Submarine Mud Volcanoes Research Articles

Methanoculleus sediminis sp. nov., a methanogen from sediments near a submarine mud volcano.

A mesophilic, hydrogenotrophic methanogen, strain S3Fa(T), was isolated from sediments collected by Ocean Researcher I cruise ORI-934 in 2010 near the submarine mud volcano MV4 located at the upper slope of south-west Taiwan. The methanogenic substrates utilized by strain S3Fa(T) were formate and H2/CO2 but not acetate, secondary alcohols, methylamines, methanol or ethanol. Cells of strain S3Fa(T) were non-motile, irregular cocci, 0.5-1.0 μm in diameter. The surface-layer protein showed an Mr of 128,000.The optimum growth conditions were 37 °C, pH 7.1 and 0.17 M NaCl. The DNA G+C content of the genome of strain S3Fa(T) was 62.3 mol%. Phylogenetic analysis revealed that strain S3Fa(T) was most closely related to Methanoculleus marisnigri JR1(T) (99.3% 16S rRNA gene sequence similarity). Genome relatedness between strain S3Fa(T) and Methanoculleus marisnigri JR1(T) was computed using both genome-to-genome distance analysis (GGDA) and average nucleotide identity (ANI) with values of 46.3-55.5% and 93.08%, respectively. Based on morphological, phenotypic, phylogenetic and genomic relatedness data, it is evident that strain S3Fa(T) represents a novel species of the genus Methanoculleus, for which the name Methanoculleus sediminis sp. nov. is proposed. The type strain is S3Fa(T) ( = BCRC AR10044(T) = DSM 29354(T)).

DEGASSING OF THE BLACK SEA BOTTOM: SIGNIFICANCE FOR GEOLOGICAL EXPLORATION, ECOLOGY AND NAVIGATION

This paper is devoted to a review of modern ideas about degassing (mainly methane) from the bottom of the Black Sea. The main goal is to describe methane emissions on the sea bottom, to delineate their spatial distribution, and to provide insight into their possible origin as well as their influence on ecosystems and navigation. It is shown that the Black Sea is the largest meromictic basin, waters of which are enriched with methane. As such, the basin holds great promise for new energy sources to supply the Black Sea countries, and most of Europe as well. The amount of methane is several timeslarger than the known gas reservoirs on Earth. Its presence under the sea bottom is evident from outbursts of submarine mud volcanoes that commonly contain ice-like aggregates of gas (largely methane) hydrates as well as many high-intensity gas seeps and gas bogs that release huge quantities of methane. While gas hydrates accumulate methane, submarine mud volcanoes, gas seeps, and gas bogs release it into the water column largely from deep sources,and much less often as a product of biochemical processes in bottom sediments. There is a certain zoning in the distribution of methane emissions; in particular, seepы are located on the periphery of the basin while gas hydrates are distributed within its central part. While gas seeps can be used as indicators for oil exploration, mud volcanoes can indicate the oil and gas deposits under the sea bottom. An interconnection between mud volcanoes and gas hydratescannot be excluded. It appears that methane in the sea water affects biota in a negative way. Eruptions of mud volcanoes are dangerous for navigation and communications or industrial equipment (cables, gas pipes, etc.) on the sea bottom.

Origins of lithium in submarine mud volcano fluid in the Nankai accretionary wedge

To investigate fluid regimes in the Nankai accretionary wedge, we estimated the temperatures of lithium (Li) reservoirs from the Li isotope ratio (7Li/6Li) in fluids recovered from Kumano mud volcano No. 5 (KMV#5) in the Nankai forearc basin. The 7Li/6Li ratios in the KMV#5 fluids are among the lightest reported from submarine mud volcanoes. The estimated Li reservoir temperatures (310 °C at maximum) were significantly higher than the smectite-to-illite conversion temperature (60–150 °C), whereas the temperature of fluid from the deeper Nankai décollement was estimated to be 150 °C at maximum. Data obtained from previous conductivity surveys across the trench suggest that there are two fluid reservoirs associated with distinct dehydration processes in the Nankai subduction zone. From these results, we inferred that the discontinuous mud diapirism in the Kumano forearc basin results from the periodic injection of deep-seated fluid accumulated in the corner of the serpentinized forearc mantle wedge that travels upward via a thrust fault. The intermittent upwelling of deep-seated fluid from the Nankai accretionary wedge due to periodic breaches of a low-permeability barrier above the fluid reservoir may be associated with seismogenic fault activity.

