ocean through two gateways: Fram Strait (FS) and the Barents Sea Opening (BSO). The AW is the dominant source of oceanic heat to the Arctic Ocean. In conjunction with the measurements in key hydrographic sections, numerical ocean modeling provides us with a useful tool to characterize and corroborate the temporal and spatial variability of the AW branches. Simulations are conducted using the regional configuration Arctic and North Hemispheric Atlantic (ANHA) of the ocean/sea‐ice model Nucleus for Modeling of the Ocean running at 1/4° and 1/12° resolution. Online passive tracers from the model configuration are used to trace the pathways of the AW inflow in the Arctic Ocean. While studying the variability of the AW through FS and the BSO, a cold mode of AW (Cold Atlantic Water [CAW]) with a temperature below 0℃ is detected along the rim of the eastern Eurasian Basin. It is formed primarily due to the intense sea surface cooling of the AW in the Barents and Kara Seas. The CAW exhibits the cascading process as it propagates downstream through the St. Anna Trough, leading to a considerable mixing with the ambient water. The CAW pulses eventually result in a significant heat content reduction in the eastern Arctic. This study provides insight into the changing AW property and its potential impact on the Arctic Basin.

Findings of Pogonophores (Annelida: Siboglinidae) in the Kara Sea Associated with the Regions of Dissociation of Seafloor and Cryogenic Gas Hydrates

The discovery of new occurrences of pogonophores Siboglinum sp. and Nereilinum sp. from the St. Anna Trough (northwestern portion of the Kara Sea) has been described in this paper. Previously, occurrences of pogonophores (Crispabrachia yenisey and Galathealinum karaense) were reported in the southern part of the Kara Sea, in the estuary of the Yenisei River. Two areas in the Kara Sea where pogonophores were found coincide with the regions of distribution of two types of gas hydrates: oceanic seafloor gas hydrates, and gas hydrates associated with permafrost. Gas hydrate deposits in the permafrost are confined to the coastal regions of the Kara Sea. A methane flux forms in areas of dissociation of gas hydrates under the influence of river runoff. This methane source is vital for the survival of pogonophores. The existence of pogonophores in the St. Anna Trough indicates the presence of a methane flux associated with the inflow of Atlantic water, which causes dissociation of seafloor gas hydrates. The possible role of Arctic warming is apparent in both processes.

The Finding of Pogonophorans (Annelida, Siboglinidae) in the St. Anna Trough (Kara Sea) in an Area of Gas Hydrate Dissociation

The Finding of Pogonophorans (Annelida, Siboglinidae) in the St. Anna Trough (Kara Sea) in an Area of Gas Hydrate Dissociation

THE DISCOVERY OF POGONOPHORES (ANNELIDA, SIBOGLINIDAE) IN THE ST. ANNA TROUGH (KARA SEA) IN THE AREA OF GAS HYDRATES DISSOCIATION

Representatives of pogonophores (Annelida, Siboglinidae), whose vital activity is provided by symbiotic chemoautotrophic bacteria that oxidize methane and hydrogen sulfide, were found in the St. Anna trough at depths of 539 m and 437 m. The discovery of pogonophores indicates high concentrations of methane, which can occur because of dissociation of bottom gas hydrates under the influence of the influx of warm Atlantic water penetrating into the Kara Sea along the St. Anna trough.

Synoptic 129I and CFC–SF6 Transit Time Distribution (TTD) Sections Across the Central Arctic Ocean From the 2015 GEOTRACES Cruises

AbstractMeasurements of the tracers, 129I, CFC‐11, and SF6 on water samples collected in the Arctic Ocean in 2015 have been used to calculate mean ages, Γ and mixing, Δ parameters using transit time distributions (TTDs) to constrain water circulation and mixing time scales. Values of Γ and Δ determined separately using the two tracer pairs, SF6‐CFC‐11, and 129I‐CFC‐11 are in good agreement for gas solubilities estimated for saturation levels of 0.90, but agreement decreases for other gas saturation levels. Both Γ and Δ increase rapidly with increasing depth below the base of the intermediate water layer (ca. 1,000 m), but maintaining a value of Δ/Γ ≅ 1 supporting the use of this proportionality in applications of TTDs to deep ocean transport of substances such as anthropogenic carbon. Isolines of Γ = 20 years deepening to depths below 1,000 m over the flank of the Mendeleyev Ridge near the North Pole outline the bathymetrically steered, return flow of recently ventilated Atlantic Water toward Fram Strait. Basin interior waters are significantly older with the Γ = 25 years mean age isoline shallowing upward to depths above 500 m in the Makarov, Canada, and Eurasian Basins. Values of Δ remain relatively constant in the 6–10 years range in upper intermediate water across all three basins indicating that flow is principally advective and that the mixing specified by Δ likely occurs upstream of the central basins in regions proximal to the outflow from the Santa Anna Trough.

