Shelf Zone Research Articles

ВИДОВОЙ СОСТАВ И РАСПРЕДЕЛЕНИЕ НЕПРОМЫСЛОВЫХ РАКООБРАЗНЫХ ШЕЛЬФА КАМЧАТСКОГО ЗАЛИВА В 2013 ГОДУ

The distribution of settlement density and biomass of non-commercial crustaceans in the shelf zone of the Kamchatka Gulf in 2013 based on the materials of 23 dredging stations was shown. 130 species of noncommercial crustaceans belonging to 5 taxonomic groups were identified. The most abundant stocks of noncommercial crustaceans were depths from 150 to 200 m. In the northern part of the Kamchatka Gulf near the Kamchatka River mouth a biocenosis has been preserved, identified earlier by A.P. Kuznetsov in his research, and according to the results of our research conducted in the central part of the Kamchatka Gulf shelf at a depth of 186 m, another biocenosis with amphipod dominance can be identified. The cold-water species of the boreal-arctic complex predominate in the shelf zone of the Kamchatka Gulf.

The hydrocarbon compounds sources in surface sediments of the Laptev Sea shelf

Rapid warming of the Arctic provokes large-scale degradation of permafrost on land terrestrial and in submarines. A vast amount of remobilized organic matter (OM) is involved in the modern biogeochemical cycle. Understanding of the fate of terrestrial OM moving from the land to the Arctic shelf is essential for predicting the potential feedback of Arctic ecosystems. In our research, an attempt was made to characterize the modern OM stored in the surface sediments of the Laptev Sea to estimate its composition variability and to identify the OM sources along with the “coastline - outer shelf” profile. Here we discuss the OM features revealed by Rock-Eval pyrolysis (RE) and the distribution of n-alkanes in combination with sediment grain-size analysis. The GC/MS records are directly comparable with RE data tracing the terrestrial OM along with the entire studied profile. However, we observe both a significant decline of terrestrial input and the rise of hydrobiont in the outer shelf zone. We assume that different OM sources may produce different ranges of RE values.

Detection Characteristics of the Parametric Method of Signal Processing in a Sparse Antenna Array of a Transportable Decameter Range Radar

Introduction. The possibility of application of modified parametric methods of spatial signal processing in a sparse antenna array (SEAA) of the receiving position of transportable over-the-horizon decameter range radar (DRR) intended for all-weather remote monitoring of the shelf zone is considered in this paper. With an operational deployment of DRR on unprepared coast, problems of the equidistant location of antenna elements (AEs) often arise. In the case of nonequidistant AEs location and matched spatial processing, antenna pattern has interference sidelobes, which level can significantly exceed the allowable or calculated one for an equidistant AA. A well-known alternative to matched processing are parametric methods of spectral analysis based on the using of models with a finite number of parameters, but their direct application requires an equidistant sampling of the spatial signal.Aim. The aim of the research is to develop and analyze the method of parametric processing of spatial signals of the SEAA which AEs are located on the line with a random step in the range from λ/2 to several λ, where λ is the DRR wavelength.Materials and methods. To construct the detection characteristics (DC) computer modeling in the MatLab environment, the reliability of which was confirmed by the construction of known and theoretically calculated DC, was used.Results. The developed method includes a procedure of restoring (synthesizing) of artificial signal of equidistant AA with subsequent application of Burg parametric algorithm to obtain an estimate of the angular spatial frequency spectrum. To prove the applicability of the parametric method of SEAA signals processing in the case of location signals detecting, DC were obtained and compared with optimal ones.Conclusions. The obtained results have proved the suboptimality of the parametric method of SEAA signal processing at the random AEs spacing step lying in the range from λ/2 to 3λ, what makes it possible to recommend it for using in transportable DRRs.