OVERVIEW OF SUBMARINE MUD VOLCANO

Mud volcanoes occur mostly within the sedimentary basins, both on land and seabed, where are weak areas of Earth crust or intersection of the fault systems. The activities of submarine mud volcano might cause potential risks for drilling operations and setting oil and gas pipeline on the sea floor. The activities of exploration and exploitation of oil and gas in the East Sea are pretty strong, especially in the sedimentary basins of the continental shelf. Therefore, in this paper, the authors focus on essential analysis of some characteristics of mud volcanoes as well as the mechanism of formation and their relationships with gas hydrate, submarine landslide as a premise for the next researches.

Eruption of a deep-sea mud volcano triggers rapid sediment movement.

Submarine mud volcanoes are important sources of methane to the water column. However, the temporal variability of their mud and methane emissions is unknown. Methane emissions were previously proposed to result from a dynamic equilibrium between upward migration and consumption at the seabed by methane-consuming microbes. Here we show non-steady-state situations of vigorous mud movement that are revealed through variations in fluid flow, seabed temperature and seafloor bathymetry. Time series data for pressure, temperature, pH and seafloor photography were collected over 431 days using a benthic observatory at the active Håkon Mosby Mud Volcano. We documented 25 pulses of hot subsurface fluids, accompanied by eruptions that changed the landscape of the mud volcano. Four major events triggered rapid sediment uplift of more than a metre in height, substantial lateral flow of muds at average velocities of 0.4 m per day, and significant emissions of methane and CO2 from the seafloor.

Hydrocarbon seepage and its sources at mud volcanoes of the Kumano forearc basin, Nankai Trough subduction zone

AbstractTwelve submarine mud volcanoes (MV) in the Kumano forearc basin within the Nankai Trough subduction zone were investigated for hydrocarbon origins and fluid dynamics. Gas hydrates diagnostic for methane concentrations exceeding solubilities were recovered from MVs 2, 4, 5, and 10. Molecular ratios (C1/C2 < 250) and stable carbon isotopic compositions (δ13C‐CH4 >−40‰ V‐PDB) indicate that hydrate‐bound hydrocarbons (HCs) at MVs 2, 4, and 10 are derived from thermal cracking of organic matter. Considering thermal gradients at the nearby IODP Sites C0009 and C0002, the likely formation depth of such HCs ranges between 2300 and 4300 m below seafloor (mbsf). With respect to basin sediment thickness and the minimum distance to the top of the plate boundary thrust we propose that the majority of HCs fueling the MVs is derived from sediments of the Cretaceous to Tertiary Shimanto belt below Pliocene/Pleistocene to recent basin sediments. Considering their sizes and appearances hydrates are suggested to be relicts of higher MV activity in the past, although the sporadic presence of vesicomyid clams at MV 2 showed that fluid migration is sufficient to nourish chemosynthesis‐based organisms in places. Distributions of dissolved methane at MVs 3, 4, 5, and 8 pointed at fluid supply through one or few MV conduits and effective methane oxidation in the immediate subsurface. The aged nature of the hydrates suggests that the major portion of methane immediately below the top of the methane‐containing sediment interval is fueled by current hydrate dissolution rather than active migration from greater depth.

Authigenic barite records of methane seepage at the Carlos Ribeiro mud volcano (Gulf of Cadiz).

Submarine mud volcanoes (MVs) are dynamic features that episodically expel gas-charged fluids and mud onto the seafloor, transferring various chemical constituents into the overlying water column. The temporal variability in MV activity is, however, poorly understood, so their importance as a source of methane (CH4) and higher hydrocarbons for the oceanic carbon budget, although thought to be significant, cannot be properly constrained. In this study, the history of fluid and gas seepage at the Carlos Ribeiro MV (Gulf of Cadiz) is assessed via geochemical analyses and transport-reaction modelling of pore fluids and barium (Ba) rich layers (Ba fronts) in sediment cores, recovered along a transect from the eye to the periphery of the MV. X-ray fluorescence data reveal that Ba fronts are absent at the eye, while a single front (with up to 1740 ppm Ba) is present at the margin of the summit. Three Ba fronts occur at 45, 85 and 130 cm depth within a mudflow to the southeast of the crater. Spectrometric analyses indicate that barite is the Ba-rich mineral in these layers. Upward advecting pore fluids are enriched in barium but depleted in calcium (Ca2 +) relative to seawater. Modelling of the Ba2 + and Ca2 + pore fluid profiles indicates that the positions of the Ba fronts reflect both the present-day hydrodynamic conditions as well as higher fluxes of methane in the past. Fluid advection appears to have decreased since 340 cal yr before present, but degassing of the mudflow is ongoing and is potentially an important source of CH4.

