Biogeochemical structure of the Laptev Sea in 2015-2020 associated with the River Lena plume

The discharge of rivers and the subsequent dispersion of their plumes play a pivotal role in the biogeochemical cycling of the Arctic Ocean. Based on the data collected during annual transects conducted in the autumn period (September-October) from 2015-2020, this study explores the effect of River Lena plume dispersion on the seasonal and interannual changes in the hydrophysical and biogeochemical structure of the southeastern Laptev Sea. The temperature-salinity relationship (T-S), Redfield ratio and multiparameter cluster analysis were used to investigate variations in the water mass structure along the transect. The results revealed that the plume’s interannual and seasonal spreading patterns play a crucial role in regulating the local physical, biogeochemical, and biological processes in the southern Laptev Sea. During September-October, the hydrochemical water mass structure along the transects shifted from highly stratified to unstratified as the plume’s mixing intensity increased. Anomalous hydrochemical distributions were observed due to coastal upwelling, which was primarily characterized by high total alkalinity and nitrate levels, and low organic phosphorus, nitrite, and ammonia levels in the seawater. Wind and cold weather conditions drive deep vertical mixing of seawater, causing the resuspension of bottom sediment and the subsequent enrichment of bottom water by nutrients. Multi-parameter cluster analysis is used to describe the details of water mass structures in the highly dynamic southern Laptev Sea, with water mass structures typically undergoing significant changes within two weeks between September and October. The migration and transformation of water masses throughout the seasons are influenced by the volume of river discharge, fall-winter cooling, and atmospheric circulation patterns. Furthermore, the general atmospheric circulation is confirmed to be the primary cause of the interannual variation in the spread of the Lena River plume over the southeast Laptev Sea.publishedVersio

Composition of Sedimentary Organic Matter across the Laptev Sea Shelf: Evidences from Rock-Eval Parameters and Molecular Indicators

Global warming in high latitudes causes destabilization of vulnerable permafrost deposits followed by massive thaw-release of organic carbon. Permafrost-derived carbon may be buried in the nearshore sediments, transported towards the deeper basins or degraded into the greenhouse gases, potentially initiating a positive feedback to climate change. In the present study, we aim to identify the sources, distribution and degradation state of organic matter (OM) stored in the surface sediments of the Laptev Sea (LS), which receives a large input of terrestrial carbon from both Lena River discharge and intense coastal erosion. We applied a suite of geochemical indicators including the Rock Eval parameters, traditionally used for the matured OM characterization, and terrestrial lipid biomarkers. In addition, we analyzed a comprehensive grain size data in order to assess hydrodynamic sedimentation regime across the LS shelf. Rock-Eval (RE) data characterize LS sedimentary OM with generally low hydrogen index (100–200 mg HC/g TOC) and oxygen index (200 and 300 CO2/g TOC) both increasing off to the continental slope. According to Tpeak values, there is a clear regional distinction between two groups (369–401 °C for the inner and mid shelf; 451–464 °C for the outer shelf). We suggest that permafrost-derived OM is traced across the shallow and mid depths with high Tpeak and slightly elevated HI values if compared to other Arctic continental margins. Molecular-based degradation indicators show a trend to more degraded terrestrial OC with increasing distance from the coast corroborating with RE results. However, we observed much less variation of the degradation markers down to the deeper sampling horizons, which supports the notion that the most active OM degradation in LS land-shelf system takes part during the cross-shelf transport, not while getting buried deeper

Biogeochemical structure of the Laptev Sea in 2015-2020 associated with the River Lena plume

The discharge of rivers and the subsequent dispersion of their plumes play a pivotal role in the biogeochemical cycling of the Arctic Ocean. Based on the data collected during annual transects conducted in the autumn period (September-October) from 2015-2020, this study explores the effect of River Lena plume dispersion on the seasonal and interannual changes in the hydrophysical and biogeochemical structure of the southeastern Laptev Sea. The temperature-salinity relationship (T-S), Redfield ratio and multiparameter cluster analysis were used to investigate variations in the water mass structure along the transect. The results revealed that the plume’s interannual and seasonal spreading patterns play a crucial role in regulating the local physical, biogeochemical, and biological processes in the southern Laptev Sea. During September-October, the hydrochemical water mass structure along the transects shifted from highly stratified to unstratified as the plume’s mixing intensity increased. Anomalous hydrochemical distributions were observed due to coastal upwelling, which was primarily characterized by high total alkalinity and nitrate levels, and low organic phosphorus, nitrite, and ammonia levels in the seawater. Wind and cold weather conditions drive deep vertical mixing of seawater, causing the resuspension of bottom sediment and the subsequent enrichment of bottom water by nutrients. Multi-parameter cluster analysis is used to describe the details of water mass structures in the highly dynamic southern Laptev Sea, with water mass structures typically undergoing significant changes within two weeks between September and October. The migration and transformation of water masses throughout the seasons are influenced by the volume of river discharge, fall-winter cooling, and atmospheric circulation patterns. Furthermore, the general atmospheric circulation is confirmed to be the primary cause of the interannual variation in the spread of the Lena River plume over the southeast Laptev Sea

