The Formation of Authigenic Carbonates at a Methane Seep Site in the Northern Part of the Laptev Sea

Authigenic carbonates from cold seeps are unique archives for studying environmental conditions, including biogeochemical processes associated with methane-rich fluid migration through the sediment column. The aim of this research was to study major oxide, mineralogical, and stable isotopic compositions of cold-seep authigenic carbonates collected in the northern part of the Laptev Sea. These carbonates are represented by Mg-calcite with an Mg content of 2% to 8%. The ?13C values range from ?27.5‰ to ?28.2‰ Vienna Peedee belemnite (VPDB) and indicate that carbonates formed due to anaerobic oxidation of methane, most likely thermogenic in origin. The authigenic pyrite in Mg-calcite is evidence of sulfate reduction during carbonate precipitation. The ?18O values of carbonates vary from 3.5‰ to 3.8‰ VPDB. The calculated ?18Ofluid values show that pore water temperature for precipitated Mg-calcite was comparable to bottom seawater temperature. The presence of authigenic carbonate in the upper horizons of sediments suggests that the sulfate–methane transition zone is shallowly below the sediment–water interface

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

Signatures of Molecular Unification and Progressive Oxidation Unfold in Dissolved Organic Matter of the Ob-Irtysh River System along Its Path to the Arctic Ocean

The Ob-Irtysh River system is the seventh-longest one in the world. Unlike the other Great Siberian rivers, it is only slightly impacted by the continuous permafrost in its low flow. Instead, it drains the Great Vasyugan mire, which is the world largest swamp, and receives huge load of the Irtysh waters which drain the populated lowlands of the East Siberian Plain. The central challenge of this paper is to understand the processes responsible for molecular transformations of natural organic matter (NOM) in the Ob-Irtysh river system along the South-North transect. For solving this task, the NOM was isolated from the water samples collected along the 3,000?km transect using solid-phase extraction. The NOM samples were further analyzed using high resolution mass spectrometry and optical spectroscopy. The obtained results have shown a distinct trend both in molecular composition and diversity of the NOM along the South-North transect: the largest diversity was observed in the Southern “swamp-wetland” stations. The samples were dominated with humic and lignin-like components, and enriched with aminosugars. After the Irtysh confluence, the molecular nature of NOM has changed drastically: it became much more oxidized and enriched with heterocyclic N-containing compounds. These molecular features are very different from the aliphatics-rich permafrost NOM. They witnesses much more conservative nature of the NOM discharged into the Arctic by the Ob-Irtysh river system. In general, drastic reduction in molecular diversity was observed in the northern stations located in the lower Ob flow

Settings of current sedimentation on the underwater slope of Buor-Khaya bay (Laptev sea)

Nowadays, the Arctic shelf is of increasing interest due to its large reserves of hydrocarbons and other mineral resources. Meanwhile, current knowledge about the processes occurring in the Arctic is still extremely inadequate. There is still not enough data on natural processes within permafrost, which raises many problems and discussions around regional issues. Therefore, new scientific information can further promote the study of the Arctic nature. This study was aimed to identify the specific features of sedimentation and organic matter transformation in the coastal zone of the Arctic seas based on long-term observations. The objects of the study are suspended matter and bottom sediments, including organic carbon content (Corg) and its isotope composition as markers of lithodynamics of the modern depositional environment. Bottom sediments samples were investigated for grain-size composition, organic carbon content and isotopic composition. Furthermore, spatio-temporal variability of the suspended matter distribution in the water column was estimated. Conclusions: for the ice-free period, there are two typical stable turbidity maxima with a suspended matter content ranging from 6,5 to 594 mg/l. Towards the continental slope, the replacement of sandy-aleuritic sediments with clays of continental slope, avandelt bottom, and thermoabrasive-accumulative terrace is accompanied by an increase in organic carbon values from 0,4 to 5,4 % with winter values ranging from 0,6 to 9,3 %. Isotopic composition of organic carbon in the bottom sediments varied from -27,9 to -22,7

Settings of current sedimentation on the underwater slope of Buor-Khaya bay (Laptev sea)