A non-phylogenetic alpha diversity approach on prokaryotic community structure in aquatic systems

Comparative analyses of accumulating phylotype-abundance data of prokaryotic communities are relatively scarce and mainly approached with phylogenetic methodologies. However, when a great fraction of phylotypes is captured within a sample, application of alpha diversity measures is also possible, enabling the exploration of structural changes in prokaryotic communities. In the present study, phylotype-abundance data of Archaea and Bacteria were compiled from previous works on freshwater, thermal springs, and submarine mud volcanoes in Eastern Mediterranean region. Samples within each environment were used as pseudo-replicates to enable comparisons between the two assemblages (Archaea and Bacteria) and among different environments whereas sampling effort was found similar among samples using rarefaction curves. Phylotypes were defined as 16S rRNA sequences with 98% similarity. The most common diversity indices were calculated and relative abundance distributions (RADs) were employed to provide a more detailed interpretation of observed diversity patterns. The freshwater and mud volcanoes environments were the most diverse with respect to Bacteria but the least diverse considering Archaea, whereas thermal springs yielded very similar diversity for both assemblages. Overall, bacterial diversity was higher than archaeal with respect to richness and evenness since Archaea were characterized by high dominance and phylotype-poor distributions. The present comparative analysis of alpha diversity may offer useful insights into ecological processes shaping prokaryotic community structure, however equal sampling effort among different environments must be verified prior to analysis.

Coseimic massive methane release from a submarine mud volcano

We report here the discovery of two methane-enriched plumes in a water column above the Kumano Knoll ♯5 submarine mud volcano (KK#5) in Nankai Trough during 2004; a slight methane enrichment was observed in this region in 2000 and 2010. The deeper of the two plumes spread horizontally at depths near the top of KK#5, whereas a shallow plume spread at a height of 300m from the top of KK#5. The end-member δ13C values of methane in both plumes, −46.1±4.8‰ and −51.4±5.8‰ in the deep and shallow plumes, respectively, and methane extracted from sediment in KK#5 (−52±2‰) are statistically indistinguishable. We conclude that the plumes were created by massive release of methane from KK#5 and that this event probably occurred in response to the large earthquakes (Mw 7.5) that occurred shortly before our observation in 2004. The discharge rates from submarine mud volcanoes (SMVs) in subduction zones may be highly variable in response to major earthquakes.

New tanaidomorph Tanaidacea (Crustacea: Peracarida) from submarine mud-volcanoes in the Gulf of Cadiz (North-east Atlantic)

New tanaidomorph Tanaidacea (Crustacea: Peracarida) from submarine mud-volcanoes in the Gulf of Cadiz (North-east Atlantic)

Viral infections stimulate the metabolism and shape prokaryotic assemblages in submarine mud volcanoes

Mud volcanoes are geological structures in the oceans that have key roles in the functioning of the global ecosystem. Information on the dynamics of benthic viruses and their interactions with prokaryotes in mud volcano ecosystems is still completely lacking. We investigated the impact of viral infection on the mortality and assemblage structure of benthic prokaryotes of five mud volcanoes in the Mediterranean Sea. Mud volcano sediments promote high rates of viral production (1.65-7.89 × 10(9) viruses g(-1) d(-1)), viral-induced prokaryotic mortality (VIPM) (33% cells killed per day) and heterotrophic prokaryotic production (3.0-8.3 μgC g(-1) d(-1)) when compared with sediments outside the mud volcano area. The viral shunt (that is, the microbial biomass converted into dissolved organic matter as a result of viral infection, and thus diverted away from higher trophic levels) provides 49 mgC m(-2) d(-1), thus fuelling the metabolism of uninfected prokaryotes and contributing to the total C budget. Bacteria are the dominant components of prokaryotic assemblages in surface sediments of mud volcanoes, whereas archaea dominate the subsurface sediment layers. Multivariate multiple regression analyses show that prokaryotic assemblage composition is not only dependant on the geochemical features and processes of mud volcano ecosystems but also on synergistic interactions between bottom-up (that is, trophic resources) and top-down (that is, VIPM) controlling factors. Overall, these findings highlight the significant role of the viral shunt in sustaining the metabolism of prokaryotes and shaping their assemblage structure in mud volcano sediments, and they provide new clues for our understanding of the functioning of cold-seep ecosystems.

