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High-resolution depositional archives were identified in the contourite drifts developed on the mid-upper slope of the western continental margin of Svalbard (Bellsund and Isfjorden drifts, Vestnesa and Svyatogor ridges) under the persistent effect of the West Spitsbergen Current (WSC). The sediment drifts contain very similar stratigraphic sequences characterised by depositional marker beds (Heinrich-like and meltwater related deposits) outlining a synchronous, almost simultaneous response of the Svalbard-Barents Sea paleo-ice sheet to changing climatic conditions. These observations strengthened the idea that the WSC, transporting warm Atlantic Waters to the Arctic ,was one of the major drivers of the Arctic climate variability and cryosphere evolution in the area.The considerations made above, inspired the writing of Proposal IODP 985-Full2 that was motivated by the necessity of retrieving continuous, high-resolution, and datable depositional sequences containing the record of the palaeoceanographic characteristics and cryosphere evolution during the past climatic transitions that followed the opening of the Fram Strait in the Arctic. Such data are greatly needed to better constrain global climate connections, forcing mechanisms and climate models. The general objective of 985-Full2 is the reconstruction of the variability of the WSC and its influence on climate changes particularly during key climate transitions (i.e. the late Miocene–Pliocene transition, late Pliocene–Pleistocene Transition, Mid-Pleistocene Transition, Mid-Brunhes Transition, and sub-orbital Heinrich-like events), its impact on the Arctic glaciations, ice shelves development and stability, and sea ice distribution over last 5.3 Ma.The proposal submitted in April 2020 was approved in May 2022 and scheduled as IODP Exp. 403 (June 4th to August 2nd, 2024).

The cruise to the Atlantic-Arctic gateway region is organized and funded through the Geological Survey of Norway (NGU) and focuses on studies of methane leakage at the seafloor on the Mid Norwegian shelf and continental margin. Cruise 20200108 in June 2020 was directed to two areas to study ongoing seepage of hydrocarbons and their controlling factors. Along the Lofoten margin, to investigate the outcropping bedrock structures in two canyons; on the Mid-Norwegian shelf, to inspect a recently discovered seep site. The cruise may be known as: CAGE20_0

CAGE 19-3 cruise with RV “Kronprins Haakon” to the Atlantic-Arctic gateway region is organized and funded through the Tromsø Forskningsstiftelse (TFS) and Research Council of Norway (RCN) supported SEAMSTRESS project and the Center of Excellence "CAGE – Centre for Arctic Gas Hydrate, Environment and Climate" at UiT-The Arctic University of Norway in Tromsø. SEAMSTRESS focuses on studies of the effect of tectonic stress on methane release at Arctic continental margins while CAGE studies the amount of methane hydrate and magnitude of methane release in Arctic Ocean environments on time scales from the Neogene to the present. CAGE 19-3 cruise is directed to the Atlantic-Arctic gateway region to provide necessary field data for these objectives. From previous cruises, we have identified key localities which will be main targets for this cruise. The cruise may be known as: CAGE19_3

Was something lost as society moved away from “traditional” media such as handwritten letters and photography and into the digital age? Some of the authors remember this age fondly, and we wanted to see if this fondness could be translated into a science dialogue project with school classes. We designed and carried out a communication process with four classes at different schools across Europe. During this process, each class would interact with a single scientist primarily via handwritten questions, letters, and a Polaroid photo album. The scientists would make this unique, one-of-a-kind album whilst on board a research expedition in the Barents Sea. We asked whether this process might show any benefits to the school students involved. To answer this, we asked the students to write up their thoughts on communicating with a scientist in this way. We analysed the texts and found that most students thought that the letters and Polaroid albums were a “beautiful experience”. Others commented on how important it is to actually put pen to paper and write since they (almost) only use digital media these days. Most importantly, the students learnt different elements of the science connected to the research expedition but also about the scientific process in general. And, equally important, some of the students were surprised and thankful that the scientists took the time to communicate with them in such a personal way. These results could possibly have been achieved using other media; however, the handwritten letters and Polaroids worked very well. They also seemed to conjure up some of the personal memories that we have about communication not so long ago. Maybe there is something to be said for slowing things down with our science communication projects and making them more personal and unique. This is something that snail mail and making photo albums forces us to do.

Cruise CAGE18-5 was the first research expedition under the helm of UiT The Arctic University of Norway in Tromsø with the new ice-going research vessel R/V Kronprins Håkon. This new vessel provides new opportunities to collect cross-disciplinary data for addressing the objectives of the Norwegian Centre of Excellence for Arctic Gas Hydrate, Environment and Climate, CAGE. CAGE investigates Arctic gas hydrate and methane seepage systems in order to better understand the effects they may have on our oceans, ecosystems and global climate. The new research vessel and its facilities allows CAGE access to a state-of-art remotely-operated vehicle, the ROV Ægir 6000, opening a new domain for experimental work and acquisition of sample material from the seafloor. The overall goal of cruise CAGE18-5 therefore was to utilize the ROV in order to provide guided video imagery and to study active gas seepage systems at the gas-hydrate pingo (GHP) site located in the outer Storfjord Trough, and at Storbanken in the northeastern part of the Barents Sea. The cruise may be known as: CAGE18_5

Do we miss something about «traditional” media such as handwritten letters and photography before the digital age? Some of the authors remember this age fondly, and we wanted to see if this fondness could be translated into a science dialogue project with school classes. We designed and carried out a communication process with 4 classes at different schools across Europe. During this process, each class would interact with a single scientist primarily via hand-written questions & letters, and a Polaroid photo album. The scientists would make this unique, one-of-a-kind album whilst on board a research expedition in the Barents Sea. We asked the question whether this process might show any benefits to the school students involved. To answer this, we asked the students to write up their thoughts on communicating with a scientist in this way. We analysed the texts and found that most students thought the letters and polaroid albums were a “beautiful experience”. Others commented on how important it is to actually put pen to paper and write, since they use (almost) only digital media these days. Most importantly, the students learnt different elements of the science connected to the research expedition, but also about the scientific process in general. And, equally important, some of the students were surprised and thankful that the scientists took the time to communicate with them in such a personal way. These results could possibly have been achieved using other media, however the hand-written letters and Polaroids worked very well. They also seemed to conjure up some of the personal memories that we have about communication not so long ago. Maybe there is something to be said for slowing things down with our science communication projects and making them more personal and unique. This is something that snail-mail and making photo albums forces us to do.