Sustainable Development of Oil and Gas Potential of the Arctic and Its Shelf Zone: The Role of Innovations

Currently, the Russian oil and gas industry is characterized by significant reserves depletion and the late stage of development of most fields. At the same time, new fields that are brought into industrial development, in the majority of cases, have hard-to-recover reserves. Furthermore, most prospective oil and gas deposits are located in the Arctic and its offshore territories and their development is much more complicated due to regional peculiarities. This substantiates the necessity of a special approach to the development of the oil and gas potential of the Arctic, based on innovation. The goal of the paper is to reveal the role of innovation activity in the sustainable development of the oil and gas potential in the Arctic and its offshore zone. The paper briefly presents the main urgent factors of Arctic development, which highlight the necessity of innovation for its sustainability. Then, it introduces the methods used for the research: the Innovation Policy Road mapping (IPRM) method in accordance with Sustainable Development Goals (SDGs) concept for clarifying how innovations will lead to sustainable development. In terms of results, this paper presents an innovation policy roadmap for the sustainable development of oil and gas resources of the Russian Arctic and its shelf zone and identifies the role of innovation within this development.

The Current Status of the Red King Crab (Paralithodes camtschaticus) Stock and Fishery off Western Kamchatka

The current status of the red king crab population off western Kamchatka is considered based on data from bottom trawl surveys and fishery statistics since 2013. Some biological parameters of this crab species are provided; its commercial stock is estimated; some features of red king crab fishery and determination of total allowable catch for the past 7 years are analyzed. The red king crab fishing was resumed in 2013 after an 8-year ban imposed due to the population decline. During this period, the stock recovered and reached values greater than those recorded before the ban: the total estimated size of red king crab population in 2017 was almost 244 million ind., which is the highest value for the recent 17 years of research; the estimated number of commercial-sized males, 110 million ind., has not been recorded from the western Kamchatka shelf for at least past 4 decades. Recently, the Severny Zapretny and Khairyuzovsky areas of the shelf zone have yielded their role of main feeding grounds for pre-recruit crabs and juveniles to the Ichinsky area located south. For the 7 years of red king crab fishery, harvest values have been steadily high. In the past 3 years, the major part of the annual catch of live crabs has been exported to China and South Korea. As the analysis of size structure show, the body size of male red king crabs has been increasing each year all over the shelf. This may be explained by the strict sorting of caught crabs aboard vessels transporting live crabs with the release of the largest individuals; another possible explanation is the relatively low recorded number of pre-recruits in the past 2 years. For the 7 years past (including 2019), the fishing mortality rate is estimated within a range of 5–16% of the crab stock actually recorded from the permitted fishery areas, which is a highly cautious approach. In the nearest future, the crab commercial stock is expected to gradually decrease, which, nevertheless, should not fall below the reference target value of biomass. The current status of the red king crab population off western Kamchatka does not raise concern, and the ongoing intense harvesting of this valuable species within the recommended catch size will not have any negative effect on its commercial stock.

Dissolved neodymium and hafnium isotopes and rare earth elements in the Congo River Plume: Tracing and quantifying continental inputs into the southeast Atlantic

The Congo River is the second largest river by discharge in the world and a major source of element inputs into the South Atlantic Ocean. Yet, the element fluxes and transport mechanisms across and beyond its estuary and their impacts on the marine distribution and cycling of many major and trace elements are not well understood. We present the first combined dissolved neodymium (Nd) and hafnium (Hf) isotope and rare earth element (REE) concentration distributions following the Congo River plume along its flow path off the West African coast and along a connected offshore latitudinal section at 3°S. The Congo River freshwater itself is characterized by extraordinarily high Nd and Hf concentrations of up to 4000 pmol/kg and 54 pmol/kg, and by Nd (εNd) and Hf (εHf) isotope compositions that range between −15.6 and −16.4 and between 0.35 and −1.4, respectively. Our near- and offshore data indicate that at salinities above 23 conservative mixing of Congo-derived Nd and Hf concentrations and isotopic signatures with ambient surface seawater occurs for at least 1000 km to the northwest of the river mouth. This demonstrates a large spatial extent of the influence of the Congo plume on trace metal distributions in the eastern south Atlantic surface waters. A comparison between dissolved Nd and Hf fluxes from the Congo River and the shelf zone estimated based on radium isotope compositions indicate that release from Congo-derived particulate phases likely balances strong estuarine REE and Hf removal in the low salinity zone. The combined riverine and shelf zone flux for Nd is almost twice as high as that estimated for the Amazon River, despite that the Amazon discharge is about five times higher than that of the Congo River. Even the offshore Nd flux estimated for the 3 °S transect based on radium isotope compositions still corresponds to ∼40% of the Congo-shelf-zone flux and reaches 150 ± 50 Mg/year for Nd. Moreover, intermediate waters below the plume are strongly affected by exchange with particulate inputs from the Congo River given that Nd isotope signatures are inconsistent with values expected from large-scale water mass mixing and instead support unradiogenic Nd release either from sinking or deposited Congo-derived detrital material. Deep and bottom water isotopic signatures are also slightly affected by interaction with particles and benthic Nd release.