В настоящее время интерес к арктическому шельфу быстро усиливается вследствие его перспективности на углеводородное сырье и другие минеральные ресурсы. Между тем уровень знаний о процессах, протекающих в арктической системе, еще крайне недостаточен. До сих пор существует дефицит данных о природных процессах в криолитозоне, что определяет дискуссионный характер решения многих региональных проблем. В такой обстановке получение любой новой научной информации вносит определенный вклад в познание развития природы Арктики. Цель работы: выявление особенностей современного осадкообразования и трансформации вещества в береговой зоне арктических морей на основе результатов многолетних наблюдений. Объекты исследования: взвешенный материал и донные осадки, включая содержание органического углерода (Сорг) и его изотопный состав - как маркеры литодинамики среды современного осадкообразования. Изучались гранулометрический (размерный) состав донных осадков, содержание и изотопный состав органического углерода, оценивался характер пространственно-временной изменчивости распределения взвешенного материала в водной толще. Выводы: для безледного периода типичны два устойчивых максимума мутности с содержанием взвеси в от 6,5 до 594 мг/л. В направлении от побережья к свалу глубин замещение песчано-алевритовых осадков илами фаций свала глубин, подножья авандельты и термоабразионно-аккумулятивной террасы сопровождается увеличением содержания органического углерода от 0,4 до 5,4 % при зимних значениях 0,6-9,3 %. Изотопный состав углерода органического вещества донных осадков варьировал от -27,9 до -22,7 %.Nowadays, the Arctic shelf is of increasing interest due to its large reserves of hydrocarbons and other mineral resources. Meanwhile, current knowledge about the processes occurring in the Arctic is still extremely inadequate. There is still not enough data on natural processes within permafrost, which raises many problems and discussions around regional issues. Therefore, new scientific information can further promote the study of the Arctic nature. This study was aimed to identify the specific features of sedimentation and organic matter transformation in the coastal zone of the Arctic seas based on long-term observations. The objects of the study are suspended matter and bottom sediments, including organic carbon content (Corg) and its isotope composition as markers of lithodynamics of the modern depositional environment. Bottom sediments samples were investigated for grain-size composition, organic carbon content and isotopic composition. Furthermore, spatio-temporal variability of the suspended matter distribution in the water column was estimated. Conclusions: for the ice-free period, there are two typical stable turbidity maxima with a suspended matter content ranging from 6,5 to 594 mg/l. Towards the continental slope, the replacement of sandy-aleuritic sediments with clays of continental slope, avandelt bottom, and thermoabrasive-accumulative terrace is accompanied by an increase in organic carbon values from 0,4 to 5,4 % with winter values ranging from 0,6 to 9,3 %. Isotopic composition of organic carbon in the bottom sediments varied from -27,9 to -22,7

Discovery and characterization of submarine groundwater discharge in the Siberian Arctic seas: A case study in Buor-Khaya Gulf, Laptev Sea

It has been suggested that increasing freshwater discharge to the Arctic Ocean may also occur as submarine groundwater discharge (SGD), yet there are no direct observations of this phenomenon in the Arctic shelf seas. This study tests the hypothesis that SGD does exist in the Siberian-Arctic shelf seas but its dynamics may be largely controlled by complicated geocryological conditions such as permafrost. The field-observational approach in the southeast Laptev Sea used a combination of hydrological (temperature, salinity), geological (bottom sediment drilling, geoelectric surveys) and geochemical (224Ra, 223Ra and 222Rn) techniques. Active SGD was documented in the vicinity of the Lena River delta with two different operational modes. In the first system, groundwater discharges through tectonogenic permafrost talik zones was registered in both wintertime and summertime seasons. The second SGD mechanism was cryogenic squeezing out of brine and water-soluble salts detected on the periphery of ice hummocks in the wintertime season. The proposed mechanisms of groundwater transport and discharge in the arctic land-shelf system is elaborated. Through salinity versus 224Ra and 224Ra/223Ra diagrams, the three main SGD-influenced water masses were identified and their end-member composition was constrained. Further studies should apply these techniques to a broader scale with the objective to reach an estimate of the relative importance of the SGD transport vector relative to surface freshwater discharge for both the water balance and aquatic components such as dissolved organic carbon, carbon dioxide, methane, and nutrients

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

Geochemical specific of sediments at methane cold seep site on the Laptev Sea outer shelf