Distribution and abundance of gas hydrates in near-surface deposits of the Håkon Mosby Mud Volcano, SW Barents Sea

The occurrence of gas hydrates at submarine mud volcanoes (MVs) located within the gas hydrate stability zone (GHSZ) is controlled by upward fluid and heat flux associated with MV activity. Determining the spatial distribution of gas hydrates at MVs is crucial to evaluate their sensitivity to known episodic changes in volcanic activity. We determined the hydrocarbon inventory and spatial distribution of hydrates at an individual MV structure. The Hakon Mosby Mud Volcano (HMMV), located at 1,250 m water depth on the Barents Sea slope, was investigated by combined pressure core sampling, heat flow measurements, and pore water chemical analysis. Quantitative pressure core degassing revealed gas-sediment ratios between 3.1 and 25.7, corresponding to hydrate concentrations of up to 21.3% of the pore volume. Hydrocarbon compositions and physicochemical conditions imply that gas hydrates incipiently crystallize as structure I hydrate, with a dissociation temperature of around 13.8 degrees C at this water depth. Based on numerous in situ measurements of the geothermal gradient in the seabed, pore water sulfate profiles and microbathymetric data, we show that the thickness of the GHSZ increases from less than 1 m at the warm center to around 47 m in the outer parts of the HMMV. We estimate the total mass of hydrate-bound methane stored at the HMMV to be about 102.5 kt, of which 2.8 kt are located within the morphological Unit I around the center and thus are likely to be dissociated in the course of a large eruption.

The driving forces behind the Caspian Sea mean water level oscillations

Closed basins such as the Caspian Sea rapidly respond to variations in atmospheric and geological events. This study has been conducted to deduce the role of natural and anthropogenic influences on the Caspian Sea mean water level fluctuations for the period of 1998–2005. It is recognized that climate is the primary mechanism of the Caspian Sea mean water level variations based on the relatively small differences of the Caspian Sea hydrologic budget residuals and the Caspian Sea mean water level fluctuations. This is further supported by the similarity in water-level variations of the Caspian Sea with those of Lake Van and Lake Urmia. On the other hand, the Caspian Sea needed to lose some of its water to attain water balance equilibrium in 2000 and 2001. The year 2000 showed anomalous seismic activity particularly in the southwestern part of the Caspian Sea. Two significant earthquakes with magnitudes of 6.8 and 6.5 Mw occurred on November 25, 2000. The focal mechanisms of these earthquakes and numerous aftershocks indicated normal faulting and, therefore, caused the Caspian Sea lake level to decline in 2000. The contribution of submarine mud volcano eruptions to the Caspian Sea lake level could be insignificant based on the comparison of water budget residuals and the mean water level variations. Neither crustal deformation (based on the GPS measurements) nor the offshore oil and natural gas production activities in the Caspian Sea are responsible for noticeable changes to the level of the Caspian Sea.

