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Studies on the involvement of intrusive magmatism in hydrocarbon generation within sedimentary basins have gained momentum owing to increasing appraisal of the role that such processes may play in controlling global carbon cycle perturbations, and the exploration potential of the volcanic sedimentary basins. Nevertheless, for many areas the causal link between the intrusions and surrounding hydrocarbon systems remains disputed, encouraging a search for methods that could aid in identifying different hydrocarbon sources. Here, we have performed a multi-proxy geochemical study of the middle Cretaceous methane-seep deposits of the Basque-Cantabrian Basin, an early-stage, peri-cratonic rift marking the Mesozoic opening of the Bay of Biscay. Infilled by a thick sedimentary succession intruded by shallow-level igneous bodies, the basin shares analogies with modern young, sedimented rifts that sustain hydrocarbon seepage. We have applied a novel approach that uses the Nd isotope composition of the seep deposits to constrain the relationship between hydrocarbon seepage and igneous activity, and to explore the general potential of Nd isotopes to trace magmatic-influenced fluids in volcanic sedimentary basins. The Nd isotope data have been combined with rare earth element analyses and carbon and oxygen isotope measurements, providing broad insight into the former composition of the seeping fluids. For three out of four investigated seeps, the Nd isotope ratios observed in authigenic seep carbonates include signatures markedly more radiogenic than that reconstructed for background seawater-derived pore waters. The level of this Nd-143-enrichment varies both between and within individual deposits, reflecting spatial and temporal differences in fluid composition typical of seep-related environments. The radiogenic Nd isotope signals provide evidence of subseafloor interactions between the seeping fluids and mafic igneous materials, supporting the model of an igneous control on the mid-Cretaceous methane expulsion in the Basque-Cantabrian Basin. The thermogenic origin of the methane is in accord with the moderately negative delta C-13 values and paragenetic successions observed in the studied seep carbonates. For a single deposit, its relatively unradiogenic Nd isotope composition can be attributed to the smallest size and shallowest emplacement depth of the underlying intrusion, likely resulting in a short-lived character and limited hydrocarbon-generation potential of the associated contact metamorphism. The study demonstrates that Nd isotope analyses of seep carbonates offer a tool in disentangling methane fluxes from different organic matter alteration pathways for the numerous, both fossil and modern sedimented rifts for which the involvement of various methane sources remains insufficiently understood. This work was supported by the National Science Centre, Poland (grant No. 2016/23/D/ST10/00444; to MJ) , and the Eusko Jaurlaritza (Ikerketa Taldeak IT930-16) and the Spanish State Research Agency (project PID2019-105670GB-I00/AEI/10.13039/501100011033; both to LMA)

Me.tha.no.coc.co'i.des. Gr. adj. suff. ‐oides similar to; N.L. neut. n. Methanococcoides organism similar to Methanococcus. Euryarchaeota / Methanomicrobia / Methanosarcinales / Methanosarcinaceae / Methanococcoides The genus Methanococcoides comprises four species, Methanococcoides methylutens, Methanococcoides burtonii, Methanococcoides alaskense, and Methanococcoides vulcani. Cells are irregular cocci, 0.5–3 μm in diameter, occurring singly or in pairs, and may be motile. Clumps of cells can also observed. Cells exhibit a blue‐green autofluorescence under UV illumination. The cell wall consists of a very thin protein S‐layer, approximately 10‐nm thick. Susceptible to lysis by hypotonic or detergent shock. Eurypsychrophilic to mesophilic. Strict anaerobe. Neutrophilic. Halophilic, optimal salinity near seawater. Cells can dismutate methylamines, methanol, glycine betaine, choline, tetramethylammonium, dimethyl sulfide, methyliodide, and N,N‐dimethylethanolamine for growth, but cannot catabolize acetate, dimethylsulfide, H2/CO2, or formate. Methanococcoides spp. are members of the phylum Euryarchaeota, class Methanomicrobia, order Methanosarcinales, and family Methanosarcinaceae. Known habitats are deep‐sea mud volcano, marine anoxic sediment, hypolimnion Ace Lake, mangrove swamp, deep hypersaline anoxic basin, and hydrothermal vents. DNA G + C content (mol%): 40.8–44. Type species: Methanococcoides methylutens Sowers and Ferry 1983, VL17.

Over half of the organic carbon on Earth’s surface is trapped in marine sediment as methane hydrates. Ocean warming causes hydrate dissociation and methane leakage to the water column, rendering the characterization of microbes from hydrate depositions a pressing matter. Through genomic, phylogenetic, and biochemical assays, we characterize the first microorganisms isolated from the Rio Grande Cone (Brazil), reservoir responsible for massive methane releases to the water column. From sediment harboring rich benthic communities, we obtained 43 strains of Brevibacillus sp., Paenibacillus sp. and groups of Bacillus sp. Methane-enriched samples yielded strains of the Pseudomonas fluorescens complex, exhibiting fluorescent siderophore production and broad multi-carbon catabolism. Genomic characterization of a novel Pseudomonas sp. strain indicated 32 genes not identified in the closest related type-species, including mercury resistance proteins. Our results provide phylogenetic and genomic insights on the first bacterial isolates retrieved from a poorly explored region of the South Atlantic Ocean.

Cold seep ecosystems are developed from methane-rich fluids in organic rich continental slopes, which are the source of various dense microbial and faunal populations. Extensive studies have been conducted on microbial populations in this unique environment; most of them were based on DNA, which could not resolve the activity of extant organisms. In this study, RNA and DNA analyses were performed to evaluate the active archaeal and bacterial communities and their network correlations, particularly those participating in the methane cycle at three sites of newly developed cold seeps in the northern South China Sea (nSCS). The results showed that both archaeal and bacterial communities were significantly different at the RNA and DNA levels, revealing a higher abundance of methane-metabolizing archaea and sulfate-reducing bacteria in RNA sequencing libraries. Site ROV07-01, which exhibited extensive accumulation of deceased Calyptogena clam shells, was highly developed, and showed diverse and active anaerobic archaeal methanotrophs (ANME)-2a/b and sulfate-reducing bacteria from RNA libraries. Site ROV07-02, located near carbonate crusts with few clam shell debris, appeared to be poorly developed, less anaerobic and less active. Site ROV05-02, colonized by living Calyptogena clams, could likely be intermediary between ROV07-01 and ROV07-02, showing abundant ANME-2dI and sulfate-reducing bacteria in RNA libraries. The high-proportions of ANME-2dI, with respect to ANME-2dII in the site ROV07-01 was the first report from nSCS, which could be associated with recently developed cold seeps. Both ANME-2dI and ANME-2a/b showed close networked relationships with sulfate-reducing bacteria; however, they were not associated with the same microbial operational taxonomic units (OTUs). Based on the geochemical gradients and the megafaunal settlements as well as the niche specificities and syntrophic relationships, ANMEs appeared to change in community structure with the evolution of cold seeps, which may be associated with the heterogeneity of their geochemical processes. This study enriched our understanding of more active sulfate-dependent anaerobic oxidation of methane (AOM) in poorly developed and active cold seep sediments by contrasting DNA- and RNA-derived community structure and activity indicators.

The submerged portions of the North-Anatolian Fault (NAF) in the Sea of Marmara and the NE-Aegean Sea are sites of large magnitude earthquakes, that leave diagnostic geological “signatures” in the sedimentary record in the form of mass-wasting deposits, turbidites, and fluid and gas escape features. This is due to the interplay of seismic-shaking, mass- and turbidity flows, sediment resuspension and fluids circulation in relatively small sub-basins with a complex paleo-oceanography, steep slopes, high rates of deformation, and diffuse fault-controlled gas and fluid seeps. To unravel the complex interrelations of these phenomena during earthquake cycles, we carried out paleoseismological studies at several key locations. Here, we report results of these studies, carried out onboard the R/V Urania over a decade, starting soon after the Mw 7.4, 1999 Izmit earthquake. Our work included high resolution mapping of active faults through multibeam bathymetry and high resolution seismic reflection profiles, multi-parameter analysis of sediment cores, as well as seafloor observations using sensors mounted on remotely-operated vehicles (ROV). The main objectives were to map active faults, determine slip-rates and earthquake recurrence times along major fault strands, and assess connections between fault deformation and fluid activity. We mapped fault geometry in the gulfs of Izmit, Gemlik and Saros, showing the trans-tensive nature of these depressions. The average slip-rates for the last ~ 10 ka was found to be 10 mm/y in the gulfs of Izmit and Saros, at the eastern and the western ends of the NAF northern strand, and 3–4 mm/yr in the Gulf of Gemlik, along the middle strand of the NAF. These rates, integrated over 10 ka of NAF activity, are smaller than those determined by the GPS geodetic measurements. Submarine paleoseismological studies in the Gulf of Izmit detected the sedimentary records of earthquakes for the last 2.4 ka, suggesting an average recurrence time of 300 years for major events. Multisensor observations and monitoring of the seafloor have shown widespread emissions of gas and fluids along the submerged part of the NAF, associated with reduced black sediments; we investigated their possible connection with the earthquake cycle.