Studying the Fluxes of the Marine Ecosystem Components from the Northwestern Shelf to the Deep Part of the Black Sea

Purpose. The study represents analysis of the features of the Black Sea ecosystem components transfer from the northwestern shelf to the deep-sea part and its dependence on circulation in the sea upper layer. Methods and Results. The fluxes of water mass, nutrients and bioproduction from the shelf zone to the deep part of the sea were calculated using the current fields and biogeochemical ones resulted from the reanalysis, which, in its turn, was carried out due to the Black Sea ecosystem model including assimilation of remote sensing data both in the numerical circulation model and in the biogeochemical block. Numerical modeling permitted to calculate the fluxes through three sections that bound the shelf zone (by the capes Kaliakra and Chersonesus, and along the 200 m isobath). Behavior of the RIM Current jet and, consequently, direction and magnitude of the flows through the boundaries of the northwestern shelf depend on the wind stress vorticity over the western part of the Black Sea. The type of circulation with the intense RIM Current jet pressed to the shelf edge, is characterized by the pattern of distribution of the inorganic nitrogen and phytoplankton surface concentration as a narrow strip of its high values along the Black Sea western and partially southern coasts. When the RIM Current jet is weak or moves from the shelf edge (that corresponds to the low values of the wind stress vorticity) the increased concentration values are located on the northwestern shelf. Conclusions. Direction, magnitude and character of horizontal distribution of the nutrient and bioproduction fluxes are determined mainly by circulation in the sea upper layer. The magnitude of these flows is significantly affected by difference between the nutrient and bioproduction concentrations in the shelf zone and in the deep part of the Black Sea.

Ecological response to changes in the structure of water masses in the pelagic of the Canary Current Marine Ecosystem

Based on the results of sea expeditions, interannual changes in structure of the ichthyocenosis in the pelagic zone of the southern shelf of Morocco in the Atlantic Ocean were studied in connection with changes in the habitat. Mass pelagic fish were selected as reference biological species: European and West African horse mackerel, European sardine, Eastern mackerel, sea bream, sea snipe, myctophids, as well as non-commercial fish species. Field data were obtained during the implementation of complex oceanographic surveys in the fall seasons (October-November) 2015–2018. The results of control trawls were used, in which any species amounted to at least 70 % of the catch. The analysis of the species composition of the control trawls, data of hydroacoustic tracking of trawls, thermohaline water characteristics is carried out. Data pairing was carried out by phased extraction and transformation using standard computer programs for processing various types of data (acoustic, hydrological, ichthyological), as well as specially designed programs that allow you to create a single database. It has been established that recent changes in the number of commercial and by-catch species observed in the ARZ of Morocco in recent years are associated with the presence or absence of so-called “settlement windows”, which appear in the T, S‑diagram field by regions of different configurations, which indicates changes in the ratios of water masses. Based on the identified relationships between changes in the ratio of water masses and changes in the species composition of the control trawls of accounting replenishment surveys, estimates of the expected changes in the biomass of mass pelagic fish in the coming years are made.

Regional features of ice cover in the West Kamchatka fishing subzone with considering яof the thermobaric conditions (according to the satellite data)

Aiming to develop the biological resources of the Okhotsk Sea shelf zone, a remote study of regional features of the ice processes dynamics in fishing areas is important. One of the main fishing areas of the Okhotsk Sea is the West Kamchatka subzone — the northeastern sector of the water area to the east of 153°30′ E, bounded from the south by latitude 54° N. Dynamics of seasonal changes in ice cover is inherent in every region of the sea, regardless of the total area of ice. Geophysical processes affect the ice cover through a complicated mediated correlation that includes changes of the atmospheric circulation parameters. Critical, anomalous states of the ice cover in the West Kamchatka fishing subzone and also the cause-effect relations of its formation are revealed during the pollock seasons in 2006–2017. The mechanism of influence of thermobaric conditions, confirming the influence of the Okhotsk tropospheric cyclone (OTC) and the Pacific tropospheric crest on the formation of abnormal ice conditions in the Okhotsk Sea both in general and in certain local areas is presented.