Structure and Circulation of Atlantic Water Masses in the St. Anna Trough in the Kara Sea

The inflow of warm and saline Atlantic water from the North Atlantic to the Western Arctic is provided by two branches, namely, the Fram Strait branch water and the Barents Sea branch water. The pathways of these branches merge at the St. Anna Trough, and then both branches propagate eastward along the continental slope, albeit at different depths. As a result, the local interaction between these branches in the trough affects the properties of the large-scale Atlantic water flow to the Eastern Arctic and the deep Arctic basins. In this study, we report extensively in situ measurements with high spatial coverage (56 hydrological stations organized into 7 transects) in the St. Anna Trough, obtained in August and October 2021. Based on these data, we reconstructed the thermohaline structure and circulation in this area and obtained new insights, which are crucial for the assessment of the interaction and heat balance of water masses in the trough. First, we state that the majority of the Fram Strait branch water is recirculated in the trough within the stable cyclonic gyre, while a smaller fraction returns to the continental slope. The formation of this gyre increases the residence time of the Fram Strait branch water in the trough and decreases the intensity of water and heat exchange between the trough and the continental slope. Second, we describe the dynamic interaction between the northward flow of the Barents Sea branch water and the surface layer. It causes intense transport of warm surface water from the Kara and Barents seas adjacent to the Novaya Zemlya toward the continental slope and its mixing with the Barents Sea branch water along the eastern part of the trough. These processes result in increased surface temperature at the eastern part of the trough, which enhances ice melting at the study area and increases the duration of the ice-free period.

Carbon Dioxide Flux at the Water\u2013Air Boundary at the Continental Slope in the Kara Sea

The values and direction of carbon dioxide flux in the area of the continental slope in the north of the Kara Sea (St. Anna Trough) are calculated based on field studies in 2020 within the Siberian Arctic Sea Ecosystems program. The existence of a stable frontal zone in this area has been confirmed, which is formed by an alongslope current and limits the northward spread of surface waters freshened by the continental runoff. The simultaneous analysis of the carbonate system in the upper sea layer and the CO2 concentration in the surface air layer shows the CO2 flux with a rate of 0.2 to 22 mmol/m2 day to be directed from the atmosphere into the water in the area of the outer shelf, which is affected by the river runoff, and in the area of the continental slope, which is beyond this effect. The highest rates of CO2 absorption by the sea surface layer are localized above the continental slope. Local processes in the area of the slope frontal zone determine the CO2 emission into the atmosphere with a rate of 0.34 mmol/m2 day.

Late Weichselian ice-sheet flow directions in the Russian northern Barents Sea from high-resolution imagery of submarine glacial landforms

Abstract The locations and orientations of more than 1000 late Quaternary subglacial and ice-marginal landforms, including streamlined sedimentary bed forms, glacitectonic hill-hole pairs, meltwater channels, and eskers, were mapped from blocks of multibeam data (area of 4861 km2) in the little-known Russian Barents Sea. Between Sentralbanken and Admiralty Bank, at ∼75°N, there is evidence for southward ice flow. Ice-flow indicators between Franz Josef Land and Novaya Zemlya show northeast flow into the head of St. Anna Trough. There is also evidence of southeast flow off the bank to the south of Franz Josef Land, and of flow convergence with northeast-flowing ice in Sedov Trough. Northeast flow of ice between Novaya Zemlya and Franz Josef Land suggests that the latter archipelago was not overrun by ice flowing north from the Barents Sea and, therefore, that a subsidiary ice dome was likely on Franz Josef Land. A major ice divide was also present at ∼76°N –77°N in the Russian Barents Sea.

