Kravchishina, Marina D

Klyuvitkin A.A., Kravchishina M.D., Starodymova D.P., Bulokhov A.V., Lein A.Y.

The mixing of hydrothermal vent fluids with deep ocean water and near-vent pelagic matter results in particle populations with a complex composition consisting of hydrothermally derived, rock-forming, and biogenic particles. This study is the first investigation of deep sediment trap material collected at the Jan Mayen hydrothermal vent field area at 71° N and 6° W of the southernmost Mohns Ridge in the Norwegian–Greenland Sea. This area is characterized by high magmatic activity, axial volcanic ridges, and mafic-hosted volcanogenic massive sulfide deposits. Data on sinking particle fluxes from two hydrothermal settings, the Troll Wall and Soria Moria vent fields, located about 4 km apart, are discussed in the article. In particular, the study emphasize the differences between two hydrothermal settings from each other that demonstrate the geodiversity of hydrothermal processes within the relatively shallow Jan Mayen hydrothermal vent field area affected by the Iceland and Jan Mayen hotspots. The fluxes of sinking hydrothermally derived particles (barite, gypsum, non-crystalline Fe-Si oxyhydroxides, and Fe, Zn, and Cu sulfides) obtained at the Jan Mayen hydrothermal vents made it possible to elucidate the characteristic features of their buoyancy plumes and compare them with similar data reported for other submarine hydrothermal systems. In terms of the composition of the deep-sea hydrothermal particles from buoyant plumes, the studied vent fields are most similar to the Menez Gwen and Lucky Strike vent fields affected by the Azores hotspot. The supply of hydrothermally derived matter is accompanied by normal pelagic/hemipelagic sedimentation, which is dominated by biogenic particles, especially in the upper water layers.

Klyuvitkin A., Kravchishina M., Starodymova D., Bulokhov A., Lein A.

Mixing of hydrothermal vent fluids with deep ocean water and near-vent pelagic matter results in particle populations with complex composition consisting of hydrothermally-derived, rock-forming, and biogenic particles. This study is the first investigating of deep sediment trap material collected at the Jan Mayen hydrothermal vent field area at 71° N and 6° W of the southernmost Mohns Ridge in the Norwegian-Greenland Sea. This area is characterized by high magmatic activity, axial volcanic ridges, and mafic-hosted volcanogenic massive sulphide deposits. Data on sinking particle fluxes from two hydrothermal settings, the Troll Wall and Soria Moria vent fields, located about 4 km apart are discussed in the article. In particular, the study emphasise the differences between two hydrothermal settings from each other that demonstrate the geodiversity of hydrothermal processes within the relatively shallow Jan Mayen hydrothermal vent field area affected by the Iceland and Jan Mayen hotspots. The fluxes of sinking hydrothermally derived particles (barite, gypsum, non-crystalline Fe-Si oxyhydroxides, and Fe, Zn, and Cu sulfides) obtained at the Jan Mayen hydrothermal vents made it possible to elucidate the characteristic features of their buoyancy plumes and compare them with similar data reported for other submarine hydrothermal systems. In terms of the composition of the deep-sea hydrothermal particles from buoyant plumes, the studied vent fields are most similar to the Menez Gwen and Lucky Strike vent fields affected by Azores hotspot.

Pautova L., Kravchishina M., Silkin V., Klyuvitkin A., Chultsova A., Vazyulya S., Glukhovets D., Artemyev V.

The modern Arctic is characterized by a decreased ice cover and significant interannual variability. However, the reaction of the High Arctic ecosystem to such changes is still being determined. This study tested the hypothesis that the key drivers of changes in phytoplankton are the position and intensity of Atlantic water (AW) flow. The research was conducted in August 2017 in the northern part of the Barents Sea and in August 2020 in the Nansen Basin. In 2017, the Nansen Basin was ice covered; in 2020, the Nansen Basin had open water up to 83° N. A comparative analysis of phytoplankton composition, dominant species, abundance, and biomass at the boundary of the ice and open water in the marginal ice zone (MIZ) as well as in the open water was carried out. The total biomass of the phytoplankton in the photic layer of MIZ is one and a half orders of magnitude greater than in open water. In 2017, the maximum abundance and biomass of phytoplankton in the MIZ were formed by cold-water diatoms Thalassiosira spp. (T. gravida, T. rotula, T. hyalina, T. nordenskioeldii), associated with first-year ice. They were confined to the northern shelf of the Barents Sea. The large diatom Porosira glacialis grew intensively in the MIZ of the Nansen Basin under the influence of Atlantic waters. A seasonal thermocline, above which the concentrations of silicon and nitrogen were close to zero, and deep maxima of phytoplankton abundance and biomass were recorded in the open water. Atlantic species—haptophyte Phaeocystis pouchettii and large diatom Eucampia groenlandica—formed these maxima. P. pouchettii were observed in the Nansen Basin in the Atlantic water (AW) flow (2020); E. groenlandica demonstrated a high biomass (4848 mg m−3, 179.5 mg C m−3) in the Franz Victoria trench (2017). Such high biomass of this species in the northern Barents Sea shelf has not been observed before. The variability of the phytoplankton composition and biomass in the Franz Victoria trench and in the Nansen Basin is related to the intensity of the AW, which comes from the Frame Strait as the Atlantic Water Boundary Current.

Novichkova E.A., Demina L.L., Starodymova D.P., Matul A.G., Kravchishina M.D., Chekhovskaia M.P., Oskina N.S., Lozinskaia L.A., Slomnyuk S.V., Solomatina A.S., Iakimova K.S.