The Svyatogor Ridge is the sedimented inside corner high of the Knipovich Ridge – Molloy Transform Fault intersection and despite its mid-ocean ridge system setting, it is host to a well-defined gas hydrate system. There is an extinct transform fault immediately south of the Svyatogor Ridge, which is partially sedimented. Our data suggests that there are distinct locations throughout the area which have elevated heat flow, usually coinciding with evidence of past or present fluid flow.In particular, we show a site along the flank of the extinct transform fault which hosts a seep-like community associated with enhanced anaerobic methane oxidation in the shallow subsurface. While transform faults and fracture zones are important components of mid-ocean ridge systems, their role in fluid exchange between the lithosphere and hydrosphere remains unclear. High resolution seismic data from the inside corner high area at the Knipovich Ridge – Molloy Transform Fault intersection hints towards the important role the Molloy Transform Fault is playing in the fluid flow system in the area. However, integrated seismic, geochemical and heat flow datasets along the extinct transform fault clearly links the fault to elevated heat flow and fluid seepage, and to sites of gas hydrate accumulation. We posit that this site is a type of hybrid seep-vent style of fluid flow system.

Do we miss something about «traditional” media such as handwritten letters and photography before the digital age? Some of the authors remember this age fondly, and we wanted to see if this fondness could be translated into a science dialogue project with school classes.We designed and carried out a communication process with 4 classes at different schools across Europe. During this process, each class would interact with a single scientist primarily via hand-written questions & letters, and a Polaroid photo album. The scientists would make this unique, one-of-a-kind album whilst on board a research expedition in the Barents Sea. We asked the question whether this process might show any benefits to the school students involved.To answer this, we asked the students to write up their thoughts on communicating with a scientist in this way. We analysed the texts and found that most students thought the letters and polaroid albums were a “beautiful experience”. Others commented on how important it is to actually put pen to paper and write, since they use (almost) only digital media these days. Most importantly, the students learnt different elements of the science connected to the research expedition, but also about the scientific process in general. And, equally important, some of the students were surprised and thankful that the scientists took the time to communicate with them in such a personal way.These results could possibly have been achieved using other media, however the hand-written letters and Polaroids seemed to work very well. They also seemed to conjure up some of the personal memories that we have about communication not so long ago. Maybe there is something to be said for slowing things down with our science communication projects and making them more personal and unique. This is something that snail-mail and making photo albums forces us to do.

Funder: M.M.E. is funded by the Research Council of Norway and the Co-funding of Regional, National, and International Programmes (COFUND) – Marie Skłodowska-Curie Actions under the EU Seventh Framework Programme (FP7), project number 274429, and the Tromsø Forskningsstiftelse, project number A31720., Changes in the Arctic climate-ocean system can rapidly impact carbon cycling and cryosphere. Methane release from the seafloor has been widespread in the Barents Sea since the last deglaciation, being closely linked to changes in pressure and bottom water temperature. Here, we present a post-glacial bottom water temperature record (18,000–0 years before present) based on Mg/Ca in benthic foraminifera from an area where methane seepage occurs and proximal to a former Arctic ice-sheet grounding zone. Coupled ice sheet-hydrate stability modeling shows that phases of extreme bottom water temperature up to 6 °C and associated with inflow of Atlantic Water repeatedly destabilized subsurface hydrates facilitating the release of greenhouse gasses from the seabed. Furthermore, these warming events played an important role in triggering multiple collapses of the marine-based Svalbard-Barents Sea Ice Sheet. Future warming of the Atlantic Water could lead to widespread disappearance of gas hydrates and melting of the remaining marine-terminating glaciers.

In marine basins, gas hydrate systems are usually identified by a bottom simulating reflection (BSR) that parallels the seafloor and coincides with the base of the gas hydrate stability zone (GHSZ). We present a newly discovered gas hydrate system, Moby-Dick, located in the Ship Basin in the northern Gulf of Mexico. In the seismic data, we observe a channel-levee complex with a consistent phase reversal and a BSR extending over an area of ∼14.2 km2, strongly suggesting the presence of gas hydrate. In contrast to classical observations, the Moby-Dick BSR abnormally shoals 150 m toward the seafloor from west to east, which contradicts the northward-shallowing seafloor. We argue that the likely cause of the shoaling BSR is a gradually changing gas mix across the basin, with gas containing heavier hydrocarbons in the west transitioning to methane gas in the east. Our study indicates that such abnormal BSRs can be controlled by gradual changes in the gas mix influencing the shape of the GHSZ over kilometers on a basin scale.