Sonar Estimation of Methane Bubble Flux from Thawing Subsea Permafrost: A Case Study from the Laptev Sea Shelf

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

Parameters of macrostructure of insoluble products obtained by thermolysis of resins and asphaltenes of the Usinskaya oil

Актуальность исследования обусловлена тем, что процессы переработки нефтяных остатков, тяжелых нефтей и природных битумов, основанные на термической деструкции высокомолекулярных компонентов сырья, приводят не только к новообразованию дистиллятных фракций. Они всегда сопровождаются образованием нерастворимых в нефтяной среде продуктов карбонизации, обычно называемых коксом. Основными источниками для образования кокса являются смолы и асфальтены исходного сырья. Термическая деструкция смол и асфальтенов широко используются для изучения их молекулярного строения. Информация о составе и свойствах нерастворимых продуктов, полученных при термическом воздействии на смолисто-асфальтеновые вещества, позволит получить информацию о путях их образования. Особенности макроструктуры нерастворимых коксообразных продуктов, полученных в процессе термолиза смол и асфальтенов усинской нефти при различных температурах, не были установлены. Цель: установление параметров макроструктуры нерастворимых продуктов, полученных при разных температурах автоклавного термолиза смол и асфальтенов усинской нефти в инертной атмосфере. Объекты: нерастворимые в хлороформе продукты автоклавного термолиза в атмосфере аргона при 250, 450 и 650 °С смол и асфальтенов тяжелой, высокосернистой, высокосмолистой нефти Усинского месторождения. Методы: спектроскопия комбинационного рассеяния, рентгенодифракционный фазовый анализ. Результаты. С использованием спектроскопии комбинационного рассеяния и рентгенодифракционного фазового анализа охарактеризованы нерастворимые продукты автоклавного термолиза при 250, 450 и 650 °С смол и асфальтенов усинской нефти. Установлено, что продукты, полученные при температурах 450 и 650 °С, по своим характеристикам соответствуют продуктам сравнительно высокой степени карбонизации. Их спектры комбинационного рассеяния содержат полосы в области 1350 и 1580 см-1 (D- и G-полоса) и их обертоны в области 2700 и 3400 см-1, характерные для углеродных материалов с невысокой степенью упорядоченности. Параметры их макроструктуры, определенные методом рентгенофазового анализа, особенности дифрактограмм также соответствуют карбено-карбоидам и коксу. В то же время нерастворимые продукты, полученные из смол при 250 °С, проявляют флуоресценцию в условиях регистрации КР-спектра, очень близки к исходным асфальтенам по параметрам макроструктуры, рассчитанным из результатов рентгенофазового анализа. Это дает основание отнести их к асфальтеноподобным веществам, что подтверждает выводы, сформулированные нами ранее на основе их элементного состава, ИК-спектров, результатов пиролитического анализа в режиме Rock Eval и «on line» флэш-пиролиза.The relevance of the research is caused by the fact that the processing of oil residues, heavy oils and natural bitumens based on thermal destruction of high-molecular components of hydrocarbon feedstock result not only in formation of new distillate fractions but they are always accompanied by the formation of oil-insoluble carbonation products, commonly known as coke. The main sources for coke formation are the resins and asphaltenes of the feedstock. Thermal destruction of resins and asphaltenes is widely used to study their molecular structure. Information on the composition and properties of insoluble products obtained by thermal treatment of resin-asphaltene substances will provide information on the pathways of their formation. The features of the macrostructure of insoluble coke-like products obtained in the course of thermolysis of resins and asphaltenes of Usinsk oil at various temperatures have not been established. The main aim of the research is to measure the parameters of the macrostructure of insoluble products obtained at different temperatures of autoclave thermolysis of resins and asphaltenes of Usinsk oil in an inert atmosphere. Objects: chloroform-insoluble products of resins and asphaltenes of the heavy, high-sulfur and highly resinous oil from the Usinsk oil field subjected to autoclave thermolysis in an argon atmosphere at 250, 450 and 650 °С. Methods: Raman spectroscopy, X-ray difraction. Results. Using Raman spectroscopy and X-ray diffraction phase analysis, the insoluble products of autoclave thermolysis of resins and asphaltenes of Usinsk oil have been characterized. It was found out that the products obtained during autoclave thermolysis at temperatures of 450 and 650 °C correspond in their characteristics to products of a relatively high degree of carbonation. Their Raman spectra contain bands in the region of 1350 and 1580 cm-1 (D- and G-bands) and their overtones lying in the region of 2700 and 3400 cm-1 are characteristic of carbon materials with a low degree of order. The parameters of their macrostructure, determined by the method of X-ray phase analysis and the features of the diffraction patterns also correspond to carbene-carbides and coke. At the same time, insoluble products obtained from resins at 250 °C exhibit fluorescence under registration of Raman spectra. Hence they are very close to the initial asphaltenes in terms of the macrostructure parameters calculated from the results of X-ray phase analysis. This gives grounds to classify them as asphaltene-like substances which confirms our conclusions drawn earlier on the basis of data of their elemental composition, IR-spectra, pyrolytic analysis in the Rock Eval mode and «on line» flash pyrolysis

