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Carbonates formed by anaerobic oxidation of methane at localized seeps have been recognized in the rock record based on a list of criteria, including anomalous deposition within detrital facies, complex petrofabrics, seep‐endemic macrofauna and 13C‐depleted isotopic signatures. While much emphasis has been placed on the latter, it is only one of several tools used for identification. This study reports on two different and rare limestone units in the forearc deposits of the Jurassic Bedford Canyon Formation in the Santa Ana Mountains, California (USA). Isolated, metre‐scale limestone pods were found to host abundant endemic Anarhynchia dimerelloid brachiopods and display diverse petrofabrics, including multiple generations of cements. However, the δ13C values of the petrofabrics ranged from −14.5 to 4.52‰ Vienna PeeDee Belemnite. These values are only slightly 13C‐depleted relative to contemporaneous seawater, thus likely recording a stronger component of oceanic dissolved inorganic carbon than hydrocarbons. Additionally, although the petrofabrics are common for seeps (primary micrite, microbialite, pelsparite, intraclastic micrite; early isopachous and botryoidal cements and yellow calcite; late‐stage void‐filling spar), the isotopic values did not follow a predicted trend of increasing δ13C with paragenetic sequence. Pelsparite δ13C values ranged from −10.65 to −7.09‰ Vienna PeeDee Belemnite while coarse spar and vein cements ranged from −11.42 to −2.44‰ Vienna PeeDee Belemnite. Olistostromes composed of brecciated pelmicrite sourced from shallow fringing‐arc environments are typical of forearc settings. Olistostromes in the Bedford Canyon Formation contain much lower δ13C values than the more classically characterized seep deposits, ranging from −21.77 to −10.78‰ Vienna PeeDee Belemnite. While the original shallow‐water source may not have a been a confined seep, the low δ13C values require the incorporation of carbon sourced from the oxidation of localized hydrocarbons. Together, these findings recommend a reconsideration of the weight placed on δ13C values as the key criterion for distinguishing seeps in the rock record. [ABSTRACT FROM AUTHOR]

This research quantifies the gas release rate from a natural shallow methane seep site in the Laspi Bay (Black Sea), whose origin is thermocatalytic. An adaptive single bubble identification technique was applied to analyze gas volume and release rates from passive acoustic data. Gas from the seafloor was emitted by single bubbles that occurred in clusters. The frequency of an individual bubble (830 Hz) was proportional to the bubble's radius (0.4 cm), which coincides with the optical method. The active seepage phases lasted longer than the pauses between bubble clusters. Distribution of bubble clusters and pauses duration for all seasons deviated significantly from a normal distribution. The daily and interseasonal periodicities of gas emissions were quite similar. The bubble gas flow rate ranged from 26 to 37 liters per day. Short-term water pressure fluctuations (up to a Δp of 46 mbar) caused by sea swell can impact gas flow variability. Continuous recording of hydrological parameters showed that average dissolved oxygen concentrations and salinity at the background station were slightly higher than those above the seep site. However, the data did not demonstrate significant environmental effects, such as hypoxia or submarine freshwater inflow, which was observed in other seepages areas. [ABSTRACT FROM AUTHOR]

Climate change disproportionately affects the Arctic, where warming is up to four times greater than the global annual average experienced in southern regions. Baffin Bay in the Canadian Arctic Archipelago is an ecologically and biologically significant area that will likely experience an increase in marine vessel traffic as a result of consistent declines in annual sea ice coverage. Along the western coast of Baffin Bay is known to be a region of active, natural hydrocarbon seeps where elevated levels of methane have been detected in previous surveys. Petroleum hydrocarbons released from the seafloor can fuel microbial production and shape the baseline microbiome. Establishing a microbial baseline is highly valuable as it contributes to a fundamental understanding of the existing microbial diversity that may be impacted in the future by anthropogenic stressors. In this study, 16S and 18S rRNA gene amplicon sequencing surveys revealed that the vertical stratification of the water column is largely driven by differences in depth, temperature, salinity, and inorganic nutrient concentrations. Chemical analysis provides further support that active petrogenic methane seepage occurs around Cape Dyer but not in areas targeted in this study. Presence of n-alkanes and toluene in association with hydrocarbon-synthesizing phytoplankton suggests biogenic production of these compounds. These findings provide a baseline for future environmental monitoring assessments to evaluate how the prokaryotic and eukaryotic microbiome may be impacted by ongoing climate change and anthropogenic stressors in western Baffin Bay. [ABSTRACT FROM AUTHOR]

The western Atlantic Ocean harbors a diverse fauna of squat lobsters, particularly in the family Munidopsidae. This study introduces Munidopsis sedna sp. nov., a species only found in the Gulf of Mexico and the first species reported to be endemic to cold seeps in the western Atlantic. Our investigation incorporates morphological analyses including micro-CT scanning evidence, multilocus molecular phylogeny, and mtDNA phylogeography, as well as ecological data derived from in situ observations and geographic distribution patterns to substantiate the recognition of the new species. Shallow molecular divergences and multiple morphological differences differentiate the new species from its closest relative, M. longimanus (A. Milne-Edwards, 1880). Additionally, we explore the potential scenario for ecological speciation within this newly identified taxon and discuss its significance in the context of conservation efforts in the Gulf of Mexico. [ABSTRACT FROM AUTHOR]

Shallow marine thrombolites from a newly discovered Lower Cretaceous cold seep in the Outer Carpathians (Poland) were analysed in order to untangle the complex sedimentological and biogeochemical processes involved in their formation and their diagenetic modifications. The studied thrombolites are made of two components: (i) microcrystalline mesoclots; and (ii) spar‐filled framework cavities. These components are dominated by calcite and show a complex spatial relationship, resulting in a heterogeneous, clotted fabric. The mesoclots exhibit digitate structures, often concentrically‐laminated, and are chiefly composed of microcrystalline material with δ13C values from −34.8 to −19.4‰ PeeDee Belemnite. Biomarkers analyses show the presence of 2, 6, 10, 15, 19‐pentamethylicosane within the mesoclots. The mesoclots host <5 mm wide microtubes filled with isopachous calcite recording even lower δ13C values (from −39.0 to −20.5‰ PeeDee Belemnite). The morphology of the mesoclots relative to their internal lamination and their geochemistry indicates that their growth was linked to anaerobic oxidation of methane while the microtubes acted as conduits for hydrocarbon‐charged fluids. The framework cavities are internally lined with framboidal pyrite, and are cemented by calcite spar with relatively high δ13C (−15.1 to −7.3‰ PeeDee Belemnite) and low δ18O values (−9.3 to −4.4‰ PeeDee Belemnite). Carbonate precipitation within the framework cavities is interpreted to have been related to bacterial sulphate reduction. U‐shaped trace fossils attributed to the ichnogenus Balanoglossites cross‐cut both mesoclots and framework cavities. The mechanisms involved in the formation and diagenesis of thrombolites at cold seeps are yet to be fully understood, and this work provides new insights on these complex biogeochemical and sedimentological processes. [ABSTRACT FROM AUTHOR]

To date, only a few microbial community studies of cold seeps at the South China Sea (SCS) have been reported. The cold seep dominated by tubeworms was discovered at South Yungan East Ridge (SYER) offshore southwestern Taiwan by miniROV. The tubeworms were identified and proposed as Paraescarpia formosa sp. nov. through morphological and phylogenetic analyses. The endosymbionts in the trunk of P. formosa analyzed by a 16S rRNA gene clone library represented only one phylotype, which belonged to the family Sedimenticolaceae in Gammaproteobacteria. In addition, the archaeal and bacterial communities in the habitat of tubeworm P. formosa were investigated by using high-phylogenetic-resolution full-length 16S rRNA gene amplicon sequencing. The results showed that anerobic methane-oxidizing archaea (ANME)-1b was most abundant and ANME-2ab was minor in a consortia of the anerobic oxidation of methane (AOM). The known sulfate-reducing bacteria (SRB) partners in AOM consortia, such as SEEP-SRB1, -SRB2, and -SRB4, Desulfococcus and Desulfobulbus, occurred in a small population (0–5.7%) at the SYER cold seep, and it was suggested that ANME-1b and ANME-2ab might be coupled with multiple SRB in AOM consortia. Besides AOM consortia, various methanogenic archaea, including Bathyarchaeota (Subgroup-8), Methanocellales, Methanomicrobiales, Methanosarcinales, Methanofastidiosales and Methanomassiliicoccales, were identified, and sulfur-oxidizing bacteria Sulfurovum and Sulfurimonas in phylum Epsilonbacteraeota were dominant. This study revealed the first investigation of microbiota in and around tubeworm P. formosa discovered at the SYER cold seep offshore southwestern Taiwan. We could gain insights into the chemosynthetic communities in the deep sea, especially regarding the cold seep ecosystems at the SCS. [ABSTRACT FROM AUTHOR]