Актуальность. Характерной особенностью шельфа моря Лаптевых является наличие участков массированной разгрузки метан-содержащих флюидов с поверхности морского дна в водную толщу - метановых сипов. Ключевыми биогеохимическими процессами, протекающими при миграции метана через осадочную среду, являются анаэробное окисление метана и бактериальная сульфатредукция. Активность этих процессов приводит к изменению окислительно-восстановительных условий седиментации, что влияет на биогеохимические циклы ряда редокс-чувствительных элементов. Цель: изучение влияния просачивающихся метан-содержащих флюидов на геохимические циклы железа, углерода и некоторых редокс-чувствительных элементов. Объект. Были проанализированы данные о концентрациях углерода, железа, и ряда редокс-чувствительных элементов (Mn, Co, Ni, Cu, Zn, Cr, Ba, Mo, U) в трех кернах донных осадков, отобранных на внешнем шельфе моря Лаптевых. Два из трех кернов получены на участках с зарегистрированной разгрузкой метан-содержащих флюидов и рассматривались в качестве осадков, подверженных анаэробному окислению метана. Методы: пиролиз (Rock-Eval 6 Turbo, Vinci Technologies), рентгенофлуоресцентный анализ (HORIBA X-Ray Analytical Microscope XGT 7200), масс-спектрометрия с индуктивно-связанной плазмой (ИСП-МС, ELAN DRC-e). Результаты. Содержания TOC и Fe в донных осадках не отражают влияния анаэробного окисления на их геохимические циклы и контролируются спецификой пространственного распределения потоков осадочного материала. Во всех изученных кернах отмечаются повышенные концентрации Mn, приуроченные к поверхностному горизонту осадков. На участках разгрузки метана поверхностный слой донных осадков характеризуется обогащением Mo, Ni и Cr. Избирательное обогащения поверхностного слоя осадков некоторыми редокс-чувствительными элементами может быть вызвано миграцией метан-содержащих флюидов, способствующих переносу элементов в растворенной форме из более глубоких горизонтов. Сорбция этих элементов органическим веществом и окислами/гидрокислами Fe-Mn, по-видимому, является ключевым механизмом, контролирующим осаждение Mo, Ni и Cr.Relevance. A specific feature of the Laptev Sea shelf is the sites of discharge of methane-containing fluids from the surface of the seabed into the water column (methane cold seeps). The key biogeochemical processes occurring during methane migration through the sedimentary environment are anaerobic oxidation of methane and bacterial sulfate reduction. The activity of these processes encourages a change in the redox conditions of sedimentation, which affects the biogeochemical cycles of some redox-sensitive elements. The aim of the research is to study the influence of methane-containing fluids on the geochemical cycles of iron, carbon and some redox-sensitive elements. Objects. The data of the concentrations of carbon, iron, and some of redox-sensitive elements (Mn, Co, Ni, Cu, Zn, Cr, Ba, Mo, U) in three bottom sediment cores sampled on the outer shelf of the Laptev Sea were analyzed. Two of the three cores were obtained at methane cold seep sites and were considered as sediments subject to anaerobic methane oxidation. Methods: pyrolysis (Rock-Eval 6 Turbo, Vinci Technologies), X-Ray analysis (HORIBA X-Ray Analytical Microscope XGT 7200), Inductively coupled plasma mass spectrometry (ICP-MS, ELAN DRC-e). Results. TOC and Fe contents in sediments do not reflect the impact of anaerobic oxidation on their geochemical cycles and controlled by the specifics of the spatial distribution of sedimentary material. In all the studied cores, there are elevated Mn concentrations confined to the surface layer of sediments. At methane cold seep sites, the surface layer of bottom sediments is characterized by enrichment in Mo, Ni and Cr. The selective enrichment of the surface layer of sediments with some redox-sensitive elements can be caused by the migration of methane-containing fluids, which facilitate the transport of elements in dissolved form from deeper horizons. The sorption of these elements by organic matter and Fe-Mn oxihydroxides appears to be the key mechanism controlling the deposition of Mo, Ni, and Cr

Methane seepage impact on authigenic pyrite morphology in sediments of the Laptev Sea continental slope