Methanogenic diversity and activity in hypersaline sediments of the centre of the Napoli mud volcano, Eastern Mediterranean Sea

Submarine mud volcanoes are a significant source of methane to the atmosphere. The Napoli mud volcano, situated in the brine-impacted Olimpi Area of the Eastern Mediterranean Sea, emits mainly biogenic methane particularly at the centre of the mud volcano. Temperature gradients support the suggestion that Napoli is a cold mud volcano with moderate fluid flow rates. Biogeochemical and molecular genetic analyses were carried out to assess the methanogenic activity rates, pathways and diversity in the hypersaline sediments of the centre of the Napoli mud volcano. Methylotrophic methanogenesis was the only significant methanogenic pathway in the shallow sediments (0-40 cm) but was also measured throughout the sediment core, confirming that methylotrophic methanogens could be well adapted to hypersaline environments. Hydrogenotrophic methanogenesis was the dominant pathway below 50 cm; however, low rates of acetoclastic methanogenesis were also present, even in sediment layers with the highest salinity, showing that these methanogens can thrive in this extreme environment. PCR-DGGE and methyl coenzyme M reductase gene libraries detected sequences affiliated with anaerobic methanotrophs (mainly ANME-1) as well as Methanococcoides methanogens. Results show that the hypersaline conditions in the centre of the Napoli mud volcano influence active biogenic methane fluxes and methanogenic/methylotrophic diversity.

New tanaidomorph Tanaidacea (Crustacea: Peracarida) from submarine mud-volcanoes in the Gulf of Cadiz (North-east Atlantic)

Faunal collections from mud-volcano sites in the Gulf of Cadiz, at depths between 355 and 3061 m, have revealed a high diversity (and in some cases high density) of tanaidaceans. The present study reports on nine new tanaidomorph species from eight different genera from this material. These include representatives of genera known elsewhere from non-ventassociated deep-sea habitats, but notably only the second and third (respectively) representatives of two genera, Coalecerotanais and Cristatotanais, known previously from cold-seep-habitats in the Gulf of Mexico. The genus Spinitanaopsis is synonymized with Cristatotanais. The tanaidacean records to date from hydrothermal vents or cold seeps are collated as a context for the present material. The possibilities of habitat-endemism in tanaidacean taxa associated with reducing environments and their biogeography are discussed.

Formation of gas hydrate reservoirs in submarine mud volcanos

Transfer mechanisms of the gas dissolved in water are investigated within the framework of the one-dimensional approximation for a submarine mud volcano. The conditions and intensity of transition of the dissolved gas into the hydrate form inside the volcano are determined. Practical recommendations on search for hydrate reservoirs in water areas are given.

Prokaryotic community structure and diversity in the sediments of an active submarine mud volcano (Kazan mud volcano, East Mediterranean Sea)

We investigated 16S rRNA gene diversity at a high sediment depth resolution (every 5 cm, top 30 cm) in an active site of the Kazan mud volcano, East Mediterranean Sea. A total of 242 archaeal and 374 bacterial clones were analysed, which were attributed to 38 and 205 unique phylotypes, respectively (> or = 98% similarity). Most of the archaeal phylotypes were related to ANME-1, -2 and -3 members originating from habitats where anaerobic oxidation of methane (AOM) occurs, although they occurred in sediment layers with no apparent AOM (below the sulphate depletion depth). Proteobacteria were the most abundant and diverse bacterial group, with the Gammaproteobacteria dominating in most sediment layers and these were related to phylotypes involved in methane cycling. The Deltaproteobacteria included several of the sulphate-reducers related to AOM. The rest of the bacterial phylotypes belonged to 15 known phyla and three unaffiliated groups, with representatives from similar habitats. Diversity index H was in the range 0.56-1.73 and 1.47-3.82 for Archaea and Bacteria, respectively, revealing different depth patterns for the two groups. At 15 and 20 cm below the sea floor, the prokaryotic communities were highly similar, hosting AOM-specific Archaea and Bacteria. Our study revealed different dominant phyla in proximate sediment layers.

Changes in seabed morphology, mud temperature and free gas venting at the Håkon Mosby mud volcano, offshore northern Norway, over the time period 2003–2006

The Hakon Mosby mud volcano is a 1.5-km-diameter geological structure located on the Southwest Barents Sea slope at a water depth of 1,270 m. High-definition seabed mapping of the mud volcano has been carried out in 2003 and 2006. A comparative analysis of the bathymetry and backscatter maps produced from the two surveys shows subtle morphological changes over the entire crater of the mud volcano, interpreted to be the consequence of mud eruption events. Mud temperature measurements point to a persistently warm mud at shallow depth in the crater. This is explained by upward fluid advection, rather than conductive cooling of mud flows. The small-scale spatial variability in the temperature distribution may be related to mud outflows or changes in the fluid flow regime. Furthermore, the locations of free gas venting observed in 2006 were found to differ from those of 2003. Our observations of overall similar topographic profiles across the mud volcano in 2003 and 2006 suggest that eruption events would have been modest. Nevertheless, the data bring evidence of significant change in activity even over short time intervals of only 3 years. This may be a characteristic shared by other submarine mud volcanoes, notably those considered to be in a quiescent stage.