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The present proposal offers an in-depth conceptual representation of the life cycle of methane seep ecosystems, showcasing their ecological development and biogeochemical processes from beginning to end. It combines current knowledge about microbial and metazoan communities, merging environmental and geological factors into a theoretical structure. A thorough review of literature on geology, biogeochemistry, and ecology supports the conceptual representation. It details five stages: birth, youth, maturity, senescence, and extinction, with each stage explaining the respective communities and their metabolic functions. It blends ideas from various fields, providing a comprehensive perspective on methane seep ecosystems and their intricate interactions. Additionally, the manuscript points out gaps in existing knowledge and proposes future research directions, highlighting the need for quantitative models and on-site investigations to validate the theoretical model. [ABSTRACT FROM AUTHOR]

Large-scale and multi-sample datasets have revealed that microbial diversity and geographic distribution patterns are distinct across various habitats, particularly between hydrothermal vent and cold seep ecosystems. To date, our understanding of the effects of spatial and geochemical gradients on marine microbial communities remains limited. Here, we report the microbial diversity and metabolic versatility of a remote seafloor sediment ecosystem at different sites (GC-2, -4, -5, -6, -8) in the Mid-Okinawa Trough (Mid-OT) using high-throughput metagenomic sequencing technology. Desulfobacteraceae (3.1%) were detected in a high abundance at GC-2 with intense methane concentrations (353 μL/L), which showed a clear correlation with cold seeping. Whereas Candidatus Brocadiaceae (1.7%), Rhodobacteraceae (0.9%), and Rhodospirillaceae (0.7%), which are commonly involved in denitrification and sulfur oxidation, were enriched at GC-8. Concurrently investigating the potential of deep-sea microbial metabolism, we gained insights into the adaptive capabilities and metabolic mechanisms of microorganisms within seafloor environments. Utilizing the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, the analysis of functional modules revealed a significant enrichment (71–74%) of genes associated with metabolic pathways. These results expand our knowledge of the relationship between microbial biodiversity and metabolic versatility in deep-sea extreme environments. [ABSTRACT FROM AUTHOR]

Cold seeps, featured by their extremely methane-rich sedimentary environments, play a significant role in the geological history and are common in marine sediments across the seafloor. Primary dolomite, possibly mediated by microorganisms, can be widely discovered in methane-rich environments. Hence, cold seeps may provide new insights into the 'dolomite problem', which has confused geologists for decades. Magnesium isotope geochemistry of seep carbonates contributes to the understanding of the dolomite formation mechanism in marine environments. In this paper, magnesium geochemical characteristics of carbonates in modern sediments are summarized, along with rare researches on magnesium isotopes of seep carbonates. Methane vigorously interacts with sulfate by anaerobic oxidation of methane at cold seeps, producing vast amounts of dissolved sulfide which can significantly promote dolomitization of seep carbonates. Compared with temperature, alkalinity, mineralogy, etc., the competition between rapid carbonate precipitation rates and aqueous ligands may be the main factor of the magnesium fractionation at cold seeps, which is controlled by the kinetic effect. The range of magnesium isotopes of seep carbonates is narrow (from -3.46‰ to -2.36‰), and an upper limit of magnesium content seems to exist. This characteristic may be a good indicator for identifying dolomitization related to anaerobic oxidation of methane. Whereas, mechanisms of magnesium isotope fractionation and dolomitization at cold seeps remain unclear, necessitating more natural samples tested, stimulated calculation and laboratory experiment. [ABSTRACT FROM AUTHOR]

Background: The deep-sea cold seep zone is characterized by high pressure, low temperature, darkness, and oligotrophy. Vesicomyidae clams are the dominant species within this environment, often forming symbiotic relationships with chemosynthetic microbes. Understanding the mechanisms by which Vesicomyidae clams adapt to the cold seep environment is significant. Acetylation modification of lysine is known to play a crucial role in various metabolic processes. Consequently, investigating the role of lysine acetylation in the adaptation of Vesicomyidae clams to deep-sea environments is worthwhile. So, a comparative study of lysine acetylation in cold seep clam Archivesica marissinica and shallow water shellfish Ruditapes philippinarum was conducted. Results: A total of 539 acetylated proteins were identified with 1634 acetylation sites. Conservative motif enrichment analysis revealed that the motifs -KacR-, -KacT-, and -KacF- were the most conserved. Subsequent gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment analyses were conducted on significantly differentially expressed acetylated proteins. The GO enrichment analysis indicated that acetylated proteins are crucial in various biological processes, including cellular response to stimulation, and other cellular processes (p < 0.05 and false discovery rate (FDR) < 0.25). The results of KEGG enrichment analysis indicated that acetylated proteins are involved in various cellular processes, including tight junction, motor proteins, gap junction, phagosome, cGMP-PKG signaling pathways, endocytosis, glycolysis/gluconeogenesis, among others (p < 0.05 and FDR < 0.25). Notably, a high abundance of lysine acetylation was observed in the glycolysis/glycogenesis pathways, and the acetylation of glyceraldehyde 3-phosphate dehydrogenase might facilitate ATP production. Subsequent investigation into acetylation modifications associated with deep-sea adaptation revealed the specific identification of key acetylated proteins. Among these, the adaptation of cold seep clam hemoglobin and heat shock protein to high hydrostatic pressure and low temperature might involve an increase in acetylation levels. Acetylation of arginine kinase might be related to ATP production and interaction with symbiotic bacteria. Myosin heavy chain (Ama01085) has the most acetylation sites and might improve the actomyosin system stability through acetylation. Further validation is required for the acetylation modification from Vesicomyidae clams. Conclusion: A novel comparative analysis was undertaken to investigate the acetylation of lysine in Vesicomyidae clams, yielding novel insights into the regulatory role of lysine acetylation in deep-sea organisms. The findings present many potential proteins for further exploration of acetylation functions in cold seep clams and other deep-sea mollusks. [ABSTRACT FROM AUTHOR]

The anaerobic oxidation of alkanes is a microbial process that mitigates the flux of hydrocarbon seeps into the oceans. In marine archaea, the process depends on sulphate-reducing bacterial partners to exhaust electrons, and it is generally assumed that the archaeal CO2-forming enzymes (CO dehydrogenase and formylmethanofuran dehydrogenase) are coupled to ferredoxin reduction. Here, we study the molecular basis of the CO2-generating steps of anaerobic ethane oxidation by characterising native enzymes of the thermophile Candidatus Ethanoperedens thermophilum obtained from microbial enrichment. We perform biochemical assays and solve crystal structures of the CO dehydrogenase and formylmethanofuran dehydrogenase complexes, showing that both enzymes deliver electrons to the F420 cofactor. Both multi-metalloenzyme harbour electronic bridges connecting CO and formylmethanofuran oxidation centres to a bound flavin-dependent F420 reductase. Accordingly, both systems exhibit robust coupled F420-reductase activities, which are not detected in the cell extract of related methanogens and anaerobic methane oxidisers. Based on the crystal structures, enzymatic activities, and metagenome mining, we propose a model in which the catabolic oxidising steps would wire electron delivery to F420 in this organism. Via this specific adaptation, the indirect electron transfer from reduced F420 to the sulphate-reducing partner would fuel energy conservation and represent the driving force of ethanotrophy. It is generally assumed that CO2 production is coupled to ferredoxin reduction during anaerobic alkane oxidation in archaea. Here, Lemaire et al. use biochemical and structural techniques to study native enzymes purified from an ethane-oxidising enrichment culture, showing that the enzymes deliver electrons to the F420 cofactor rather than to ferredoxin. [ABSTRACT FROM AUTHOR]

The article in the journal "Frontiers in Earth Science" explores contemporary studies on cold seeps, hydrothermal vents, mud volcanoes, and related seafloor features. These features provide insights into deep processes that are typically inaccessible to scientists. The research emphasizes multidisciplinary approaches to studying seafloor fluid emissions, highlighting the importance of geologic, physical, chemical, and biological processes in these environments. The studies cover a wide range of topics, including microbial processes, fluid dynamics, mineralization, and the role of seafloor emissions in global biogeochemical cycles. [Extracted from the article]

