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Bubble transport of methane from shallow seep sites in the Black Sea west of the Crimea Peninsula between 70 and 112 m water depth has been studied by extrapolation of results gained through different hydroacoustic methods and direct sampling. Ship‐based hydroacoustic echo sounders can locate bubble releasing seep sites very precisely and facilitate their correlation with geological or other features at the seafloor. Here, the backscatter strength of a multibeam system was integrated with single‐beam data to estimate the amount of seeps/m2 for different backscatter intensities, resulting in 2709 vents in total. Direct flux measurements by submersible revealed methane fluxes from individual vents of 0.32–0.85 l/min or 14.5–37.8 mmol/min at ambient pressure and temperature conditions. A conservative estimate of 30 mmol/min per site was used to estimate the flux into the water to be 1219–1355 mmol/s. The flux to the atmosphere was calculated by applying a bubble dissolution model taking release depth, temperature, gas composition, and bubble size spectra into account. The flux into the atmosphere (3930–4533 mol/d) or into the mixed layer (6186–6899 mol/d) from the 21.8 km2 large study area is three times higher than independently measured fluxes of dissolved methane for the same area using geochemical methods (1030–2495 mol/d). The amount of methane dissolving in the mixed layer is 2256–2366 mol/d. This close match shows that the hydroacoustic approach for extrapolating the number of seeps/m2 and the applied bubble dissolution model are suitable to extrapolate methane fluxes over larger areas.

The distribution and origin of shallow gas seeps in the vicinity of the Posolsky Bank in Lake Baikal were studied based on the integration of detailed seismic, multibeam, and hydro-acoustic water-column investigations. In all, 65 acoustic flares have been detected on the Posolsky Fault scarp near the crest of the bank and in a similar, nearby setting at water depths of −43 to −332 m. The seismic data reveal BSRs (bottom-simulating reflectors) occurring up to water depths of −300 m. Calculations involving hydrate stability, heat flow, and topographic modulation based on BSR occurrence and multibeam bathymetry enabled prediction of a methane–ethane gas mixture and heat-flow values that would account for gas hydrate stability in the lake sediments under prevailing ambient conditions. These predictions are supported by ground truth data. The findings suggest that seeps concentrated along the crest of the Posolsky Bank are fed mainly by gas coming from below the base of the gas hydrate stability zone, which would migrate updip via permeable stratigraphic pathways beneath the bank. Gas would ultimately be released into the water column where these pathways are cut off by faults. Figure Conceptual seep model for the Posolsky Bank, Lake Baikal

A multibeam echosounder survey was conducted (deeper than ca. 300 m water depth, total area: ca. 1.8 × 103 km2) in the southern basin of Lake Baikal, Russia, in June 2015, 2016, and 2017. Characteristic morphology of the lake floor was mapped on the ancient Tankhoy stratum, covered with present sediment, by high-resolution bathymetry. Sediment core sampling operations were conducted in August 2015 and August 2016 at a characteristic mound-like landform named Kedr (after the Kedrovaya River). Sub-surface gas hydrates (GH), containing not only microbial but also thermogenic gases (Hachikubo et al. 2016), were retrieved. Core lithology and sub-bottom profiler survey suggest that Kedr is a mud volcano (MV). Hydrogen and oxygen isotopic anomalies were observed in the sediment pore waters. This suggests the water results from clay mineral dehydration, which is the first observation of this process in Lake Baikal sediment pore water. The thermogenic gases, mud breccia, and water from clay mineral dehydration suggest potential ascending gas as well as water from greater depths, presumably from the ancient Tankhoy stratum under the Kedr MV.