A complex of sedimentological, geochemical, and micropaleontological methods was used to study and compare five new sediment cores along a submeridional transect from the middle to the north of the Norwegian Sea. A combined analysis of the distribution of ice-rafted debris, polar/subpolar foraminifera, calcium carbonate, organic carbon, and continuous geochemical scanning records revealed an alternation of Middle–Late Quaternary glacial and interglacial intervals over the last 260 000 years. In the Late Middle Pleistocene glaciation (MIS 6, 8), the supply of terrigenous material had a much greater influence on regional sedimentation than in the Late Pleistocene (MIS 2–4). Local (between the central and northern parts of the Norwegian Sea) differences in glacial and interglacial sedimentation are shown.

Kozina N.V., Reykhard L.Y., Kravchishina M.D., Filippov A.S., Dara O.M., Novichkova Y.A., Lozinskaya L.A., Slomnyuk S.V.

Vivianite, an authigenic mineral from the phosphate class, was discovered in Kara Sea bottom sediments for the first time. Similar finds of vivianite were previously known only for the outer shelf of the Laptev Sea, the northern Barents Sea, and the eastern White Sea. Its presence in the subsurface sedimentary strata indicates desalinization of the surface layer of the sea. Core 7444, sampled in a tectonic depression in the Kara Sea during the first stage of cruise 89 of the R/V Akademik Mstislav Keldysh (2022), uncovered Holocene sedimentary strata up to 6.19 m thick. Coarse-silty and sandy vivianite formations are found throughout the entire core, starting from 0.11 m. Vivianite was investigated by a set of methods: optical microscopy, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy. The morphology, microstructures, and chemical composition of vivianite formations have been studied. Three morphological types of these formations have been identified: micronodules and their intergrowths, crystalline aggregates and their intergrowths, and tubular aggregates.

Kravchishina M.D., Klyuvitkin A.A., Novigatsky A.N., Matul A.G., Ivanov V.V., Pestunov D.A., Shtabkin Y.A., Baranov B.V., Galkin S.V., Ambrosimov A.K., Kozina N.V., Lukianova O.N., Nemirovakaya I.A.

Multidisciplinary studies of the bottom sediments–water column–atmospheric water layer system in the Barents and Pechora seas and Baydaratskaya Bay of the Kara Sea were carried out on the expedition European Arctic–2023: Geological Record of Environmental and Climate Change during the season of polar night and active development of autumn–winter thermal convection. Fundamentally new data on a number of areas of oceanology were obtained in the cruise.

Bryukhanov A.L., Sevastyanov V.S., Kravchishina M.D., Voropaev S.A., Dushenko N.V., Kurakov A.V., Fedulova V.Y.

A study of the distribution of methane cycle microbial communities in the upper layers of bottom sediments above large hydrocarbon reservoirs in the South Kara petroleum region of the West Siberian Province revealed the presence in these layers of both aerobic methanotrophic bacteria and anaerobic methanogenic archaea, as well as numerous heterotrophic microorganisms of various phylogenetic groups. Research was carried out in the Baydaratskaya Bay and in the east of the Pukhuchan Depression (southern part of the Kara Sea). Aerobic methanotrophic bacteria belonged to the families Methyloligellaceae, Methylophagaceae and Methylomonaceae were detected in the surface oxidized layers (0–2 cm, Eh from 60 to 175 mV) of bottom sediments. Moreover, representatives of Methyloligellaceae were found in quite significant amount (1.52–2.61% of all 16S rRNA gene sequence reads) at all studied stations of the Kara Sea. In the subsurface reduced layers (18–20 cm, Eh from –63 to –246 mV), methanogenic archaea were dominated by representatives of the order Methanomassiliicoccales (up to 3.3% of all 16S rRNA gene sequence reads). Methanogenic archaea of the orders Methanofastidiosales, Methanobacteriales and Methanomicrobiales were also discovered. In addition, aerobic/facultative anaerobic methanotrophic bacteria of the families Methylococcaceae and Methylomonadaceae were found on these reduced layers of the bottom sediments, but the relative abundance (in percentage of sequence reads of their total number) of anaerobic methanotrophic archaea was extremely low there. Apparently, the oxidation of methane in bottom sediments of the Kara Sea, where its concentration at most of the studied stations dramatically increased with sediment depth, occurs predominantly under aerobic conditions in the surface layers, where the relative abundance and phylogenetic diversity of methanotrophs are higher.

Belyaev N.A., Fedulov V.Y., Kravchishina M.D., Shchuka S.A.

The article summarizes data on the suspended particulate matter content and dissolved and particulate organic carbon concentrations in Kara Sea water for 2007–2022. A difference in the distributions of dissolved (DOC) and particulate (POC) organic carbon in the water column during autumn (September) and spring–summer (July–August) was revealed. An increase in dissolved organic carbon concentrations was recorded both on the surface and in the water column in summer. Analysis of the dependences of DOC concentrations on salinity showed that the increase in these concentrations is not associated with an increase in DOC concentrations in river runoff water. There was also a significant increase in DOC and POC concentrations in phytoplankton bloom zones throughout the water column. Thus, a relationship has been identified between seasonal increases in organic matter concentrations in the open part of the sea and phytoplankton bloom processes.

Klyuvitkina T.S., Agafonova E.A., Novichkova E.A., Lozinskaia L.A., Chekhovskaya M.P., Matul A.G., Kravchishina M.D.

