Search Results (18)

Variability in the Laptev Sea–East Siberian Sea circulation system modulates freshwater circulation in the Arctic Ocean, yet details of these wind-driven mechanisms remain poorly understood. Based on in situ observations from the 2018 Sino-Russian joint Arctic expedition, this study investigates the modulatory influence of wind on circulation structures and freshwater transport in the study area and examines the long-term variation characteristics of this circulation and its inherent connection with the Arctic wind. In situ measurements confirm two freshwater transport pathways: a coastal-current route and a geostrophic slope-current route. As the Beaufort High moves toward the Canadian Basin, it shifts wind patterns from anticyclonic to cyclonic, which regulates the transport of shelf water by influencing the prevailing wind direction. Furthermore, our analysis identifies two main modes of long-term changes in summer surface circulation: the first mode characterizes the coastal-current architecture, while the second mode delineates slope-current configurations. Crucially, large-scale modes of the Arctic wind play an important role in regulating circulation. Its first mode corresponds to the summer anticyclonic circulation pattern of the Arctic Ocean Oscillation, which drives the eastward strengthening of the coastal current, while the third mode presents a mechanism similar to the Arctic Dipole, which promotes the development of the slope current by enhancing the convergence of the polar current and wind. This has led to the long-term strengthening of the slope current. Full article

The key area of the Arctic Ocean for atmospheric venting of CH₄ is the East Siberian Arctic Shelf (ESAS). Leakage of methane through shallow ESAS waters needs to be considered in interactions between the biogeosphere and a warming Arctic climate. The development of remote sensing techniques for gas seepage detection and mapping is crucially needed for further applications in the ESAS and other areas of interest. Given the extent of the seepage areas and the magnitude of current and potential future emissions, new approaches are required to effectively, rapidly, and quantitatively survey the large seepage areas. Here, we consider the main features of gas seep detection on the sea surface in the characteristics of wind waves and radar signals. The kinematics of wave packets based on the kinetic equation for the spectral density of the wave action of surface waves is described. The results of a full-scale experiment on the remote radar observation of a model gas seep to the sea surface in the radar equipment signals are considered. The characteristic radar signatures of the gas seep in a wide range of hydrometeorological conditions, the parameters of which were recorded synchronously with the radar mapping, were determined. The results of the first radar observations of natural methane seeps on the ESAS are presented, and their radar contrasts are evaluated. The theoretical conclusions are in good qualitative agreement with the results of the model experiment and field studies and can be used for further research in aquatic areas with potential gas seepage, both of natural or anthropogenic origin, such as bubbling release from broken underwater gas pipelines. Full article

The interannual features of the salinity in the Chukchi Sea during the ice-free period of a year are investigated on the base of Soil Moisture Active Passive (SMAP) satellite measurements and GLORYS12v1 reanalysis data. Analysis of salinity measurements revealed two types of Bering Summer Waters (BSW) propagation: “western” and “eastern”. The first is characterized by the penetration of Pacific waters into the northwest part of the sea, as well as the propagation of BSW to 180°W and 72.5°N. During the “eastern” type, salty waters are pressed to the eastern part of the shelf. Their area decreases and the northern boundary of the BSW area shifts to 174–176°W. Areas with low salinity, ~29 psu, are observed in the western part of the sea. Our study reveals that the formation of these types is affected not only by the inflow of Pacific waters through the Bering Strait but also by the East Siberian Current (ESC). Both factors are related and lead to correlated changes in the salinity of the Chukchi Sea waters. ESC carries Arctic freshwaters from west to east and leads to a decrease in salinity in the western part of the sea. At the same time, southward ESC caused the blockage of the northward currents in the Bering Strait and a decrease in the influx of saline Pacific waters in the southern part of the Chukchi Sea. The intensification of ESC occurred in 1994, 2002, 2012, and 2016, when the volume transport of ESC increased by approximately 0.2 Sv, while the influx through the Bering Strait decreased. As a result, in the years with intense ESC, the spatial structure of the salinity of the Chukchi Sea changed significantly and the shelf-averaged salinity decreased by 0.3–0.5 psu. Full article