ICOS-Oceans is the marine domain of the European Research Infrastructure Consortium “Integrated Carbon Observation System” (ICOS). It aims at delivering high quality greenhouse gas (GHG) observations and derived data products (e.g. regional GHG-flux maps) for constraining the GHG balance on a European level, on a sustained long-term basis. ICOS-Oceans currently consists of 11 Ship of Opportunity lines (SOOP – Ship of Opportunity Program) and 10 Fixed Observation Stations (FOS) spread across European waters, including the North Atlantic Ocean and the Barents, North, Baltic and Mediterranean Seas. The stations operate in a harmonised and standardised way based on community-proven protocols and methods for ocean GHG observations improving operational conformity as well as quality control and assurance of the data. This enables the network to focus on long term research into the marine carbon cycle and the anthropogenic carbon sink, while preparing the network to include other GHG fluxes. ICOS data are processed on a near real-time basis and will be published on the ICOS Carbon Portal, allowing monthly estimates of CO2 air-sea exchange to be quantified for European waters. ICOS establishes transparent operational data management routines following the FAIR (Findable, Accessible, Interoperable and Reusable) guiding principles allowing amongst others reproducibility, interoperability and traceability. The ICOS-Oceans network is actively integrating with the atmospheric (e.g. improved atmospheric measurements onboard SOOP lines) and ecosystem (e.g. oceanic direct gas flux measurements) domains of ICOS, and utilises techniques developed by the ICOS Central Facilities and the Carbon Portal. There is a strong interaction with the international ocean carbon cycle community to enhance interoperability and harmonise data flow. The future vision of ICOS-Oceans includes ship-based ocean survey sections to obtain a 3-dimensional understanding of marine carbon cycle processes and optimise the existing network design.

New high-resolution multibeam bathymetry data recorded in 2009 in the deepest lake in the World, Lake Baikal, Siberia, enabled a better understanding of the morphology of ten known lake-bed structures—the Bolshoy, Malenki, Malyutka and Stari mud volcanoes in the South Baikal Basin, the K1–4 structures in the Selenga delta, and the Novosibirsk and St. Petersburg structures in the Central Baikal Basin—and also the discovery of 29 new lake-bed structures. These new structures are the S1, Tolstiy, mTSG and S2 in the South Baikal Basin, the P1–P4, P6–P19 and K5–K8 in the Selenga delta accommodation zone, and the C1, C3 and C4 edifices in the Central Baikal Basin. In all, 39 positive relief structures were identified and their large-scale distribution mapped. Based on their typical shape, the observation of high-reflectivity areas on side-scan sonar data records, and evidence of feeder channels on subsurface data, these structures can be classified as mud volcanoes. This has already been confirmed in other publications for the Bolshoy, Malenki and K2 structures, by the recovery of mud breccias in sediment cores. Most structures occur on or near faults and have orientations parallel with the major faults and main stress orientations in the basins, suggesting a strong structural control on the formation of the mud volcanoes. Their slopes are generally steeper than 5°, consistent with interpretation as mud cones formed by high-viscosity, stiff mud plugs. Only few structures appear to be characterised by a crater, in which case this apparent crater seems to be formed by the coalescence of several single cones, leaving a depression in the centre. Some structures have a moat, which has probably an erosional origin. Furthermore, three depressions have been found, named P5, P20 and C2, which are suggested to be pockmarks.

Lithodid crabs (and other skeleton-crushing predators) may have been excluded from cold Antarctic continental shelf waters for more than 14 Myr. The west Antarctic Peninsula shelf is warming rapidly and has been hypothesized to be soon invaded by lithodids. A remotely operated vehicle survey in Palmer Deep, a basin 120 km onto the Antarctic shelf, revealed a large, reproductive population of lithodids, providing the first evidence that king crabs have crossed the Antarctic shelf. DNA sequencing and morphology indicate the lithodid is Neolithodes yaldwyni Ahyong & Dawson, previously reported only from Ross Sea waters. We estimate a N. yaldwyni population density of 10 600 km–2 and a population size of 1.55 x 106 in Palmer Deep, a density similar to lithodid populations of commercial interest around Alaska and South Georgia. The lithodid occurred at depths of more than 850 m and temperatures of more than 1.4°C in Palmer Deep, and was not found in extensive surveys of the colder shelf at depths of 430–725 m. Where N. yaldwyni occurred, crab traces were abundant, megafaunal diversity reduced and echinoderms absent, suggesting that the crabs have major ecological impacts. Antarctic Peninsula shelf waters are warming at approximately 0.01°C yr–1; if N. yaldwyni is currently limited by cold temperatures, it could spread up onto the shelf (400–600 m depths) within 1–2 decades. The Palmer Deep N. yaldwyni population provides an important model for the potential invasive impacts of crushing predators on vulnerable Antarctic shelf ecosystems.