Climatic events of the last millennia in the northeastern part of the Norwegian-Greenland basin were reconstructed based on micropaleontological studies of sediments from the AMK-6150 core. New results were obtained from analyses of dinoflagellate cysts, diatoms, and benthic and planktonic foraminifers. These results allow us to infer the time of sediment accumulation and the prevailing natural conditions. According to preliminary data on climatostratigraphy based on the composition of microfossils, the period of sediment formation in the AMK-6150 core does not exceed 7 thousand years. The composition of microfossil assemblages and the results of reconstructions indicate repeated changes in marine environmental conditions during this time. Sediments at the depth of 23-24 cm recorded the beginning of a significant growth of temperature and salinity of surface waters due to a possible increase of the Norwegian Current influence. According to the species and quantitative composition of dinocyst and diatom assemblages, sediments in the short depth range of 14-12 cm accumulated during a period of noticeable decrease in temperature and increased influence of Arctic water masses. The analysis of dinocysts by the method of modern analogues allows reconstruction of the quantitative values of summer paleotemperatures of surface waters and the duration of ice cover. It was found that the cooling episodes and probable formation of seasonal sea ice were possible during the accumulation of sediments at the depths of 29-24, 14-12 and 3-1 cm.

Pautova L.A., Kravchishina M.D., Klyuvitkin A.A., Kudryavtseva E.A., Silkin V.A.

Klyuvitkin A.A., Kravchishina M.D., Novigatsky A.N., Politova N.V., Bulokhov A.V., Gulev S.K.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23060132

Kudryavtseva E., Kravchishina M., Pautova L., Rusanov I., Glukhovets D., Shchuka A., Zamyatin I., Torgunova N., Chultsova A., Politova N., Savvichev A.

The seasonally ice-covered marine region of the European Arctic has experienced warming and sea ice loss in the last two decades. During expeditions in August 2020 and 2021, new data on size-fractioned primary production (PP), chlorophyll a concentration, phytoplankton biomass and composition and carbon fixation rates in the dark were obtained in the marginal ice zone (MIZ) of the Barents Sea, Nansen Basin and Greenland Sea to better understand the response of Arctic ecosystems to ongoing climate changes. Four different situations were observed in the study region: (i) a bloom of the large-cell diatom Podosira glacialis, whose biomass was trapped in a strong halocline at the edge of a dense ice cover; (ii) a bloom of the chain-like colonies of Thalassiosira diatoms on the shelf in mixed waters in fields of shallow ice that could be supported by “fresh” elements in the polynya condition, as well as by terrestrial run-off and drifting ices; at the late stage, this bloom was accompanied by intensive growth of Phaeocystis pouchetti; (iii) dominance of small-cell phytoplankton under weakened stratification and the significant influence of the Atlantic water, depleted of microelements and silicates; (iv) dominance of dinoflagellates of eutrophic water in the contact zone between the water masses of Arctic origin and Atlantic origin in clear water under conditions of increased light intensity. The >10 µm phytoplankton cell size group increased its relative contribution to PP as a response to stratification, light and nutrient load associated with sea ice conditions. Small phytoplankton with sizes < 2 µm formed the basis of total PP in the MIZ regardless of the state of the sea ice.

Kravchishina M., Politova N., Klyuvitkin A., Lokhov A., Migdisova I., Kudryavtseva E., Penner I., Ambrosimov A., Schuka A., Novigatsky A.

Kruglinsky I.A., Kabanov D.M., Kalashnikova D.А., Kravchishina M.D., Makarov V.I., Popova S., Pochufarov A.O., Sakerin S.M., Simonova G.V., Shikhovtsev M.Y.

Klyuvitkin A., Kravchishina M., Novigatsky A., Politova N., Ambrosimov A., Glukhovets D., Sahling I., Bulokhov A.

Sergeeva V.M., Stepanova S.V., Flint M.V., Sukhanova I.N., Fedorov A.V., Artemiev V.A.

Su G., Guan M., Su M.

Ianiri H.L., Campbell P., Gartman A., Prouty N.G.

Lalande C., Yang E.J., Ko E., Park J., Jung J., Kim J., Moon J., Kim D., Jeon S.

AbstractFew in situ measurements are conducted early in the productive season in the Arctic Ocean, making it difficult to accurately assess the impact of the recent decline in sea ice cover on algal fluxes. Since 2017, time‐series sediment traps have been deployed to collect sinking particles at two sites in the Pacific Arctic region. Here, we present algal fluxes obtained in the East Siberian Sea (ESS) and in the northern Chukchi Sea (NCS) between August 2017 and November 2022. Despite interruptions in sampling, algal fluxes reflected large spatial and temporal variations in the magnitude and timing of algal blooms and export in the region. In the ESS, peak diatom fluxes > 600 million cells m−2 d−1 in early August 2018 reflected the occurrence of an unusually large and long‐lasting diatom bloom sustained by an episodic inflow of nutrient‐rich waters. Diatom fluxes were usually lower in the NCS than in the ESS, reaching a peak flux of > 170 million cells m−2 d−1 in late August 2017. As diatoms consistently contributed to the majority of algal fluxes, their rapid decrease and near absence frequently observed during July or August at both sites reflected low nutrient concentrations in the upper water column leading to a dominance of small algal cells typically retained in upper waters. Overall, whereas nutrient supply influenced the magnitude and duration of the diatom fluxes, sea ice breakup determined the timing of peak diatom export in the Pacific Arctic slope region.

Poojari M., Vardhan H., Hanumanthappa H., Jathanna H.M., Reddy D.G.