Single-cell cyanobacteria, being an integral part of picoplankton in marine ecosystems, have been suggested to be important contributors to primary production and carbon cycles in the global ocean. The spatial distribution, abundance and diversity of natural communities of picocyanobacteria (PC) in estuaries of Khatanga, Indigirka and Kolyma rivers and adjacent shelves of the Laptev and East Siberian seas were studied in September 2017. The PC concentrations were higher in the estuaries than in the shelf stations of the seas. The abundance of PC was 1.25 × 10⁶ cells/L, 0.42 × 10⁶ cells/L and 1.58 × 10⁶ cells/L in the surface layer of Khatanga, Indigirka and Kolyma estuaries, respectively. The contribution of PC to total autumn picophytoplankton abundance averaged 6% and 3% in the Khatanga and Indigirka estuaries and reached 5% in the Kolyma estuary. Phylogenetic analysis of the 16S rRNA gene and ITS region clone libraries revealed picocyanobacterial sequences related to marine Synechococcus subclusters 5.1-I, 5.2 and 5.3. Of the phylotypes from Synechococcus S5.1-I and S5.2 that were found, only several were discovered earlier, while the remaining clones were unique. Two groups of phylotypes (clades A and E) were found that were not closely similar to those previously described in both marine and freshwater habitats. It can be expected that a more detailed study of the phytoplankton of the Arctic seas will further expand our understanding of the diversity of these key components of the food chains of oceanic biocenoses. Full article

This paper presents the results of an acoustic survey carried out from the fast ice in the shallow waters of the East Siberian Arctic Shelf (ESAS) using a single beam echosounder. The aim of this paper is to demonstrate an improved approach to study seafloor seepages in the Arctic coastal zone with an echosounder calibrated on site. During wintertime field observations of natural rising gas bubbles, we recorded three periods of their increased activity with a total of 63 short-term ejections of bubbles from the seabed. This study presents quantitative estimates of the methane (CH₄) flux obtained in wintertime at two levels of the water column: (1) at the bottom/water interface and (2) at the water/sea ice interface. In winter, the flux of CH₄ transported by rising bubbles to the bottom water in the shallow part of the ESAS was estimated at ~19 g·m⁻² per day, while the flux reaching the water/sea ice interface was calculated as ~15 g·m⁻² per day taking into account the diffusion of CH₄ in the surrounding water and the enrichment of rising bubbles with nitrogen and oxygen. We suggest that this bubble-transported CH₄ flux reaching the water /sea ice interface can be emitted into the atmosphere through numerous ice trenches, leads, and polynyas. This CH₄ ebullition value detected at the water/sea ice interface is in the mid high range of CH₄ ebullition value estimated for the entire ESAS, and two orders higher than the upper range of CH₄ ebullition from the northern thermocarst lakes, which are considered as a significant source to the atmospheric methane budget. Full article

The East Siberian Sea (ESS) is a large and the shallowest part of the Arctic Ocean. It is characterized by high biogeochemical activity, but the seawater carbonate system remains understudied, especially during the late autumn season. Data from the research vessel (RV) “Professor Multanovsky” cruise were used to assess the dynamics of the seawater carbonate system, air–sea CO₂ fluxes, and the calcium carbonate corrosive waters in the two biogeochemical provinces of the ESS shortly before freeze-up. The ESS waters were mainly a sink for atmospheric CO₂ due to the limited dispersion of river waters, autumn water cooling, and phytoplankton blooms in its eastern autotrophic province. The mean value of the CO₂ air–sea flux was 11.2 mmol m⁻² day⁻¹. The rate of CO₂ uptake in the eastern ESS was an order of magnitude larger than that in the western ESS. The specific waters and ice cover dynamics determined intensive photosynthesis processes identified on the eastern shelf and in the northern deep oligotrophic waters. A part of the surface and most of the bottom ESS waters were corrosive with respect to calcium carbonate, with the lowest saturation state of aragonite (0.22) in the bottom layer of the eastern ESS. The eastern ESS was the main source of these waters into the deep basin. The observed export of corrosive shelf waters to the deep sea can have a potential impact on the ocean water ecosystem in the case of mixing with layers inhabited by calcifying organisms. Full article

Subsea permafrost stability is the key to whether pre-performed methane sequestered in hydrate deposits escapes to the overlying strata. By making use of the 1D numerical modeling and field data, we analyze the capabilities of the time-domain (transient) electromagnetic method (TDEM) when being applied for subsea permafrost mapping, and study the effect of the background resistivity structure on the inversion models’ accuracy for a series of settings typical for the East Siberian Arctic Shelf—the broadest and shallowest shelf in the world ocean, which represents more than 70% of the subsea permafrost. The synthetic response analysis included the construction of a series of resistivity models corresponding to different settings (presence/absence of ice-bonded permafrost layer, different position of its top and bottom boundaries, different width and thickness of thawed bodies or taliks, variable seawater depth and its resistivity), and calculation of synthetic apparent resistivity responses used to assess their sensitivity to changes in the target parameters of the resistivity structure. This was followed by regularized inversion of synthetic responses and comparing resulting models with original (true) ones, which allowed us to understand the possible uncertainties in the geometry and resistivity of the reconstructed permafrost layer, depending on seawater depth and unfrozen layer thickness, as well as confirm the overall efficacy of TDEM technology for the subsea permafrost imaging. That is crucially important for understanding the current state of the subsea permafrost-hydrate system and possible future dynamics. Full article