New data on the fauna and the biogeographic structure of the Hydrozoa, Scyphozoa, Staurozoa and Alcyonacea (Anthozoa) of the Kara Sea

The paper considers the species composition of the fauna of several cnidarian groups of the Kara Sea. The author presents a list of species of the studied groups and indicates the types of habitat for each species. The analysis was based on the literature data, the collections of the Zoological Institute of the Russian Academy of Sciences and material collected in the Kara Sea during the expedition to the R/V Professor Multanovsky in 2019. In total, 87 species of Hydrozoa, 3 species of Scyphozoa, 4 species of Staurozoa, and 5 species of the order Alcyonacea from the class Anthozoa were recorded for the fauna of the Kara Sea, based on the new material obtained by the author and published literature data. The report presents the biogeographic structure of the discussed cnidarian groups. According to the types of biogeographic ranges, the fauna of the above-mentioned cnidarian groups in the Kara Sea mostly consists of representatives of the Boreal-Arctic type of habitat (63%), the Boreal and Amphiboreal biogeographic groups each containing 12% of the total number of described species, and the Panoceanic and Arctic groups together accounting for only 9% and 4% of the fauna of the Kara Sea. Two species new for the Kara Sea, Neoturris pileata (Forsskål, 1775) and Neoturris pileata (Forsskål, 1775), are described. Neoturris pileata is an element of the warm-water Atlantic fauna that penetrated into the Kara Sea with waters of Atlantic genesis. Nausithoe werneri is an element of the cold-water Arctic fauna that penetrated into the Novaya Zemlya Trough of the Kara Sea from the north-western side from the St. Anna Trough, which was open to the Polar Basin.

Природа региональных магнитных аномалий северо-востока Баренцево-Карской континентальной окраины по результатам интерпретации сейсмических данных

Based on the interpretation of seismic sections via seismic reflection method, the lines of which intersect the positive magnetic anomalies in the St. Anna Trough and on the North Kara Shelf, the authors have substantiated the position of the Early Cretaceous dike belt in the north of the Barents-Kara platform for the first time. They traced the belt from the arch-block elevation of arch. Franz Josef Land, which belongs to the Svalbard platе through the Saint Anna Trough and further into the Kara platе to arch. Severnaya Zemlya. The distinguished dyke belt has discordant relationships with the structural-tectonic plan of the region under consideration. The authors illustrate the manifestations of dyke magmatism in the marked tectonic elements in seismic sections, and conclude that the dyke belt relates to the formation of the structural system of the Arctic basin.

Assessing the current and future Arctic Ocean observing system with observing system simulating experiments

AbstractArctic Ocean Observing System Simulation Experiments (OSSEs) were performed with a pan‐Arctic coupled ocean–sea ice data assimilation system to assess the impacts of assimilating available observations on the Arctic ocean–sea ice state. To this end, the adjoint method with a 3‐year assimilation window was used to assimilate synthetic observations sampled from a 4 km model simulation at the spatio‐temporal distribution of the existing observing system. After data assimilation, the sea ice state, including sea ice concentration (SIC), sea ice thickness (SIT), and sea ice volume (SIV), were significantly improved, benefiting from the high spatio‐temporal coverage of SIC observations and the wintertime SIT observations. In contrast, the ocean state is not very well constrained with the existing hydrographic observing system. An additional 1° × 1° ocean profiling array with a 10‐day sampling frequency was seen to substantially improve the estimated ocean temperature and freshwater content. Data from additional moorings deployed in the Fram Strait and continental slope of the Laptev Sea could also improve the pathway of Atlantic inflow to the Arctic Ocean and the temperature of the Atlantic inflow but degrade the mean volume transport through the Fram Strait. Moreover, estimated exchanges between the Arctic Ocean and the Atlantic Ocean through the Fram Strait, Davis Strait and the St. Anna Trough were found to benefit from the high‐density profiling array.

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.

Phytoplankton of the St. Anna Trough: Influence of Abiotic Factors

Samples were collected in the area of the St. Anna Trough in the northern Kara Sea in September 2015 and July–August 2016. Based on salinity and temperature distribution, four areas have been distinguished: the shelf adjacent to the St. Anna Trough, the shelf edge, and the upper and lower parts of the continental slope. The variability of the structure of phytoplankton communities has been analyzed in view of environmental conditions in the distinguished areas. It is shown that changes in the species structure of phytoplankton are more associated with seasonal reorganization in the community than with the effect of river runoff and waters of the Barents Sea and Atlantic. In the shelf area, the presence of Barents Sea winter water led to an increase in the number of species of early spring diatoms and an increase in the abundance of early and late spring diatoms. An increase in the abundance and biomass of phytoplankton and changes in their vertical distribution in mid-July–early August occurred against the effect of Barents Sea and Atlantic waters on the area and desalination of the upper layer under the effect of river runoff in early September.

