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Hydroacoustic surveys at the accretionary wedge southwest of Taiwan reveal a confined active hydrocarbon seepage area of ~ 49,000 m2 in ~ 1350 m water depth on the northern crest of the Four-Way Closure Ridge, which we call Yam Seep. In this study, multibeam and side-scan sonar data acquired during surveys with an autonomous underwater vehicle during an expedition with R/V Ocean Researcher I in 2017 showed that the area is characterized by rough topography and high seafloor backscatter. Seafloor observations with a video sled and sediment sampling with gravity corers and the MeBo seafloor drill rig during an expedition with R/V SONNE in 2018 revealed that the area is almost entirely covered by intensely fractured methane-derived carbonates, which indicate that seepage has been ongoing for thousands of years. Hydroacoustic anomalies (‘flares’) in the water column indicated the presence of several gas bubble emission sites mostly at the center and eastern flank of the area in 2019. Drilling through massive carbonates in the northwestern part of Yam Seep induced free gas escape from a depth of ~ 5.1 m. This suggests the presence of gas hydrates in the subsurface as the seep area is located well within the gas hydrate stability zone. The inter-disciplinary investigations of the Yam Seep demonstrate that upward migration of light hydrocarbons and seafloor discharge has a considerable influence on the seabed properties.

The YAM seep area is an active gas seep region among the widespread seep sites offshore south-western Taiwan. The seep area covers a seafloor region of 49,000 m2 at the northern crest of Four-Way Closure Ridge in 1,347 m water depth. During several research cruises (ORI-1163, SO266), shipborne and AUV-related hydro-acoustic investigations revealed that the area of seepage is well documented by high backscatter and a changing micro-bathymetry between rough and flat in the otherwise very flat seabed in the area. During expedition SO266, RV Sonne, gas emission sites were observed at the center and eastern flank of the area using ship-borne multi-beam data in the water column. Seawater methane concentrations above the seafloor were collected from the middle west to east of the central transect, revealing concentrations ranging 5.5-18.2 nmol/L with general higher methane concentrations at the rim of the area. Authigenic carbonate samples were collected during gravity coring and MeBo drilling. MeBo drilling was stopped below 5 mbsf because of continuous release of free gas out of the borehole. Carbon isotope measurements of the carbonates showed δ13C values between -38.25 to -52.17 ‰, indicating a mixing of biogenic and thermogenic gas in the methane-derived carbonates. Seismic investigations of the Four-Way Closure Ridge show a well-defined fault below the ridge crest which extends from below the gas hydrate stability zone to the seafloor and acts as a pathway for the methane ascent to the seafloor. Seafloor observation using a TV-sled showed a seafloor paved by carbonate rocks consisting of different featured crusts, slabs, and irregular build-ups. Thin-layered crusts were mainly observed at the paved area's rim, while thick-layered slabs and free-standing build-ups were the main features at the elevated region. Chemosynthetic communities, like mussels and clams, mainly were observed within certain carbonate fractures. At the same time, other animals, bacterial mats, and tube worms are presented generally along the whole survey path among the rough seep area. Hydro-acoustic data correlated with visual observation results indicate wide variation through the region of the seep area. Based on our interpretation, the YAM seep area developed over a longer time at the crest of the accretionary ridge, seepage, uplifting of the ridge, tectonic fracturing, and seafloor erosion highly influenced the seafloor manifestation.

Two isolates of heterotrophic, facultatively anaerobic, marine bacteria, designated DM1 and DM2T, were recovered from a lagoon sediment sample of Dongsha Island, Taiwan. Cells were Gram-reaction-negative rods. Nearly all of the cells were non-motile and non-flagellated during the late exponential to early stationary phase of growth, while a few of the cells exhibited motility with monotrichous flagellation. The two isolates required NaCl for growth and grew optimally at about 30 °C, 2–3 % NaCl and pH 7–8. They grew aerobically and could achieve anaerobic growth by fermenting d-glucose or other carbohydrates with production of acids and the gases, including CO2 and H2. Ubiquinone Q-8 was the only respiratory quinone. Cellular fatty acids were predominated by C16 : 0, C18 : 1ω7c and C16 : 1ω7c. The major polar lipid was phosphatidylethanolamine. Strains DM1 and DM2T had DNA G+C contents of 52.0 and 51.8 mol%, respectively, as determined by HPLC analysis. Phylogenetic analyses based on 16S rRNA gene sequences clearly indicated that the two isolates formed a distinct genus-level lineage in the family Aeromonadaceae of the class Gammaproteobacteria and was an outgroup with respect to a stable supragenic clade comprising species of the genera Oceanimonas , Oceanisphaera and Zobellella . The phylogenetic data and those from chemotaxonomic, physiological and morphological characterizations support the establishment of a novel species and genus inside the family Aeromonadaceae , for which the name Dongshaea marina gen. nov., sp. nov. is proposed. The type strain is DM2T (=BCRC 81069T=JCM 32096T).