The relation of the northwestern shelf deep geological structure of the Black Sea with the phenomenon of gas seeps

Geophysical model inputs were the results of a survey on an anomalous magnetic field and a gravitational field of the Black Sea’s north-western shelf. Thegeophysical profiles of the complex effective parameter (CEP) are calculated and graphed. Complex effective parameter characterizes the relationship between the effective densities and the magnetization by their spatial distribution. Effective parameters (magnetization, density, CEP) were calculated within the studyarea with their distribution on the optimum depth. The profiles are meridional and parallel to each other, direction of the profiles from south to north. The distance between the profiles is 50 kilometers. The generalized deep structure of the study area was elucidated using the graphed profiles. The distribution of CEP on vertical sections within the shelf zone of the western Black Sea basin emphasizes the position in the space of tectonic elements. That is gives an idea about the nature and structure of the region’s lithosphere and their relationship with the spatial distribution of deposits and manifestations of hydrocarbons. Structural and geological interpretation of the CEP profile data was performed. According to the spatial consistency of the correlation by structures, the profiles are conditionally divided into two groups, the western and the eastern. Structural differences in profiles are explained by the presence of the Odesa-Sinop fault zone between the groups. According to the results of profiles interpretation and works of previous researchers, paleogeodynamic processes were established. That significantly complicated the geological structure of the Black Sea’s north-western shelf. The interpretation of the CEP field distribution gives additional arguments in favour of the Earth crust evolution on the north-western shelf of the Black Sea in the conditions of a passive continental margin with short periods of reverse motions with obligatory subduction due to the activation of rifting, the nature of which is yet to be studied. According to the results of interpretation, the presence of the Earth’s crust destruction zone was established. With the help of spatial analysis, the spatial regularities of the gas seeping manifestations with the zone of destruction of the Earth’s crust of continental type and sites of rising of the mantle surface are established.

Massive silicon utilization facilitated by a benthic‐pelagic coupled feedback sustains deep‐sea sponge aggregations

AbstractBiogeochemical cycling of silicon (Si), largely affected by biological drivers, is pivotal to the ecological functioning of the ocean. Most knowledge regarding biological utilization of Si derives from research on phototrophic organisms circumscribed to the photic ocean (i.e., diatoms). Utilization of Si in the aphotic ocean, where heterotrophic silicifiers become relevant Si users, remains poorly investigated. Here we quantify the flux rates and stocks characterizing Si cycling across dense aggregations of the hexactinellid sponge Vazella pourtalesii established in the aphotic zone of the central Scotian Shelf, Nova Scotia, Canada. Although individual rates of silicic acid consumption were low compared to other sponge species and diatoms, the large abundance of individuals (6.5 million) over the extension of these sponge grounds (2105 km2) leads to massive annual silicic acid consumption, invested in producing their siliceous skeletons of biogenic silica. This sponge activity accumulates large biogenic silica stocks both in the living population and in the sediments. Skeletal pieces in sediment revealed that a good portion of biogenic silica deposited to the bottom after sponge death recycles as silicic acid before being permanently buried. This biogenic silica–silicic acid turnover, facilitated by an unconventional silicification pattern that favors delamination and dissolution of V. pourtalesii spicules, causes silicic acid enrichment at oceanographic dimensions in the bottom water of the central Scotian Shelf. Silicic acid efflux from the bottom sustains a feedback mechanism that fulfills sponge needs for silicic acid and facilitates the persistence of sponge aggregations in the long term.