Background: Ammonia-oxidizing archaea (AOA) of the phylum Thaumarchaeota mediate the rate-limiting step of nitrification and remove the ammonia that inhibits the aerobic metabolism of methanotrophs. However, the AOA that inhabit deep-sea methane-seep surface sediments (DMS) are rarely studied. Here, we used global DMS metagenomics and metagenome-assembled genomes (MAGs) to investigate the metabolic activity, evolutionary history, and ecological contributions of AOA. Expression of AOA-specific ammonia-oxidizing gene (amoA) was examined in the sediments collected from the South China Sea (SCS) to identify their active ammonia metabolism in the DMS. Results: Our analysis indicated that AOA contribute > 75% to the composition of ammonia-utilization genes within the surface layers (above 30 cm) of global DMS. The AOA-specific ammonia-oxidizing gene was actively expressed in the DMS collected from the SCS. Phylogenomic analysis of medium-/high-quality MAGs from 18 DMS-AOA indicated that they evolved from ancestors in the barren deep-sea sediment and then expanded from the DMS to shallow water forming an amoA-NP-gamma clade-affiliated lineage. Molecular dating suggests that the DMS-AOA origination coincided with the Neoproterozoic oxidation event (NOE), which occurred ~ 800 million years ago (mya), and their expansion to shallow water coincided with the Sturtian glaciation (~ 713 mya). Comparative genomic analysis suggests that DMS-AOA exhibit higher requirement of carbon source for protein synthesis with enhanced genomic capability for osmotic regulation, motility, chemotaxis, and utilization of exogenous organic compounds, suggesting it could be more heterotrophic compared with other lineages. Conclusion: Our findings provide new insights into the evolutionary history of AOA within the Thaumarchaeota, highlighting their critical roles in nitrogen cycling in the global DMS ecosystems. EWMb7UH3jhRcWd8tHNUGyq Video Abstract [ABSTRACT FROM AUTHOR]

The Pliocene cold‐seep carbonate of the Crotone Basin (South Italy) represents a key site for dimension, outcropping exposure and quality. These deposits form a large carbonate (calcite) body (350 m long, 100 m wide and 40 m thick), and are characterized by a conduit facies made of authigenic calcite interpreted as previously active gas/fluid escape pipes and by a pavement facies, depicted as the surrounding early calcite‐cemented bioclastic and siliciclastic sediments. Pavement facies are commonly colonized by chemosymbiotic and non‐chemosymbiotic macrofauna (Lucinid and Solemyid bivalves, gastropods and serpulids). The conduit microfacies is characterized by the inward accretion of dark micritic laminae alternating with whitish sparitic layers. The micritic laminae show a microbial peloidal to dendrolitic fabric, which commonly incorporates planktonic foraminifera and coprolites, whereas the crystalline layers consist of microsparitic and sparitic crusts of prismatic zoned calcite crystals. The pavement facies shows more variability, because it is typified by laminated microbial boundstones, chemosymbiotic–bivalves packstone, foraminiferal packstone/wackestone and hybrid arenites. The stratigraphic constraint coupled with the foraminiferal assemblage (planktonic taxa) suggest a deep‐water setting occasionally affected by siliciclastic sedimentary flows. The pavement facies also shows common brecciation features, suggesting the establishment of post‐depositional overpressure conditions due to the early cementation of the conduits, which triggered localized rock failure. Stable isotope analysis of the different facies reveals overall negative δ13C values (−6.8 to −37.4‰ Vienna PeeDee Belemnite), indicating the presence of a complex mixture of methane with other hydrocarbons consumed microbially via anaerobic oxidation of methane; whereas δ18O is relatively positive (0.0 to 3.4‰ Vienna PeeDee Belemnite) suggesting the possible dehydration of clay minerals and/or destabilization of gas hydrates. This study, besides helping in the definition of the migration pathways and modality of accumulation of hydrocarbon‐rich fluids, can also help in building more and more realistic models for the complex genesis of cold‐seep carbonates. [ABSTRACT FROM AUTHOR]

There is evidence from the near‐infrared observations of space missions of the presence of carbonates on the surface of several ocean worlds. However, their genesis remains unresolved. We investigate the hypothesis that these carbonates may be in the form of clathrites assuming that clathrate hydrates are stable phases in the crust and ocean of these ocean worlds. In order to support this, we studied a sample of a potential clathrite from the Hydrate Ridge cold seep (Cascadia Subduction Zone), the carbonate rock fossil of clathrate hydrates, as a terrestrial analogue. We characterised the mineralogy and texture of the sample by using a coupled confocal Raman microscope and scanning electron microscopy instrument with the aim of identifying possible geo‐ and biosignatures, which could be relevant for future missions of exploration to ocean worlds and Mars. Our results show that aragonite is the dominant mineral phase in the clathrite sample, but Mg‐calcite and dolomite were also identified. These three carbonates constitute a pattern related to clathrate hydrate formation and dissociation processes. Dolomite was defined as a biosignature of gas hydrate microbiomes because it was integrated within Mg‐calcite grains precipitated after clathrate hydrate dissociation. Nevertheless, no spectral changes were observed in Raman bands of carbonate minerals that would indicate the influence of clathrate hydrates in their genesis. We also observed that Raman band positions of the associated framboidal pyrites are a characteristic signature of the associated framboid‐like texture because its potential as biosignature may only be attributed by biochemical analysis. [ABSTRACT FROM AUTHOR]

Active and relic marine methane‐seep sites are widely distributed globally and are distinguished by distinctive geology, biogeochemistry, and ecosystems. The discovery of methane‐seep sites in the Krishna‐Godavari (K‐G) basin has created exciting new opportunities for methane‐seep research in the Bay of Bengal. In this study, we document the occurrence of authigenic carbonates, including micro‐crystalline aragonite crust (arg‐crusts) admixed with chemosynthetic shells and high‐magnesium carbonate tubular structures (HMC‐tube), from the methane‐seep site SSD‐045/4 in the K‐G basin. The δ13C values of HMC‐tubes (−54.5 to −46.2‰) and arg‐crusts (−57.6 to −34.8‰) indicate biogenic methane as the likely carbon source. Enhanced porewater alkalinity driving carbonate precipitation may be attributed to microbial‐mediated SO₄2−‐AOM processes. Additionally, δ13C values (−35.2 ± 8‰) of the residual organic matter within the carbonates suggest a contribution of methanotrophic bacterial biomass. The δ18Ocarb values of HMC and aragonite indicate methane hydrate degassing and crystallization pathways, respectively. Pelloid‐filled burrows suggest the reworking of shallow HMC deposit by burrowing organisms, whereas the polyphase cementations (aragonite and HMC) within burrows indicate early and burial diagenetic pathways. The wide range in ΣLREE/ΣHREE ratios and Ceanom values in arg‐crusts reflect micro‐spatial variations in redox conditions, likely due to cementation occurring in both open and closed diagenetic systems. In contrast, more constrained Ceanom values and ΣLREE/ΣHREE ratios in HMC tubes suggest persistent sulfidic conditions. Overall, these findings provide insights into the pathways of carbonate formation at the K‐G basin methane‐seep site, highlighting the complex interplay of microbial processes, fluid dynamics, and diagenetic alterations. Plain Language Summary: Methane cold‐seeps are regions on the seabed where methane (CH4) gas oozes out across the sediment‐water interface into the water column. Both active and inactive seepage sites are known across the oceans. Active methane seep sites expel significant quantities of methane into the seawater which influences the oceanic methane budget as well as the carbon cycle. In contrast, the preserved authigenic carbonate deposits and chemosynthetic fauna at the relic seep sites are archives of past seepage activities. The seep ecosystem comprises a variety of chemosynthetic and non‐chemosynthetic organisms, whereas the geological features include mounds, mud volcanoes, carbonate crusts, chimneys, etc. formed due to methane expulsion processes. Here, we investigate the origin of calcium carbonate structures formed in a cold seep region off the east coast of India. The carbonate structures include tubular‐shaped high magnesian carbonates (HMC) and crusts composed of aragonite minerals. These tubes and crusts archive biological and geological processes, including past variations in methane effusion and diffusion through the sediment. Tubular structures are formed by gas flow through the sediments as chimneys and by burrowing activities of benthic organisms. On the other hand, the aragonite crusts are formed where methane flow is high across the seabed. Key Points: Relics of methanogenic high magnesian calcite tubes and aragonite crust recovered from cold seep site K‐G basin east coast of IndiaHMC precipitation is confined to sulfidic conditions in contrast to a wider redox range for aragonite precipitationReworking of unconsolidated HMC produced the pelloid rich tubular structures, whereas aragonite crust formed at high CH4 flow conditions [ABSTRACT FROM AUTHOR]

