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Nitrous oxide (N2O) is a strong greenhouse gas and stratospheric ozone-depleting substance. Around 20% of global emissions stem from the ocean, but current estimates and future projections are uncertain due to poor spatial coverage over large areas and limited understanding of drivers of N2O dynamics. Here, we focus on the extensive and particularly data-lean Arctic Ocean shelves north of Siberia that experience rapid warming and increasing input of land-derived nitrogen with permafrost thaw. We combine water column N2O measurements from two expeditions with on-board incubation of intact sediment cores to assess N2O dynamics and the impact of land-derived nitrogen. Elevated nitrogen concentrations in water column and sediments were observed near large river mouths. Concentrations of N2O were only weakly correlated with dissolved nitrogen and turbidity, reflecting particulate matter from rivers and coastal erosion, and correlations varied between river plumes. Surface water N2O concentrations were on average close to equilibrium with the atmosphere, but varied widely (N2O saturation 38%-180%), indicating strong local N2O sources and sinks. Water column N2O profiles and low sediment-water N2O fluxes do not support strong sedimentary sources or sinks. We suggest that N2O dynamics in the region are influenced by water column N2O consumption under aerobic conditions or in anoxic microsites of particles, and possibly also by water column N2O production. Changes in biogeochemical and physical conditions will likely alter N2O dynamics in the Siberian Arctic Ocean over the coming decades, in addition to reduced N2O solubility in a warmer ocean.

Biogeochemical cycling in the semi-enclosed Arctic Ocean is strongly influenced by land–ocean transport of carbon and other elements and is vulnerable to environmental and climate changes. Sediments of the Arctic Ocean are an important part of biogeochemical cycling in the Arctic and provide the opportunity to study present and historical input and the fate of organic matter (e.g., through permafrost thawing). Comprehensive sedimentary records are required to compare differences between the Arctic regions and to study Arctic biogeochemical budgets. To this end, the Circum-Arctic Sediment CArbon DatabasE (CASCADE) was established to curate data primarily on concentrations of organic carbon (OC) and OC isotopes (δ13C, Δ14C) yet also on total N (TN) as well as terrigenous biomarkers and other sediment geochemical and physical properties. This new database builds on the published literature and earlier unpublished records through an extensive international community collaboration. This paper describes the establishment, structure and current status of CASCADE. The first public version includes OC concentrations in surface sediments at 4244 oceanographic stations including 2317 with TN concentrations, 1555 with δ13C-OC values and 268 with Δ14C-OC values and 653 records with quantified terrigenous biomarkers (high-molecular-weight n-alkanes, n-alkanoic acids and lignin phenols). CASCADE also includes data from 326 sediment cores, retrieved by shallow box or multi-coring, deep gravity/piston coring, or sea-bottom drilling. The comprehensive dataset reveals large-scale features of both OC content and OC sources between the shelf sea recipients. This offers insight into release of pre-aged terrigenous OC to the East Siberian Arctic shelf and younger terrigenous OC to the Kara Sea. Circum-Arctic sediments thereby reveal patterns of terrestrial OC remobilization and provide clues about thawing of permafrost. CASCADE enables synoptic analysis of OC in Arctic Ocean sediments and

The relevance of the research is caused by the need to develop a scientifically based approach to quantitative estimation of bubble transfer of methane and other gases based on acoustic techniques, which allow reliable estimate of methane flow from the bubble unloading areas by sound locators and submarine sonars. The main aim of the research is to investigate the possible application of an acoustical technique based on acoustic scattering in bubble plumes vs the acoustical technique based on calibration which was applied to quantify in situ sonar observations; to show that both techniques can be used for a quantification of methane ebullition in the bottom-water column system. Objects: gas flares or seeps - the emanations of gas in the form of rising bubbles from the seabottom, which form stable regions of their increased concentration in the water column. Methods: modification of acoustical techniques based on acoustic scattering in bubble plumes and on ist calibration which was applied by authors to quantify in situ single sonar observations. Results. We demonstrate a first attempt to use acoustical techniques based on (1) acoustic scattering in bubble plumes vs acoustical technique based on (2) calibration which was applied to quantify in situ sonar observations. It has been shown that both techniques can be used for a quatitative express-evaluation of methane ebullition in the bottom-water system in any aquatic ecosystem including seas, lakes, and rivers, while the first acoustical technique gives the bubble efflux values -20 % lower then the second acoustical technique.