Gar’kusha D., Fedorov Y., Ovsepyan A., Popov Y., Andreev Y., Talpa B., Tambieva N., Myakinnikov I.

Baskunchak is a large drainless, highly saline lake located in the Caspian lowland. The chemical and gas composition of water (brine) and bottom sediments lying under a 10 cm layer of salt in the lake has been studied; specific fluxes of CH4 and CO2 at the water–atmosphere interface have been measured. The lake’s sodium chloride brine is characterized by high mineralization (313.5–334.7 g/L) and a slightly acidic–neutral pH (5.75–6.80). Bottom sediments are characterized by a slightly acid–neutral pH (6.27–6.64) and a reducing condition (Eh from −104.7 to +22.0 mV). Specific fluxes of CH4 into the atmosphere were low (0.11–0.12 mg CH4/(m2 h)) due to its low concentrations in the brine of the lake (0.91–2.66 µL/L). The appearance of an excess of HCO3 during the anaerobic oxidation of CH4 in the bottom sediments of the lake contributes to the formation of autigenic gypsum and calcite. Specific CO2 fluxes into the atmosphere ranged from 12.2 to 73.1 mg CO2/(m2 h). The probable source of CO2 in the brine of the lake and its emission into the atmosphere, in addition to the process of organic matter cycling and uptake by microorganisms, is the chemogenic precipitation of sulfates and calcium carbonates.

Drachev S.S., Ershova V.B., Shkarubo S.I.

Abstract The Laptev Sea in the East Siberian Arctic is characterized by a system of extensional structures known as the Laptev Rift System (LRS), developed at the continental prolongation of an active divergent plate boundary - the Gakkel spreading ridge. The LRS hosts as much as 13–14 km of siliciclastic sedimentary strata of supposedly Late Cretaceous to Recent age. The strata accumulated atop of stretched and thinned continental crust that before the rifting onset was a complex tectonic juncture of Late Paleozoic/Early Mesozoic Taimyr and Late Mesozoic Verkhoyansk fold-and-thrust belts formed along the edges of the Siberian Palaeocontinent. In the context of this volume, the LRS is described as a composite tectono-sedimentary element that includes sedimentary rocks accumulated during pre-rift and syn-rift phases. The latter includes at least two syn-rift sedimentary cycles separated by a sedimentary succession formed during a stalled rift phase. In the absence of deep exploration wells, many aspects of the LRS geology and its petroleum prospects remain poorly constrained.

Efimova T., Churilova T., Skorokhod E., Buchelnikov A., Moiseeva N.

Zhang X., Chen J., Xu Z., Liu H.

Ye Y., Munhoven G., Köhler P., Butzin M., Hauck J., Gürses Ö., Völker C.

Abstract. This study describes the coupling of the process-based Model of Early Diagenesis in the Upper Sediment with Adaptable complexity (MEDUSA version 2) to an existing ocean biogeochemistry model consisting of the Finite-volumE Sea ice–Ocean Model (FESOM version 2.1) and the Regulated Ecosystem Model (REcoM version 3). Atmospheric CO2 in the model is a prognostic variable which is determined by the carbonate chemistry in the surface ocean. The model setup and its application to a pre-industrial control climate state is described in detail. In the coupled model, 1390 PgC is stored in the top 10 cm of the bioturbated sediment, mainly as calcite, but also as organic matter (10 %). In the coupled simulation, atmospheric CO2 stabilizes at ∼295 ppm after 2000 years, in line with the CO2 level expected from the climate forcing conditions. Sediment burial of carbon, alkalinity, and nutrients in the coupled simulation is set to be compensated by riverine input. The spatial distribution of biological production is altered depending on the location of riverine input and reduction in sedimentary input, as well as the strength of local nutrient limitation, while the global productivity is not affected substantially. With this coupled ocean–sediment system the model is able to simulate the carbonate compensation feedback under moderate perturbation of CO2 in the atmosphere.

Sevastyanov V.S., Fedulova V.Y., Kuznetsova O.V., Dushenko N.V., Fedulov V.S., Bazhanova A.E.

Zhou C., Liu M., Mason R.P., Assavapanuvat P., Zhang N.H., Bianchi T.S., Zhang Q., Li X., Sun R., Chen J., Wang X., Raymond P.A.

Maslov A.V., Starodymova D.P., Migdisova I.A., Kozina N.V., Novichkova E.A., Alekseeva T.N., Shevchenko V.P.

Hoogakker B.A., Davis C., Wang Y., Kusch S., Nilsson-Kerr K., Hardisty D.S., Jacobel A., Reyes Macaya D., Glock N., Ni S., Sepúlveda J., Ren A., Auderset A., Hess A.V., Meissner K.J., et. al.

Abstract. A growing body of observations has revealed rapid changes in both the total inventory and the distribution of marine oxygen over the latter half of the 20th century, leading to increased interest in extending oxygenation records into the past. The use of paleo-oxygen proxies has the potential to extend the spatial and temporal range of current records, constrain pre-anthropogenic baselines, provide datasets necessary to test climate models under different boundary conditions, and ultimately understand how ocean oxygenation responds beyond decadal-scale changes. This review seeks to summarize the current state of knowledge about proxies for reconstructing Cenozoic marine oxygen: sedimentary features, sedimentary redox-sensitive trace elements and isotopes, biomarkers, nitrogen isotopes, foraminiferal trace elements, foraminiferal assemblages, foraminiferal morphometrics, and benthic foraminiferal carbon isotope gradients. Taking stock of each proxy reveals some common limitations as the majority of proxies functions best at low-oxygen concentrations, and many reflect multiple environmental drivers. We also highlight recent breakthroughs in geochemistry and proxy approaches to constraining pelagic (in addition to benthic) oxygenation that are rapidly advancing the field. In light of both the emergence of new proxies and the persistent multiple driver problem, the need for multi-proxy approaches and data storage and sharing that adhere to the principles of findability, accessibility, interoperability, and reusability (FAIR) is emphasized. Continued refinements of proxy approaches and both proxy–proxy and proxy–model comparisons are likely to support the growing needs of both oceanographers and paleoceanographers interested in paleo-oxygenation records.