Siboglinids were sampled from four mud volcanoes in the Gulf of C&aacute, diz (El Cid MV, Bonjardim MV, Al Gacel MV, and Anastasya MV). These invertebrates are characteristic to cold seeps and are known to host chemosynthetic endosymbionts in a dedicated trophosome organ. However, little is known about their tube as a potential niche for other microorganisms. Analyses by scanning and transmission electron microscopy showed dense biofilms on the tube in Al Gacel MV and Anastasya MV specimens by prokaryotic cells. Methanotrophic bacteria were the most abundant forming these biofilms as further supported by 16S rRNA sequence analysis. Furthermore, elemental analyses with electron microscopy and energy-dispersive X-ray spectroscopy point to the mineralization and silicification of the tube, most likely induced by the microbial metabolisms. Bacterial and archaeal 16S rRNA sequence libraries revealed abundant microorganisms related to these siboglinid specimens and certain variations in microbial communities among samples. Thus, the tube remarkably increases the microbial biomass related to the worms and provides an additional microbial niche in deep-sea ecosystems.

Background High primary productivity in the midst of high toxicity defines hydrocarbon seeps; this feature usually results in significantly higher biomass, but in lower diversity communities at seeps rather than in the surrounding non-seep benthos. Qualitative estimates indicate that this dichotomy does not necessarily hold true in high latitude regions with respect to megafauna. Instead, high latitude seeps appear to function as local hotspots of both megafaunal diversity and abundance, although quantitative studies do not exist. In this study, we tested this hypothesis quantitatively by comparing georeferenced seafloor mosaics of a seep in the southwestern Barents Sea with the adjacent non-seep seafloor. Methods Seafloor images of the Svanefjell seep site and the adjacent non seep-influenced background seabed in the southwestern Barents Sea were used to construct georeferenced mosaics. All megafauna were enumerated and mapped on these mosaics and comparisons of the communities at the seep site and the non-seep background site were compared. Sediment push cores were taken in order to assess the sediment geochemical environment. Results Taxonomic richness and abundance were both considerably higher at the seep site than the non-seep location. However, taxa were fewer at the seep site compared to other seeps in the Barents Sea or the Arctic, which is likely due to the Svanefjell seep site exhibiting relatively low seepage rates (and correspondingly less chemosynthesis based primary production). Crusts of seep carbonates account for the higher diversity of the seep site compared to the background site, since most animals were either colonizing crust surfaces or using them for shelter or coverage. Our results indicate that seeps in northern latitudes can enhance local benthic diversity and this effect can take place even with weak seepage. Since crusts of seep carbonates account for most of the aggregating effect of sites experiencing moderate/weak seepage such as the study site, this means that the ability of seep sites to attract benthic species extends well beyond the life cycle of the seep itself, which has important implications for the larger marine ecosystem and its management policies.

Deep-sea ecosystems have attracted considerable commercial interest in recent years because of their potential to sustain a diverse range of mankind's industrial needs. If these systems are to be preserved or exploited in a sustainable manner, mapping habitats and species distributions is critical. As biodiversity at cold-seeps or other deep-sea ecosystems is driven by habitat heterogeneity, imagery is the obvious choice for characterizing these systems and has indeed proven extremely valuable towards mapping biogenic habitats formed by dense aggregations of large sized species, such as coral reefs, tubeworm bushes or bivalve beds. However, the acquisition of detailed images with resolution sufficient for reliable identification is extremely time consuming, labor intensive and highly susceptible to logistical issues. We developed a novel method for quickly mapping cold seep fauna and habitats over large areas, at the scale of squares of kilometers. Our method uses multibeam echosounder bathymetry and acoustic backscatter data, both segmented and reclassified based on topographical features and then combined to obtain a raster containing unique values incorporating both backscatter and bathymetry data. Two datasets, obtained from 30 m and 8 m above the seafloor were used and the results from the two datasets were compared. The method was applied to a cold seep community located in a pockmark in the deep Congo channel and we were able to ground truth the accuracy of our method against images of the area. The two datasets, obtained from different altitudes gave varying results: the 8 m altitude dataset reliably predicted tubeworms and carbonate rock, while the 30 m altitude dataset predicted tubeworms and vesicomyid clams. The 30 m dataset was more accurate than the 8 m altitude dataset in predicting distributions of tubeworms. Overall, all the predictions were quite accurate, with at least 90% of predictions being within 5 m of real distributions.

Two redox-sensitive metalloids, arsenic (As) and antimony (Sb), are examined here to determine what can be their help in the deciphering of past depositional conditions. The enrichment factors of the two elements are compared for a set of geological formations and marine deposits covering a relatively wide range of paleoenvironmental settings, from oxic to euxinic conditions. This work confirms that As and Sb are not robust paleoredox proxies but examining their relative enrichment may be useful. These preliminary results indicate that a co-enrichment of both elements with Sb being more enriched than As could be the mark of the so-called particulate shuttle effect. Notably, Sb would be more sensitive to Mn-shuttling than As. If confirmed, this trend could be used to further identify the cause of As-enrichment in marine sediments impacted by cold seepage fluids.

Carbonate blocks with silicified fossils were recovered from a newly recognized cold seep deposit, the Satsop Weatherwax site, in the basal Humptulips Formation, along the West Fork of Satsop River in Washington State, USA. The petrography and the stable carbon isotope signature of the carbonate, with values as low as -43.5‰, indicate that these carbonate blocks formed at an ancient methane seep. The fossils recovered from this block include five vesicomyid specimens, two fragments of a thyasirid, five specimens of the peltospirid Depressigyra, two specimens of the hyalogyrinid Hyalogyrina, 25 specimens of the neritimorph Thalassonerita eocenica, and three limpet specimens of two different species. Five species can be described as new: Nuculana acutilineata (Nuculanoidea), Desbruyeresia belliatus (Provannidae), Provanna fortis (Provannidae), Orbitestella dioi (Orbitestellidae), and Leptochiton terryiverseni (Polyplacophora). Other fossils recovered from this site are numerous serpulid tubes, echinoid spines, one brachiopod fragment and two neogastropods. Almost all species recovered belong to extant genera and the fauna has a modern character, but are different from species found in younger seeps in Washington State. This is the first record of an orbitestellid from an ancient cold seep deposit, the first fossil provannids from the Humptulips Formation, and the first fossil record of Desbruyeresia from North America.

Cold seeps, characterized by the methane, hydrogen sulfide, and other hydrocarbon chemicals, foster one of the most widespread chemosynthetic ecosystems in deep sea that are densely populated by specialized benthos. However, scarce genomic resources severely limit our knowledge about the origin and adaptation of life in this unique ecosystem. Here, we present a genome of a deep-sea limpet Bathyacmaea lactea, a common species associated with the dominant mussel beds in cold seeps. We yielded 54.6 gigabases (Gb) of Nanopore reads and 77.9-Gb BGI-seq raw reads, respectively. Assembly harvested a 754.3-Mb genome for B. lactea, with 3,720 contigs and a contig N50 of 1.57 Mb, covering 94.3% of metazoan Benchmarking Universal Single-Copy Orthologs. In total, 23,574 protein-coding genes and 463.4 Mb of repetitive elements were identified. We analyzed the phylogenetic position, substitution rate, demographic history, and TE activity of B. lactea. We also identified 80 expanded gene families and 87 rapidly evolving Gene Ontology categories in the B. lactea genome. Many of these genes were associated with heterocyclic compound metabolism, membrane-bounded organelle, metal ion binding, and nitrogen and phosphorus metabolism. The high-quality assembly and in-depth characterization suggest the B. lactea genome will serve as an essential resource for understanding the origin and adaptation of life in the cold seeps.