Methane emissions from Arctic continental margins may increase due to global warming. Present-day ocean fluxes seem to provide a minor contribution to the atmosphere methane pool, but large uncertainties still remain on the magnitude of future emissions from methane seeps and gas hydrate-bearing sediments. The Barents Sea is a natural laboratory to study the evolution of methane seeps in relation to climate change, as it recorded several phases of ice-sheet advance and retreat during the Pleistocene. Glaciations and its concurrent denudation of the Barents Sea influenced the subsurface, causing reservoir expansion and fracturing, thereby driving hydrocarbon (mostly gas) migration which resulted in a sustained regional fluid flow system. New data from this area can shed light on future response of other high-latitude continental shelves worldwide. Here, we present reconstructed methane emission dynamics at Leirdjupet Fault Complex (LFC), SW Barents Sea, since last deglaciation (occurred after ~19 cal Ka BP). The geochemical composition of sediment cores indicate prolonged methane emissions, which started after 14.5 cal Ka BP. Geochemical proxies for anaerobic oxidation of methane in the sediment (barium, calcium and sulfur enrichments, isotopic composition of foraminifera) indicate an overall decrease in seepage intensity over the Holocene toward present-day conditions. Methane-derived authigenic carbonates with aragonite mineralogy and heavy δ18O signature recorded an episode of gas hydrate destabilization in this region. Paleo-hydrate stability models suggest that this event was triggered by the influx of warm Atlantic water and isostatic uplift linked to the retreat of the Barents Sea Ice Sheet. Present-day distribution of methane seeps at LFC is strongly linked to underlying faults. Methane hydrates are stable in the southern part of the investigated seepage area and might respond to a future increase in bottom water temperatures.

Accepted manuscript version, licensed CC BY-NC-ND 4.0. The Barents Sea has experienced intense erosion throughout the Cenozoic due to uplift and repeated episodes of glaciation. This, in turn, has driven large pressure and temperature fluctuations in the sediment substrate along with rearrangement of thermogenic oil and gas accumulations. As a result, some hydrocarbon fields have relatively shallow depths, and natural gas release is widespread. This study focuses on the process of hydrocarbon leakage from the Realgrunnen reservoir - encompassing the Hanssen and Wisting discoveries - to the shallow subsurface caused by repeated cycles of glacial erosion in the central Barents Sea throughout the Quaternary. We apply 2D basin and petroleum system modeling to two seismic sections using data from two wells and run ten different scenarios that test model sensitivity to key parameters. We find that the primary factors governing gas leakage are the erosion amount, its distribution between glacial and preglacial stages, and the timing of the glaciations. Our results demonstrate that intense oil and gas leakage from the Realgrunnen reservoir occurs primarily through widespread faults activated during the first deglaciation episode. Further considerable gas leakage occurs by the seal breach after a critical overburden thickness is eroded and pressure on the reservoir decreases to ca. 9 MPa. Modeling reveals that the first deglaciation episode causes up to ca. 20% loss of oil and gas from the reservoir, whereas leakage after the seal breach yields a further ca. 15% decrease in gas. Our results are supported by seismic analyses that demonstrate hydrocarbon leakage in the study area

The Svyatogor Ridge and surroundings, located on the sediment-covered western flank of the Northern Knipovich Ridge, host extensive gas hydrate and related fluid flow systems. The fluid flow system here manifests in the upper sedimentary sequence as gas hydrates and free gas, indicated by bottom simulating reflections (BSRs) and amplitude anomalies. Using 2D seismic lines and bathymetric data, we map tectonic features such as faults, crustal highs, and indicators of fluid flow processes. Results indicate a strong correlation between crustal faults, crustal highs and fluid accumulations in the overlying sediments, as well as an increase in geothermal gradient over crustal faults. We conclude here that gas generated during the serpentinization of exhumed mantle rocks drive the extensive occurrence of gas hydrate and fluid flow systems in the region and transform faults act as an additional major pathway for fluid circulation.

Gas hydrates exist within a relatively narrow envelope of thermal and pressure conditions, small changes in which may lead to widespread dissociation and methane release. During past glacials, extensive ice sheets covered the continental margins of the Arctic Basin yielding ideal high pressure and low temperature conditions for the sequestration of thermogenic and biogenic methane in hydrate-bearing subglacial sediments. On ice sheet retreat at the end of the last glacial, these hydrate reservoirs experienced major perturbations in thermal and pressure conditions leading to decomposition and methane mobilization over a variety of magnitude, temporal and spatial scales. Using geophysical data to constrain state-of-the-art ice sheet/gas hydrate modelling, we investigate how past Northern Hemisphere ice sheets modulated carbon sequestration and release. Our results provide the first quantitative assessment of widespread subglacial hydrate formation and mobilization during the last glacial, yields insights into global carbon cycle dynamics and informs potential future atmospheric greenhouse composition and feedbacks associated with shrinkage of the contemporary cryosphere.

Sediments deposited by marine-based ice sheets are dominantly fine-grained glacial muds, which are commonly known for their sealing properties for migrating fluids. However, the Peon and Aviat hydrocarbon discoveries in the North Sea show that coarse-grained glacial sands can occur over large areas in formerly glaciated continental shelves. In this study, we use conventional and high-resolution 2D and 3D seismic data combined with well information to present new models for large-scale fluid accumulations within the shallow subsurface of the Norwegian Continental Shelf. The data include 48,000 km2 of high-quality 3D seismic data and 150 km2 of high-resolution P-Cable 3D seismic data, with a vertical resolution of 2 m and a horizontal resolution of 6 to 10 m in these data sets. We conducted horizon picking, gridding and attribute extractions as well as seismic geomorphological interpretation, and integrated the results obtained from the seismic interpretation with existing well data.The thicknesses of the Quaternary deposits vary from hundreds of meters of subglacial till in the Northern North Sea to several kilometers of glacigenic sediments in the North Sea Fan. Gas-charged, sandy accumulations are characterized by phase-reserved reflections with anomalously high amplitudes in the seismic data as well as density and velocity decreases in the well data. Extensive (>10 km2) Quaternary sand accumulations within this package include (i) glacial sands in an ice-marginal outwash fan, sealed by stiff glacial tills deposited by repeated glaciations (the Peon discovery in the Northern North Sea), (ii) sandy channel-levee systems sealed by fine-grained mud within sequences of glacigenic debris flows, formed during shelf-edge glaciations, (iii) fine-grained glacimarine sands of contouritic origin sealed by gas hydrates, and (iv) remobilized oozes above large evacuation craters and sealed by megaslides and glacial muds. The development of the Fennoscandian Ice Sheet resulted in a rich variety of depositional environments with frequently changing types and patterns of glacial sedimentation. Extensive new 3D seismic data sets are crucial to correctly interpret glacial processes and to analyze the grain sizes of the related deposits. Furthermore, these data sets allow the identification of localized extensive fluid accumulations within the Quaternary succession and distinguish stratigraphic levels favorable for fluid accumulations from layers acting as fluid barriers.