Актуальность исследования обусловлена необходимостью разработки научно-обоснованного подхода к количественной оценке пузырькового переноса метана (СН 4) и других газов на основе акустических методов, позволяющих проводить достоверную оценку потока метана из областей его пузырьковой разгрузки с помощью эхолотов и гидролокаторов. Цель исследования: разработка репрезентативного акустического метода количественной оценки потока метана из областей пузырьковой разгрузки в системе донные осадки - водная толща, основанного на определении количества всплывающих пузырьков, по данным о сечении их обратного рассеяния; обоснование репрезентативности разработанного метода путем сравнения с методом, основанным на проведении специальной калибровки научного эхолота по искусственному газовому факелу. Объекты: газовые факелы - эманации газа в виде всплывающих со дна пузырьков, которые образуют в водной толще устойчивые области их повышенной концентрации. Методы: разработанные авторским коллективом методы оценки потока СН 4 из областей пузырьковой разгрузки, основанные на измерении: 1) сечения рассеяния всплывающих пузырьков; 2) калибровки по искусственному газовому факелу. Результаты. Представлен обзор современных акустических дистанционных методов, применяемых для оценки потоков СН 4 в водной толще, связанных с выходящими из дна и всплывающими пузырьками. На примере обширной области пузырьковой разгрузки СН 4 на шельфе моря Лаптевых обоснована репрезентативность предложенного нового метода, основанного на расчете по сечению обратного рассеяния всплывающих пузырьков СН 4. Показано, что оценки величины пузырькового потока, полученные двумя методами: 1) новым методом, разработанным авторами, и 2) методом калибровки эхолота по искусственному газовому факелу, дают схожие результаты: 0,27±0,06 и 0,33±0,07 ммоль м-2 с-1 , соответственно. Таким образом, на практике для дистанционной и оперативной оценки потоков СН 4 с участков его пузырьковой разгрузки можно использовать оба метода, с учетом, The relevance of the research is caused by the need to develop a scientifically based approach to quantitative estimation of bubble transfer of methane and other gases based on acoustic techniques, which allow reliable estimate of methane flow from the bubble unloading areas by sound locators and submarine sonars. The main aim of the research is to investigate the possible application of an acoustical technique based on acoustic scattering in bubble plumes vs the acoustical technique based on calibration which was applied to quantify in situ sonar observations; to show that both techniques can be used for a quantification of methane ebullition in the bottom-water column system. Objects: gas flares or seeps - the emanations of gas in the form of rising bubbles from the seabottom, which form stable regions of their increased concentration in the water column. Methods: modification of acoustical techniques based on acoustic scattering in bubble plumes and on ist calibration which was applied by authors to quantify in situ single sonar observations. Results. We demonstrate a first attempt to use acoustical techniques based on (1) acoustic scattering in bubble plumes vs acoustical technique based on (2) calibration which was applied to quantify in situ sonar observations. It has been shown that both techniques can be used for a quatitative express-evaluation of methane ebullition in the bottom-water system in any aquatic ecosystem including seas, lakes, and rivers, while the first acoustical technique gives the bubble efflux values ~20 % lower then the second acoustical technique.