Influence of Environmental Factors on the Distribution of Pteropods Limacina helicina (Phipps, 1774) in Siberian Arctic Seas

Analysis of zooplankton collected on five cruises (2007–2016) in the Kara and Laptev seas has revealed considerable heterogeneity in the spatial distribution of the biomass of the pteropod Limacina helicina, one of the important components of the Arctic zooplankton. The biomass and abundance of mollusks in 2014–2016 were significantly lower than in the previous period, in 2007 and 2011. The existence of persistent aggregations of L. helicina in the area of the continental slope of the Kara Sea (St. Anna Trough) with a biomass an order of magnitude higher than in the adjacent areas has been shown. Such aggregations of L. helicina were related to a combination of favorable factors: high salinity (≥33 psu), optimal temperature range (1–5°C), and local hydrophysical processes associated with the slope frontal zone. Results of the General Linear Mixed Model (GLMM) have shown that the biomass of pteropods is primarily related to salinity and temperature. No relationship between the biomass of pteropods and the average chlorophyll concentration in the upper layer has been found. However, within L. helicina aggregations, the biomass of mollusks correlated with the concentration of chlorophyll a in the layer of its maximum.

Variability of the thermohaline structure and transport of Atlantic water in the Arctic Ocean based on NABOS (Nansen and Amundsen Basins Observing System) hydrography data

Abstract. Conductivity–temperature–depth (CTD) transects across continental slope of the Eurasian Basin and the St. Anna Trough performed during NABOS (Nansen and Amundsen Basins Observing System) project in 2002–2015 and a transect from the 1996 Polarstern expedition are used to describe the temperature and salinity characteristics and volume flow rates (volume transports) of the current carrying the Atlantic water (AW) in the Arctic Ocean. The variability of the AW on its pathway along the slope of the Eurasian Basin is investigated. A dynamic Fram Strait branch of the Atlantic water (FSBW) is identified in all transects, including two transects in the Makarov Basin (along 159∘ E), while the cold waters on the eastern transects along 126, 142, and 159∘ E, which can be associated with the influence of the Barents Sea branch of the Atlantic water (BSBW), were observed in the depth range below 800 m and had a negligible effect on the spatial structure of isopycnic surfaces. The geostrophic volume transport of AW decreases farther away from the areas of the AW inflow to the Eurasian Basin, decreasing by 1 order of magnitude in the Makarov Basin at 159∘ E, implying that the major part of the AW entering the Arctic Ocean circulates cyclonically within the Nansen and Amundsen basins. There is an absolute maximum of θmax (AW core temperature) in 2006–2008 time series and a maximum in 2013, but only at 103∘ E. Salinity S(θmax) (AW core salinity) time series display a trend of an increase in AW salinity over time, which can be referred to as an AW salinization in the early 2000s. The maxima of θmax and S(θmax) in 2006 and 2013 are accompanied by the volume transport maxima. The time average geostrophic volume transports of AW are 0.5 Sv in the longitude range 31–92∘ E, 0.8 Sv in the St. Anna Trough, and 1.1 Sv in the longitude range 94–107∘ E.

Assessment of phytoplankton photosynthetic efficiency based on measurement of fluorescence parameters and radiocarbon uptake in the Kara Sea

Spatial distribution of relative electron transport rate (rETR) values, the maximum quantum efficiency of PSII (Fv/Fm), and biomass-specific primary production (PB, mg C (mg Chl a)−1 h−1) were described for the eastern part of the Kara Sea in the autumn (September). A characteristic feature of this period was a noticeable decrease in the length of the day and the elevation angle of the sun, leading to a significant decrease in surface photosynthetically active radiation (PAR). Despite low light in the euphotic zone, the phytoplankton maximum quantum efficiency of PSII (Fv/Fm) was high (0.5–0.7) in the upper 30-m layer of the water column, which indicates a potentially active state of phytoplankton. At the same time, the main productive activity of phytoplankton was linked to the surface 0–3 m and was closely related to the daily incident PAR and the share of diatoms in the total phytoplankton biomass. Despite a decrease in light level and following a reduction in the values for productive characteristics of the phytoplankton community, diatoms continued to play a major role in primary productivity in the eastern Kara Sea at the end of the vegetative season. Comparative analysis of data obtained by two different techniques – fluorescence measurements and experimental carbon fixation estimations – demonstrated a close relationship between rETR and PB. However, surface values of PB changed more strongly than rETR, which may, apparently, reflect different efficiency in the use of absorbed light energy in the synthesis processes. Photosynthetic efficiency, reflecting the extent of use of the light energy caught in processes of organic matter synthesis, can be expressed through the ratio between PB and rETR values. The PB/rETR ratio increased in areas characterized by drastic gradients of hydrophysical conditions: over the external coastal shelf, central shelf and lower continental slope of the St Anna Trough.