Актуальность. В работе представлены результаты изучения морфологии и размеров аутигенного пирита, присутствующего в донных осадках как в рассеянном виде, так и в ассоциации с карбонатными стяжениями. С позиции изучения условий раннего диагенеза аутигенный пирит считается наиболее важным сульфидным минералом железа по причине его наибольшей диагенетической стабильности относительно других сульфидов железа. Ранее проведенные многочисленные исследования морфологии и размеров аутигенного пирита показывают возможность использования этой информации для оценки окислительно-восстановительных условий осадконакопления и раннего диагенеза как в современных, так и в древних осадочных бассейнах. Целью работы являлось изучения морфологических и размерных характеристик аутигенного пирита для оценки влияния сульфат-управляемого анаэробного окисления метана на условия раннего диагенеза. Методы: гидроакустические исследования (Kongsberg EA600), рентгенодифракционный анализ (Bruker D2 Phaser), сканирующая электронная микроскопия с локальным энергодисперсионным анализом (TESCAN VEGA 3 SBU). Основные результаты. В морфологическом отношении пирит представлен идиоморфными и гипидиоморфными кристаллами, фрамбоидами и их скоплениями, радиальными наростами, а также стержневидными агрегатами. Средний диаметр фрамбоидов, а также высокое значение стандартного отклонения в обеих рассматриваемых выборках свидетельствует о диагенетическом происхождении пирита. Сульфат-управляемое анаэробное окисление метана является доминирующим процессом, контролирующим формирование сульфидов железа, что подтверждается наличием достаточно крупных фрамбоидов диаметром до 49 мкм. Наблюдаемое разнообразие морфологических форм пирита может отражать изменение диагенетической среды с течением времени, вызванное вариативностью потока метан-содержащих флюидов.Relevance. The paper presents the results of studying the morphology and size distribution of authigenic pyrite, both present in sediments and in carbonate nodules. From the point of view of studying the conditions of early diagenesis, authigenic pyrite is considered the most important iron sulfide mineral due to its greatest diagenetic stability relative to other iron sulfides. Numerous previous studies of the morphology and size of authigenic pyrite show the possibility of using this information to assess the redox conditions of sedimentation and early diagenesis in both modern and ancient sedimentary basins. The aim of the research was to study the morphology and size distribution of authigenic pyrite to assess the effect of sulfate-controlled anaerobic oxidation of methane on the conditions of early diagenesis. Methods: field hydroacoustic researches (Kongsberg EA600), X-ray diffraction (Bruker D2 Phaser), scanning electron microscopy with local energy dispersive analysis (TESCAN VEGA 3 SBU). Results. Morphologically, pyrite is represented by idiomorphic and hypidiomorphic crystals, framboids and their clusters, radial outgrowths, and also rod like aggregates. The mean diameter of framboids, as well as the high value of standard deviation, indicate the diagenetic origin of pyrite. Sulfate-driven anaerobic oxidation of methane is the dominant process that controls the formation of iron sulfides, which is confirmed by the presence of fairly large framboids up to 49 μm in diameter. The observed diversity of pyrite morphology may reflect the change in the diagenetic environment over time, due to the variability of the flow of methane-bearing fluids

Authigenic minerals in the bottom sediments from seeps of the Laptev Sea

Метановые сипы являются широко распространенным явлением, наблюдаемым на шельфах и континентальных склонах внутренних и окраинных морей по всему миру, в том числе и в море Лаптевых. Ключевыми биогеохимическими процессами, протекающими в донных осадках этих районов, являются анаэробное окисление метана в сочетании с бактериальной сульфатредукцией. Оба этих процесса контролируют образование специфической аутигенной минерализации. Целью настоящей работы являлось изучение аутигенных минералов донных осадков с аномально высокими концентрациями метана, отобранных на двух сиповых участках в северо-восточной части моря Лаптевых, для определения признаков их идентификации в древних осадочных породах. Приведены результаты литологических и минералогических исследований донных осадков. Было установлено, что основными аутигенными минералами в исследованных образцах донных осадков, отобранных с двух сиповых участков в северо-восточной части моря Лаптевых, являются магнезиальный кальцит, гипс и пирит. Разная специфика аутигенной минерализации, предположительно, указывает на различия в режимах миграции метан-содержащих флюидов на этих участках. Временное снижении интенсивности просачивания метана в пределах «восточного сипа» способствовало насыщению поровой воды ионами SO[4]{2-} и Ca{2+} и, как следствие, осаждению гипса. Близповерхностное положение сульфат-метановой транзитной зоны в «западном сипе», обусловленное высокими потоками метана, благоприятствовало осаждению магнезиального кальцита в верхних горизонтах донных осадков. Присутствие пирита в осадках как восточного, так западного сиповых участков является свидетельством активности процесса бактериальной сульфат-редукции при анаэробном окислении метана.Methane seeps is a widespread phenomenon observed on the shelves and continental slopes of inland and border seas around the world, including the Laptev Sea. Key biogeochemical processes occurring in the bottom sediments of these areas are the anaerobic oxidation of methane in combination with bacterial sulfate reduction. Both of these processes control the formation of specific autigenic mineralization. The aim of this work was to study authigenic minerals of bottom sediments with abnormally high concentrations of methane taken from two seeps in the north-eastern part of the Laptev Sea to determine the signs of their identification in ancient sedimentary rocks. The paper presents the results of lithological and mineralogical studies of bottom sediments. It was found that magnesium calcite, gypsum and pyrite are the main authigenic minerals in the studied samples of bottom sediments taken from two seeps in the north-eastern part of the Laptev Sea. The different specifics of authigenic mineralization indicate differences in conditions of migration of methane-containing fluids in these areas, presumably. Temporary decrease in the rate of methane seepage within the «eastern seep» contributed to the saturation of pore water with SO[4]{2-} and Ca{2+} and, as a consequence, gypsum deposition. The near-surface position of the sulfate-methane transition zone in the «western seep» due to high methane flows favored the precipitation of magnesian calcite in the upper horizons of bottom sediments. The presence of pyrite in sediments of eastern and western seep is evidence of the activity of the bacterial sulfate reduction during anaerobic methane oxidation