The Bathymodiolinae are pervasive in reducing environments in the deep sea, yet data on post-larval and juvenile development and on the process of symbiont acquisition remain elusive. To understand how these opportunistic metazoans survive in ephemeral reducing habitats, individuals of the small bathymodiolin, Idas modiolaeformis, were examined histologically to trace their reproductive development, and with fluorescence and transmission electron microscopy to identify patterns of infection by their environmentally acquired bacterial symbionts. A size series of these mussels was retrieved from larval colonisation devices containing vegetative substrates, deployed for 51 weeks (November 2006–2007) in the central ‘Pockmarks’ region (site 2A) of the Nile deep-sea fan in the eastern Mediterranean (NDSF), a zone where methane seepage can occur (N 32° 31.97, E 30° 21.18, 1,693 m deep). Developmental patterns of germ cell migration, size at first maturity, and symbiont acquisition and localisation are presented for the post-larva to adult transition. The smallest mature adult was a male with shell length (SL) 2.35 mm.All larger individuals in the series were male (maximum SL 6.54 mm). Based on the absence of bacterial signals, plantigrades were asymbiotic, indicating strict heterotrophy in larvae and early post-larvae. During the early stages of dissoconch deposition, extracellular symbiont infection was non-specific. This was followed by increasing specificity on non-ciliated gill epithelia in adults. These observations on early development in I. modiolaeformis represent evolutionary adaptations to their ephemeral, reducing habitats.

The Mazatán barite deposits, Sonora, NW Mexico, represent an outstanding example of Paleozoic bedded barite, a poorly understood type of mineral deposit of major economic interest. The deposits of this type commonly occur hosted by shales and are characterized by the lack of base-metal sulfide mineralization, in contrast to classic sedimentary-exhalative (or SEDEX) deposits. A throughout study of the Mazatán barite deposits, based on petrography, fluid inclusions analyses and isotope geochemistry, confirmed the link between bedded barite and fossil hydrocarbon seeps, thereby leaving hydrothermal vent-related processes ruled out. Hence, modern cold seeps in continental margins would account for the geological setting and genetic aspects of this type of deposit.The largest barite bodies of Mazatán are hosted within an Upper Carboniferous flysch succession, which formed part of an accretionary wedge related to the subduction of the Rheic Ocean beneath Gondwana. As well, a few barite occurrences are hosted in Upper Devonian, pre-orogenic turbidites. A variety of mineralized structures is displayed by barite, including: septaria nodules, enterolitic structures, rosettes and debris-flow conglomerates. Barite is accompanied by chalcedony, pyrite (framboids) and berthierine. Gas-rich fluid inclusions in barite were analyzed by micro-Raman spectroscopy and methane was identified, suggesting the occurrence of light hydrocarbons in the environment within which barite precipitated. 13C-depleted carbonates (δ13C: -24.3 to -18.7‰) were found in the barite deposits; they likely formed through anaerobic oxidation of methane coupled to sulfate reduction. Besides, these carbonates yield negative δ18O values (-11.9 to -5.2‰) reflecting the isotopic composition of Devonian-Carboniferous seawater; alternatively, this 18O-depletion could reflect late diagenetic processes. Methane-derived carbonates occur at modern hydrocarbon seeps and have been reported from Mesozoic, Cenozoic and even Paleozoic seep sediments, but they have never before been described in Paleozoic bedded barite deposits. δ34S values of barite vary from +17.6 to +64.1‰, with the lowest values overlapping the range for coeval seawater sulfate; this distribution indicates a process of sulfate reduction. Barite precipitation can be explained by mixing methane- and barium-rich fluids with pore-water (seawater) containing sulfate residual from microbial reduction. Two analyses from barite gave an 87Sr/86Sr within and slightly above the range for seawater at the time of deposition, with 0.708130 and 0.708588, which would preclude the involvement of hydrothermal fluids in the mineralization process. © 2013 Elsevier B.V., Funding was provided by the projects IN103211 (PAPIIT, UNAM) and 2009SGR-00444 (AGAUR, Generalitat de Catalunya).

A geochemical study on fluids from selected spontaneous seepages and drilled wells was carried out together with geologic investigation and deep cross-sections reconstruction to examine the petroleum system in the western Northern Apennines foothills. The hydrocarbons occurring in the Miocene foredeep units that form the reservoirs are commonly interpreted as generated in a source/reservoir system. However, the low Total Organic Carbon, its elevated dilution in the sediment pile and the limited amount of successions that entered in the oil window indicate a low potential for the hydrocarbons generation. The structures deformation in the Northern Apennines foothills is mainly late Miocene to Pliocene in age and involves successions that are progressively younger towards southeast. The earlier structure forms the Salsomaggiore anticline in the western sector. The comparison of the fluids from the wells and the mud volcanoes shows high geochemical and thermal history similarities. Saline waters originate from the connate pore water entrapped in the Miocene reservoir rocks during their deposition. The gaseous hydrocarbons are a mixture of secondary biogenic methane and primary and secondary thermogenic gases. The associated oils show both early and late maturities. These evidences account for different generation and migration steps, depending on burial conditions and deformation time. The various reservoirs appear confined by the thrust detachment at different depths and by the occurrence of reactivated lateral ramps. These results suggest the occurrence of a common source rock deeper than the Tertiary reservoir units, which progressively entered in the oil window. This source rock could have wide lateral extension, at least comparable with the width of the studied area, and represent a prime exploration target to evaluate the undiscovered oil and gas resources. (c) 2013 Elsevier Ltd. All rights reserved.

International audience; Extreme marine environments cover more than 50% of the Earth's surface and offer many opportunities for investigating the biological responses and adaptations of organisms to stressful life conditions. Extreme marine environments are sometimes associated with ephemeral and unstable ecosystems, but can host abundant, often endemic and well-adapted meiofaunal species. In this review, we present an integrated view of the biodiversity, ecology and physiological responses of marine meiofauna inhabiting several extreme marine environments (mangroves, submarine caves, Polar ecosystems, hypersaline areas, hypoxic/anoxic environments, hydrothermal vents, cold seeps, carcasses/sunken woods, deep-sea canyons, deep hypersaline anoxic basins [DHABs] and hadal zones). Foraminiferans, nematodes and copepods are abundant in almost all of these habitats and are dominant in deep-sea ecosystems. The presence and dominance of some other taxa that are normally less common may be typical of certain extreme conditions. Kinorhynchs are particularly well adapted to cold seeps and other environments that experience drastic changes in salinity, rotifers are well represented in polar ecosystems and loriciferans seem to be the only metazoan able to survive multiple stressors in DHABs. As well as natural processes, human activities may generate stressful conditions , including deoxygenation, acidification and rises temperature. The behaviour and physiology of different meiofaunal taxa, such as some foraminiferans, nematode and copepod species, can provide vital information on how organisms may respond to these challenges and can provide a warning signal of anthropogenic impacts. From an evolutionary perspective, the discovery of new meiofauna taxa from extreme environments very often sheds light on phylogenetic relationships, while understanding how meiofaunal organisms are able to survive or even flourish in these conditions canexplain evolutionary pathways. Finally, there are multiple potential economic benefits to be gained from ecological, biological, physiological and evolutionary studies of meiofauna in extreme environments. Despite all the advantages offered by meiofauna studies from extreme environments, there is still an urgent need to foster meiofauna research in terms of composition, ecology, biology and physiology focusing on extreme environments.