Rationale Otolith strontium:calcium (Sr:Ca) ratios have been extensively used to study fish migration across a river, estuary and ocean at each life stage. However, otolith Sr:Ca ratios only explain partial variations in salinity and quantitative reconstruction of salinity history of fishes remains a challenge. Using a euryhaline fish Lateolabrax japonicus as an example, this study demonstrated an isotopic method of quantitatively reconstructing the salinity histories and habitat uses of the fish. Methods Otolith oxygen stable isotopic ratios (δ18 Ooto values) were measured using a mass spectrometer for subsamples sequentially milled from the otolith core to the edge, and otolith Sr:Ca ratios were measured by an electron probe microanalyzer for the comparison. The mean water temperature within the studied area in the time period of each milled subsample was estimated from the Copernicus database. Based on an isotopic fractionation equation, each δ18 Ooto value and water temperature pair determined the water δ18 O value, which was then converted into salinity using published linear equations or an equation that was newly generated for this study. Results Individual fish clearly revealed different preferences in habitat use. The retrospectively reconstructed salinity history indicated that most L. japonicus inhabit and can spawn in seawater as well as in brackish estuaries. Few fish lived in freshwater during the young stage based on the analysis of δ18 Ooto profiles; however, otolith Sr:Ca ratios can only reveal freshwater residence and cannot distinguish residence in brackish water or seawater. Conclusions This study demonstrated that otolith temporal microstructure and δ18 Ooto values are well-suited approaches for quantitative reconstruction of salinity histories of the fish. This method can improve the understanding of the habitat uses of other fishes inhabiting diverse habitats among the rivers, estuaries and oceans.

The major processes that determine the distribution of methane (CH4) in anoxic marine sediments are methanogenesis and the anaerobic oxidation of methane (AOM), with organoclastic sulfate reduction exerting an important secondary control. However, the factors leading to the distribution of stable carbon isotopes (δ13C) of CH4 are currently poorly understood, in particular the commonly-observed minimum in δ13C-CH4 at the sulfate-methane transition (SMT) where AOM rates reach maximum values. Conventional isotope systematics predict 13C-enrichment of CH4 in the SMT due to preferential 12CH4 consumption by AOM. Two hypotheses put forward to explain this discrepancy are the addition of 12C-enriched CH4 to porewaters by methanogenesis in close proximity to AOM, and enzymatically-mediated carbon isotope equilibrium between forward and backward AOM at low concentrations of sulfate. To examine this in more detail, field data including δ13C of CH4 and dissolved inorganic carbon (DIC) from the continental margin offshore southwestern Taiwan were simulated with a reaction-transport model. Model simulations showed that the minima in δ13C-CH4 and δ13C-DIC in the SMT could only be simulated with carbon isotope equilibrium during AOM. The potential for carbon cycling between methanogenesis and AOM in and just below the SMT was insignificant due to very low rates of methanogenesis. Backward AOM also gives rise to a pronounced kink in the δ13C-DIC profile several meters below the SMT that has been observed in previous studies. We suggest that this kink marks the true base of the SMT where forward and backward AOM are operating at very low rates, possibly sustained by cryptic sulfur cycling or barite dissolution.