Widespread methane release from thawing Arctic gas hydrates is a major concern, yet the processes, sources, and fluxes involved remain unconstrained. We present geophysical data documenting a cluster of kilometer-wide craters and mounds from the Barents Sea floor associated with large-scale methane expulsion. Combined with ice sheet/gas hydrate modeling, our results indicate that during glaciation, natural gas migrated from underlying hydrocarbon reservoirs and was sequestered extensively as subglacial gas hydrates. Upon ice sheet retreat, methane from this hydrate reservoir concentrated in massive mounds before being abruptly released to form craters. We propose that these processes were likely widespread across past glaciated petroleum provinces and that they also provide an analog for the potential future destabilization of subglacial gas hydrate reservoirs beneath contemporary ice sheets.

The Vestnesa Ridge comprises a > 100 km long sediment drift located between the western continental slope of Svalbard and the Arctic mid-ocean ridges. It hosts a deep-water (>1000 m) gas hydrate and associated seafloor seepage system. Near-seafloor headspace gas compositions and its methane carbon isotopic signature along the ridge indicate a predominance of thermogenic gas sources feeding the system. Prediction of the base of the gas hydrate stability zone for theoretical pressure and temperature conditions and measured gas compositions, results in an unusual underestimation of the observed bottom simulating reflector (BSR) depth. The BSR is up to 60 m deeper than predicted for pure methane and measured gas compositions with > 99 % methane. Models for measured gas compositions with > 4% higher order hydrocarbons result in a better BSR approximation. However, the BSR remains > 20 m deeper than predicted in a region without active seepage. A BSR deeper than predicted is primarily explained by unexpected spatial variations in the geothermal gradient and by larger amounts of thermogenic gas at the base of the gas hydrate stability zone. Hydrates containing higher order hydrocarbons form at greater depths and higher temperatures and contribute with larger amounts of carbons than pure methane hydrates. In thermogenic provinces, this may imply a significant upward revision (up to 50 % in the case of Vestnesa Ridge) of the amount of carbon in gas hydrates.

Large national programs in the United States and several Asian countries have defined and characterised their marine methane hydrate occurrences in some detail, but European hydrate occurrence has received less attention. The European Union-funded project “Marine gas hydrate – an indigenous resource of natural gas for Europe” (MIGRATE) aimed to determine the European potential inventory of exploitable gas hydrate, to assess current technologies for their production, and to evaluate the associated risks. We present a synthesis of results from a MIGRATE working group that focused on the definition and assessment of hydrate in Europe. Our review includes the western and eastern margins of Greenland, the Barents Sea and onshore and offshore Svalbard, the Atlantic margin of Europe, extending south to the northwestern margin of Morocco, the Mediterranean Sea, the Sea of Marmara, and the western and southern margins of the Black Sea. We have not attempted to cover the high Arctic, the Russian, Ukrainian and Georgian sectors of the Black Sea, or overseas territories of European nations. Following a formalised process, we defined a range of indicators of hydrate presence based on geophysical, geochemical and geological data. Our study was framed by the constraint of the hydrate stability field in European seas. Direct hydrate indicators included sampling of hydrate; the presence of bottom simulating reflectors in seismic reflection profiles; gas seepage into the ocean; and chlorinity anomalies in sediment cores. Indirect indicators included geophysical survey evidence for seismic velocity and/or resistivity anomalies, seismic reflectivity anomalies or subsurface gas escape structures; various seabed features associated with gas escape, and the presence of an underlying conventional petroleum system. We used these indicators to develop a database of hydrate occurrence across Europe. We identified a series of regions where there is substantial evidence for hydrate occurrence (some areas offshore Greenland, offshore west Svalbard, the Barents Sea, the midNorwegian margin, the Gulf of Cadiz, parts of the eastern Mediterranean, the Sea of Marmara and the Black Sea) and regions where the evidence is more tenuous (other areas offshore Greenland and of the eastern Mediterranean, onshore Svalbard, offshore Ireland and offshore northwest Iberia). We provide an overview of the evidence for hydrate occurrence in each of these regions. We conclude that around Europe, areas with strong evidence for the presence of hydrate commonly coincide with conventional thermogenic hydrocarbon provinces., Sí