Khreptugova A.N., Konstantinov A.I., Mikhnevich T.A., Matsubara F., Gustafsson Ö., Semiletov I.P., Perminova I.V.

Starodymova D.P., Kotova E.I., Shevchenko V.P., Titova K.V., Lukyanova O.N.

Luan Q., Mitchell E., Henley S.F., Orkney A.C., Bouman H.A., Braun J.S., Poulton A.J., Davidson K.

AbstractArctic phytoplankton are highly sensitive to seawater physical and chemical conditions, especially in the context of rapid climate change and sea ice loss. We studied the spatial and seasonal distributions of diatoms, dinoflagellates and coccolithophores, and clarified their associations with light, temperature and nutrients in the western Barents Sea in late summer 2017, and winter, spring and early summer 2018. Diatoms, composed mainly of Chaetoceros, Fragilariopsis and Thalassiosira, bloomed in spring at the southern border of the marginal ice zone with mean abundance of 1.1 × 106 cells L−1 and biomass of 119.5 µg C L−1, and were observed to follow the retreat of sea ice in the Arctic water to the north at the shelf break near Nansen Basin, contributing to the progression of the summer situation. Dinoflagellates flourished in surface waters south of Svalbard in summer, with maxima of 2.2 × 105 cells L−1 and 78.2 µg C L−1. High abundances and calcite mass of coccolithophores were detected in the southern Barents Sea and southwest of Svalbard in summer, with maxima of 3.3 × 105 cells L−1 and 4.7 µg C L−1. Two distinct phytoplankton assemblages, closely linked with Atlantic water and Arctic water, were geographically separated by the Polar Front in two summers, with a percent similarity below 11.9%, suggesting great influence of the two water masses on large-scale distributions of phytoplankton. Redundancy analysis revealed that temperature was one of the most important factors in shaping the seasonal distributions of diatoms, while irradiance showed positive correlation with dominant dinoflagellates of each season. From the perspectives of phytoplankton composition and carbon biomass, our findings highlight the governing effect of physical seawater conditions on driving seasonal patterns of phytoplankton biogeography, as well as the pivotal role of nutrients in supporting the phytoplankton growing seasons in the western Barents Sea.

Jahn A., Holland M.M., Kay J.E.

Observed Arctic sea ice losses are a sentinel of anthropogenic climate change. These reductions are projected to continue with ongoing warming, ultimately leading to an ice-free Arctic (sea ice area <1 million km2). In this Review, we synthesize understanding of the timing and regional variability of such an ice-free Arctic. In the September monthly mean, the earliest ice-free conditions (the first single occurrence of an ice-free Arctic) could occur in 2020–2030s under all emission trajectories and are likely to occur by 2050. However, daily September ice-free conditions are expected approximately 4 years earlier on average, with the possibility of preceding monthly metrics by 10 years. Consistently ice-free September conditions (frequent occurrences of an ice-free Arctic) are anticipated by mid-century (by 2035–2067), with emission trajectories determining how often and for how long the Arctic could be ice free. Specifically, there is potential for ice-free conditions in May–January and August–October by 2100 under a high-emission and low-emission scenario, respectively. In all cases, sea ice losses begin in the European Arctic, proceed to the Pacific Arctic and end in the Central Arctic, if becoming ice free at all. Future research must assess the impact of model selection and recalibration on projections, and assess the drivers of internal variability that can cause early ice-free conditions. With continued anthropogenic warming, an ice-free Arctic (sea ice area <1 million km2) is inevitable. This Review outlines the various characteristics of an ice-free Arctic, highlighting that future emission trajectories will determine where, how frequently and how long the Arctic will be ice free each year.

Wheeler B., Cannat M., Chavagnac V., Fontaine F.

AbstractWe report on a 3 years monitoring experiment of low to medium temperature diffuse venting at two vent sites (Tour Eiffel and White Castle) of the Lucky Strike, black smoker‐type hydrothermal field, Mid‐Atlantic Ridge. Diffuse vents account for a large part of the energy flux of mid‐ocean ridges hydrothermal fields and provide key habitats for the hydrothermal fauna. We document the time and space variability of diffuse venting temperature and chemistry, describe the effect of tidal loading and currents and discuss the extent of mixing, cooling of black smoker fluids, heating of entrained seawater and anhydrite precipitation/dissolution in the substratum. We emphasize the role of a thin (<2 m) volcaniclastic formation capping the brecciated basalt substratum. This formation is porous, but becomes impermeable when indurated by hydrothermal precipitates. It forms an intermediate layer between the vents at the seabed and the fluids as they discharge out of the brecciated basalts. Diffuse fluids inferred to discharge out of meter‐spaced cracks in the brecciated basalts beneath this volcaniclastic layer are hot (>80°C) and contain >10% of the hot endmember fluid component, over distances of up to 25 m from the black smokers. These results provide a geologically integrated framework in which to study site‐scale, near seafloor hydrothermal circulation and associated vent habitats at Lucky Strike and other black smoker‐type hydrothermal fields. They suggest diffuse heat fluxes in the upper range of previously published estimates at the two studied Lucky Strike hydrothermal vent sites.