Контроль влияния природных условий на подводные трубопроводы коммунальных систем на черноморском побережье Кавказа

Currently, several tens of subsea pipelines are in operation on the Black Sea coast of the Caucasus – sea water intakes and wastewater outlets. Wastewater outlets are divided into shallow water (up to 5 m), deep water (up to 10 m) and abyssal water (over 25 m) outlets depending on the depth of the outlet head location. Shallow water outlets are used to drain rain waters into the sea, while deep and abyssal water outlets are designed to dump purified wastewater from sewage purification plants. Most of the existing subsea pipelines were built in the 60s-80s of the 20th century and are now physically significantly worn out, partially destroyed or simply decommissioned. The pollution of the marine environment off the Black Sea coast of the Caucasus with household wastewater poses a serious threat to the local population and numerous tourists. Periodic dumping of unpurified wastewater and pipeline accidents require regular monitoring of the coastal waters. At the same time, it is possible to significantly reduce the risk of accidents on pipelines already at the design stage. In particular, a brief analysis of the natural conditions of the Russian shelf of the Black Sea coast of the Caucasus and the accident rate of subsea pipelines makes it possible to recommend the use of steel pipes in the construction of communal systems of marine water supply and sewerage. The use of plastic pipes is permissible only at depths of more than 25 m. In the upper shelf zone, the construction of completely plastic submarine pipelines is reasonable only if they are properly buried in the layer of loose bottom sediments or in the bedrock of the bench. Additionally, we can recommend application of measures to compensate for linear temperature deformations of the pipes.

Circulation of Circumpolar Deep Water and marine environment traced by 127I and 129I speciation in the Amundsen Sea Polynya, Antarctica

The long-lived anthropogenic 129I released from human nuclear activities has been widely employed as an effective oceanographic tracer to investigate circulation of water masses in marine environment. Depth profiles of seawater collected from the Amundsen Sea Polynya, Antarctica were analyzed for total 129I and 127I, as well as their species of iodide and iodate. The measured 129I concentrations ((1.15–3.43) × 106 atoms/L) and 129I/127I atomic ratios ((0.53–1.19) × 10−11) indicate that anthropogenic 129I has not only reached the Antarctic surface marine environment but also the deep water due to a strong vertical mixing of water masses. The Circumpolar Deep Water (CDW) flowed southward along continental shelf towards the ice shelf zone (74.25°S) at a depth of 1025 m and then migrated upward and northward to the polynya and finally to the sea ice zone (71.95°S). The maximum upwelling depth of the CDW was around 200 m in the polynya. The source of 129I− in the polynya is predominantly the intrusion of source waters rather than the in-situ reduction of iodate by phytoplankton, implying a considerably slow reduction process of iodate to iodide in this region.

Issledovaniye potokov komponentov morskoy ekosistemy s severo-zapadnogo shel'fa v glubokovodnuyu chast' Chernogo morya

Purpose. The study represents analysis of the features of the Black Sea ecosystem components transfer from the northwestern shelf to the deep-sea part and its dependence on circulation in the sea upper layer. Methods and Results. The fluxes of water mass, nutrients and bioproduction from the shelf zone to the deep part of the sea were calculated using the current fields and biogeochemical ones resulted from the reanalysis, which, in its turn, was carried out due to the Black Sea ecosystem model including assimilation of remote sensing data both in the numerical circulation model and in the biogeochemical block. Numerical modeling permitted to calculate the fluxes through three sections that bound the shelf zone (by the capes Kaliakra and Chersonesos, and along the 200 m isobath). Behavior of the RIM Current jet and, consequently, direction and magnitude of the flows through the boundaries of the northwestern shelf depend on the wind stress vorticity over the western part of the Black Sea. The type of circulation with the intense RIM Current jet pressed to the shelf edge, is characterized by the pattern of distribution of the inorganic nitrogen and phytoplankton surface concentration as a narrow strip of its high values along the Black Sea western and partially southern coasts. When the RIM Current jet is weak or moves from the shelf edge (that corresponds to the low values of the wind stress vorticity) the increased concentration values are located on the northwestern shelf. Conclusions. Direction, magnitude and character of horizontal distribution of the nutrient and bioproduction fluxes are determined mainly by circulation in the sea upper layer. The magnitude of these flows is significantly affected by difference between the nutrient and bioproduction concentrations in the shelf zone and in the deep part of the Black Sea

Dinosaur Footprints in Terrigenous Sediments on the Early Jurassic Shelf of the Central North Caucasus: Sedimentological and Paleoecological Settings