The northern part of the South China Sea is characterized by widespread occurrence of bottom simulating reflectors (BSR) indicating the presence of marine gas hydrate. Because the area covers both a tectonically inactive passive margin and the termination of a subduction zone, the influence of tectonism on the dynamics of gas hydrate systems can be studied in this region. Geophysical data show that there are multiple thrust faults on the active margin while much fewer and smaller faults exist in the passive margin. This tectonic difference matches with a difference in the geophysical characteristics of the gas hydrate systems. High hydrate saturation derived from ocean bottom seismometer data and controlled source electromagnetic data and conspicuous high‐amplitude reflections in P‐Cable 3D seismic data above the BSR are found in the anticlinal ridges of the active margin. In contrast all geophysical evidence for the passive margin points to normal to low hydrate saturations. Geochemical analyses of gas samples collected at seep sites on the active margin show methane with heavy δ13C isotope composition, while gas collected at the passive margin shows light carbon isotope composition. Thus, we interpret the passive margin as a typical gas hydrate province fuelled by biogenic production of methane and the active margin gas hydrate system as a system that is fuelled not only by biogenic gas production but also by additional advection of thermogenic methane from the subduction system.

Huge quantity of terrigenous particles was exported from oceanic island small rivers in delivering to the ocean (Dadson et al., 2003; Milliman and Syvitsky, 1992). Quantity of river particles entering the ocean could be related to river basin area, elevation, erosion rate, and seismic activity. However, limited data are available regarding differences between physical and chemical weathering on erosion and their effects on particles export from oceanic type of small rivers nor data on extreme event, the typhoon, and its effect on weathering at this setting. Here we report and quantify particles as well as dissolved materials export from an oceanic small river, the Lanyang River at the northeastern Taiwan, during typhoon period and those under normal weather condition. Our objectives are to quantify river particles and dissolved components export during normal and typhoon period; to understand factors controlling their variations; to compare efficiency of chemical and physical weathering under extreme weather condition and those at normal condition. River particles and dissolved components were sampled monthly and during typhoons at every four hours frequency and filtered, weighted for particle concentrations as well as chemical analyses of particle and dissolved compositions in lab. Chemical analyses include solid and dissolve silica, aluminum, iron, sodium, calcium, magnesium, and potassium as well as dissolved chloride, sulfate, and alkalinity. River discharge data were from Taiwan Water Resources Agency and precipitation data from Taiwan Central Weather Bureau. Our results demonstrated that typhoon is the primary mechanism in driving concentration variations of both dissolved phases and solid components in the study river. Huge amount of precipitation flushed into river during typhoon, resulting in rapid dilution of dissolved components as well as rapid increase of suspended particles concentration in reaching hyperpycnal level. During the period of rapid increase of particles in the river, shift of types of particles as well as dissolve components were observed. TDS (total dissolved solid) represent a small portion of the materials export to the ocean. TSM (total suspended matter) flushed out of river during typhoon represent a major fraction (85%) of the annual total particles, however, the amount of particles for each typhoon varied significantly (from ~10 to ~45%).

Qualitative and quantitative assessments of fluid cycling are essential to address the role and transport of deeply sourced fluids in subduction systems. In this study, sediment cores distributed across a submarine mud volcano (SMV) offshore southwestern Taiwan were investigated to determine the characteristics of fluids generated through the convergence between the Eurasian and Phillippine Sea Plates. The low dissolved chloride concentration combined with the enrichment of 18O, and depletion of 2H of pore fluids suggest the discharge of deep freshwater formed by smectite dehydration at an equilibrium temperature of 100 to 150 °C. The upward fluid velocities, decreasing from 2.0 to 5.0 cm yr−1 at the center to a negligible value at margin sites, varied with the rate and efficiency of anaerobic methanotrophy, demonstrating the impact of fluid migration on biogeochemical processes and carbon cycling. By extrapolating the velocity pattern, the flux of fluids exported from 13 SMVs into seawater amounted up to 1.3–2.5 × 107 kg yr−1, a quantity accounting for 1.1–28.6% of the smectite-bound water originally stored in the incoming sediments. Our results imply that SMVs could act as a conduit to channel the fluids produced from great depth/temperature into seafloor environments in a subduction system of the western Pacific Ocean.