Xie F., Zhao S., Zhan X., Zhou Y., Li Y., Zhu W., Pope P.B., Attwood G.T., Jin W., Mao S.

Abstract Background Methanomassiliicoccales are a recently identified order of methanogens that are diverse across global environments particularly the gastrointestinal tracts of animals; however, their metabolic capacities are defined via a limited number of cultured strains. Results Here, we profile and analyze 243 Methanomassiliicoccales genomes assembled from cultured representatives and uncultured metagenomes recovered from various biomes, including the gastrointestinal tracts of different animal species. Our analyses reveal the presence of numerous undefined genera and genetic variability in metabolic capabilities within Methanomassiliicoccales lineages, which is essential for adaptation to their ecological niches. In particular, gastrointestinal tract Methanomassiliicoccales demonstrate the presence of co-diversified members with their hosts over evolutionary timescales and likely originated in the natural environment. We highlight the presence of diverse clades of vitamin transporter BtuC proteins that distinguish Methanomassiliicoccales from other archaeal orders and likely provide a competitive advantage in efficiently handling B12. Furthermore, genome-centric metatranscriptomic analysis of ruminants with varying methane yields reveal elevated expression of select Methanomassiliicoccales genera in low methane animals and suggest that B12 exchanges could enable them to occupy ecological niches that possibly alter the direction of H2 utilization. Conclusions We provide a comprehensive and updated account of divergent Methanomassiliicoccales lineages, drawing from numerous uncultured genomes obtained from various habitats. We also highlight their unique metabolic capabilities involving B12, which could serve as promising targets for mitigating ruminant methane emissions by altering H2 flow.

Koenig Z., Muilwijk M., Sandven H., Lundesgaard Ø., Assmy P., Lind S., Assmann K.M., Chierici M., Fransson A., Gerland S., Jones E., H. H. Renner A., Granskog M.A.

Strong seasonality is a key feature of high-latitude systems like the Barents Sea. While the interannual variability and long-term changes of the Barents Sea are well-documented, the seasonal progression of the physical and biological systems is less known, mainly due to poor accessibility of the seasonally ice-covered area in winter and spring. Here, we use an extensive set of physical and biological in situ observations from four scientific expeditions covering the seasonal progression from late winter to late summer 2021 in the northwestern Barents Sea, from fully ice-covered to ice-free conditions. We found that sea ice meltwater and the timing of ice-free conditions in summer shape the environment, controlling heat accumulation, light and nutrient availability, and biological activity vertically, seasonally, and meridionally. In March and May, the ocean north of the Polar Front was ice-covered and featured a deep mixed layer. Chlorophyll-a concentrations increased from March to May along with greater euphotic depth, indicating the beginning of the spring bloom despite the absence of surface layer stratification. By July and in September, sea ice meltwater created a shallow low-density surface layer that strengthened stratification. In open water, chlorophyll-a maxima were found at the base of this layer as surface nutrients were depleted, while in the presence of ice, maxima were closer to the surface. Solar heating and the thickness of the surface layer increased with the number of ice-free days. The summer data showed a prime example of an Arctic-like space-for-time seasonal variability in the key physical and biological patterns, with the summer situation progressing northwards following sea ice retreat. The amount of sea ice melt (local or imported) has a strong control on the conditions in the northwestern Barents Sea, and the conditions in late 2021 resembled pre-2010 Arctic-like conditions with high freshwater content and lower ocean heat content.

Fu C., Myers P.G.

AbstractAn important question is will deep convection sites, where deep waters are ventilated and air-gas exchange into the deep ocean occurs, emerge in the Arctic Ocean with the warming climate. As sea ice retreats northward and as Arctic sea ice becomes younger and thinner, air-sea interactions are strengthening in the high-latitude oceans. This includes new and extreme deep convection events. We investigate the associated physical processes and examine impacts and implications. Focusing on a region near the Arctic gateway of Fram Strait, our study confirms a significant sea ice cover reduction north of Svalbard in 2018 compared to the past decade, shown in observations and several numerical studies. We conduct our study using the regional configuration Arctic and North Hemisphere Atlantic of the ocean/sea ice model NEMO, running at 1/12° resolution (ANHA12). Our numerical study shows that the open water condition during the winter of 2018 allows intense winter convection over the Yermak Plateau, as more oceanic heat is lost to the atmosphere without the insulating sea ice cover, causing the mixed layer depth to reach over 600 m. Anomalous wind prior to the deep convection event forces offshore sea ice movement and contributes to the reduced sea ice cover. The sea ice loss is also attributed to the excess heat brought by the Atlantic Water, which reaches its maximum in the preceding winter in Fram Strait. The deep convection event coincides with enhanced mesoscale eddy activity on the boundary of the Yermak Plateau, especially to the east. The resulting substantial heat loss to the atmosphere also leads to a heat content reduction integrated over the Yermak Plateau region. This event can be linked to the minimum southward sea ice volume flux through Fram Strait in 2018, which is a potential negative freshwater anomaly in the subpolar Atlantic.

Renner A.H., Bailey A., Reigstad M., Sundfjord A., Chierici M., Jones E.M.