Introduction: The Aotearoa New Zealand ghost shrimp of the infraorders Axiidea and Gebiidea have never been comprehensively reviewed, with recent work uncovering a diverse regional fauna representing eight of the 14 known families. Methods: Using standard morphological and DNA sequencing tools, the family Callianopsidae is, for the first time, recorded off New Zealand, represented by a new species of Vulcanocalliax. Results: The new species was found near hydrocarbon seeps on the Hikurangi Margin, on the eastern New Zealand continental slope, and is only the second species now known in this genus. The single congener, V. arutyunovi, is only known from a mud volcano in the Gulf of Cádiz, off the Iberian Peninsula. Vulcanocalliax sp. nov. was formerly reported as an unnamed host of a new endemic New Zealand rhizocephalan barnacle Parthenopea australis and is here formally described as Vulcanocalliax beervana sp. nov. Discussion: The new species differs, e.g., in the shape of the anterior carapace margin (convexly rounded and without elevated postantennal shoulder present in V. arutyunovi), the ocular peduncle having a convex anterolateral margin (compared to a straight margin), and the uropodal exopod has a dorsomedian ridge, lacking the elevated anterior portion that is distinct in V. arutyunovi. This brings the number of described New Zealand ghost shrimp species to 18. A key to all known Callianopsidae is provided. [ABSTRACT FROM AUTHOR]

Cold seeps, where geofluids containing methane and other hydrocarbons originating from the subseafloor seeps through the sediment surface, play important roles in the elemental and energy flux between sediment and seawater. These seep sites often harbor communities of endemic animals supported by chemolithoautotrophic bacteria, either through symbiosis or feeding. Despite these animal communities being intensively studied since their discovery in the 1980's, the contribution of carbon from seep fluid to symbiotic microbes and subsequently host animals remains unclear. Here, we used natural-abundance radiocarbon to discern carbon sources: the ambient bottom water or the seeping geofluid. The 14C concentrations were measured for vesicomyid clams, a parasitic calamyzine polychaete, and a siboglinid tubeworm species from four different cold seep sites around Japan. We found most vesicomyid clams exhibiting 14C concentrations slightly lower than that of the ambient bottom water, suggesting up to 9% of C for chemolithoautotrophy originates from geofluid DIC. The different extent of fluid contribution across species may be explained by different routes to incorporate DIC and/or different DIC concentrations in the geofluid at each seep site. Stable nitrogen isotopic compositions further suggested N incorporation from geofluids in these clams, where the burrowing depth may be a key factor in determining their δ15N values. The siboglinid tubeworm showed a clear dependency for geofluid DIC, with a contribution of > 40%. Our results demonstrate the effectiveness of 14C analyses for elucidating the nutritional ecology of cold seep animals and their symbionts, as was previously shown for hydrothermal vent ecosystems. [ABSTRACT FROM AUTHOR]

As a special type of seep carbonate, the many details concerning the formation mode and mechanism of tubular seep carbonates are rarely reported. Here, new geochemical and mineralogical data regarding tubular seep carbonate (SQW-65) are reported. Sample SQW-65 had anomalously negative d13C values and positive d18Ovalues, which suggested the dissociation of gas hydrate. Additionally, almost all the sub-samples showed no Ce anomaly (Ce/Ce*average = 0.93), with obvious U enrichment (21.3< UEF <240.3), which indicates that the studied tubular seep carbonate was formed in an anoxic environment. Subsequently, the formation process of the studied tubular seep carbonate is further discussed according to the variability of mineralogical and geochemical characteristics from the rim to the core of the tubular formation. In the early stage of the studied tubular seep carbonate (periphery), owing to the influence of terrigenous components, the quartz and Ti content and Y/Ho ratio were high. However, with the formation of the periphery, the influence of terrigenous components was gradually weakened. In addition, from the rim to the core, the carbon and oxygen isotope values showed a "covariation" coupling relationship, an enrichment of U, and a reduction in total rare earth element content. This is because as the outer wall thickens and the internal fluid channel narrows, the intensity of the sulphatedriven anaerobic oxidation of methane and the associated precipitation rate of carbonate also increase. [ABSTRACT FROM AUTHOR]

Thermospores, the dormant resting stages of thermophilic bacteria, have been shown to be frequent but enigmatic components of cold marine sediments around the world. Multiple hypotheses have been proposed to explain their distribution, emphasizing their potential as model organisms for studying microbial dispersal via ocean currents. In the Arctic Ocean, the abundance and diversity of thermospores have previously been assumed to be low. However, this assessment has been based on data mainly from the western fjords of Svalbard, thus leaving most of the Arctic unexplored. Here, we expand the knowledge about the distribution of thermospores in the Arctic Ocean by investigating the abundance and diversity of thermospores in heated shelf sediments from three sites in the outer Laptev Sea. Two of the sites are located in an area with methane‐emitting cold seeps with a thermogenic source signature suggestive of an origin in a deep hydrocarbon reservoir, while the third site is a reference site not known to be impacted by seepage. We found that activity of viable thermospore populations was more prominent at one of the investigated seep sites. This finding is supported by both radiotracer growth experiments showing thermophilic, sulfate‐reducing activity triggered by heating, as well as 16S gene sequence analyses showing significantly enriched ASVs affiliated to the phylum Firmicutes following high‐temperature incubations. An enrichment of the sulfate‐reducing, endospore‐forming class Desulfotomaculia in heated samples compared to unheated samples was also observed. Furthermore, several ASVs identified at the seep site are closely related to thermospore‐producing bacteria associated with the deep biosphere, including hydrocarbon and hydrothermal systems. Based on the combined information from induced activity, estimated abundance, and phylogenetic composition using 16S rRNA gene sequencing, we propose likely source environments and dispersal vectors for thermospores in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

Caudofoveata is a class of worm-like molluscs (aplacophorans) that typically have an infaunal lifestyle, burrowing in soft bottoms in a wide range of marine habitats from shallow to deep waters. Here, we describe a very large new species of caudofoveate from South China Sea methane seeps growing up to 154 mm in length: Chaetoderma shenloong sp. nov. It is the first caudofoveate to be named from a chemosynthetic ecosystem and the first aplacophoran mollusc associated with seeps. Our new species stands out from other Pacific Chaetoderma species by its large size, a wide body relative to its length, a barely sclerotised radula, and the presence of isosceles-triangular sclerites. Phylogenetic reconstruction using the mitochondrial cytochrome c oxidase subunit I (COI) gene placed it within a paraphyletic clade comprising Chaetodermatidae and Limifossoridae, in line with a previous phylogenetic analysis. This also revealed that C. shenloong sp. nov. is conspecific with a Chaetoderma sp. whose whole genome was recently sequenced and assembled but remained undescribed until now. The most closely related species with an available COI sequence was C. felderi, the largest caudofoveate species recorded. Our discovery suggests caudofoveates may be present in other seeps globally but so far neglected; a potential example is C. felderi from the Gulf of Mexico, where seeps are abundant but whose exact habitat remains unclear. [ABSTRACT FROM AUTHOR]

Areas of the seafloor enriched with seeping fluids host unique chemosynthetic communities, and their interactions not only linked to the presence of oil and gas resources, but directly impact global geochemical cycles. These ecosystems can be found in diverse geological settings, spanning from passive to active continental margins, and encompass environments such as mid-ocean ridges, seamounts, cold brine lakes, mud volcanoes, and carbonate pinnacles. This review aims to examine seep environments in the Western Atlantic, the Caribbean, and Colombia, with a focus on understanding: I) their nature and origin, Itheir associated seabed characteristics, III) the biological communities directly connected to them, and IV) the chemistry and flow of the emitted fluids. The review identifies the close relationship of cold seeps to various geomorphological features, including linear diapir systems, salt diapirs resulting from salt tectonics, regions of mud volcanism, and compact seafloor mounds likely associated with buried mud diapirs. However, existing data on the fauna within these environments predominantly focus on megafauna, such as vestimentiferan tubeworms (Annelida), mussels, and vesicomyid bivalves (Mollusca), overlooking the crucial role of communities of small organisms, including fungi or macrofauna. This review highlights the absence of a consistent consensus among researchers regarding the factors controlling fauna distribution and presence in seep environments. Various authors have put forth divergent factors that influence seep community structures, with some emphasizing water depth, others the geological environment, and some the relationship with geomorphological conditions and fluid emissions. These findings underscore the need for further research into environmental factors and their roles in the observed distribution, presenting a promising avenue for future investigations. [ABSTRACT FROM AUTHOR]