Sulfate reduction could go through dissimilatory sulfate reduction and anaerobic methane oxidation couple with sulfate reduction (AOM-SR) with pyrite the end product. While AOM-SR is an important process in oxidizing methane and limiting methane entering the ocean, there is limited information available regarding pyrite formation and preservation under methane dominated environment. The purpose of this study is to report pyrite formation and preservation at a methane dominated environment, the YuanAn Ridge, where methane seeps have been observed, and to evaluate how would that differ from typical anoxic environment. Pore water methane, sulfate, dissolved sulfide, barium, and sediment pyrite, barium/Al ratio and organic carbon in sediments were analyzed from sediments collected by piston cores on board the R/V Ocean Researcher I (OR-I) from the study environment. The results showed methane flux is controlling pyrite formation in this methane dominated environment. Pyrite concentration is linearly correlated with methane flux with exceptions to shallower sulfate methane transition zone (SMTZ) sites where methane could have vent directly to the overlying water and contribute less to the pyrite formation. The more methane entering the SMTZ, the more pyrite formed and preserved in the sulfate methane transition zone sediments. Authigenic pyrite from dissimilatory sulfate reduction is a small fraction of the pyrite found in the methane dominant and low in organic carbon environment, with majority of pyrite derived from AOM-SR. Large spatial variations on rate of sulfate reduction, pyrite and methane concentrations were observed in the studied area sediments. Depth of sulfate methane transition zone varied between 1 and 14 m and is a log function of methane flux. Pore water sulfate profiles displayed three different types, linear, concave up and down, indicating methane flux have varied in time. Pyrite burial efficiency is high, approximately 50% of sulfate entering the SMTZ were preserved in sediments as pyrite. This efficiency of sulfate reduction through AOM-SR is much higher than pyrite formation from dissimilatory sulfate reduction in normal marine sediments. The AOM-SR and pyrite formation occurred at depth within the SMTZ favor a higher degree of pyrite preservation. Time require for the pyrite formation is about 4400 years in the YAR sediments, based on diffusion model calculation of barium sulfate precipitation.

Due to its toxicity causing serious health problems, persistence in the environment and non-biodegradability, lead (Pb) is considered as one of the most harmful metals on earth. In this study, dried aquatic plants as sorbents including Nymphoides peltata (NP), Typha laxmannii (TL), and Eichhornia crassipes (EC) were examined and compared to discover the best biosorption for Pb. The effect of physical and chemical parameters including pH (2.0–5.5), sorbent dosage (1–5 g/l), metal concentration (20–100 mg/l), and contact time (~240 min) were investigated to determine the optimal condition for Pb(II) biosorption. As a result, the optimum pH, sorbent dosage, and contact time were 5.0, 1 g/l, and 120 minutes, respectively. Pb2+ biosorption data were found to follow the Langmuir isotherm model while the kinetic biosorption data followed pseudo-second-order model. The maximum biosorption capacity from Langmuir model was calculated as 63.3, 82.9, and 51.9 mg/g for EC, NP, and TL, respectively. All the results showed that biosorption efficiencies of Pb(II) by different biosorbents were in following order NP>EC>TL.

Multi-scale reflection seismic data, from deep-penetration to high-resolution, have been analyzed and integrated with near-surface geophysical and geochemical data to investigate the structures and gas hydrate system of the Formosa Ridge offshore of southwestern Taiwan. In 2007, dense and large chemosynthetic communities were discovered on top of the Formosa Ridge at water depth of 1125 m by the ROV Hyper-Dolphin. A continuous and strong BSR has been observed on seismic profiles from 300 to 500 ms two-way-travel-time below the seafloor of this ridge. Sedimentary strata of the Formosa Ridge are generally flat lying which suggests that this ridge was formed by submarine erosion processes of down-slope canyon development. In addition, some sediment waves and mass wasting features are present on the ridge. Beneath the cold seep site, a vertical blanking zone, or seismic chimney, is clearly observed on seismic profiles, and it is interpreted to be a fluid conduit. A thick low velocity zone beneath BSR suggests the presence of a gas reservoir there. This “gas reservoir” is shallower than the surrounding canyon floors along the ridge; therefore as warm methane-rich fluids inside the ridge migrate upward, sulfate carried by cold sea water can flow into the fluid system from both flanks of the ridge. This process may drive a fluid circulation system and the active cold seep site which emits both hydrogen sulfide and methane to feed the chemosynthetic communities.