Accepted manuscript version. Accepted for publication in Geochemistry Geophysics Geosystems. Copyright 2019 American Geophysical Union. Further reproduction or electronic distribution is not permitted. Source at https://doi.org/10.1029/2018GC007930 In 2014, the discovery of seafloor mounds leaking methane gas into the water column in the northwestern Barents Sea became the first to document the existence of non‐permafrost related gas hydrate pingos (GHP) on the Eurasian Arctic shelf. The discovered site is given attention because the gas hydrates occur close to the upper limit of the gas hydrate stability, thus may be vulnerable to climatic forcing. In addition, this site lies on the regional Hornsund Fault Zone marking a transition between the oceanic and continental crust. The Hornsund Fault Zone is known to coincide with an extensive seafloor gas seepage area; however, until now lack of seismic data prevented connecting deep structural elements to shallow seepages. Here we use high‐resolution P‐Cable 3D seismic data to study the subsurface architecture of GHPs and underlying glacial and pre‐glacial deposits. The data show gas hydrates, authigenic carbonates and free gas within the GHPs on top of gas chimneys piercing a thin section of low‐permeability glacial‐sediments. The chimneys connect to faults within the underlying tilted and folded fluid and gas hydrate bearing sedimentary rocks. Correlation of our data with regional 2D seismic surveys shows a spatial connection between the shallow subsurface fluid flow system and the deep‐seated regional fault zone. We suggest that fault‐controlled Paleocene hydrocarbon reservoirs inject methane into the low‐permeability glacial deposits and near‐seabed sediments, forming the GHPs. This conceptual model explains the existence of climate sensitive gas hydrate inventories and extensive seabed methane release observed along the Svalbard‐Barents Sea margin.

We find that summer methane (CH4) release from seabed sediments west of Svalbard substantially increases CH4 concentrations in the ocean but has limited influence on the atmospheric CH4 levels. Our conclusion stems from complementary measurements at the seafloor, in the ocean, and in the atmosphere from land-based, ship and aircraft platforms during a summer campaign in 2014. We detected high concentrations of dissolved CH4 in the ocean above the seafloor with a sharp decrease above the pycnocline. Model approaches taking potential CH4 emissions from both dissolved and bubble-released CH4 from a larger region into account reveal a maximum flux compatible with the observed atmospheric CH4 mixing ratios of 2.4–3.8 nmol m−2 s−1. This is too low to have an impact on the atmospheric summer CH4 budget in the year 2014. Long-term ocean observatories may shed light on the complex variations of Arctic CH4 cycles throughout the year.

Source at https://doi.org/10.1038/s41598-018-32826-z. Geophysical data from the South Kara Sea reveal U-shaped erosional structures buried beneath the 50–250 m deep seafloor of the continental shelf across an area of ~32 000 km2. These structures are interpreted as thermokarst, formed in ancient yedoma terrains during Quaternary interglacial periods. Based on comparison to modern yedoma terrains, we suggest that these thermokarst features could have stored approximately 0.5 to 8 Gt carbon during past climate warmings. In the deeper parts of the South Kara Sea (>220 m water depth) the paleo thermokarst structures lie within the present day gas hydrate stability zone, with low bottom water temperatures −1.8oC) keeping the gas hydrate system in equilibrium. These thermokarst structures and their carbon reservoirs remain stable beneath a Quaternary sediment blanket, yet are potentially sensitive to future Arctic climate changes.

Methane (CH4) is a powerful greenhouse gas. Its atmospheric mixing ratios have been increasing since 2005. Therefore, quantification of CH4 sources is essential for effective climate change mitigation. Here we report observations of the CH4 mixing ratios measured at the Zeppelin Observatory (Svalbard) in the Arctic and aboard the research vessel (RV) Helmer Hanssen over the Arctic Ocean from June 2014 to December 2016, as well as the long-term CH4 trend measured at the Zeppelin Observatory from 2001 to 2017. We investigated areas over the European Arctic Ocean to identify possible hotspot regions emitting CH4 from the ocean to the atmosphere, and used state-of-the-art modelling (FLEXPART) combined with updated emission inventories to identify CH4 sources. Furthermore, we collected air samples in the region as well as samples of gas hydrates, obtained from the sea floor, which we analysed using a new technique whereby hydrate gases are sampled directly into evacuated canisters. Using this new methodology, we evaluated the suitability of ethane and isotopic signatures (δ13C in CH4) as tracers for ocean-to-atmosphere CH4 emission. We found that the average methane / light hydrocarbon (ethane and propane) ratio is an order of magnitude higher for the same sediment samples using our new methodology compared to previously reported values, 2379.95 vs. 460.06, respectively. Meanwhile, we show that the mean atmospheric CH4 mixing ratio in the Arctic increased by 5.9±0.38 parts per billion by volume (ppb) per year (yr−1) from 2001 to 2017 and ∼8 pbb yr−1 since 2008, similar to the global trend of ∼ 7–8 ppb yr−1. Most large excursions from the baseline CH4 mixing ratio over the European Arctic Ocean are due to long-range transport from land-based sources, lending confidence to the present inventories for high-latitude CH4 emissions. However, we also identify a potential hotspot region with ocean–atmosphere CH4 flux north of Svalbard (80.4∘ N, 12.8∘ E) of up to 26 nmol m−2 s−1 from a large mixing ratio increase at the location of 30 ppb. Since this flux is consistent with previous constraints (both spatially and temporally), there is no evidence that the area of interest north of Svalbard is unique in the context of the wider Arctic. Rather, because the meteorology at the time of the observation was unique in the context of the measurement time series, we obtained over the short course of the episode measurements highly sensitive to emissions over an active seep site, without sensitivity to land-based emissions.