The Arctic Ocean, especially the East Siberian Arctic Shelf (ESAS), has been proposed as a significant source of methane that might play an increasingly important role in the future. However, the underlying processes of formation, removal and transport associated with such emissions are to date strongly debated. CH4 concentration and triple isotope composition were analyzed on gas extracted from sediment and water sampled at numerous locations on the shallow ESAS from 2007 to 2013. We find high concentrations (up to 500 µM) of CH4 in the pore water of the partially thawed subsea permafrost of this region. For all sediment cores, both hydrogen and carbon isotope data reveal the predominant occurrence of CH4 that is not of thermogenic origin as it has long been thought, but resultant from microbial CH4 formation. At some locations, meltwater from buried meteoric ice and/or old organic matter preserved in the subsea permafrost were used as substrates. Radiocarbon data demonstrate that the CH4 present in the ESAS sediment is of Pleistocene age or older, but a small contribution of highly 14C-enriched CH4, from unknown origin, prohibits precise age determination for one sediment core and in the water column. Our sediment data suggest that at locations where bubble plumes have been observed, CH4 can escape anaerobic oxidation in the surface sediment.

The Arctic Ocean, especially the East Siberian Arctic Shelf (ESAS), has been proposed as a significant source of methane that might play an increasingly important role in the future. However, the underlying processes of formation, removal and transport associated with such emissions are to date strongly debated. CH4 concentration and triple isotope composition were analyzed on gas extracted from sediment and water sampled at numerous locations on the shallow ESAS from 2007 to 2013. We find high concentrations (up to 500 μM) of CH4 in the pore water of the partially thawed subsea permafrost of this region. For all sediment cores, both hydrogen and carbon isotope data reveal the predominant occurrence of CH4 that is not of thermogenic origin as it has long been thought, but resultant from microbial CH4 formation. At some locations, meltwater from buried meteoric ice and/or old organic matter preserved in the subsea permafrost were used as substrates. Radiocarbon data demonstrate that the CH4 present in the ESAS sediment is of Pleistocene age or older, but a small contribution of highly 14C-enriched CH4, from unknown origin, prohibits precise age determination for one sediment core and in the water column. Our sediment data suggest that at locations where bubble plumes have been observed, CH4 can escape anaerobic oxidation in the surface sediment., SCOPUS: ar.j, info:eu-repo/semantics/published

The rates of subsea permafrost degradation and occurrence of gas-migration pathways are key factors controlling the East Siberian Arctic Shelf (ESAS) methane (CH4) emissions, yet these factors still require assessment. It is thought that after inundation, permafrost-degradation rates would decrease over time and submerged thaw-lake taliks would freeze; therefore, no CH4 release would occur for millennia. Here we present results of the first comprehensive scientific re-drilling to show that subsea permafrost in the near-shore zone of the ESAS has a downward movement of the ice-bonded permafrost table of similar to 14 cm year(-1) over the past 31-32 years. Our data reveal polygonal thermokarst patterns on the seafloor and gas-migration associated with submerged taliks, ice scouring and pockmarks. Knowing the rate and mechanisms of subsea permafrost degradation is a prerequisite to meaningful predictions of near-future CH4 release in the Arctic.

info:eu-repo/semantics/published

info:eu-repo/semantics/published

Vast quantities of carbon are stored in shallow Arctic reservoirs, such as submarine and terrestrial permafrost. Submarine permafrost on the East Siberian Arctic Shelf started warming in the early Holocene, several thousand years ago. However, the present state of the permafrost in this region is uncertain. Here, we present data on the temperature of submarine permafrost on the East Siberian Arctic Shelf using measurements collected from a sediment core, together with sonar-derived observations of bubble flux and measurements of seawater methane levels taken from the same region. The temperature of the sediment core ranged from -1.8 to 0 degrees C. Although the surface layer exhibited the lowest temperatures, it was entirely unfrozen, owing to significant concentrations of salt. On the basis of the sonar data, we estimate that bubbles escaping the partially thawed permafrost inject 100-630 mg methane m(-2) d(-1) into the overlying water column. We further show that water-column methane levels had dropped significantly following the passage of two storms. We suggest that significant quantities of methane are escaping the East Siberian Shelf as a result of the degradation of submarine permafrost over thousands of years. We suggest that bubbles and storms facilitate the flux of this methane to the overlying ocean and atmosphere, respectively., AuthorCount:11