A cruise was conducted in the summer of 2023 from the Pearl River Estuary (PRE) to the adjacent waters of the Xisha Islands in the northern South China Sea (NSCS) to investigate the distribution, community structure, and assembly patterns of eukaryotic and prokaryotic phytoplankton using high-throughput sequencing (HTS) and microscopic observation. Dinophyta were the most abundant phylum in the eukaryotic phytoplankton community based on HTS, accounting for 92.17% of the total amplicon sequence variants (ASVs). Syndiniales was the most abundant order among eukaryotic phytoplankton, whereas Prochlorococcus was the most abundant genus within cyanobacteria. The alpha diversity showed the lowest values in the PRE area and decreased gradually with depth, while cyanobacteria exhibited higher alpha diversity indices in the PRE and at depths ranging from 75 m to 750 m. The morphological results were different from the data based on HTS. Diatoms (37 species) dominated the phytoplankton community, with an average abundance of 3.01 × 104 cells L-1, but only six species of dinoflagellate were observed. Spearman correlation analysis and redundancy analysis (RDA) showed that the distribution and community structure of phytoplankton were largely influenced by geographical location and environmental parameters in the NSCS. The neutral community model (NCM) and null model indicated that deterministic processes played a significant role in the assembly of eukaryotic phytoplankton, with heterogeneous selection and homogeneous selection accounting for 47.27 and 29.95%, respectively. However, stochastic processes (over 60%) dominated the assembly of cyanobacteria and undominated processes accounted for 63.44%. In summary, the formation of eukaryotic phytoplankton was mainly influenced by environmental factors and geographic location, but the assembly of cyanobacteria was shaped by both stochastic processes, which accounted for over 60%, and environmental selection in the NSCS. [ABSTRACT FROM AUTHOR]

Introduction: Methane seeps influence surrounding benthic communities in different ways from slight changes in benthic abundance and biomass to major altering the species composition. Materials and Methods: We studied benthic communities of 14 methane seep flares in Laptev and East Siberian seas with comparative analysis of species composition and abiotic parameters at the nearby areas not affected by methane seeps. The species diversity was comparable at seep and non-seep sites varying from 3.9 to 39.6 taxa per 100 individuals and from 4.5 to 34.8 taxa per 100 individuals, correspondingly. Results: The Laptev Slope community corresponds with the Polychaeta-community, encircling the upper continental slope area of the entire Siberian Arctic. The Lower Shelf community described in this study apparently corresponds with the Ophiocten sericeum community identified in the shelf areas of the Kara, Laptev and East Siberian seas. The Upper Shelf community is mostly inhabited by the bivalves species such as Portlandia arctica, Ennucula tenuis and Astarte montagui communities. The Estuarine community, which is the poorest by diversity but has high values of abundance and biomass is directly influenced by the Lena River runoff in terms of lower salinities and higher sedimentation rates. Discussion: Throughout the study area, the differences between the Estuarine, Upper Shelf Lower Shelf and Laptev Slope communities exceeded the differences between the seep and background non-seep areas. Several taxa demonstrated correlations with different environmental factors, including the latitude, depth, temperature, salinity, pH and methane content, not depending on the revealed benthic community. Eight taxa demonstrated correlations with the methane content measured at different sediment depths. Two siboglinids taxa demonstrated high abundances at stations with highest methane content deep in the sediment. At the Siberian shelf, our geochemical data for siboglinid habitats are the first to be published so far. [ABSTRACT FROM AUTHOR]

Bathymodioline mussels dominate deep-sea methane seep and hydrothermal vent habitats and obtain nutrients and energy primarily through chemosynthetic endosymbiotic bacteria in the bacteriocytes of their gill. However, the molecular mechanisms that orchestrate mussel host-symbiont interactions remain unclear. Here, we constructed a comprehensive cell atlas of the gill in the mussel Gigantidas platifrons from the South China Sea methane seeps (1100 m depth) using single-nucleus RNA-sequencing (snRNA-seq) and whole-mount in situ hybridisation. We identified 13 types of cells, including three previously unknown ones, and uncovered unknown tissue heterogeneity. Every cell type has a designated function in supporting the gill's structure and function, creating an optimal environment for chemosynthesis, and effectively acquiring nutrients from the endosymbiotic bacteria. Analysis of snRNA-seq of in situ transplanted mussels clearly showed the shifts in cell state in response to environmental oscillations. Our findings provide insight into the principles of host-symbiont interaction and the bivalves' environmental adaption mechanisms. [ABSTRACT FROM AUTHOR]

Sea‐air methane flux was measured directly by the eddy‐covariance method across approximately 60,000 km of Arctic and Antarctic cruises during a number of summers. The Arctic Ocean (north of 60°N, between 20°W and 50°E) and Southern Ocean (south of 50°S, between 70°W and 30°E) are found to be on‐shelf sources of atmospheric methane with mean sea‐air fluxes of 9.17 ± 2.91 (SEM (standard error of the mean)) μmol m−2 d−1 and 8.98 ± 0.91 μmol m−2 d−1, respectively. Off‐shelf, this region of the Arctic Ocean is found to be a source of methane (mean flux of 2.39 ± 0.68 μmol m−2 d−1), while this region of the Southern Ocean is found to be a methane sink (mean flux of −0.77 ± 0.37 μmol m−2 d−1). The highest fluxes observed are found around west Svalbard, South Georgia, and South Shetland Islands and Bransfield Strait; areas with evidence of the presence of methane flares emanating from the seabed. Hence, this study may provide evidence of direct emission of seabed methane to the atmosphere in both the Arctic and Antarctic. Comparing with previous studies, the results of this study may indicate an increase in sea‐air flux of methane in areas with seafloor seepage over timescales of several decades. As climate change exacerbates rising water temperatures, continued monitoring of methane release from polar oceans into the future is crucial. Plain Language Summary: The amount of methane released from oceans into the atmosphere is uncertain. Most oceanic methane is stored in the seabed and can escape into the water at seafloor seeps, but the extent to which it escapes into the atmosphere remains unclear. This study uses a relatively new method, eddy‐covariance, to measure sea‐air methane fluxes during Arctic and Antarctic cruises. This is the first time this technique has been applied to sea‐air methane fluxes in both polar oceans. Our findings show that on‐shelf regions of the Arctic and Southern Oceans release methane into the atmosphere, with average fluxes of 9.17 ± 2.91 μmol m−2 d−1 and 8.98 ± 0.91 μmol m−2 d−1, respectively. We also identified areas with significant methane release in regions where methane has been found seeping into the water from the seabed. This study provides potential evidence that methane from seabed seeps may be directly emitted into the atmosphere in both the Arctic and Antarctic. Comparing with earlier studies, there is indication that the amount of methane released has increased over the last decades. As climate change drives increasing water temperatures, there is a potential for increased methane release from the seabed into the atmosphere, therefore on‐going observations of methane release from polar oceans are necessary. Key Points: Coastal regions of the Arctic Ocean and Southern Ocean are found to be sources of atmospheric methaneThe ocean releases elevated quantities of methane where seabed methane seeps have been observed in both the Arctic and Southern OceansThis study suggests a possible rise in methane release from oceanic areas with seabed seeps over last decades compared with a prior study [ABSTRACT FROM AUTHOR]

The article discusses the development and deployment of an indigenously designed low-cost underwater camera system for seabed videography in deep-sea environments, particularly focusing on cold seep ecosystems. It highlights the camera's technical specifications, cost-effectiveness, and its role in documenting marine biodiversity and ecological processes at significant depths.

Due to tectonic uplift in the Cenozoic and numerous shelf-wide glaciations during the Quaternary, -1-2.5 km of sedimentary overburden has been eroded from the Barents Sea shelf, leading to the exhumation and partial uncapping of hydrocarbon accumulations. Widespread natural gas and oil leakage from the glacially eroded middle-upper Triassic reservoir directly into the water column has been documented at the Sentralbanken high in the northern Norwegian Barents Sea. However, it remains unclear whether the hydrocarbon leakage occurs only from the middle-upper Triassic reservoir units in geological settings exceptionally conducive to hydrocarbon leakage, or if other reservoir formations contributed to the release of hydrocarbons into the water column. It is also not clear whether complete erosion of the caprock is a prerequisite for widespread liberation of natural gas and oil from glacially eroded reservoirs across Arctic continental shelves. Here we analyze multibeam echosounder data covering -5,000 km2 and a suite of high-resolution P-cable seismic lines from a range of geological structures across the northern Norwegian Barents Sea. Our analyses reveal that -21,700 natural gas seeps originate from exhumed, faulted and variably eroded structural highs bearing a range of Mesozoic reservoir formations. All investigated structural highs fuel seabed methane release hotspots with no exception. Evident from observations of seismic anomalies, fluid accumulations are pervasive in the subsurface and likely to continue fuelling seabed gas seepage into the future. We also document that gas seepage through faults piercing overburden, caprocks and reaching potential reservoir levels is pervasive at all investigated structural highs. On the Storbanken high and the Kong Karl platform, such fault-controlled seepage is more prevalent than seepage from reservoir formations subcropping below the seafloor. Using a simple parametrization approach, we estimate that seeps identified within our multibeam data coverage produce a seabed methane flux of 61 x 107 mol/yr (9,803 ton/yr), which is one to two orders of magnitude higher than other globally known submarine methane seepage provinces. Fluxes of methane from sea water to the air above the thermogenic gas seep provinces in the northern Norwegian Barents Sea remain to be determined. [ABSTRACT FROM AUTHOR]