‘Cold’ seeps (or cold vents) are seafloor manifestations of fluid migration through sediments from the subsurface to the seabed and into the water column, and may reach the atmosphere. They are an important but not fully understood process in our oceans that has important repercussions on human society and on the climate. Modern sonar systems can obtain seafloor images of cold seep features from tens to thousands of meters wide with metric resolution, providing key information on the formation and evolution of the various seabed expressions of cold seeps. In this chapter we attempt to address cold seep systems with an emphasis on their origin, evolution, form, and occurrence, approaching them primarily from their morphologies and the acoustic character of the seafloor and near bottom erupted sediments. We address morphological characteristics of mud volcanoes, pockmarks, carbonate-related structures including MDAC, AOM and giant carbonate mounds and ridges, offering various examples mainly from recent discoveries in Mediterranean region which are among the most spectacular and most frequently cited examples. Detailed focus on topics such as acoustic backscatter, brine pools, etc. have been described in separate gray boxes of text with the aim to highlight their particular significance. Finally, gaps in knowledge and key research questions on cold seep studies have been outlined with the aim of orienting young researchers and students towards those topics that deserve the highest attention as they are still unresolved., Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Italia, FREMER Laboratoire Aléas géologiques et Dynamique Sédimentaire Centre Bretagne, Francia, Área de Geología Marina, Instituto Geológico y Minero de España, España, Lyngby Marine Geophysical Research, Países Bajos

15 pages, 5 figures, 1 table, The oceans were observed to be deep during the great age of exploration in the early to mid-nineteenth century. Subsequent exploration demonstrated that the ocean was bisected by underwater mountain ranges and dotted with abyssal hills. With the advent of the echosounder and latterly multichannel swath bathymetry, we now know that the deep ocean has topography as diverse as found on land. In the last 30 years, with an increase in deep-sea scientific activity and the use of underwater vehicles, we have learned that the deep sea consists of a series of habitats and ecosystems interconnected by hydrography and topography. The more recent challenges have been how to sample and analyse these separate habitats and ecosystems. This chapter describes the different environments and briefly outlines the main methods of sampling for each habitat or ecosystem. More detailed aspects of these sampling methods are found in subsequent chapters

International audience; Cold seeps have recently been discovered in the Nile deep-sea fan (Eastern Mediterranean), and data regarding associated fauna are still scarce. In this study, two bivalve species associated with carbonate crusts and reduced sediment are identified based on sequence analysis of their 18S and 28S rRNAencoding genes, and associated bacterial symbioses are investigated using 16S rRNA gene sequencing and microscopy-based approaches. The specimens are closely related to Myrtea spinifera and Thyasira flexuosa, two species previously documented at various depths from other regions but not yet reported from the Eastern Mediterranean. Both species harbour abundant gammaproteobacterial endosymbionts in specialized gill epithelial cells. The Myrtea-associated bacterium is closely related to lucinid symbionts from both deep-sea and coastal species, whereas the Thyasira-associated bacterium is closely related to the symbiont of a T. flexuosa from coastal waters off the U.K. An epsilonproteobacterial sequence has also been identified in Thyasira which could correspond to a helicoid-shaped morphotype observed by electron microscopy, but this was not confirmed using fluorescent in situ hybridization. Virus-like particles were observed within some symbionts in Thyasira, mostly in bacteriocytes localized close to the ciliated zone of the gill filament. Overall, results indicate that very close relatives of shallow species M. spinifera and T. flexuosa occur at cold seeps in the Eastern Mediterranean and harbour chemoautotrophic symbioses similar to those found in their coastal relatives.

The abundance and higher taxonomic composition of epizooic metazoan meiobenthic communities associated with mussel and tubeworm aggregations of hydrocarbon seeps at Green Canyon, Atwater Valley, and Alaminos Canyon in depths between 1400 and 2800m were studied and compared to the infaunal community of non-seep sediments nearby. Epizooic meiofaunal abundances of associated meiobenthos living in tubeworm bushes and mussel beds at seeps were extremely low (usually

On continental margins, oxidation of methane-rich fluids from the sediment often leads to formation of authigenic carbonate pavements on the seafloor. The biogeochemical processes involved during this carbonate precipitation are increasingly understood, but little is known about the duration or mode of carbonate crust formation. Here, we report uranium and thorium concentrations and isotope compositions for a set of 14 samples drilled across an authigenic carbonate pavement, which provide the first stratigraphy for a cold-seep carbonate crust. The 5.5-cm thick crust (NL7-CC2) was collected by submersible on the Nile deep-sea fan in an area of active fluid venting. U-Th analyses must be corrected for initial Th and measurement of co-existing sediments indicates the presence of both scavenged and detrital initial 230Th, which must be considered during this correction. The calculated 230Th/U age-depth profile for NL7-CC2 provides evidence for continuous downward carbonate precipitation at the studied location over the last ~ 5000 years. Three distinct phases can be distinguished from top to bottom with average growth rates of ~ 0.4, 5 and 0.8 cm/kyr, respectively, corresponding to carbonate precipitation rates ranging from ~ 7 to 92 μmol m2 h- 1 (rates consistent with previous estimates). High-resolution δ13C profiles [Gontharet, S., Pierre, C., Blanc-Valleron, M.-M., Rouchy, J.M., Fouquet, Y., Bayon, G., Foucher, J.P., Woodside, J., Mascle, J., The Nautinil Scientific Party, 2007. Nature and origin of diagenetic carbonate crusts and concretions from mud volcanoes and pockmarks of the Nile deep-sea fan (eastern Mediterranean Sea). Deep Sea Res. II 54, 1292-1311] and major elements across NL7-CC2 show that the variations in carbonate precipitation rates were also accompanied by changes in carbonate mineralogy and fluid composition. We suggest that these changes primarily reflect modification of the diagenetic environment, i.e. a progressive depletion of dissolved sulphate through anaerobic oxidation of methane, caused by the initial carbonate crust formation and the resulting reduction in bioirrigation. Overall, U-Th dating of cold seep carbonates offers a promising tool to bring new insights into biogeochemical processes at cold seeps and to assess the timing and duration of fluid venting on continental margins. © 2008 Elsevier B.V. All rights reserved.

Bathymodioline mussels occur in chemosynthesis-based ecosystems such as cold seeps, hydrothermal vents and organic debris worldwide. Their key adaptation to these environments is their association with bacterial endosymbionts which ensure a chemosynthetic primary production based on the oxidation of reduced compounds such as methane and sulfide. We herein report a multiple symbiosis involving six distinct bacterial 16S rRNA phylotypes, including two belonging to groups not yet reported as symbionts in mytilids, in a small Idas mussel found on carbonate crusts in a cold seep area located north to the Nile deep-sea fan (Eastern Mediterranean). Symbionts co-occur within hosts bacteriocytes based on fluorescence in situ hybridizations, and sequencing of functional genes suggests they have the potential to perform autotrophy, and sulfide and methane oxidation. Previous studies indicated the presence of only one or two symbiont 16S rRNA phylotypes in bathymodioline mussels. Together with the recent discovery of four bacterial symbionts in the large seep species Bathymodiolus heckerae, this study shows that symbiont diversity has probably been underestimated, and questions whether the common ancestor of bathymodioline mussels was associated with multiple bacteria.

Several species of crabs from hydrothermal vent sites in the Pacific Ocean Were found to be infested by small, symbiotic nemertean worms. Worms occurred on both male and female crabs, and were located in mucous sheaths adhering to the axillae between the limbs of males and females, the setae of the pleopods of females, and the sterna of infested male and female crabs. Only juvenile and regressed adult worms were observed, primarily because no ovigerous hosts were examined. Similar species of worms mature by eating eggs, then regress or die after host eclosion. Based on the size of the worms from file vent crabs, their habitus with their crustacean hosts, the presence of accessory stylet pouches, and the presence of a single stylet on a large basis (monostiliferous), we place the worms in the family Carcinonemertidae, within the genus Ovicides. Infestations were found on crabs from vent sites on the western Pacific back-arc basins, on the southern East Pacific Ridge, and on the Pacific-Antarctic Ridge, indicating a widespread distribution of the symbioses. This represents the first record of Carcinonemertidae from a deep-sea host, a new host family, Bythograeidae, for these symbionts, as well as the first record of parasitism on a deep-sea bythograeid crab.