Changes in the inflow of Atlantic Water (AW) and its properties to the Arctic Ocean bring more warm water, contribute to sea ice decline, promote borealisation of marine ecosystems, and affect biological and particularly primary productivity in the Eurasian Arctic Ocean. One of the two branches of AW inflow follows the shelf break north of Svalbard, where it dominates oceanographic conditions, bringing in heat, salt, nutrients and organisms. However, the interplay with sea ice and Polar Surface Water (PSW) determines the supply of nutrients to the euphotic layer especially northeast of Svalbard where AW subducts below PSW. In an effort to build up a time series monitoring the key characteristics of the AW inflow, repeat sampling of hydrography, macronutrients (nitrate, phosphate and silicate), and chlorophyll a (chl a) was undertaken along a transect across the AW inflow at 31∘ E, 81.5∘ N since 2012 - first during late summer and in later years during early winter. Such time series are scarce but invaluable for investigating the range of variability in hydrography and nutrient concentrations. We investigate linkages between late summer hydrographic conditions and nutrient concentrations along the transect and the preceding seasonal dynamics of surface chl a and sea ice cover in the region north of Svalbard. We find large interannual variability in hydrography, nutrients and chl a, indicating varying levels of nutrient drawdown by primary producers over summer. Sea ice conditions varied considerably between the years, impacting upper ocean stratification, light availability and potential wind-driven mixing, with a strong potential for steering chl a concentration over the productive season. Early winter measurements show variable efficiency of nutrient re-supply through vertical mixing when stratification was low, related to autumn wind forcing and sea ice conditions. While this re-supply elevates nutrient levels sufficiently for primary production, it likely happens too late in the season when light levels are already low, limiting the potential for autumn blooms. Such multidisciplinary observations provide insight into the interplay between physical, chemical and biological drivers in the marine environment and are key to understanding ongoing and future changes, especially at this entrance to the central Arctic Ocean.

Bodur Y.V., Renaud P.E., Goraguer L., Amargant-Arumí M., Assmy P., Maria Dąbrowska A., Marquardt M., Renner A.H., Tatarek A., Reigstad M.

The northern Barents Sea is a productive Arctic inflow shelf with a seasonal ice cover and as such, a location with an efficient downward export of particulate organic matter through the biological carbon pump.The region is under strong influence of Atlantification and sea-ice decline, resulting in a longer open water and summer period. In order to understand how these processes influence the biological carbon pump, it is important to identify the seasonal and spatial dynamics of downward vertical flux of particulate organic matter. In 2019 and 2021, short-term sediment traps were deployed between 30 and 200m depth along a latitudinal transect in the northwestern Barents Sea during March, May, August, December. Vertical flux of particulate organic carbon, δ13C and δ15N values, Chl-a, protists and fecal pellets were assessed. We identified a clear seasonal pattern, with highest vertical flux in May and August (178 ± 202 and 159 ± 79 mg C m-2 d‾1, respectively). Fluxes in December and March were < 45 mg C m-2 d‾1. May was characterized by diatom- and Chl a-rich fluxes and high spatial variability, while fluxes in August had a higher contribution of fecal pellets and small flagellates, and were spatially more homogenous. Standing stocks of suspended particulate organic matter were highest in August, suggesting a more efficient retention system in late summer. The strong latitudinal sea-ice gradient and the influence of Atlantic Water probably led to the high spatial variability of vertical flux in spring, due to their influence on primary productivity. We conclude that the efficiency of the biological carbon pump in a prolonged open-water period depends on the reworking of small, slow sinking material into efficiently sinking fecal pellets or aggregates, and the occurrence of mixing.

Reshetnikov M.G.

The paper discusses the main directions of interaction between economic and climate policy. It is stated that, despite external shocks and an increased level of uncertainty, the climate agenda remains in the focus of attention of the Government of the Russian Federation. The significant contribution of Russia to the achievement of the global goals of climate regulation is emphasized. The position of Russia regarding the reduction of greenhouse gas emissions in the medium and long term is substantiated. The important role of scientific research in substantiating the national climate policy is noted.

Borrel G., Fadhlaoui K., Ben Hania W., Gaci N., Pehau-Arnaudet G., Chaudhary P.P., Vandekerckove P., Ballet N., Alric M., O’Toole P.W., Fardeau M., Ollivier B., Brugère J.

The methanogenic strain Mx-05T was isolated from the human fecal microbiome. A phylogenetic analysis based on the 16S rRNA gene and protein marker genes indicated that the strain is affiliated with the order Methanomassiliicoccales. It shares 86.9% 16S rRNA gene sequence identity with Methanomassiliicoccus luminyensis, the only member of this order previously isolated. The cells of Mx-05T were non-motile cocci, with a diameter range of 0.4–0.7 μm. They grew anaerobically and reduced methanol, monomethylamine, dimethylamine, and trimethylamine into methane, using H2 as an electron donor. H2/CO2, formate, ethanol, and acetate were not used as energy sources. The growth of Mx-05T required an unknown medium factor(s) provided by Eggerthella lenta and present in rumen fluid. Mx-05T grew between 30 °C and 40 °C (optimum 37 °C), over a pH range of 6.9–8.3 (optimum pH 7.5), and between 0.02 and 0.34 mol.L−1 NaCl (optimum 0.12 mol.L−1 NaCl). The genome is 1.67 Mbp with a G+C content of 55.5 mol%. Genome sequence annotation confirmed the absence of the methyl branch of the H4MPT Wood–Ljungdahl pathway, as described for other Methanomassiliicoccales members. Based on an average nucleotide identity analysis, we propose strain Mx-05T as being a novel representative of the order Methanomassiliicoccales, within the novel family Methanomethylophilaceae, for which the name Methanomethylophilus alvi gen. nov, sp. nov. is proposed. The type strain is Mx-05T (JCM 31474T).