Comparative characteristics of insoluble products obtained by autoclave thermolysis of resins and asphsltenes from the Usinskaya oil

The relevance of the research is caused by the fact that thermal destruction is one of the most common processes used to refine oil residues, heavy oils and natural bitumen. The use of such technologies promotes the formation of distillate fractions due to destruction of high-molecular components of feedstock and is always accompanied by the formation of oil-insoluble carbonization products, usually called coke. Some processes of oil refining are purposefully used to produce coke. Resin-asphaltene substances are considered as the main coke genes. Various options of resin and asphaltene thermal destruction are widely used to study their molecular structures. The study of the composition and properties of insoluble products obtained by thermal treatment of resin-asphaltene substances will provide information on the ways of their formation. The nature of insoluble products of resin and asphaltene thermal destruction at relatively low temperatures (160...250 °C) has not been studied yet. The main aim of the research is the comparative study of composition and properties of insoluble products obtained at different temperatures of autoclave thermolysis of resins and asphaltenes from the Usinskaya oil in an inert atmosphere. Objects: resins and asphaltenes of heavy, high-sulfur and highly resinous oil from the Usinskoye oil field, chloroform-insoluble products of their autoclave thermolysis in an argon atmosphere at 250, 450 and 650 °C. Methods: autoclave thermolysis in argon atmosphere, extraction, elemental analysis, IR and Raman spectroscopy, «Rock-Eval» pyrolytic analysis, flash pyrolysis (600 °C, 20 s) with «on-line» analysis of volatile products by gas chromatography with a mass+spectrometric detector. Results. The paper introduces the results on the study of insoluble products obtained at autoclave thermolysis of resins and asphaltenes from the Usinskaya oil in argon atmosphere at 160...650 °С. Chloroform-insoluble thermolysis products obtained with high yield from the resins of heavy high-sulfur oil at 250 °C significantly differ from the insoluble products obtained from resins and asphaltenes at 450 and 650 °C. By elemental composition, IR- and Raman spectra, the results of Rock Eval pyrolytic analysis and «on-line» flash pyrolys is (600 °C, 20 s) they correspond to «asphaltenelike» substances. Their formation is probably due to the breakage at 250 °C of the most labile S-S or C-S bonds in the resin molecules with generation and subsequent recombination of macroradicals. The thermal destruction of these sub-stances at higher temperatures (450 and 650 °C) is accompanied by formation of more carbonized coke-like products

East Siberian Sea: Interannual heterogeneity of the suspended particulate matter and its biogeochemical signature

The East Siberian Sea (ESS) is the largest, shallowest and most icebound Arctic marginal sea. It receives substantial input of terrigenous material and climate-vulnerable old organic carbon from both coastal erosion and rivers draining the extensive permafrost-covered watersheds. This study focuses on the interannual variability and spatial distribution of suspended particulate matter (SPM) in the surface and bottom waters of the ESS during the ice-free period in 2000, 2003, 2004, 2005 and 2008. We report on the composition and variability of particulate organic carbon (POC), total nitrogen (TN), POC/TN ratios, carbon and nitrogen isotopes (δ13C, δ15N) and provide estimates of the contribution of terrestrial organic carbon (terrOC) based on the δ13C isotopic values. The results show that interannual SPM distribution and elemental-isotopic characteristics of POC differ significantly between the western biogeochemical province (WBP; West of 165oE) and the eastern biogeochemical province (EBP; East of 165oE) of the ESS. The SPM mean concentration in the WBP is almost an order of magnitude higher than in the EBP. From west-to-east of the ESS, SPM tends to become more depleted in δ15N, while the δ13C becomes isotopically heavier. This trend can be explained by a shift in organic matter sources from terrigenous origin (erosion of the coastal ice complex and riverine POC) to becoming dominantly from marine plankton. The maximum contribution of terrOC to POC reached 99% in parts of the WBP, but accounts for as low as 1% in parts of the EBP. At the same time, the type of atmospheric circulation and its associated regime of both water circulation and ice transport control a displacement of the semi-stable biogeochemical border between WBP and EBP to the east or to the west if compared to its long-term average position near 165oE. Our multi-year investigation provides a robust observational basis for better understanding of the transport and fate of terrigenous material upon entering the ESS shelf waters. Our results also provide deeper insights into the interaction in the land-shelf sea system of the largest shelf sea system of the World Ocean, the East Siberian Arctic Shelf system