In this study, we used pore water dissolved inorganic carbon (DIC), SO 4 2− , Ca 2+ and Mg 2+ gradients at the sulfate-methane transition zone (SMTZ) to estimate biogeochemical fluxes for cored sediments collected offshore SW Taiwan. Net DIC flux changes (Δ DIC-Prod ) were applied to determine the proportion of sulfate consumption by organic matter oxidation (heterotrophic sulfate reduction) and anaerobic oxidation of methane (AOM), and to determine reliable CH 4 fluxes at the SMTZ. Our results show that SO 4 2− profiles are mainly controlled by AOM rather than heterotrophic sulfate reduction. Refinement of CH 4 flux estimates enhance our understanding of methane abundance from deep carbon reservoirs to the SMTZ. Concentrations of chloride (Cl − ), bromide (Br − ) and iodide (I − ) dissolved in pore water were used to identify potential sources that control fluid compositions and the behavior of dissolved ions. Constant Cl − concentrations throughout ∼30 m sediment suggest no influence of gas hydrates for the compositions within the core. Bromide (Br − ) and Iodine (I − ) concentrations increase with sediment depth. The I − /Br − ratio appears to reflect organic matter degradation. SO 4 2− concentrations decrease with sediment depth at a constant rate, and sediment depth profiles of Br − and I − concentrations suggests diffusion as the main transport mechanism. Therefore diffusive flux calculations are reasonable. Coring sites with high CH 4 fluxes are more common in the accretionary wedge, amongst thrust faults and fractures, than in the passive continental margin offshore southwestern Taiwan. AOM reactions are a major sink for CH 4 passing upward through the SMTZ and prevent high methane fluxes in the water column and to the atmosphere.

Mongolia has been a pristine environment without much pollution. Our objective is to study a section of the Tuul River to evaluate the present condition of this pristine environment. Sediment metal (Al, Fe, Mn, Cu, Zn, Pb, Ni, Cd, Hg, and Cr) concentrations and Pb-210 were sampled and analyzed. Results showed that metal concentrations are much higher at areas near the capital city and municipal sewage outlet, with enrichment factor values up to 18 for Cu, and 26 for Cr. Higher copper concentrations were found at sites about ~ 50 km downstream from the source, an indication that pollutions are spreading further down the river. Vertical metal concentration profiles indicated that pollutions could be traced back to the 1960s. Inefficient sewage treatment plants and poorly managed power plant ash ponds were major sources of metals leaking into the Tuul River. Sewage wastewater is carrying metals through Tuul River to the lower river basin. Dusts from ash ponds are airborne and transport to greater area. These findings indicate that new and alternative measures have to be enforced to prevent further pollution entering the Tuul River drainage basin and airborne dust to other broader regions of the Asia and ocean.

A shipboard experiment using R/V Ocean Researcher III was conducted on July 6–9, 2012 to focus on the temporal variability of the suspended particle characteristics off the Zhuoshui River mouth in central Taiwan. The experiment included hydrographic profiling using a CTD rosette with a LISST-100X and collection of near-surface water samples. These samples were immediately filtered on-board by a nested filtration system Catnet to separate the suspended particles into four grain-size classes (> 153 μm, 63–153 μm, 10–63 μm, and < 10 μm). The filtered particles were analyzed for suspended sediment concentration (SSC), POC and PN. A downward-looking ADCP (Aquadopp, 1200 kHz) mounted on a tethered floating platform measured the current velocity profile. The results show that the river plume fluctuating at the semidiurnal tidal frequency was the most important factor affecting suspended particle characteristics. In the ambient seawater regime, surface suspended particles consisted of fine-grained size-classes (< 10 μm, 10–63 μm) with low SSC values (10 mg/l). In the statically stable river plume regime, SSC value reached 40–60 mg/l, surface particles were composed of biological particles and flocs with fluffy structures. In the unstable plume-front regime, floc breakage occurred, resulting in particles of high bulk density values. Also, biological particles were drawn by the convergent flows to the frontal zone. EOF (Empirical Orthogonal Function) analysis indicates that the three most important processes affecting the characteristics of the suspended particles at the study site include: 1) tidal currents that affect dispersal of the buoyant river plume in the surface water; 2) convergence and water-column instability in the frontal zone of the plume; and 3) resuspension of the seafloor sediment into the water column.