Klyuvitkin A.A., Kravchishina M.D., Novigatsky A.N., Politova N.V., Bulokhov A.V., Gulev S.K.

Abstract Continuous two-year studies of particle fluxes and associated environmental parameters in the axial zone of the Arctic segment of the Mid-Atlantic Ridge at the junction of the Mohns and Knipovich ridges (Norwegian Sea) have been carried out for the first time. Sediment traps were deployed from the R/V Akademik Mstislav Keldysh in June 2019 in the northeastern part of the Mohns Ridge with revision in August 2020 and lifting in July 2021. It is shown that the sedimentation of particles in the study area was affected by the global transport of water masses in the northeasterly direction, with Atlantic waters in the subsurface layer and water masses of Arctic origin recirculating deeper in the subsurface. A weak positive temperature trend at a depth of more than 2500 m (0.02°C over two years) is detected. The bimodal vertical distribution of fluxes and changes in the composition of sinking particles corresponded to the pattern of sediment recycling in the ocean. The annual course of fluxes in the subsurface layer is determined by the activity of Si-concentrating and calcifying plankton, while the maximum bloom period is also manifested in the deep layer. At the same time, the main significant source of the flux deeper than 2000 m is the supply of lithogenic matter from the near-bottom nepheloid layer.

Voropaev S.A., Sevastyanov V.S., Dushenko N.V., Bryukhanov A.L.

During the expedition of cruise 81 on R/V Akademik Mstislav Keldysh in 2020, extensive material, representing columns of bottom sediments up to 6 m deep in the Kara Sea, was selected. After the lithological description of the columns, sediment samples were taken from the different horizons for degassing of pore gases. The extracted gas samples were analyzed for the content of the main gases, such as methane (CH4), carbon dioxide (CO2), and light hydrocarbons. The characteristic features of changes in the CH4 and CO2 content with the depth of the bottom sediments at station 6879 (the Kara Sea shelf) were studied. A model of gas diffusion was constructed taking into account the biochemical reactions of methanogenesis and methane oxidation. The rate of methane formation can be estimated by the value J ≈ 3 × 10−10 μg s−1 L−1 (per liter of sediment). The coefficient of rate of methane consumption by microorganisms is K ≈ 0.5 × 10−10 s−1. The methane flow from the bottom surface of the Kara Sea near station 6879 is q ≈ 3.47 × 10−1 μL m−2 yr−1.

Kokhan A.V., Moroz E.A., Eremenko E.A., Denisova A.P., Ananiev R.A., Sukhikh E.A., Nikiforov S.L., Sokolov S.Y., Razumovskiy A.A.

The study is based on the results of multibeam echo-sounding and high-frequency seismic profiling during the 2018-2022 cruises of the R/V “Akademik Nikolai Strakhov” and “Akademik Boris Petrov”. Regular changes of morphometric parameters and the internal structure of pingo-like formations of the shelves of the Pechora and Kara seas were revealed. A morphometric analysis of pingo-like formations was carried out, which made it possible to draw conclusions about their relative age, as well as the role of near-bottom currents and slope processes in their modern dynamics. It was found that the density and morphological variety of pingo-like formations depend on the geological and tectonic features of the bottom area, the presence and nature of permafrost, the intensity of degassing, and the time of shelf flooding during the Holocene transgression. Pingo-like formations on the shelf, where the depth exceeds 70-80 m, emerged at the early stages of the Holocene transgression, and by now the permafrost there has largely thawed out. At the same time, pingo-like formations are still prominent in the relief and actively transformed by bottom currents, slope and, possibly, pseudovolcanic processes associated with ongoing degassing. Pingo-like formations are rare within shallow (up to 20-30 m) shelf areas close to the shore, and, apparently, continue their evolution at present. At the same time, the large thickness and continuity of permafrost prevent active fluid flow, acting as a seal. Pingo-like formations in the shallow-water zones are mainly cone-shaped mounds without intensive degassing. The density of pingo-like formations is maximum at the intermediate depths (from 20-30 to 70-80 m), in the presence of insular or discontinuous permafrost, under high fluid flow intensity within the fault zones and oil- and gas-bearing structures. Near-surface sediments in such areas are characterized by a combination of localized processes of heaving and active degassing. It predetermines a wide variety of the morphological types of pingo-like formations.Keywords: Arctic, bottom topography, degassing, pingo-like features, acoustic anomalies, multibeam echo sounding, seismoacoustic profiling

Stubseid H.H., Bjerga A., Haflidason H., Pedersen L.E., Pedersen R.B.

AbstractNearly 30% of ocean crust forms at mid-ocean ridges where the spreading rate is less than 20 mm per year. According to the seafloor spreading paradigm, oceanic crust forms along a narrow axial zone and is transported away from the rift valley. However, because quantitative age data of volcanic eruptions are lacking, constructing geological models for the evolution of ultraslow-spreading crust remains a challenge. In this contribution, we use sediment thicknesses acquired from ~4000 km of sub-bottom profiler data combined with 14C ages from sediment cores to determine the age of the ocean floor of the oblique ultraslow-spreading Mohns Ridge to reveal a systematic pattern of young volcanism outside axial volcanic ridges. Here, we present an age map of the upper lava flows within the rift valley of a mid-ocean ridge and find that nearly half of the rift valley floor has been rejuvenated by volcanic activity during the last 25 Kyr.