Accepted manuscript version. Published version available at https://doi.org/10.1130/G36440.1. Biotic gas generation from the degradation of organic carbon in marine sediments supplies and maintains gas hydrates throughout the world’s oceans. In nascent, ultraslow-spreading ocean basins, methane generation can also be abiotic, occurring during the high-temperature (>200 °C) serpentinization of ultramafic rocks. Here, we report on the evolution of a growing Arctic gas- and gas hydrate–charged sediment drift on oceanic crust in eastern Fram Strait, a tectonically controlled, deep-water gateway between the subpolar North Atlantic and Arctic Oceans. Ultraslow-spreading ridges between northwest Svalbard and northeast Greenland permit the sustained interaction of a mid-ocean ridge transform fault and developing sediment drift, on both young (10 Ma) oceanic crust, since the late Miocene. Geophysical data image the gas-charged drift and crustal structure and constrain the timing of a major 30 km lateral displacement of the drift across the Molloy transform fault. We describe the buildup of a 2 m.y., long-lived gas hydrate– and free gas–charged drift system on young oceanic crust that may be fed and maintained by a dominantly abiotic methane source. Ultraslow-spreading, sedimented ridge flanks represent a previously unrecognized carbon reservoir for abiotic methane that could supply and maintain deep-water methane hydrate systems throughout the Arctic.

Greenhouse gas methane trapped in sub-seafloor gas hydrates may play an important role in a potential climate feedback system. The impact of future Arctic Ocean warming on the hydrate stability and its contribution to atmospheric methane concentrations remains an important and unanswered question. Here, we estimate the climate impact of released methane from oceanic gas hydrates in the Arctic to the atmosphere towards the end of the 21st century, integrating hydrate stability and atmospheric modeling. Based on future climate models, we estimate that increasing ocean temperatures over the next 100 years could release up to 17 ± 6 Gt C into the Arctic Ocean. However, the released methane has a limited or minor impact on the global mean surface temperature, contributing only 0.1 % of the projected anthropogenic influenced warming over the 21st century.

Source at https://doi.org/10.21046/2070-7401-2017-14-5-248-258. Проанализированы результаты спутникового зондирования с помощью европейского орбитального интерферометра IASI/MetOP-A и алгоритма обработки данных, разработанного в NOAA. Спутниковые измерения для умеренных и высоких широт Северного полушария дают рост скорости концентрации метана от 4–9 ppbv/год (частей на миллиард по объему) в 2010–2013 гг. до 12–17 ppbv/год в 2015–2016 гг. Глобальные оценки на основе приземных измерений NOAA на прибрежных станциях показывают возрастание от ~5–6 ppbv/год в 2007–2013 гг. до 9–12 ppbv/год в последние два года. Спутниковые данные позволяют анализировать концентрацию метана как над сушей, так и над Арктическими морями при отсутствии приповерхностных инверсий температуры. Результаты дистанционных измерений сравниваются с прямыми самолетными измерениями на Аляске в летне-осенний период в ходе эксперимента CARVE (Carbon in Arctic Reservoirs Vulnerability Experiment). Максимальные аномалии метана (по сравнению с районом между Скандинавией и Исландией) наблюдались в ноябре-декабре над морской поверхностью вдоль берегов Норвегии, Новой Земли, Шпицбергена и других районов Арктики. В летний период аномалии над океаном были незначительны. С годами аномалии росли: максимальная скорость отмечена для района к западу от Новой Земли (9,4±3,7) ppb/год. Над Аляской аномалия концентрации метана в летнее время, когда активны микробиологические источники, росла со скоростью (2,6±1,0) ppb/год. Местоположение максимумов аномалии вокруг Шпицбергена соответствует наблюдавшимся выходам метана с морского дна и предсказанным районам диссоциации метаногидратов. Отмеченное в данной работе увеличение скорости возрастания метана в течение последних двух лет не обязательно говорит о долгосрочной тенденции: 2015–2016 гг. характеризуются как период одного из наиболее сильных эффектов Эль-Ниньо. European orbital IASI/MetOP-A interferometer TIR radiation data were processed by NOAA for methane profiles and uploaded in a publicly accessible archive. Satellite measurements for the middle and high latitudes of the Northern Hemisphere reveal a concentration growth rate of 4–9 ppbv/year in 2010–2013 and up to 12–17 ppbv/year in the 2015–2016. Global estimates based on surface measurements of NOAA at coastal stations for the same periods show an increase from 5-6 ppbv/year after 2007 to 9–12 ppbv/year last two years. Satellite data allow analyzing the methane concentration both over land and over the Arctic seas in the absence of near-surface temperature inversions. The results of remote measurements are compared with direct aircraft measurements in summer-autumn Alaska during the CARVE experiment. The maximum anomalies of methane (in comparison with a relatively clean area between Scandinavia and Iceland) were observed in November-December over the sea surface along the coasts of Norway, Novaya Zemlya, Svalbard and other regions of the Arctic. Anomalies were insignificant in summer. Over the years, the winter anomalies (contrasts) grew: the maximum rate was recorded for the area to the west of Novaya Zemlya (9.4±3.7) ppbv/year. Above Alaska, the anomaly of methane concentration in summer, when the microbiological sources are active, increased at a rate (2.6±1.0) ppbv/year. The locations of the maxima of the anomaly around Svalbard correspond to the observed methane seeps from the seabed and the predicted regions of dissociation of methane hydrates. The observed methane acceleration during the last two years does not necessarily indicate a long-term tendency: 2015–2016 was a strong El Niño period.

Source at https://doi.org/10.1002/2016GL071841. The Barents Sea is a major part of the Arctic where the Gulf Stream mixes with the cold Arctic waters. Late Cenozoic uplift and glacial erosion have resulted in hydrocarbon leakage from reservoirs, evolution of fluid flow systems, shallow gas accumulations, and hydrate formation throughout the Barents Sea. Here we integrate seismic data observations of gas hydrate accumulations along with gas hydrate stability modeling to analyze the impact of warming ocean waters in the recent past and future (1960–2060). Seismic observations of bottom‐simulating reflectors (BSRs) indicate significant thermogenic gas input into the hydrate stability zone throughout the SW Barents Sea. The distribution of BSR is controlled primarily by fluid flow focusing features, such as gas chimneys and faults. Warming ocean bottom temperatures over the recent past and in future (1960–2060) can result in hydrate dissociation over an area covering 0.03–38% of the SW Barents Sea.