00000 WOS:000361524900012; International audience; Understanding the ecological processes and connectivity of chemosynthetic deep-sea ecosystems requires comparative studies. In the Guaymas Basin (Gulf of California, Mexico), the presence of seeps and vents in the absence of a biogeographic barrier, and comparable sedimentary settings and depths offers a unique opportunity to assess the role of ecosystem-specific environmental conditions on macrofaunal communities. Six seep and four vent assemblages were studied, three of which were characterised by common major foundation taxa: vesicomyid bivalves, siboglinid tubeworms and microbial mats. Macrofaunal community structure at the family level showed that density, diversity and composition patterns were primarily shaped by seep- and vent-common abiotic factors including methane and hydrogen sulfide concentrations, whereas vent environmental specificities (higher temperature, higher metal concentrations and lower pH) were not significant. The type of substratum and the heterogeneity provided by foundation species were identified as additional structuring factors and their roles were found to vary according to fluid regimes. At the family level, seep and vent similarity reached at least 58 %. All vent families were found at seeps and each seep-specific family displayed low relative abundances (\textless 5 %). Moreover, 85% of the identified species among dominant families were shared between seep and vent ecosystems. This study provides further support to the hypothesis of continuity among deep-sea seep and vent ecosystems.

Ancient hydrocarbon seep-carbonates of Miocene age have been reported from marine sedimentary successions of the northern Apennines in the form of irregularly shaped micritic masses containing abundant fossil remains of oligotypic assemblages. They are recognized by their peculiar biological, sedimentological and geochemical features, and represent an excellent on-land example of carbonate bodies interpreted as the remains of ancient cold seeps. In the Apenninic chain, the abundance and the extent of the outcrops provide a rare opportunity to study the geometry, facies distribution and internal structures of fossil methane-derived carbonates. The present study reports an integrated view of the sedimentology, mineral paragenesis and geochemistry of these seep-carbonates in two different tectono-sedimentary settings: foredeep and satellite basins. The main result of this study is the recognition of 17 facies in the investigated seepcarbonates. The detailed facies and microfacies analysis led to the identification of different structures, which occur in welldefined parts of the carbonate masses. The recurring and broadly similar stratigraphy and facies association from the two considered geological environments is diagnostic of the different stages of seep-carbonate formation and evolution. D 2005 Elsevier B.V. All rights reserved.

To understand the role played by microorganisms in the formation of cold seep carbonates, we conducted an integrated microbial, mineralogical and organic geochemical study of methane-related authigenic carbonate crusts formed on eastern Mediterranean mud volcanoes. We show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane. Combined lipid biomarker analysis and 16S rRNA gene surveys identified a highly diversified methane-consuming archaeal community possibly comprising novel species, implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation. Moreover, pore-water sulphate gradients produced by co-occurring methane-based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation. We propose that this may be the dominant mode of carbonate crust formation at cold seeps world-wide, in agreement with aquatic chemistry predictions and explaining carbonate mineralogy. (C) 2002 Elsevier Science B.V. All rights reserved.

International audience; Reducing conditions with elevated sulfide and methane concentrations in ecosystems such as hydrothermal vents, cold seeps or organic falls, are suitable for chemosynthetic primary production. Understanding processes driving bacterial diversity, colonization and dispersal is of prime importance for deep-sea microbial ecology. This study provides a detailed characterization of bacterial assemblages colonizing plant-derived substrates using a standardized approach over a geographic area spanning the NorthEast Atlantic and Mediterranean. Wood and alfalfa substrates in colonization devices were deployed for different periods at 8 deep-sea chemosynthesis-based sites in four distinct geographic areas. Pyrosequencing of a fragment of the 16S rRNA-encoding gene was used to describe bacterial communities. Colonization occurred within the first 14 days. The diversity was higher in samples deployed for more than 289 days. After 289 days, no relation was observed between community richness and deployment duration, suggesting that diversity may have reached saturation sometime in between. Communities in long-term deployments were different, and their composition was mainly influenced by the geographical location where devices were deployed. Numerous sequences related to horizontally-transmitted chemosynthetic symbionts of metazoans were identified. Their potential status as free-living forms of these symbionts was evaluated based on sequence similarity with demonstrated symbionts. Results suggest that some free-living forms of metazoan symbionts or their close relatives, such as Epsilonproteobacteria associated with the shrimp Rimicaris exoculata, are efficient colonizers of plant substrates at vents and seeps.