East Siberian Sea: Interannual heterogeneity of the suspended particulate matter and its biogeochemical signature

The East Siberian Sea (ESS) is the largest, shallowest and most icebound Arctic marginal sea. It receives substantial input of terrigenous material and climate-vulnerable old organic carbon from both coastal erosion and rivers draining the extensive permafrost-covered watersheds. This study focuses on the interannual variability and spatial distribution of suspended particulate matter (SPM) in the surface and bottom waters of the ESS during the ice-free period in 2000, 2003, 2004, 2005 and 2008. We report on the composition and variability of particulate organic carbon (POC), total nitrogen (TN), POC/TN ratios, carbon and nitrogen isotopes (δ13C, δ15N) and provide estimates of the contribution of terrestrial organic carbon (terrOC) based on the δ13C isotopic values. The results show that interannual SPM distribution and elemental-isotopic characteristics of POC differ significantly between the western biogeochemical province (WBP; West of 165oE) and the eastern biogeochemical province (EBP; East of 165oE) of the ESS. The SPM mean concentration in the WBP is almost an order of magnitude higher than in the EBP. From west-to-east of the ESS, SPM tends to become more depleted in δ15N, while the δ13C becomes isotopically heavier. This trend can be explained by a shift in organic matter sources from terrigenous origin (erosion of the coastal ice complex and riverine POC) to becoming dominantly from marine plankton. The maximum contribution of terrOC to POC reached 99% in parts of the WBP, but accounts for as low as 1% in parts of the EBP. At the same time, the type of atmospheric circulation and its associated regime of both water circulation and ice transport control a displacement of the semi-stable biogeochemical border between WBP and EBP to the east or to the west if compared to its long-term average position near 165oE. Our multi-year investigation provides a robust observational basis for better understanding of the transport and fate of terrigenous material upon entering the ESS shelf waters. Our results also provide deeper insights into the interaction in the land-shelf sea system of the largest shelf sea system of the World Ocean, the East Siberian Arctic Shelf system

Comparative characteristics of insoluble products obtained by autoclave thermolysis of resins and asphsltenes from the Usinskaya oil