The Cenozoic CH 4-derived carbonates of Monferrato (NW Italy): A solid evidence of fluid circulation in the sedimentary column

Two types of methane-derived carbonates, each with different lithological and paleontological signatures, have been distinguished in the Oligocene–Miocene sediments of Monferrato (NW Italy): 1) Irregularly-shaped, metre-sized rock bodies characterized by the widespread occurrence of remains of large bivalves ( Lucina sp.). These bodies include two subtypes, differing in the lithological characteristics of the cemented sediments: a) Lucina-rich marly limestones, encased in Langhian outer shelf marls. They document a slow seepage of CH 4-rich fluids at the paleo-sea floor; b) Lucina-bearing cemented mud breccias, found either as cemented masses in the original stratigraphic position or as redeposited blocks within Upper Messinian chaotic (block-in-matrix) sediments. These carbonate bodies document the activity of submarine mud volcanoes during the late Messinian. In particular, they document intermittent fluid emission ranging from violent eruptive phases, responsible for the extrusion of soft mud breccias at the sea floor, to quiet degassing phases, that promoted colonization by chemosymbiotic communities and localized cementation. 2) Very irregularly shaped strongly cemented, mainly coarse-grained, clastic sediments, reaching the lateral extent of few hundred meters and the thickness of few tens of meters. They occur within Oligocene to Messinian sediments, lack remains of chemosymbiotic taxa and are highly fractured, with fractures filled with sediments and cements. These carbonate-cemented masses, here referred to as macroconcretions, result from the precipitation of carbonate cements within buried sediments flushed by ascending CH 4-rich fluids. They document a complex fluid circulation pattern in the sedimentary column, in which SO 4-rich waters were drawn from surrounding sediments by the fast and prolonged flow of CH 4-rich fluids and promoted anaerobic oxidation of methane and the precipitation of carbonate cements. The polyphase network of clastic dykes and veins that characterize macroconcretions is related to an intermittent fluid flow regime: dykes formed during fast upward flows of sediment-rich fluids whereas carbonate-filled veins formed during slower, degassing phases. The local lithostratigraphic and structural framework allow to correlate genetically and chronologically the macroconcretions to Lucina-bearing mud breccias. Consequently, macroconcretions are here regarded as the result of cementation along fluid conduits feeding Messinian mud volcanoes at the sea floor. The massive release of fluids could have played a role in triggering large-scale mass wasting events responsible for the emplacement of sedimentary mélanges including CH 4-derived rocks in the Messinian.

Distinct activity phases during the recent geologic history of a Gulf of Mexico mud volcano

Laser line scan imaging and chirp sub-bottom profiling were used to detail the morphology of a submarine mud volcano and brine-filled crater at 652 m water depth in the northern Gulf of Mexico. The mud volcano has a relief of 6 m and a basal diameter of about 80 m. The feature comprises a central, brine-filled crater (253 m 2) surrounded by a continuous bed of methanotrophic mussels ( Bathymodiolus childressi) covering 434 m 2 and a patchy bed covering an additional 214 m 2 of the periphery. The brine pool was mostly <2 m deep, but there were two holes of >28 m and 12 m deep, respectively at the northern end of the pool which emitted continual streams of small clear bubbles. Sub-bottom profiles indicated three distinct strata beneath the present surface of the mud volcano. Integration of 17 profiles shows that the mud volcano has been built in at least three successive stages: the lowest stage deposited 35,400 m 3, while the middle and upper stages deposited 7700 and 20,400 m 3, respectively. Piston cores were taken at the northern edge of the mussel bed and a site ∼100 m southwest of the pool. Mussel and lucinid shells were recovered from the closer core, lucinid shells from the distant core. A mussel shell from 3.4 m sub-bottom had a Δ 14C age of 16.2 ka. Mixture of modern carbon with “carbon dead” reservoir material would produce actual ages ∼2 ka less than the radiocarbon ages.