Marine sediments all over the world bear methane, generated from organic matter and deposited at the seafloor. By diffusion or ascending fluids the methane is transported to the sediment surface and emitted into the oceans and further into the atmosphere, where it acts as greenhouse gas. However, most of the methane is anaerobically or aerobically oxidized by microbes in the upper sediments and in the water column. One of the most important methane oxidizing processes is the anaerobic oxidation of methane (AOM) in the microbial benthic methane filter. Consortia of anaerobic methanotroph (ANME) archeae and sulfate reducing bacteria (SRB) consume the methane with sulfate as final electron acceptor. While the methane is delivered from deeper reservoirs, sulfate originates from the seawater and has to diffuse into the sediment. AOM occurs mainly in the intersection of sulfate and methane, the sulfate methane transition zone (SMTZ). At continental margins gas hydrate bearing sediments form huge reservoirs of methane. Methane can be transported by upward migrating fluids from dewatered and dehydrated sediments. At the sediment surface, advecting fluids form so called “cold seeps”. The microbial benthic methane filter of cold seeps is well established and adapted to the flow conditions. However, increasing fluid flux can challenge the microbial benthic filter by higher methane flux and lower sulfate penetration depth, by resulted higher methane emissions. The aim of this thesis is to study efficiency and adaptability of the benthic methane filter under non-steady state conditions. For this purpose I developed a sediment flow-through (SLOT) system to mimic the fluid regime of the benthic methane filter and to monitor long-term incubations of undisturbed sediment cores from cold seeps under varying fluid fluxes. All experiments were performed under anoxic conditions and with two parallel sediments cores under varying fluid flow conditions. The presented thesis combines field data and experimental data from sediments of different cold seep sites and their microbial benthic methane filter. First experiments with coastal gassy sediments from Eckernförde Bay constrain the possibility of SLOT to simulate fluid flow regimes of microbial benthic filters under fluid flux differences of one magnitude. Additionally, other seep related processes such as sulfide oxidation and precipitation were observed and prove the usefulness of the SLOT system for biogeochemical studies. Two neighboring mounds with different steady state conditions were studied offshore Costa Rica. These mounds differ in fluid source, fluid flux as well as methane flux. Both mounds exhibit a well established microbial benthic filter which is adapted to their respective flow conditions. Fluid and methane source are reflected in the isotopic signature of authigenic carbonates, which are the archive of cold seep systems. Field and experimental data from the Quepos Slide offshore Costa Rica were combined to study the benthic methane filter. In the experiments the microbial benthic methane filter was highly efficient and shows a good adaption within 150-170 d response time with low methane efflux within the transition. A fluid pulse with higher methane emissions reveals how fast the methane efflux can change when fluid flux is increased. Furthermore, three different cold seep habitats from a recently discovered cold seep area at the continental margin of Chile were studied. Experiments with a bacterial mat habitat from a young seep site show a uniform fluid flow through the sediment and reveal a high adaptability of the benthic methane filter. In a clam field with high sulfide production an enormous methane efflux occured before the benthic filter was adapted to the new fluid regime. In sediments with an aerobic benthic methane filter from a tubeworm habitat, fluids were channeled by biogenic tubes. The benthic methane filter changed during the 150 d of anoxic incubation from an aerobic to an anaerobic methane sink. In the present thesis it is demonstrated for the first time how enthic methane filters adapt to increased fluid flux. The studies reveal that beside preconditions and the intensity of the variation the sediment matrix flow conditions through the sediment is prime important for the adaptability of the benthic methane filter. Zusammenfassung: Marine Sedimente enthalten überall auf der Welt Methan, welches aus organischem Material gebildet wurde. Dieses Methan kann durch Diffusion oder mit aufsteigenden Fluiden in die Ozeane und von dort aus weiter in die Atmosphäre gelangen, wo es als Treibhausgas wirkt. Allerdings wird das meiste Methan im Sediment als auch in der Wassersäule aerob oder anaerob oxidiert. Eine der wichtigsten Reaktionen zur Methan oxidation ist die anaerobe Methanoxidation (AOM) innerhalb des benthischen Methanfilters. Konsortien aus anaeroben methanotrophen Archaen (ANME) und sulfatreduzierende Bakterien oxidieren das Methan mit Sulfat als abschließendem Elektronenakzeptor. Während das Methan aus tieferen Speichern aufsteigt, erfolgt der Sulfatnachschub per Diffusion aus dem Meereswasser. AOM findet größtenteils in der Übergangszone von Sulfat und Methan statt, der Sulfat-Methan-Übergangszone (SMTZ). An den Kontinentalhängen bilden Sedimente, welche Gashydrate enthalten riesige Methanspeicher. Methan kann durch aufsteigende Fluide aus entwässerten und dehydrierten Sedimenten aufwärts transportiert werden. An der Sedimentoberfläche formen diese ausströmenden Fluide so genannte „Cold Seeps“. Der benthische Methanfilter ist in diesen Cold Seeps gut ausgeprägt und an die Fließbedingungen angepasst. Erhöhte Fließgeschwindigkeiten, welche einen höheren Methanfluss sowie eine geringere Eindringtiefe des Sulfats zur Folge haben, können den benthischen Methanfilter stark strapazieren. Das Ziel dieser Doktorarbeit ist die Effizienz und die Anpassungsfähigkeit des benthischen Methanfilters unter nicht stationären Bedingungen zu untersuchen. Aus diesem Grund habe ich ein Durchflusssystem (SLOT System) entwickelt um die Fließbedingungen des benthischen Methanfilters zu imitieren und Langzeituntersuchengen von ungestörten Sedimenten mit verschiedenen Volumenströmen aufzuzeichnen. Alle Versuche wurden unter anoxischen Bedingungen und mit zwei parallelen Sedimentkernen, welche unterschiedliche Fließbedingungen hatten, ausgeführt. Die vorliegenden Doktorarbeit vereint Feld und Versuchsmesswerte von Cold Seep Sedimenten unterschiedlicher Standorte und ihren benthischen Methanfiltern. Erste Versuche mit gasigen Küstensedimenten aus der Eckernförder Bucht belegen die Eignung des SLOT Systems Flussbedingungen des mikrobisch benthischen Methanfillters bei Volumenflußunterschieden von einer Größenordung zu simulieren. Zusätzlich konnten andere mit Cold Seeps verbundene Prozesse wie Sulfidoxidation und -präzipitation beobachtet werden. Dies zeigt die Nutzen des SLOT-Systems für biogeochemische Untersuchungen. Zwei benachbarte „Mounds“ mit unterschiedlichen stationären Zuständen wurden vor Costa Rica untersucht. Diese Mounds unterschieden sich in Fluidquelle, Fluidströmung und Methanfluss. Beide enthielten einen gut ausgebildeten benthischen Methanfilter, der sich an die jeweiligen Flussbedingungen angepasst hatte. Fluid- und Methanquellen spiegelten sich in der Isotopensignatur der autochthonen Karbonate wider, welche das Archiv der Cold Seep Geschichte darstellen. Feld- und Versuchsergebnisse vom Quepos Slide vor Costa Rica wurden kombiniert um den benthischen Methanfilter zu untersuchen. Der mikrobielle benthische Methanfilter war sehr effizient und konnte sich mit einer Reaktionszeit von 150-170 Tagen an die geänderten Fließbedingungen anpassen. Während dieser Anpassungszeit kam es zu geringem Methanausfluss. Durch einen Fluidimpuls welcher einen hohen Methanausfluss zur Folge hatte, wurde verdeutlicht wie schnell sich der Methanausfluss ändern kann wenn das Flussvolumen ansteigt. Des Weiteren wurden drei Habitate eines kürzlich am chilenischen Kontinentalhang entdeckten Cold Seep-Gebiets untersucht. Versuche mit Sedimenten aus einem Bakterienmattenhabitat bei einer jungen Seepstelle zeigen einen gleichmäßigen Fluidfluss durch das Sediment und verdeutlichen somit eine hohe Anpassungsfähigkeit des benthischen Methanfilters. In Sedimenten aus einem Muschelfeld mit hoher Sulfidproduktion gab es einen enormen Methanausfluß bevor sich der benthische Methanfilter an die neuen Flussbedingungen angepaßt hatte. In Sedimenten mit einem aeroben Methanfilter von einen Röhrenwurmfeld wurden die Fluide durch die biogenen Röhren kanalisiert. Der benthische Methanfilter wandelte sich innerhalb von 150 Tagen anoxischer Inkubation von einer aeroben zu einer anearoben Methansenke. In der vorliegenden Arbeit konnte zum ersten Mal gezeigt werden, wie sich benthische Methanfilter an erhöhten Fluidfluß anpassen. Die Untersuchungen zeigen, dass neben vorherigem Zustand und Grad der Veränderung auch die Sedimentmatrix und die Fließbedingungen durch das Sediment von großer Wichtigkeit für die Anpassunsfähigkeit des benthischen Methanfilters sind.

RATIONALE: Studies of archaeal glycerol dibiphytanyl glycerol tetraethers (GDGTs) in the environment and cultures have exclusively focused on compounds with fully saturated alkyl moieties. Here we report a number of novel unsaturated GDGTs (uns-GDGTs) whose alkyl chains contain up to six double bonds and zero to two cyclopentyl moieties. METHODS: The identification of these lipids was achieved via comparison of lipid distribution before and after hydrogenation, characteristic retention time patterns, and diagnostic ions using liquid chromatography/tandem mass spectrometry (LC/MS/MS), and ether cleavage products using gas chromatography/mass spectrometry (GC/MS). Isomerism resulting from different unsaturation patterns in the alkyl moieties was observed and specific positions of double bonds in the biphytene and biphytadiene moieties were tentatively assigned. RESULTS: Uns-GDGTs were detected in sediment and microbial mat samples as both core lipids (CLs) and intact polar lipids (IPLs) associated with mono- or diglycosyl or phosphatidylglycerol headgroups. However, these lipids were overlooked in past investigations because conventional methods for archaeal lipid analysis are unsuitable for uns-GDGTs. Samples from distinct marine environments (Black Sea, Cariaco Basin, Discovery Basin, Eastern Mediterranean Sea, upwelling area off NW Africa, and seep sites off Crimea and Pakistan) were screened for uns-GDGTs using a new LC/MS protocol. The results show that uns-GDGTs contribute significantly to the archaeal lipid pool in anoxic methane-rich environments (Black Sea, Cariaco Basin, and both seep sites) but they were barely detected in the oxic or hypersaline settings. CONCLUSIONS: The characteristic distribution of uns-GDGTs implies that they are attractive targets for future studies aiming at the chemotaxonomy of uncultivated archaea and regulation of uns-GDGT biosynthesis.

The bacterial endosymbionts of the vesicomyid clam Calyptogena fossajaponica, collected from the hadal zone in the Japan Trench, were characterized. Transmission electron microscopic (TEM) observations showed numerous bacteria in epithelial cells of the gill tissues of C. fossajaponica. Sulfur content and isotope analyses of this clam also suggested the presence of sulfur-oxidizing bacteria (thioautotrophs). Phylogenetic analysis based on the 16S ribosomal RNA gene (rDNA) sequence indicated that the bacteria was related to sulfur-oxidizing endosymbionts of other vesicomyid clams from deep-sea hydrothermal vents and cold seeps. The symbionts of C. fossajaponica formed a monophyletic group with the symbionts of C. magnifica, C. phaseoliformis and Calyptogena sp. (Florida Escarpment). These 4 species live relatively deeper than other vesicomyid clams whose symbionts have been phylogenetically characterized. Vertical distribution patterns of vesicomyid clams are likely influenced by their symbionts.