Актуальность исследования обусловлена тем, что термическая деструкция является одним из самых распространенных процессов переработки нефтяных остатков, тяжелых нефтей и природных битумов. Использование таких технологий приводит не только к новообразованию дистиллятных фракций за счет деструкции высокомолекулярных компонентов сырья, но всегда сопровождается образованием нерастворимых в нефтяной среде продуктов карбонизации, обычно называемых коксом. Некоторые процессы переработки нефти целенаправленно используются для получения кокса. Считается, что основными коксогенами являются смолисто-асфальтеновые вещества. Различные варианты термической деструкции смол и асфальтенов широко используются для изучения их молекулярного строения. Изучение состава и свойств нерастворимых продуктов, образовавшихся при термическом воздействии на смолисто-асфальтеновые вещества, позволит получить информацию о путях их образования. Природа нерастворимых продуктов термодеструкции смол и асфальтенов при относительно низких температурах (160...250 °С) практически не изучена. Цель исследования: сравнительная характеристика состава и свойств нерастворимых продуктов, полученных при разных температурах автоклавного термолиза смол и асфальтенов усинской нефти в инертной атмосфере. Объекты: смолы и асфальтены тяжелой, высокосернистой, высокосмолистой нефти Усинского месторождения, нерастворимые в хлороформе продукты их автоклавного термолиза в атмосфере аргона при температурах 250, 450 и 650 °С. Методы: автоклавный термолиз в атмосфере аргона, экстракция, анализ элементного состава, ИК- и КР-спектроскопия, пиролитический анализ в варианте «Rock-Eval», флэш-пиролиз (600 °С, 20 с) с анализом летучих продуктов в режиме «on-line» методом газовой хроматографии с масс-спектрометрическим детектором. Результаты. Представлены результаты изучения нерастворимых продуктов, полученных при автоклавном термолизе смол и асфальтенов нефти Усинского месторождения в атмосфере аргона и температурах 160...650 °С. Нерастворимые в хлороформе продукты термолиза, полученные с высоким выходом из смол тяжелой высокосернистой усинской нефти при 250 °С, существенно отличаются от нерастворимых продуктов, полученных из смол и асфальтенов при 450 и 650 °С. По элементному составу, ИК- спектрам и спектрам комбинационного рассеяния, результатам пиролитического анализа в режиме Rock Eval и «on line» флэш-пиролиза (600 °С, 20 c) они соответствуют «асфальтеноподобным» веществам. Их образование, по-видимому, обусловлено разрывом при 250 °С наиболее лабильных S-S или C-S связей в молекулах смол с генерацией и последующей рекомбинацией макрорадикалов. Термодеструкция этих веществ при более высоких температурах (450 и 650 °С) сопровождается образованием более карбонизированных коксообразных продуктов.The relevance of the research is caused by the fact that thermal destruction is one of the most common processes used to refine oil residues, heavy oils and natural bitumen. The use of such technologies promotes the formation of distillate fractions due to destruction of high-molecular components of feedstock and is always accompanied by the formation of oil-insoluble carbonization products, usually called coke. Some processes of oil refining are purposefully used to produce coke. Resin-asphaltene substances are considered as the main coke genes. Various options of resin and asphaltene thermal destruction are widely used to study their molecular structures. The study of the composition and properties of insoluble products obtained by thermal treatment of resin-asphaltene substances will provide information on the ways of their formation. The nature of insoluble products of resin and asphaltene thermal destruction at relatively low temperatures (160...250 °C) has not been studied yet. The main aim of the research is the comparative study of composition and properties of insoluble products obtained at different temperatures of autoclave thermolysis of resins and asphaltenes from the Usinskaya oil in an inert atmosphere. Objects: resins and asphaltenes of heavy, high-sulfur and highly resinous oil from the Usinskoye oil field, chloroform-insoluble products of their autoclave thermolysis in an argon atmosphere at 250, 450 and 650 °C. Methods: autoclave thermolysis in argon atmosphere, extraction, elemental analysis, IR and Raman spectroscopy, «Rock-Eval» pyrolytic analysis, flash pyrolysis (600 °C, 20 s) with «on-line» analysis of volatile products by gas chromatography with a mass+spectrometric detector. Results. The paper introduces the results on the study of insoluble products obtained at autoclave thermolysis of resins and asphaltenes from the Usinskaya oil in argon atmosphere at 160...650 °С. Chloroform-insoluble thermolysis products obtained with high yield from the resins of heavy high-sulfur oil at 250 °C significantly differ from the insoluble products obtained from resins and asphaltenes at 450 and 650 °C. By elemental composition, IR- and Raman spectra, the results of Rock Eval pyrolytic analysis and «on-line» flash pyrolys is (600 °C, 20 s) they correspond to «asphaltenelike» substances. Their formation is probably due to the breakage at 250 °C of the most labile S-S or C-S bonds in the resin molecules with generation and subsequent recombination of macroradicals. The thermal destruction of these sub-stances at higher temperatures (450 and 650 °C) is accompanied by formation of more carbonized coke-like products

Lithological features of surface sediment and their influence on organic m atter distribution across the East-Siberian Arctic shelf

The Arctic is undergoing rapid climate change, which affects the global and regional carbon cycles. The East Siberian Arctic shelf, that is believed to store huge amounts of organic carbon in different pools, has been the subject of growing scientific interest in recent decades. The aim of the work was to study the lithological features of bottom sediments on the East Siberian Arctic shelf and to assess their influence on the spatial distribution of organic material in the study area. Materials and methods. The sediment samples were collected during the 45-day multidisciplinary SWERUS-C3 expedition on IB ODEN in summer 2014. Surface sediments from inner and middle East Siberian Arctic shelf were collected in summer 2008 during the International Siberian Shelf Study (ISSS-08) campaign onboard the HV Yakob Smirnitsky. The samples were analyzed for the grain size and specific surface area characteristics and total organic carbon content. It is shown that the subglacial sedimentation and the accumulation of predominantly fine-grained sediments prevail within the study area. Nevertheless, atypical sand zones were identified on the outer shelf. The authors have suggested several external factors, including modern and paleo ice scouring in the early Holocene, and intensive gas venting, which are accompanied by removal of fine-grained sediments. The paper considers spatial distribution of organic matter in the bottom sediments of the East Siberian Arctic shelf and its interrelation with their lithological properties