Source at: http://doi.org/10.1073/pnas.1619288114 Seafloor methane release due to the thermal dissociation of gas hydrates is pervasive across the continental margins of the Arctic Ocean. Furthermore, there is increasing awareness that shallow hydrate-related methane seeps have appeared due to enhanced warming of Arctic Ocean bottom water during the last century. Although it has been argued that a gas hydrate gun could trigger abrupt climate change, the processes and rates of subsurface/ atmospheric natural gas exchange remain uncertain. Here we investigate the dynamics between gas hydrate stability and environmental changes from the height of the last glaciation through to the present day. Using geophysical observations from offshore Svalbard to constrain a coupled ice sheet/gas hydrate model, we identify distinct phases of subglacial methane sequestration and subsequent release on ice sheet retreat that led to the formation of a suite of seafloor domes. Reconstructing the evolution of this dome field, we find that incursions of warm Atlantic bottom water forced rapid gas hydrate dissociation and enhanced methane emissions during the penultimate Heinrich event, the Bølling and Allerød interstadials, and the Holocene optimum. Our results highlight the complex interplay between the cryosphere, geosphere, and atmosphere over the last 30,000 y that led to extensive changes in subseafloor carbon storage that forced distinct episodes of methane release due to natural climate variability well before recent anthropogenic warming.

The SW Barents Sea is a large hydrocarbon-prone epi-continental Sea of the Norwegian Arctic region. A significant portion of the hydrocarbon gases generated in deep source rocks has leaked or migrated into the shallow subsurface and is now trapped in gas hydrate and shallow gas reservoirs. The evolution of sedimentary basins of this region has controlled the leakage of these fluids through marine sediments. Understanding the distribution of various fluid-flow systems may enhance our knowledge of the evolution of different basins in the SW Barents Sea and could help find potential targets for future hydrocarbon exploration. We analyze approximately 3000 2D multi-channel seismic profiles and data from 60 wells covering the entire SW Barents Sea, to identify and classify fluid-flow features, and study their relationship to tectonic elements and geological history. Gas chimneys are the most abundant feature among various other fluid-flow features such as fluid leakage along faults and fractures, seepage pipes, and high amplitude anomalies potentially indicating trapped fluids. Large fluid-flow features, covering areas as large as 600 km 2 , occur close to known hydrocarbon fields such as Snohvit, Skrugard, and Havis. The fluid-flow features occur above major deep-seated faults in the area suggesting a close relation to it. The number of fluid-flow features in the western part of the study area is significantly higher than in the eastern part. The amount of net erosion in the study area shows no direct control over the distribution of fluid-flow features, suggesting that the faults and distribution of mature source rocks control the fluid flow. The strong correlation between the locations of fluid-flow features and structural elements indicates that extensional tectonics, uplift and glaciations could have played major roles in the timing and activity of the fluid leakage, although erosion might have had an added effect.

Methane stored in seabed reservoirs such as methane hydrates can reach the atmosphere in the form of bubbles or dissolved in water. Hydrates could destabilize with rising temperature further increasing greenhouse gas emissions in a warming climate. To assess the impact of oceanic emissions from the area west of Svalbard, where methane hydrates are abundant, we used measurements collected with a research aircraft (Facility for Airborne Atmospheric Measurements) and a ship (Helmer Hansen) during the Summer 2014 and for Zeppelin Observatory for the full year. We present a model‐supported analysis of the atmospheric CH4 mixing ratios measured by the different platforms. To address uncertainty about where CH4 emissions actually occur, we explored three scenarios: areas with known seeps, a hydrate stability model, and an ocean depth criterion. We then used a budget analysis and a Lagrangian particle dispersion model to compare measurements taken upwind and downwind of the potential CH4 emission areas. We found small differences between the CH4 mixing ratios measured upwind and downwind of the potential emission areas during the campaign. By taking into account measurement and sampling uncertainties and by determining the sensitivity of the measured mixing ratios to potential oceanic emissions, we provide upper limits for the CH4 fluxes. The CH4 flux during the campaign was small, with an upper limit of 2.5 nmol m−2 s−1 in the stability model scenario. The Zeppelin Observatory data for 2014 suggest CH4 fluxes from the Svalbard continental platform below 0.2 Tg yr−1. All estimates are in the lower range of values previously reported., Key Points Measurements around Svalbard show no atmospheric methane (CH4) enhancements from CH4 releases into seawater from the ocean floorWe provide an upper limit for oceanic CH4 emissions compatible with the lack of an observable atmospheric signalSea‐air emission fluxes of CH4 are small offshore Svalbard, both for transfer via bubbles and via diffusive flux of dissolved CH4

It is established that late-twentieth and twenty-first century ocean warming has forced dissociation of gas hydrates with concomitant seabed methane release. However, recent dating of methane expulsion sites suggests that gas release has been ongoing over many millennia. Here we synthesize observations of ∼1,900 fluid escape features—pockmarks and active gas flares—across a previously glaciated Arctic margin with ice-sheet thermomechanical and gas hydrate stability zone modelling. Our results indicate that even under conservative estimates of ice thickness with temperate subglacial conditions, a 500-m thick gas hydrate stability zone—which could serve as a methane sink—existed beneath the ice sheet. Moreover, we reveal that in water depths 150–520 m methane release also persisted through a 20-km-wide window between the subsea and subglacial gas hydrate stability zone. This window expanded in response to post-glacial climate warming and deglaciation thereby opening the Arctic shelf for methane release., Methane release across the Arctic continental shelf has been attributed to modern dissociation of gas hydrate, accelerated by ocean warming. Here, the authors show that thermogenic methane was stored as subglacial gas hydrate during the last glaciation, and subsequently released following ice sheet retreat.