The characteristics of eddy mass transport are estimated depending on the values of the parameters of a large-scale flow that forms under the conditions of the shelf seas in the Arctic. For this, the results of numerical simulation of the Kara Sea with a horizontal resolution permitting the development of mesoscale eddies are used. The multiple realizations of eddy mass flux resulting from a numerical experiment are considered as a statistical sample and are analyzed using methods of sensitivity study and clustering of sample elements. Functional dependencies are obtained that are closest to the simulated distributions of quantities. These expressions make it possible, within the framework of large-scale models, to evaluate the characteristics of the cross-isobathic eddy mass transport in the diffusion approximation with a counter-gradient flux. Numerical experiments using the SibCIOM model showed that areas along the Fram branch of the Atlantic waters trajectory in the Arctic as well as the shelf of the East Siberian and Laptev seas with adjacent deep water areas are most sensitive to the proposed parametrization of eddy exchanges. Accounting for counter-gradient eddy fluxes turned out to be less important. Full article

The East Siberian Arctic shelf is the area where the largest natural gas reserves are concentrated. The formation of permafrost of the Arctic shelf during the Ice Age contributed to the emergence of a zone of stable existence of gas hydrates in the sedimentary layer, and subsequent flooding of the shelf led to its gradual degradation, the thawing of gas hydrates and the subsequent emissions of methane into the atmosphere. In the first part of the paper, we use mathematical modeling to study the processes of the formation of subsea permafrost on the Arctic shelf considering changes in the sea levels over the past 200 thousand years. Numerical simulations show the influence of climate warming up to 2200 on the degradation of subsea permafrost and the violation of the conditions for the stable existence of methane hydrates in bottom sediments using the example of the East Siberian shelf. The second part of the paper proposes a method for seismic monitoring of the state of gas hydrates based on a solution of multi-parameter inverse seismic problems. In particular, the degree of attenuation of seismic energy is one of the objective parameters for assessing the consolidation of gas hydrates: the closer they are to the beginning of decomposition, the higher the attenuation and, hence, the lower the quality factor. In this publication, we do not solve a multi-parameter inverse seismic problem for a real geological object. This would be impossible due to the lack of necessary data. Instead, we focus on substantiating the possibility of correct solutions for the problem of the reconstruction of the absorption and velocities for a viscoelastic medium in relation to the problem of monitoring the state of gas hydrate deposits. As noted in a range of publications, the thawing of gas hydrates leads to an increase in the fluid saturation of the geological medium followed by an increase in the absorption of seismic energy—that is, a decrease in the quality factor. Thus, the methods of seismic monitoring of the state of gas hydrates to predict the possibility of developing dangerous scenarios should be based on solving a multi-parameter inverse seismic problem. This publication is devoted to the presentation of this approach. Full article

The East Siberian Arctic Shelf (ESAS) is a key area of CH₄ venting in the Arctic Ocean. The ESAS region stores more than 80% of the world’s predicted subsea permafrost and associated permafrost-related gas hydrates. Gas emissions from subsea permafrost are controlled by its current thermal state, which, in turn, depends on environmental factors. The aim of the manuscript is to show that the thermal state of subsea permafrost and phase transitions of its pore moisture can be estimated remotely by echo soundings, which can resolve the structure of shallow bottom sediments. It has been found that the duration of the seabed acoustic response (echo duration, Δ) at frequencies of 50 and 200 kHz correlates with sediment temperatures and generally increases with cooling below 0.5 °C. This correlation, explained by assuming a layered structure of the bottom sediments, establishes the basis for high-frequency acoustic thermometry. The technique is an advantageous tool for many applications: fast contouring of low-temperature zones, remote measurements of seabed surface temperature, and estimation of the thickness of frozen sediments near the bottom. The latter estimates have implications for the distribution of subsea permafrost and the stability of gas hydrates on the Arctic shelf. Full article

Based on a regional ice-ocean model, we simulated the state of the water masses of the Arctic Ocean to analyze the transport of dissolved methane on the Arctic shelves. From 1970 to 2019, we obtained estimates of methane emissions at the Arctic seas due to the degradation of submarine permafrost and gas release at the ocean–bottom interface. The calculated annual methane flux from the Arctic shelf seas into the atmosphere did not exceed 2 Tg CH₄ year⁻¹. We have shown that the East Siberian shelf seas make the main contribution to the total methane emissions of the region. The spatial variability of the methane fluxes into the atmosphere is primarily due to the peculiarities of the water circulation and ice conditions. Only 7% of the dissolved methane originating from sediment enters the atmosphere within the study area. Most of it appears to be transported below the surface and oxidized by microbial activity. We found that increasing periods and areas of ice-free water and decreasing ice concentration have contributed to a steady increase in methane emissions since the middle of the first decade of the current century. Full article