Dinosaur footprints were found in Pliensbachian terrigenous rocks in the central North Caucasus. Tracks of different sizes (12‒35 cm) were identified at three levels of the Mizur Formation section. The sediments accumulated on the wide (15‒20 km) shelf of a paleobasin. The coastal land was covered with abundant vegetation. The warm and humid climate favored the development of weathering crusts, lake–bog systems, and peat accumulation. The seawater temperature ranged from 21 to 25°C. The accumulation of sediments on the shallow shelf and their distribution over the area were influenced by wave activity, currents, and tidal phenomena. At low tide, small dinosaurs visited the shelf zone in order to search for food in the form of benthic fauna, which was abundant in clayey–silty sediments. The simultaneous presence of significantly different–size animal tracks may indicate that large individuals preyed on smaller ones. The presence of dinosaur tracks at different levels of the upper Pliensbachian strata indicates that representatives of the terrestrial fauna periodically visited the paleoshelf during the Domerian.

Implications of the depth profile on the functional structure of the fish community of the Perdido Fold Belt, Northwestern Gulf of Mexico

Studies have demonstrated that environmental conditions affect the richness, diversity, and abundance of fish communities. Depth is an important variable with many species showing preferences for specific depth ranges. Here, we present a functional analysis of the fish community in the Perdido Fold Belt (PFB), Gulf of Mexico. The sampling design was structured across a depth range of 40–3500 m, using 20 oceanographic stations. The aims of our study were: (1) to determine the functional arrangement of the fish community in the PFB; and (2) to describe the effect of the environmental variables on fish richness and functional diversity. A total of 232 species were identified; 195 were grouped into 42 functional groups (FGs). Thirty-seven species did not group with any others and are referred to as “functionally independent species” (FIS). According to our results, depth changes in physicochemical variables allow us to segregate three vertically stratified zones: shelf, slope, and deep. Temperature was the most important environmental variable constraining functional distribution of fishes. The highest FG diversity, species diversity, and biomass were found in the shelf/slope zone (SSo), while the highest diversity of FIS was found in the shelf zone. As the SSo displays its highest diversity, and since greater diversity has been linked with greater resilience and stability of fish communities, the SSo may be the most resilient zone of the PFB. Our study provides the first description of the diversity and resilience of the PFB fish community and helps our understanding of the factors constraining the distribution and functional diversity of fishes across depth gradients.

Impact of climate change on the primary production and related biogeochemical cycles in the coastal and sea ice zone of the Southern Ocean

Climate change in the Southern Hemisphere has exerted impact on the primary production in the Southern Ocean (SO). Using a recently released reanalysis dataset on global biogeochemistry, a comprehensive analysis was conducted on the complex biogeochemical seasonal cycle and the impact of climate change with a focus in areas within the meridional excursion of the sea ice boundary—coastal and continental shelf zone (CCSZ) and seasonal sea ice zone (SIZ). The seasonal cycles of primary production and related nutrients are closely linked with the seasonal changes in sea ice and sea surface temperatures. As sea ice retreats and allows energy and gas exchange across the sea surface, phytoplankton growth is initiated, consuming accumulated nutrients within the shallow depth of ~40 m. The seasonal evolutions of physical, biological and chemical variables show both spatial and temporal consistency with each other. Climate change has altered the timing and amplitude of the seasonal cycle. While primary production has generally increased along with an intensified uptake of CO2, some areas show a reduction in production (e.g., Prydz Bay, eastern Indian Ocean). In the CCSZ, increased iron utilization and light availability allowed production to be increased. However, the mechanism by which these factors are altered varies from one location to another, including changes in sea ice cover, surface stratification, and downwelling/upwelling. In the SIZ, where iron is generally a limiting factor, iron supply is a key driver of changes in primary production regardless of other nutrients. There is a clear influence of climatic change on the biogeochemical cycle although the signal is still weak.

Observations of Buried Lake Drainage on the Antarctic Ice Sheet.