Gas hydrate systems offshore western Svalbard are extensive and include the whole Vestnesa Ridge, an elongated sediment drift north of the Molloy Transform and just east of the Molloy Ridge, one of the shortest segments of the slow spreading North Atlantic Ridge system. The crest of the Vestnesa Ridge at water depth between 1200–1300 m is pierced with fluid flow features. Seafloor pockmarks vary in size up to 700 m in diameter. Pockmarks are generally larger at the eastern start of the Vestnesa Ridge than at its western termination. A recent cruise with R/V Jan Mayen discovered methane flares in the water column above the pockmark field at the onset of the Vestnesa Ridge. Over a period of two days at least 3 pockmarks were continuously active and methane flares in the water column reached a height of approximately 800 m. It is still unclear what has triggered the increase in gas expulsion from seafloor sediments. High-resolution 3D seismic data acquired in 2007 and 2010 show significant differences of the subseafloor expression of these fluid leakage systems. At the western end of the Vestnesa Ridge, sub-seafloor fluid flow features resemble well-described chimney structures. However, the seismic expression of the active fluid flow features is much broader, much more chaotic, dome-shaped and is not very similar to a typical chimney structure. The Vestnesa Ridge gas-hydrate and free-gas system occurs within few kilometers of a mid-oceanic ridge and transform fault, which makes this gas-hydrate system unique on Earth. The close proximity to the spreading center and its hydrothermal circulation system affects the dynamics of the gas-hydrate and free-gas system. The high heat flow together with the high tectonic activity of this region, a thick sedimentary cover, a shallow maturation window and an accelerated rate of biogenic and thermogenic gas production cause substantial disturbance to the free-gas system leading to high variability in gas supply, gas migration and gas hydrate build up and dissociation.

Submitted manuscript version. Published version available: http://dx.doi.org/10.1016/j.marpetgeo.2015.07.023 The location and stability of gas hydrates in the SW Barents Sea is poorly constrained due to complex geological, geochemical, and geophysical conditions, including poor controls on regional heat flow and gas chemistry. Understanding the stability of gas hydrates in this region is important, as recent studies suggest destabilizing hydrates may lead to methane discharge into the ocean and possibly in to the atmosphere. Here, we use high-resolution 3D P-Cable seismic data, combined with 3D heat flow and fluid flow models to place new constraints on gas hydrate stability in this region. The 3D P-Cable seismic data, acquired in 2009 west of Loppa High, show cross-cutting, reverse polarity, high-amplitude reflectors interpreted as the base of gas hydrate stability. To constrain heat flow, fluid flow, and gas hydrate stability within the 3D seismic volume, we use a 3D steady-state, finite difference diffusive thermal model that incorporates regional bottom water temperature from CTD casts, expected geothermal gradients, and gas composition derived from well data. In general, modelled bottom simulating reflectors are deeper than observed BSRs. Our analysis weighs multiple factors that might explain the discrepancy between observed and modelled bottom simulating reflector depths. From this analysis, we propose that the most significant discrepancies in BSR depth are likely related to changes in regional fluid/heat flow and fluid geochemistry. The anomalously shallow bottom simulating reflectors can be explained via vertical fluid flow that might include ensuing potential effects on gas composition, pore water salinity and temperature. Our estimate suggest that a maximum vertical fluid flux of approximately 12 mm/y is necessary to explain the most significant anomalies. Our study provides new insight into regional heat flow, geochemistry, and endmember vertical fluid flux rates in the Barents Sea. Moreover, it documents that the fluid flow system is active and most likely, very dynamic.

A large grounded ice sheet covered the epicontinental Barents Sea multiple times during the Late Pleistocene and left its erosional imprint (Solheim et al. 1990; Knies et al. 2009). Erosion involved the removal of large amounts of sediments from the Tertiary and Cretaceous sedimentary successions of the Barents Sea. The Upper Regional Unconformity (URU) represents the erosional base for continental-shelf glaciations (Vorren et al. 1988). Here, we present palaeo-landforms from this erosional base imaged using high-resolution P-Cable seismic data acquired along the border between the Ringvassoya Fault Complex and the Loppa High in the SW Barents Sea (Fig. 1). P-Cable seismic data have a frequency bandwidth of up to 300 Hz and spatial resolution of 6×6 m, which is much better than conventional 3D seismic data. Hence, interpretation of P-Cable data allows visualization of buried geomorphic landscapes in exceptional detail. In addition, amplitude information is readily available and complements grid-based interpretations. Fig. 1. Buried subglacial landforms in …

Iceberg ploughmarks are common features of glaciated continental margins worldwide. They form when iceberg keels plough through sediments on the ocean floor. They occur in various sizes and shapes, but generally exhibit a linear or curvilinear geometry. The SW Barents Sea is a heavily glaciated margin and its seafloor shows numerous ploughmarks among other glacial landforms (Andreassen et al. 2008). We present seafloor features formed during the late Weichselian glaciation (Solheim et al. 1990) imaged using high-resolution P-Cable 3D seismic data. P-Cable 3D seismic data have a spatial resolution of 6×6 m which is better than many hull-mounted multibeam systems, particularly in deep water. However, the cumulative seismic response of the seafloor is slightly different due to the lower-frequency bandwidth (30–350 Hz) of P-Cable compared to multibeam systems (up to 500 kHz). In addition, amplitude information is readily available and complements grid-based interpretations. Numerous linear and curvilinear depressions occur on the seafloor near …