Methane is a potent greenhouse gas that enters the marine system in large quantities at seafloor methane seeps. At a newly discovered seep site off the coast of Point Dume, CA, ~ meter‐scale carbonate chimneys host microbial communities that exhibit the highest methane‐oxidizing potential recorded to date. Here, we provide a detailed assessment of chimney geobiology through correlative mineralogical, geochemical, and microbiological studies of seven chimney samples in order to clarify the longevity and heterogeneity of these highly productive systems. U‐Th dating indicated that a methane‐driven carbonate precipitating system at Point Dume has existed for ~20 Kyr, while millimeter‐scale variations in carbon and calcium isotopic values, elemental abundances, and carbonate polymorphs revealed changes in carbon source, precipitation rates, and diagenetic processes throughout the chimneys' lifespan. Microbial community analyses revealed diverse modern communities with prominent anaerobic methanotrophs, sulfate‐reducing bacteria, and Anaerolineaceae; communities were more similar within a given chimney wall transect than in similar horizons of distinct structures. The chimneys represent long‐lived repositories of methane‐oxidizing communities and provide a window into how carbon can be transformed, sequestered, and altered over millennia at the Point Dume methane seep. [ABSTRACT FROM AUTHOR]

The evolution of gas hydrates influenced by the seawater environment is unknown. We present a model of structural transformation from sI hydrate to sII hydrate due to the influence of seawater environment and vent fluid in nature through in situ experiments of gas hydrate formation in the Haima cold seep area. The in situ experimental results indicate that gas hydrates preferentially form as sI hydrates even in cold seep environments where C2+ hydrocarbons are present. During subsequent evolution, the sI hydrates could restructured at the effect of seawater environment and vent fluid, causing transformation to sII hydrates under the influence of hydrate stability. The supply of gas and direct contact with seawater environment are critical factors for structural transformation. Such structural transformation is the result of gas hydrates seeking thermodynamic stability and may be common in active cold seep areas. Plain Language Summary: At high pressures and low temperatures, methane molecules are able to be captured by water in a solid hydrate state, known as natural gas hydrate. The significance of the abundant reserves of natural gas hydrates in the oceans, both in terms of global climate issues and energy resources, has been widely recognised. Since most natural gas reservoirs are dominated by methane (>90%), it is generally accepted that gas hydrates in the oceans tend to be structure I. However, through a field experiment in an active cold seep area, we found that newly generated gas hydrates under the influence of the same cold seep area were of structure I, whereas naturally exposed gas hydrates that had existed for a long period of time on the seafloor were instead of structure II. Based on this, we propose a model of structural transformation (structure I to structure II) of gas hydrates under the influence of seawater environment and vent fluid. This structural transformation may be a natural phenomenon that is common in active cold seep areas. Key Points: In situ experiments have demonstrated that gas hydrates can undergo structural transformation under the influence of seawater environmentNatural structural transformations of gas hydrates are probably common, especially in active cold seep where C2+ hydrocarbons present [ABSTRACT FROM AUTHOR]

Understanding methane flux dynamics in Arctic cold seep systems and the influence of oceanic currents on microbial methane-oxidizing bacteria (MOB) is crucial for assessing their impact on Arctic methane emissions. Here, we investigate methane dynamics and associated microbial communities at two cold seep areas, Norskebanken and Hinlopen Trough, North of Svalbard. Methane concentrations and methane oxidation rates (MOx) were measured in bottom and surface waters, with higher values observed in bottom waters, particularly at Hinlopen Trough. Dominant water column MOB clusters were Milano-WF1B-03 and Methyloprofundus. Methane availability drove MOx activity, as indicated by higher concentrations in bottom waters and sediments where MOx was elevated, too. Sediment MOB communities varied among locations, with Hinlopen featuring higher diversity and abundance. Similarities between sediments and water column MOBs suggest potential recruitment from sediments, possibly via a bubble shuttle mechanism. In addition, bottom water MOB community composition also showed similarities between the Norskebanken and Hinlopen seeps, implying an exchange of water column microbes between the two seep areas, which may likely be driven by the regional current regime. Together, our results show that bubble-mediated transport and translocation via currents are important processes shaping the community structure and efficiency of the microbial methane filter in the water column. [ABSTRACT FROM AUTHOR]

Heimdallarchaeia is a class of the Asgardarchaeota, are the most probable candidates for the archaeal protoeukaryote ancestor that have been identified to date. However, little is known about their life habits regardless of their ubiquitous distribution in diverse habitats, which is especially true for Heimdallarchaeia from deep-sea environments. In this study, we obtained 13 metagenome-assembled genomes (MAGs) of Heimdallarchaeia from the deep-sea cold seep and hydrothermal vent. These MAGs belonged to orders o_Heimdallarchaeales and o_JABLTI01, and most of them (9 MAGs) come from the family f_Heimdallarchaeaceae according to genome taxonomy database (GTDB). These are enriched for common eukaryote-specific signatures. Our results show that these Heimdallarchaeia have the metabolic potential to reduce sulfate (assimilatory) and nitrate (dissimilatory) to sulfide and ammonia, respectively, suggesting a previously unappreciated role in biogeochemical cycling. Furthermore, we find that they could perform both TCA and rTCA pathways coupled with pyruvate metabolism for energy conservation, fix CO2 and generate organic compounds through an atypical Wood-Ljungdahl pathway. In addition, many genes closely associated with bacteriochlorophyll and carotenoid biosynthesis, and oxygen-dependent metabolic pathways are identified in these Heimdallarchaeia MAGs, suggesting a potential light-utilization by pigments and microoxic lifestyle. Taken together, our results indicate that Heimdallarchaeia possess a mixotrophic lifestyle, which may give them more flexibility to adapt to the harsh deep-sea conditions. [ABSTRACT FROM AUTHOR]

The NC10 phylum links anaerobic methane oxidation to nitrite denitrification through a unique O2‐producing intra‐aerobic methanotrophic pathway. Although numerous amplicon‐based studies revealed the distribution of this phylum, comprehensive genomic insights and niche characterization in deep‐sea environments were still largely unknown. In this study, we extensively surveyed the NC10 bacteria across diverse deep‐sea environments, including waters, sediments, cold seeps, biofilms, rocky substrates, and subseafloor aquifers. We then reconstructed and analysed 38 metagenome‐assembled genomes (MAGs), and revealed the extensive distribution of NC10 bacteria and their intense selective pressure in these harsh environments. Isotopic analyses combined with gene expression profiling confirmed that active nitrite‐dependent anaerobic methane oxidation (n‐DAMO) occurs within deep‐sea sediments. In addition, the identification of the Wood–Ljungdahl (WL) and 3‐hydroxypropionate/4‐hydroxybutyrat (3HB/4HP) pathways in these MAGs suggests their capability for carbon fixation as chemoautotrophs in these deep‐sea environments. Indeed, we found that for their survival in the oligotrophic deep‐sea biosphere, NC10 bacteria encode two branches of the WL pathway, utilizing acetyl‐CoA from the carbonyl branch for citric acid cycle‐based energy production and methane from the methyl branch for n‐DAMO. The observed low ratios of non‐synonymous substitutions to synonymous substitutions (pN/pS) in n‐DAMO‐related genes across these habitats suggest a pronounced purifying selection that is critical for the survival of NC10 bacteria in oligotrophic deep‐sea environments. These findings not only advance our understanding of the evolutionary adaptations of NC10 bacteria but also underscore the intricate coupling between the carbon and nitrogen cycles within deep‐sea ecosystems, driven by this bacterial phylum. [ABSTRACT FROM AUTHOR]

• Sahune (Oxfordian, Late Jurassic) in south-eastern France Basin is newly described. • Carbonate bodies enclosed within Terres Noires Formation formed at cold seeps. • Associated fauna indicate seepage at bathyal depth ca. 1.500 m. • Several seep ostracod families have evolved at seeps since the Oxfordian. • Colonization of bathyal environments occurred earlier than thought. Hydrocarbon seeps represent some of the most extreme marine habitats but are also home to rich communities developed around chemosynthesis rather than photosynthesis. Here we describe the outcrop of Sahune (Drôme department, south-eastern France), that illustrates a new seeping site during the Late Jurassic (middle Oxfordian), as formally demonstrated by geochemical proxies. We report the associated fauna composed of foraminifers, radiolarians, crinoids, echinoids and ostracods that all point to seepage at bathyal depth. The foraminifer assemblage and the occurrence of the irregular echinoid Tithonia oxfordiana together point to a middle Oxfordian age. We provide an in-depth analysis of the ostracod community, which is the oldest so far reported in such environments. The new species Procytherura praecoquum may be cognate to the seepage site and could illustrate the oldest known example of pore clusters, sometimes proposed as representing ectosymbiosis. The Sahune assemblage demonstrates that cold seep ostracod communities were already a mixture of taxa from platform and deep-sea oligotrophic environments. The post-Jurassic diversification of ostracods at cold seeps was related to colonization events and diversification of families that have been inhabitants of such ecosystems at least since the Oxfordian. The Sahune record changes our current conception of the deep-sea colonization by the ostracods Tethysia and Procytherura that occurred earlier than traditionally considered. [ABSTRACT FROM AUTHOR]