Organic falls create localised patches of organic enrichment and disturbance where enhanced degradation is mediated by diversified microbial assemblages and specialized fauna. The view of organic falls as “stepping stones” for the colonization of deep-sea reducing environments has been often loosely used, but much remains to be proven concerning their capability to bridge dispersal among such environments. Aiming the clarification of this issue, we used an experimental approach to answer the following questions: Are relatively small organic falls in the deep sea capable of sustaining taxonomically and trophically diverse assemblages over demographically relevant temporal scales? Are there important depth- or site-related sources of variability for the composition and structure of these assemblages? Is the proximity of other reducing environments influential for their colonization? We analysed the taxonomical and trophic diversity patterns and partitioning (α- and β-diversity) of the macrofaunal assemblages recruited in small colonization devices with organic and inorganic substrata after 1-2 years of deployment on mud volcanoes of the Gulf of Cadiz. Our results show that small organic falls can sustain highly diverse and trophically coherent assemblages for time periods allowing growth to reproductive maturity, and successive generations of dominant species. The composition and structure of the assemblages showed variability consistent with their biogeographic and bathymetric contexts. However, the proximity of cold seeps had limited influence on the similarity between the assemblages of these two habitats and organic falls sustained a distinctive fauna with dominant substrate-specific taxa. We conclude that it is unlikely that small organic falls may regularly ensure population connectivity among cold seeps and vents. They may be a recurrent source of evolutionary candidates for the colonization of such ecosystems. However, there may be a critical size of organic fall to create the necessary intense and persistent reducing conditions for sustaining typical chemosymbiotic vent and seep organisms.

The Mediterranean Sea contains a vast spectrum of chemosynthetic habitats from shallow marine to bathyal depths. These habitats (hydrothermal vents, cold seeps, reducing sediment) are home to bacteria and archaea acting as primary producers using the energy obtained by oxidizing reducing compounds in fluids (e.g., H2S and hydrocarbons such as CH4) to synthesize organic matter. Such sites may make a large microbial biomass available to consumers and promote the development of complex symbiotic relationships between prokaryotes and hosting eukaryotes. Shallow water (200 m) with also metazoans with chemoautotrophic symbionts are present at various sites in the Mediterranean, encompassing both cold seeps and hydrothermal vents. Cold seeps are diffuse and geologically diverse, and comprise mud volcanoes, brine pools and active pockmark fields, whose reducing environments are often exploited by endemic chemosymbiotic metazoans, including bivalves and siboglinid polychaetes. Such environments are clustered in the Eastern Mediterranean (Nile Deep Sea Fan, Anaximander mud volcano field, Olimpi mud volcano field, Eratosthenes Seamount, Calabrian Arc, Marmara deep fault systems) but equally occur in the Strait of Sicily, Adriatic, Tyrrhenian and Alboran Seas. Deep hyperhaline anoxic basins occur in the Eastern Mediterranean and even host metazoans that live in anoxic conditions. Deep-water hydrothermal vents characterized by microbial communities and metazoans (siboglinid polychaetes) are documented so far only from some Tyrrhenian seamounts (Marsili, Palinuro) and Aegean submerged volcanic craters (Santorini, Kolumbo). The geo-biological relevance of such complex habitats often situated in the high seas, calls for an international effort towards the implementation of proper protection and sustainable management.

International audience; Small mytilids of the genus Idas are related to the large mussels found worldwide at deep-sea hydrothermal vents and cold seeps. They are therefore keys to a better understanding of the colonization of vents and seeps by symbiont-bearing organisms, but still little is known about their biology. For this study, specimens of a mytilid referred to the genus Idas were collected from various substrates in a cold seep area near the Nile deep sea fan. Based on molecular and morphological data, all specimens are confirmed to belong to a single species of the genus Idas, which was previously shown to host six distinct bacterial symbionts. Its larval shell characteristics indicate a long planktonic phase, which could explain its close relationship to a mussel species that occurs in the Gulf of Mexico. 3-D FISH indicates the dominance of sulfur-oxidizing, methane-oxidizing and methylotrophic symbionts in all specimens analysed.; Les mytilidés du genre Idas forment un groupe monophylétique avec ceux associés aux sources hydrothermales et aux suintements froids. Ils sont donc la clé d'une meilleure compréhension du scénario de colonisation de ces environnements par les organismes symbiotiques. Pour autant, leur biologie est encore aujourd'hui fort peu connue. Pour la présente étude, des moules ont été collectées à partir de différents substrats aux alentours du delta profond du Nil. Nous utilisons ici une approche moléculaire et morphologique pour démontrer que ces spécimens appartiennent à une espèce du genre Idas, dont il a été montré précédemment qu'elle était en association symbiotique avec 6 lignées bactériennes, un cas sans précédent dans ce taxon. La coquille larvaire suggère une longue phase planctonique qui pourrait expliquer la parenté avec une espèce présente dans le Golfe du Mexique. Une approche de 3D-FISH indique la dominance de symbiontes de types sulfoxydants, méthanotrophes et méthylotrophes dans tous les individus analysés.

The expulsion of liquids, gases and fluids at continental margins covers a wide range of processes including not only mud volcanism, mud diapirism and gas flares, but also continuously seeping methane-rich fluids leading to cold vent sites and even outbursts of over-pressured gases. Seepage of fluids frequently leads to precipitation of authigenic carbonates that modify sedimentary processes along the margin, and finally, the fluids constitute the energy source for a number of diverse and complex ecosystems. During the last two decades, researchers gained significant knowledge about the impact of fluid seepage on local ecosystems and the biogeochemical processes that result in carbonate formation via the anaerobic oxidation of methane (AOM). However, all the knowledge was gained in different areas and geological settings of the world ocean but left a regional gap in our knowledge about seeps at the continental margin offshore Costa Rica. Those processes including authigenic carbonate precipitation, quantification of the impact of fluid seepage and methane budgets are documented in the present thesis. Chapter II presents comprehensive results from five cold seep structures at the Costa Rican continental margin addressing the relationship between fluid advection, dissolved calcium concentrations in upward migrating fluids, and authigenic calcium carbonate precipitation. A numerical transport-reaction model was used to determine rates of AOM, CaCO3 precipitation, and benthic fluxes of solutes. Production of carbonate alkalinity and formation of authigenic carbonates is most intense at intermediate flow rates (3-40 cm a-1) and reduced under low and high flux conditions (0.1 and 200 cm a-1). Systematic model runs showed that high Ca concentrations in ascending fluids enhance the rate of authigenic carbonate production at moderate flow rates leading to an almost quantitative fixation of deeply derived Ca in authigenic carbonates. Hence, CaCO3 precipitation is not only controlled by Ca diffusing into the sediment from bottom water, but also by the Ca concentration in ascending fluids. Based on average precipitation rates deduced from the systematic model runs the global Ca-fixation at cold seeps (~2·1010 mol Ca a-1) suggesting that cold seeps are most likely not of key importance with respect to Ca cycling in the ocean. Chapter 3 comprises the quantitative estimates of dissolved methane discharge from wellstudied mud mounds (Mound 11 and Mound 12) at the submarine section of the Costa Rica fore-arc combining geochemical and geoacoustic data. The study is supported by 75 kHz sidescan sonar data, pore-water analysis and visual sea-floor observations by remotely operated vehicle (ROV). A numerical transport reaction model was applied to determine dissolved methane fluxes considering AOM and upward fluid flow. Model results reveal that a significant portion of methane from greater depth is discharged into the bottom water only at high fluid flow velocities that are not sufficiently moderate to allow for AOM. The overall amount of dissolved methane released from the entire mud mounds into the water column was moderate with a discharge of 0.36·106 mol a-1 at Mound 11 whereas it was calculated as 0.58·106 mol a-1 at Mound 12. Compared to other active cold seeps (mainly mud volcanoes), mud mounds at the submarine section of the Costa Rica fore arc do not represent a pathway for significant methane discharge from the seafloor. Sea floor methane emissions from bacterial mat sites of a submarine slide at the Costa Rica continental margin are presented in Chapter IV. The estimates of methane fluxes into the water column are based on (i) detailed mapping in order to determine the abundance of seeps, and thus the spatial validity of the flux measurements; and (ii) application of numerical model to estimate the amount of methane that is transported into the bottom water. Model results illustrate that the majority of the studied seeps transport rather limited amount of methane into the water column due to medium to low advection rates (average 10 cm a-1 ) allowing high methane consumption by AOM (average 45%) and limiting the methane discharge into the water column. Depth-integrated AOM rates (56-1538 μmol CH4 cm-2 a-1) are comparable with the values reported at other very active vents sites, suggesting that the Quepos Slide should be regarded as one of the most active sites at the seafloor. The overall amount of dissolved methane released from the entire bacterial mat sites into the water column is determined as 0.56·106 mol a-1. This conservative estimate, relying on rather accurate determinations of sea floor methane fluxes out of bacterial mats emphasizes the importance of submarine slides as sites of natural methane seepage.