Between 1992 and 2017, the Antarctic Ice Sheet (AIS) lost ice equivalent to 7.6 ± 3.9 mm of sea level rise. AIS mass loss is mitigated by ice shelves that provide a buttress by regulating ice flow from tributary glaciers. However, ice‐shelf stability is threatened by meltwater ponding, which may initiate, or reactivate preexisting, fractures, currently poorly understood processes. Here, through ground penetrating radar (GPR) analysis over a buried lake in the grounding zone of an East Antarctic ice shelf, we present the first field observations of a lake drainage event in Antarctica via vertical fractures. Concurrent with the lake drainage event, we observe a decrease in surface elevation and an increase in Sentinel‐1 backscatter. Finally, we suggest that fractures that are initiated or reactivated by lake drainage events in a grounding zone will propagate with ice flow onto the ice shelf itself, where they may have implications for its stability.

Organic carbon and microbial activity in marine sediments on a global scale throughout the Quaternary

Microbial degradation of organic carbon in marine sediments is a key driver of global element cycles on multiple time scales. However, it is not known to what depth microorganisms alter organic carbon in marine sediments or how microbial rates of organic carbon processing change with depth, and thus time since burial, on a global scale. To better understand the connection between the dynamic carbon cycle and life’s limits in the deep subsurface, we have combined a number of global data sets with a reaction transport model (RTM) describing first, organic carbon degradation in marine sediments deposited throughout the Quaternary Period and second, a bioenergetic model for microbial activity. The RTM is applied globally, recognizing three distinct depositional environments – continental shelf, margin and abyssal zones. The results include the masses of particulate organic carbon, POC, stored in three sediment-depth layers: bioturbated Holocene (1.7 × 1017 g C), non-bioturbated Holocene (2.5 × 1018 g C) and Pleistocene (1.4 × 1020 g C) sediments. The global depth-integrated rates of POC degradation have been determined to be 1.3 × 1015, 1.3 × 1014 and 3.0 × 1014 g C yr−1 for the same three layers, respectively. A number of maps depicting the distribution of POC, as well as the fraction that has been degraded have also been generated. Using POC degradation as a proxy for microbial catabolic activity, total heterotrophic processing of POC throughout the Quaternary is estimated to be between 10−11 and 10−6 g C cm−3 yr−1, depending on the time since deposition and location. Bioenergetic modeling reveals that laboratory-determined microbial maintenance powers are poor predictors of sediment biomass concentration, but that cell concentrations in marine sediments can be accurately predicted by combining bioenergetic models with the rates of POC degradation determined in this study. Our model can be used to quantitatively describe both the carbon cycle and microbial activity on a global scale for marine sediments less than 2.59 million years old.

Current state of stock and fishery of red king crab Paralithodes camtschaticus at West Kamchatka

Current state of the red king crab population at West Kamchatka is considered on the data of bottom trawl surveys and fishery statistics since 2013. Some biological parameters of the crabs and assessments of the commercial stock are presented; recent condition of the red king crab fishery and evaluation of the total allowable catch are discussed. The red king crab fishery was resumed in 2013, after 8 years of ban caused by the population decrease. During the ban, the stock restored and exceeded the value observed before the ban: the total accounted abundance of red king crab in 2017 was about 244 . 106 ind. that was the highest level for the last two decades, with the number of commercial males estimated as 110 . 106 ind. — this amount was never observed before on the shelf of western Kamchatka, at least in four decades of surveys. Recently the northern forbidden district and Khayryuzovsky district of the shelf zone lost their role of the main areas of crabs reproduction and their juveniles feeding, in favour to the Ichinsky district located southward. Recent fishery of red king crab is fruitful and sustainable. In the last 3 years, the major part of annual catch is transported alive to ports of China and South Korea. For this purpose, the caught crabs are sorted strictly aboard fishing vessels and the largest males are released back to the sea. Possibly, year-to-year increasing of the males size on the West Kamchatka shelf is caused by this sorting and releasing; another effect of the large-sized crabs releasing is relatively low number of recruits in the last couple of years. The fishery elimination coefficient is estimated in the range 5–16 % of the total accounted stock for 2013–2019, that shows a highly precautionary approach. Gradual decreasing of the crab commercial stock is forecasted for the nearest future, though the stock will remain above the target value. Current state of the red king crab population at West Kamchatka is not considered as dangerous, and ongoing intense fishery of this valuable species within the recommended volumes will not affect this sustainable state.