Climate change poses a significant challenge for life on Earth. Different climate modes have been shown to come along with changes of the magnesium/calcium (Mg/Ca) ratio of seawater, and such changes are believed to control the primary mineral phase of marine authigenic carbonates. However, factors controlling marine carbonate phases other than seawater Mg/Ca ratios exist. Fibrous cements forming at methane seeps in the Black Sea provide new insight into the factors governing elemental and mineral phase compositions of fibrous carbonates. In this study, the distribution of aragonite and fibrous Mg calcite cements from three seep sites in the Black Sea is described as a function of water depth. The Mg/Ca ratio of seawater, as well as the ratio in shallow pore water, is close to four at the examined sites. Fibrous Mg calcite post‐dated aragonite cement in seep carbonates from shallow water depth of 120 to 190 m, whereas Mg calcite is the only cement at a greater depth of ca 2000 m. The primary formation of fibrous Mg calcite is confirmed by its zonation under cathodoluminescence, crystal morphologies agreeing with competitive growth, uniformly distributed MgCO3 contents and precipitation in equilibrium with local conditions calculated from δ18O values. The MgCO3 contents (4.5 to 12.2 mol%) are negatively correlated with δ13C values, indicating that the incorporation of Mg into the calcite crystal structure was favoured by high concentrations of sulphide generated by sulphate‐driven anaerobic oxidation of methane. Unlike open oceanic basins, stratification in the Black Sea leads to euxinic conditions in the deeper water column, favouring fibrous Mg calcite formation. This observation is consistent with sulphide catalysis as a critical agent for the formation of low‐Mg calcite to very high‐Mg calcite at high Mg/Ca ratios and is possibly relevant to carbonate cements forming during times of oceanic euxinia. [ABSTRACT FROM AUTHOR]

Deep‐sea methane seeps are amongst the most biologically productive environments on Earth and are often characterised by stable, low oxygen concentrations and microbial communities that couple the anaerobic oxidation of methane to sulfate reduction or iron reduction in the underlying sediment. At these sites, ferrous iron (Fe2+) can be produced by organoclastic iron reduction, methanotrophic‐coupled iron reduction, or through the abiotic reduction by sulfide produced by the abundant sulfate‐reducing bacteria at these sites. The prevalence of Fe2+in the anoxic sediments, as well as the availability of oxygen in the overlying water, suggests that seeps could also harbour communities of iron‐oxidising microbes. However, it is unclear to what extent Fe2+ remains bioavailable and in solution given that the abiotic reaction between sulfide and ferrous iron is often assumed to scavenge all ferrous iron as insoluble iron sulfides and pyrite. Accordingly, we searched the sea floor at methane seeps along the Cascadia Margin for microaerobic, neutrophilic iron‐oxidising bacteria, operating under the reasoning that if iron‐oxidising bacteria could be isolated from these environments, it could indicate that porewater Fe2+ can persist is long enough for biology to outcompete pyritisation. We found that the presence of sulfate in our enrichment media muted any obvious microbially‐driven iron oxidation with most iron being precipitated as iron sulfides. Transfer of enrichment cultures to sulfate‐depleted media led to dynamic iron redox cycling relative to abiotic controls and sulfate‐containing cultures, and demonstrated the capacity for biogenic iron (oxyhydr)oxides from a methane seep‐derived community. 16S rRNA analyses revealed that removing sulfate drastically reduced the diversity of enrichment cultures and caused a general shift from a Gammaproteobacteria‐domainated ecosystem to one dominated by Rhodobacteraceae (Alphaproteobacteria). Our data suggest that, in most cases, sulfur cycling may restrict the biological "ferrous wheel" in contemporary environments through a combination of the sulfur‐adapted sediment‐dwelling ecosystems and the abiotic reactions they influence. [ABSTRACT FROM AUTHOR]

The article titled "Hansel and Gretel Retold" is a poem that offers different perspectives on the classic fairy tale. The first section is from Hansel's point of view, expressing his distrust and resentment towards women. The second section is from Gretel's perspective, describing her experiences of hunger and her longing for freedom. The third section is from the woodcutter's perspective, reflecting on his loss and his acceptance of the situation. The final section is from the stepmother's point of view, portraying her as a victim and justifying her actions. The poem explores themes of power dynamics, gender roles, and the consequences of choices. [Extracted from the article]

This study investigates the temporal variations in methane concentration and flare activity in the Hola trough (offshore Norway) during May 2018 and June 2022. Between these time periods, methane seep activity exhibits 3.5 times increase, as evidenced by hydroacoustic measurements. As the seep area in the Hola trough is constantly within the hydrate stability zone, the observed increase cannot be attributed to migration of its shallow boundary due to temperature increase. However, a combination of low tide conditions resulting in a lower sediment pore pressure and a bottom water temperature increase resulting in a lower methane solubility is likely to explain the increase in the number of seeps observed in June 2022. The hypothesis of tide influence is supported by data collected from a piezometer deployed and recovered during the cruise showing that the tidal effect was observed 3 m below the seafloor. Despite the numerous methane seeps detected, methane concentration and gas flow rates near the seafloor were low (<19 nM and <70 mL min−1, respectively) compared to other areas with methane seep activity. This is likely due to strong currents rapidly dispersing methane in the water column. Sub‐seafloor investigations identified pathways for gas migration in methane seep areas, influenced by topography. This study provides valuable insights into the temporal dynamics of methane concentrations, flare activity, and gas distribution in the Hola trough, contributing to our understanding of offshore methane dynamics in the region. Plain Language Summary: The Hola Trough, offshore Norway's Lofoten‐Vesterålen (LoVe) area, has been of interest for many years due to its rich marine life and potential oil and gas resources. There, coral mounds thrive around methane seepage. The LoVe observatory network monitors this unique environment. Using this observatory platform, associated data set and research expeditions at sea, the project EMAN7 (Environmental impact of Methane seepage and sub‐seabed characterization at LoVe‐Node 7) aims to understand the environmental impact of methane seepage as well as its spatio‐temporal variability. The comparison of methane seep activity during two summers with different environmental conditions revealed 3.5 times more seeps when a combination of warmer bottom water and low tide changes the sediment pore properties. A sensor recording subseafloor pore pressure and bottom temperature supports these findings. Sub‐seafloor investigations identified routes for gas migration in methane seep areas, influenced by topography. Key Points: A combination of warmer bottom water and low tide increases methane seeps 3.5 times by altering sediment gas solubility and pore pressureIntermittent seeps and strong oceanic currents explain the limited microbial mats and the low methane concentration in the water columnWe found sub‐seafloor pathways for gas migration in methane seep areas, influenced by topography [ABSTRACT FROM AUTHOR]

Methane-derived authigenic carbonate often constitutes the sole remaining record of relic methane seeps. The clumped (Δ47) and oxygen isotopic composition of seep carbonates often yield inaccurate temperatures, attributed to kinetic isotope effects and modification of seawater isotope composition by hydrate water. Here, we analyzed the dual-clumped isotope (Δ47/Δ48) composition of authigenic carbonate from a modern methane seep. We demonstrate that aragonite forms closest to isotopic equilibrium such that its Δ47 can directly yield the correct formational temperature, whereas calcite is unambiguously biased by kinetic isotope effects. Numerical models show that the observed bias in the isotopic composition arises from rate-limiting dehydration/dehydroxylation of HCO3-alongside diffusive fractionation, which can be corrected for with analysis of carbonate Δ47/Δ48 values. We demonstrate the utility of dual-clumped isotope analysis for studying seep carbonates, as it reveals the origin and magnitude of kinetic biases and can be used to reconstruct paleotemperature and seawater δ18O. [ABSTRACT FROM AUTHOR]