We report on the isotopic composition of dissolved inorganic carbon (DIC) in pore-water samples recovered by gravity coring from near-bottom sediments at gas hydrate-bearing mud volcanoes/gas flares (Malenky, Peschanka, Peschanka 2, Goloustnoe, and Irkutsk) in the Southern Basin of Lake Baikal. The δ 13 C values of DIC become heavier with increasing subbottom depth, and vary between −9.5 and +21.4‰ PDB. Enrichment of DIC in 13 C indicates active methane generation in anaerobic environments near the lake bottom. These data confirm our previous assumption that crystallization of carbonates (siderites) in subsurface sediments is a result of methane generation. Types of methanogenesis (microbial methyl-type fermentation versus CO 2 -reduction) were revealed by determining the offset of δ 13 C between dissolved CH 4 and CO 2 , and also by using δ 13 C and δD values of dissolved methane present in the pore waters. Results show that both mechanisms are most likely responsible for methane generation at the investigated locations.

A total of 84 seismic profiles, mainly from the western and eastern deltas of Lake Issyk-Kul, were used to identify lake-level changes. Seven stratigraphic sequences were reconstructed, each containing a series of delta lobes that were formed during former lake-level stillstands or during slow lake-level increase or decrease. The lake level has experienced at least four cycles of stepwise rise and fall of 400 m or more. These fluctuations were mainly caused by past changes in the atmospheric circulation pattern. During periods of low lake levels, the Siberian High was likely to be strong, bringing dry air masses from the Mongolian steppe blocking the midlatitude Westerlies. During periods of high lake levels, the Siberian High must have been weaker or displaced, and the midlatitude Westerlies could bring moister air masses from the Mediterranean and North Atlantic regions.

A total of 84 seismic profiles mainly from the western and eastern deltas of Lake Issyk-Kul were used to identify lake-level changes. Seven stratigraphic sequences were identified each containing a series of delta lobes that were formed during former lake-level stillstands. Lake-level has experienced at least four cycles of stepwise fall and rise of 400 m or more. These fluctuations were mainly caused by past changes in the atmospheric circulation pattern during the past. During periods of low lake levels, the Siberian High likely was strong, bringing dry air masses from the Mongolian steppe. The strong Siberian High blocked the mid-latitude Westerlies. During periods of high lake levels, the Siberian High must have been weaker or displaced, and the mid-latitude Westerlies could bring moister air masses from the Mediterranean and North Atlantic regions.

Lithodid crabs (and other skeleton-crushing predators) may have been excluded from cold Antarctic continental shelf waters for more than 14 Myr. The west Antarctic Peninsula shelf is warming rapidly and has been hypothesized to be soon invaded by lithodids. A remotely operated vehicle survey in Palmer Deep, a basin 120 km onto the Antarctic shelf, revealed a large, reproductive population of lithodids, providing the first evidence that king crabs have crossed the Antarctic shelf. DNA sequencing and morphology indicate the lithodid is Neolithodes yaldwyni Ahyong & Dawson, previously reported only from Ross Sea waters. We estimate a N. yaldwyni population density of 10 600 km-2 and a population size of 1.55 x 106 in Palmer Deep, a density similar to lithodid populations of commercial interest around Alaska and South Georgia. The lithodid occurred at depths of more than 850 m and temperatures of more than 1.4°C in Palmer Deep, and was not found in extensive surveys of the colder shelf at depths of 430-725 m. Where N. yaldwyni occurred, crab traces were abundant, megafaunal diversity reduced and echinoderms absent, suggesting that the crabs have major ecological impacts. Antarctic Peninsula shelf waters are warming at approximately 0.01°C yr-1; if N. yaldwyni is currently limited by cold temperatures, it could spread up onto the shelf (400-600 m depths) within 1-2 decades. The Palmer Deep N. yaldwyni population provides an important model for the potential invasive impacts of crushing predators on vulnerable Antarctic shelf ecosystems.