Data on the elemental composition of the diatom Chaetoceros spp. from natural phytoplankton communities of Arctic marine ecosystems are presented for the first time. Samples were collected during the 69th cruise (22 August–26 September 2017) of the R/V Akademik Mstislav Keldysh in the Kara, Laptev, and East Siberian Seas. The multi-element composition of the diatom microalgae was studied by ICP-AES and ICP-MS methods. The contents of major (Na, Mg, Al, Si, P, S, K and Ca), trace (Li, Be, B, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Mo, Ag, Cd, Sn, Sb, Cs, Ba, Hg, Tl, Pb, Bi, Th and U) and rare earth (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) elements varied greatly, which was probably associated with the peculiarities of the functional state and mineral nutrition of phytoplankton in the autumn period. Biogenic silicon was the dominant component of the chemical composition of Chaetoceros spp., averaging 19.10 ± 0.58% of dry weight (DW). Other significant macronutrients were alkaline (Na and K) and alkaline earth (Ca and Mg) metals as well as biogenic (S and P) and essential (Al and Fe) elements. Their total contents varied from 1.26 to 2.72% DW, averaging 2.07 ± 0.43% DW. The Al:Si ratio for natural assemblages of Chaetoceros spp. of the shelf seas of the Arctic Ocean was 5.8 × 10⁻³. The total concentrations of trace and rare earth elements on average were 654.42 ± 120.07 and 4.14 ± 1.37 μg g⁻¹ DW, respectively. We summarize the scarce data on the average chemical composition of marine and oceanic phytoplankton and discuss the limitations and approaches of such studies. We conclude on the lack of data and the need for further targeted studies on this issue. Full article

Environmental issues in the Arctic region are of primary importance due to the fragility of the Arctic ecosystem. Mainly persistent organic compounds are monitored in the region by nine stationary laboratories. Information on the volatile (VOC) and semi volatile (SVOC) organic priority pollutants is very limited, especially for the Russian Arctic. Air samples from 16 sites along the Russian Arctic coast from the White Sea to the East Siberian Sea were collected on sorption tubes packed with Tenax, Carbograph, and Carboxen sorbents with different selectivity for a wide range of VOCs and SVOCs in 2020 within the framework of the International Siberian Shelf Study Expedition on the research vessel Akademik Keldysh. Thermal desorption gas chromatography–high-resolution mass spectrometry with Orbitrap was used for the analysis. Eighty-six VOCs and SVOCs were detected in the air samples at ng/m³ levels. The number of quantified compounds varied from 26 to 66 per sample. Benzoic acid was the major constituent, followed by BTEX, phenol, chloroform, bis(2-ethylhexyl) phthalate, and carbon tetrachloride. The study allowed for obtaining the first ever data on the presence of 138 priority pollutants in the air of Russian Arctic, whereas the thorough assessment of their possible sources will be the aim of a next investigation. Full article

East Siberian Arctic Shelf, the widest and the shallowest shelf of the World Ocean, covering greater than two million square kilometers, has recently been shown to be a significant modern source of atmospheric methane (CH₄). The CH₄ emitted to the water column could result from modern methanogenesis processes and/or could originate from seabed deposits (pre-formed CH₄ preserved as free gas and/or gas hydrates). This paper focuses primarily on understanding the source and transformation of geofluid in the methane seepage areas using ions/trace elements and element ratios in the sediment pore-water. Six piston cores and totally 42 pore-water samples were collected in the East Siberian Sea and the Laptev Sea at water depths ranging from 22 to 68 m. In the active zones of methane release, concentrations of vanadium, thorium, phosphorus, aluminum are increased, while concentrations of cobalt, iron, manganese, uranium, molybdenum, copper are generally low. The behavior of these elements is determined by biogeochemical processes occurring in the pore-waters at the methane seeps sites (sulfate reduction, anaerobic oxidation of methane, secondary precipitation of carbonates and sulfides). These processes affect the geochemical environment and, consequently, the species of these elements within the pore-waters and the processes of their redistribution in the corresponding water–rock system. Full article

Seeps found offshore in the East Siberian Arctic Shelf may mark zones of degrading subsea permafrost and related destabilization of gas hydrates. Sonar surveys provide an effective tool for mapping seabed methane fluxes and monitoring subsea Arctic permafrost seepage. The paper presents an overview of existing approaches to sonar estimation of methane bubble flux from the sea floor to the water column and a new method for quantifying CH₄ ebullition. In the suggested method, the flux of methane bubbles is estimated from its response to insonification using the backscattering cross section. The method has demonstrated its efficiency in the case study of single- and multi-beam acoustic surveys of a large seep field on the Laptev Sea shelf. Full article