The ocean remains a reservoir of unknown biodiversity, particularly in the deep sea. Chemosynthesis-based ecosystems, such as hydrothermal vents and hydrocarbon seeps, host unique and diverse life forms that continue to be discovered and described. The present study focuses on patelliform gastropods (limpets) collected from Pacific Costa Rica Margin hydrocarbon seeps during three research cruises from 2017 to 2019. Genetic and morphological analyses revealed the presence of several new lineages within the genera Bathyacmaea Okutani, Tsuchida & Fujikura,1992, Cocculina Dall, 1882, Paralepetopsis McLean, 1990, and the family Lepetodrilidae McLean, 1988: Bathyacmaea levinae sp. nov., Paralepetopsis variabilis sp. nov., Pseudolepetodrilus costaricensis gen. et sp. nov., and Cocculina methana sp. nov. These investigations also expanded the known ranges of the species Pyropelta corymba McLean, 1992 and Lepetodrilus guaymasensis McLean, 1988 to the Costa Rica Margin. This research highlights the uniqueness of gastropod fauna at the Costa Rica Margin and contributes to our understanding of the biodiversity at chemosynthesis-based deep-sea ecosystems in the face of global biodiversity loss and increased commercial interest in deep-sea resources. [ABSTRACT FROM AUTHOR]

Methane release from marine sediments strongly influences the local seafloor environment and ecosystems, and may impact Earth's climate system. Recent studies revealed anomalous molybdenum (Mo) enrichment in seep sediments, which was linked to methane release events. Marine seep sediments are a potential sink of Mo for the global ocean, while the mechanisms leading to local Mo enrichment are not fully understood. The sediments from a gas hydrate-bearing area of the South China Sea analyzed herein reveal authigenic Mo (Mo auth) contents ranging from 0 and 31.4 µg/g and δ98Mo auth values ranging from 0.18 ‰ to 3.31 ‰. The range of δ98Mo auth values of seep sediments is therefore similar to values of modern iron-rich sediments with low concentrations of dissolved porewater hydrogen sulfide and sediments deposited under weakly euxinic sediments. Among the obtained South China Sea data, the more positive δ98Mo auth values (>ca. 1.5 ‰) are interpreted to reflect diffusion of seawater Mo into the sediment at moderate seepage rates and Mo isotope fractionation during the formation of thiomolybdates in the sulfidic seep environment. The lower δ98Mo auth values (

We conducted an acoustic telemetry study of native golden perch (Macquaria ambigua) to examine movement behaviour in areas affected by methane seeps and hypoxia in the intermittent Condamine River, Murray‐Darling Basin (MDB), Australia.Fish were collected during periods of no flow and hypoxia (dissolved oxygen [DO] <1 mg/L). Despite these conditions, 38 of 43 fish tagged with acoustic transmitters were detected for >3 months post‐tagging in the study reach and 27 fish were being detected after 14 months. During periods of elevated river flow and relatively high DO, 30 fish moved away from their original tagging locations, with three undertaking movements (>7 km) outside the study reach and not returning.Generalised additive mixed models showed a significant increase in the probability of movement as soon as flow commenced and when water temperatures exceeded 19°C. As flows receded, most fish that had moved exhibited accurate homing behaviour to their original tagging location.The patterns of movement and site fidelity exhibited by golden perch correspond with previous studies of the species in intermittent rivers not affected by methane seeps and severe hypoxia, suggesting that the methane seeps and hypoxia did not inhibit fish movement nor render the affected habitats unsuitable for habitation.Golden perch can survive and remain active in water with much lower DO (<1 mg/L) than previously described for large‐bodied native fishes in the MDB. However, fish condition in the study reach was slightly lower than other regions of the MDB, providing preliminary evidence that fish residing in habitats affected by chronic hypoxia and methane seepage may experience sub‐lethal stress.Our results demonstrate the importance of field‐based data on the behavioural and physiological responses of fish to chronic hypoxia and methane exposure to guide appropriate management responses. [ABSTRACT FROM AUTHOR]

In the past decade, thousands of previously unknown methane seeps have been identified on continental margins around the world. As we have come to appreciate methane seep habitats to be abundant components of marine ecosystems, we have also realized they are highly dynamic in nature. With a focus on discrete depth ranges across the Cascadia Margin, we work to further unravel the drivers of seep‐associated microbial community structure. We found highly heterogenous environments, with depth as a deterministic factor in community structure. This was associated with multiple variables that covaried with depth, including surface production, prevailing oxygen minimum zones (OMZs), and geologic and hydrographic context. Development of megafaunal seep communities appeared limited in shallow depth zones (~ 200 m). However, this effect did not extend to the structure or function of microbial communities. Siboglinid tubeworms were restricted to water depths > 1000 m, and we posit this deep distribution is driven by the prevailing OMZ limiting dispersal. Microbial community composition and distribution covaried most significantly with depth, but variables including oxygen concentration, habitat type, and organic matter, as well as iron and methane concentration, also explained the distribution of the microbial seep taxa. While members of the core seep microbiome were seen across sites, there was a high abundance of microbial taxa not previously considered within the seep microbiome as well. Our work highlights the multifaceted aspects that drive community composition beyond localized methane flux and depth, where environmental diversity adds to margin biodiversity in seep systems. [ABSTRACT FROM AUTHOR]

We report a newly discovered hydrocarbon seep deposit from the Eocene bathyal flysch, exposed in the town of Buje in Istria, Croatia. Molecular fossils of methane‐oxidizing prokaryotes and abundant banded botryoidal cements indicate strong fluid flux at this site. We systematically describe the fauna of this and another seep deposit previously reported from Buje. The faunal assemblages are composed of eight species, these being an unidentified solemyid protobranch bivalve, the nuculid Nucula bowerbanki?, the nuculanid Nuculana? sp., the mytilid Brachidontes? amanoi sp. nov., the two thyasirids Channelaxinus dinaricus sp. nov. and Thyasira histriaensis sp. nov., the lucinid bivalve Amanocina bujensis sp. nov., and a possible provannid gastropod. The two assemblages are of low diversity (4 and 5 species, respectively), and are dominated by chemosymbiotic species whose occurrence is largely restricted to seeps. Despite their spatial and stratigraphic proximity, the two deposits share only a single species, Channelaxinus dinaricus, probably due to different fluid flux regimes at both seeps. The Buje seep assemblages are among the very few Late Cretaceous to Palaeogene chemosynthesis‐based faunal assemblages from the Tethys Ocean (the others being Late Cretaceous vent assemblages from Cyprus). From an evolutionary perspective, the Buje seep communities consist of genera with Mesozoic origins but lack Cenozoic novelties such as bathymodiolin mussels and vesicomyid clams, which are known from coeval deposits from the Pacific and dominate vents and seeps today. Thus, the Buje seep fauna support previous assertions that the Eocene Tethyan seep faunas preserved an ancient aspect, whereas evolutionary novelties arose in the Pacific. [ABSTRACT FROM AUTHOR]

Areas of the seafloor enriched with seeping fluids host unique chemosynthetic communities, and their interactions not only linked to the presence of oil and gas resources, but directly impact global geochemical cycles. These ecosystems can be found in diverse geological settings, spanning from passive to active continental margins, and encompass environments such as mid-ocean ridges, seamounts, cold brine lakes, mud volcanoes, and carbonate pinnacles. This review aims to examine seep environments in the Western Atlantic, the Caribbean, and Colombia, with a focus on understanding: I) their nature and origin, Itheir associated seabed characteristics, III) the biological communities directly connected to them, and IV) the chemistry and flow of the emitted fluids. The review identifies the close relationship of cold seeps to various geomorphological features, including linear diapir systems, salt diapirs resulting from salt tectonics, regions of mud volcanism, and compact seafloor mounds likely associated with buried mud diapirs. However, existing data on the fauna within these environments predominantly focus on megafauna, such as vestimentiferan tubeworms (Annelida), mussels, and vesicomyid bivalves (Mollusca), overlooking the crucial role of communities of small organisms, including fungi or macrofauna. This review highlights the absence of a consistent consensus among researchers regarding the factors controlling fauna distribution and presence in seep environments. Various authors have put forth divergent factors that influence seep community structures, with some emphasizing water depth, others the geological environment, and some the relationship with geomorphological conditions and fluid emissions. These findings underscore the need for further research into environmental factors and their roles in the observed distribution, presenting a promising avenue for future investigations.

This article is an editorial that discusses the applications of environmental DNA (eDNA) in the aquatic ecosystem management of East Asia. eDNA is genetic material from target species that allows for the detection of species without direct observation or capturing whole organisms. The use of eDNA analysis has rapidly developed as a promising tool in various research fields, including biodiversity assessment, invasive species monitoring, and rare species conservation. The article includes six papers on eDNA research in East Asia, covering topics such as fish diversity, larval fish diversity, intracellular DNA detection, bacterial communities in deep-sea sponges, protistan community structures, and the detection of aquatic invasive species. The authors advocate for researchers to participate in the "Making eDNA FAIR" project to improve the discoverability and accessibility of eDNA data. [Extracted from the article]