During the Miocene, hydrocarbon seep-carbonates located atop intrabasinal highs and associated with sediment instability, formed commonly at the deformation front of the Northern Apennine collisional orogen. The parallelism between the structural trend and the distribution of seep-carbonates suggests a close relationship between tectonics and gas/fluid emission. The “Montepetra intrabasinal high” was formed during the closure stage of the foredeep, being related to the synsedimentary growth of an anticline. Field geometry suggests that detachment folding was the leading mechanism of anticline growth and synsedimentary instability along the anticline flanks. Ten different bodies of seep-carbonates occur in the Tortonian–early Messinian sediments: nine in the hinge zone and one in the southern backlimb of the anticline. Foraminiferal study, geochemistry, facies investigation and the three-dimensional geometry of carbonate bodies with respect to the encasing terrigenous sediments indicate a protracted (late Tortonian–early Messinian) activity of fluid migration with re-mobilization and ascent of sediments from the core of the anticline, stabilization of chemosynthesis-related communities, and in-situ brecciation. Seepage atop the intrabasinal high was fed by different circuits: one related to the compaction-dewatering of shallow (Tortonian–early Messinian) sediments, and a deeper one related to the deformation of the anticline core and to the activity of detachment surfaces and of faults propagating through the sedimentary cover.

16 pages, 10 figures, 1 table, Quantification of fluid fluxes from cold seeps depends on accurate estimates of the spatial validity of flux measurements. These estimates are strongly influenced by the choice of geoacoustic mapping tools. Multibeam bathymetry, side-scan sonar, and Chirp subbottom profiler data of several mound-shaped cold seeps offshore central Costa Rica show great variety in morphology and structure although the features are only a few kilometers apart. Mound 11 (a 35 m high and 1000 m in diameter structure), situated in the SE of the study area, has an irregular morphology but a smooth surface on side-scan sonar data, while mound 12 (30 m high, 600 m across) is a cone of more regular outline but with a rough surface, and mound Grillo (5 m high, 500 m across) shows the same rough surface as mound 12 but without relief. Video observations and sediment cores indicate that the structures are formed by the precipitation of authigenic carbonates and indications for extensive mud extrusion are absent, except for one possible mudflow at mound 11. Different sonar frequencies result in variable estimates of the extent of these mounds with low frequencies suggesting much wider cold seeps, consequently overestimating fluid fluxes. The absence of mud volcanism compared to accretionary prisms where mud volcanism occurs is related to different tectonic styles: strong sediment overpressure and thrust faulting in typical accretionary prisms can generate mud volcanism, while subduction erosion and normal faulting (extension) of the overriding plate at the Costa Rican margin result in fluid venting driven by only slight fluid overpressures, Funding for the cruise and subsequent work has been provided by the German Ministry of Education and Research (BMBF) and the German Research Foundation (DFG). This publication is contribution 179 of the Sonderforschungsbereich 574 “Volatiles and fluids in subduction zones” at Kiel University

La mayor parte del sistema de dorsales oceanicas y los margenes continentales de nuestro planeta todavia no han sido explorados. Un numero limitado de fuentes hidrotermales y frias han sido estudiadas y son el objeto de programas de investigacion a largo termino. Sin embargo, la exploracion de nuevas areas quimiosinteticas llevara sin lugar a dudas a descubrir nuevas fuentes hidrotermales y coladuras frias. Ademas, el estudio de estas localidades llevara a descripciones de nuevas especies, asi como a un mayor y mas completo conocimiento sobre la abundancia, la diversidad y la distribucion de especies de sistemas quimiosinteticos, alrededor de los oceanos del mundo. Uno de los componentes principales de ChEss es un programa de campo a largo termino para el descubrimiento y la exploracion de nuevas fuentes hidrotermales y surgencias frias en areas claves, asi como la descripcion de su fauna y el estudio de los procesos que dirigen a dichas comunidades. El objetivo principal es obtener un conocimiento solido sobre la biogeografia de ecosistemas quimiosinteticos de profundidad a escala global. Este objetivo solo se puede alcanzar a traves de cooperacion internacional, la cual sera coordinada por el comite cientifico internacional de ChEss. En cuanto a sistemas quimiosinteticos de profundidad se refiere, los oceanos del hemisferio sur engloban las regiones menos exploradas del planeta. Las dorsales del Oceano Indico, el sur de la dorsal Atlantica, la dorsal artica de Scotia y la dorsal de Chile para fuentes hidrotermales, asi como los margenes continentales de Brasil, Peru, Chile y Africa para surgencias frias, son esenciales para resolver el puzle biogeografico de sistemas quimiosinteticos.

During several cruises carried out by the Ifremer (Institut français de recherche pour l’exploitation de la mer) with the submersile “Nautile” at different hydrothermal sites and cold seeps, an important collection of anthozoans - mainly actiniarians - was sampled. Additional material was collected by an American cruise with the submersile “Alvin”. The goal of the present contribution is to describe part of this actiniarian fauna inhabiting three chemoautotrophic sites, one of them in the Mid-Atlantic Rise and the other two in the Eastern Pacific. A new genus and species of actinostolids is proposed after the study of specimens collected at hydrothermal vents in the Guaymas Basin (East Pacific Rise, Gulf of California, 27º00’N-111º24’W, 2020 m). Furthermore, some specimens collected in cold seeps along the MAT (Middle America Trench, off Mexico, 18º21’-20°01’N 104º21’-106º17’W, 3354-3795 m) are reported as Hadalanthus aff. knudseni. This material is discussed and compared with the existing type ma

During several cruises carried out by the Ifremer (Institut français de recherche pour l’exploitation de la mer) with the submersile “Nautile” at different hydrothermal sites and cold seeps, an important collection of anthozoans - mainly actiniarians - was sampled. Additional material was collected by an American cruise with the submersile “Alvin”. The goal of the present contribution is to describe part of this actiniarian fauna inhabiting three chemoautotrophic sites, one of them in the Mid-Atlantic Rise and the other two in the Eastern Pacific. A new genus and species of actinostolids is proposed after the study of specimens collected at hydrothermal vents in the Guaymas Basin (East Pacific Rise, Gulf of California, 27º00’N-111º24’W, 2020 m). Furthermore, some specimens collected in cold seeps along the MAT (Middle America Trench, off Mexico, 18º21’-20°01’N 104º21’-106º17’W, 3354-3795 m) are reported as Hadalanthus aff. knudseni. This material is discussed and compared with the existing type ma

Mussels of the subfamily Bathymodiolinae thrive around chimneys emitting hot fluids at deep sea hydrothermal vents, as well as at cold seeps and on sunken organic debris (sunken wood, whale falls). Despite the absence of light-driven primary production in these deep-sea ecosystems, mussels succeed reaching high biomasses in these harsh conditions thanks to chemosynthetic, carbon-fixing bacterial symbionts, located in their gill tissue. Since the discovery of mussel symbioses about three decades ago our knowledge has increased, yet new findings are published regularly regarding their diversity, role and evolution. This article attempts to summarize current knowledge about symbiosis in Bathymodiolinae, focusing on mussel species for which information is available regarding both hosts and symbionts. Moreover, new data obtained from small mussels inhabiting sunken woods around the Philippines are provided. Indeed, mussel species from organic falls remain poorly studied compared to their vent and seep relatives despite their importance for the understanding of the evolution of symbiosis in the subfamily Bathymodiolinae. To cite this article: S. Duperron et al., C. R. Biologies 332 (2009).

During the European Commission's Framework Six Programme, HERMES, we investigated three main areas along the European margin, each characterized by the presence of seep-related structures exhibiting different intensity of activity and biological diversity. These areas are: (1) the Nordic margin with the Hakon Mosby mud volcano and many pockmarks, (2) the Gulf of Cadiz, and (3) the eastern Mediterranean with its hundreds of mud volcanoes and brine pool structures. One of the main goals of the HERMES project was to unravel the biodiversity associated with these seep-associated ecosystems, and to understand their driving forces and functions, using an integrated approach. Several multidisciplinary research cruises to these three areas provided evidence of high variability in ecosystem processes and associated biodiversity at different spatial scales, illustrating the "hotspot" nature of these deep water systems. HERMES (EC) - GOCE-CT-2005-511234