Temporal variations in hydrographic parameters and nutrients were observed in a 300 m deep submarine canyon (Hungtsai Trough) near the southern tip of Taiwan. A vigorous oscillation below the surface layer has been observed which relates closely to an internal tidal wave generated from the nearby Luzon Strait. The vertical movement can be measured by monitoring an 18 °C isothermal depth which shows an up-and-down oscillation between 90 and 240 m with an average displacement of 110 m within a tidal cycle, a scale significantly larger than has been reported elsewhere. The frequency of this oscillation coincides with the surface tide but in an almost opposite phase. All hydrographic and chemical parameters (oxygen, density, fluorescence, transmittance and nutrients including nitrate, phosphate and silicate) synchronize with the tidal movement, as judged by normalized plots against temperature. When the nutrient-rich deep water upwells and becomes an outcrop over the trough rim at 100 m deep, it is swept horizontally by the strong alongshore tidal current. Consequently, the trough acts as a source point to supply extra nutrients to the coastal ecosystem.

Within the accretionary prism offshore SW Taiwan, widespread gas hydrate accumulations are postulated to occur based on the presence of a bottom simulating reflection. Methane seepage, however, is also widespread at accretionary ridges offshore SW Taiwan and may indicate a significant loss of methane bypassing the gas hydrate system. Four Way Closure Ridge, located in 1,500 m water depth, is an anticlinal ridge that would constitute an ideal trap for methane and consequently represents a site with good potential for gas hydrate accumulations. The analysis of high-resolution bathymetry, deep-towed sidescan sonar imagery, high-resolution seismic profiling and towed video observations of the seafloor shows that Four Way Closure Ridge is and has been a site of intensive methane seepage. Continuous seepage is mainly evidenced by large accumulations of authigenic carbonate precipitates, which appear to be controlled by the creation of fluid pathways through faulting. Consequently, Four Way Closure Ridge is not a closed system in terms of fluid migration and seepage. A conceptual model of the evolution of gas hydrates and seepage at accretionary ridges suggests that seepage is common and may be a standard feature during the geological development of ridges in accretionary prisms. The observation of seafloor seepage alone is therefore not a reliable indicator of exploitable gas hydrate accumulations at depth.

The recording of oxygen isotope composition (δ18O) in biogenic carbonates is a powerful tool for investigating temperature changes in organisms’ habitats, especially in relation to their growth, migration, movement, adaptation, and acclimation. Temperature-dependent equations of δ18O values have been established from biogenic carbonates in various organisms, but no equation has yet been validated for cephalopods, thus limiting the application of this approach to the field of cephalopod ecology. In this study, we established a temperature-dependent equation of δ18O values in statoliths and cuttlebones of the pharaoh cuttlefish, Sepia pharaonis, through a controlled experiment involving three temperatures (20 °C, 25 °C, and 30 °C). The established equations for statoliths and cuttlebones follow the general trend in inorganic carbonates, fish otoliths, and mollusc shells, revealing that δ18O values are lower when the temperature is higher. Noticeably, the intercept and slope of the equations obtained from cuttlebones and statoliths differed even when these two carbonate structures formed within the same individual cuttlefish. The isotopic difference between statoliths and cuttlebones suggests that temperature-dependent fractionation is structure specific and may result from the functional demands and chemistry of the internal fluids surrounding these two biogenic carbonates. The use of δ18O values recorded in statoliths and cuttlebones as a temperature proxy can benefit studies of cephalopod ecology and thermal history.

A mesophilic, hydrogenotrophic methanogen, strain S3FaT, 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 S3FaTwere formate and H2/CO2but not acetate, secondary alcohols, methylamines, methanol or ethanol. Cells of strain S3FaTwere 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 S3FaTwas 62.3 mol %. Phylogenetic analysis revealed that strain S3FaTwas most closely related toMethanoculleus marisnigriJR1T(99.3 % 16S rRNA gene sequence similarity). Genome relatedness between strain S3FaTandMethanoculleus marisnigriJR1Twas 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 S3FaTrepresents a novel species of the genusMethanoculleus, for which the nameMethanoculleus sediminissp. nov. is proposed. The type strain is S3FaT( = BCRC AR10044T = DSM 29354T).

Source at https://doi.org/10.1002/2017GC006798 To systematically quantify the production, consumption, and migration of methane, 210 sediment cores were collected from offshore southwestern Taiwan and analyzed for their gas and aqueous geochemistry. These data, combined with published results, were used to calculate the diffusive methane fluxes across different geochemical transitions and to develop scenarios of mass balance and constrain deep microbial and thermogenic methane production rates within the accretionary prism. The results showed that methane diffusive fluxes ranged from 2.71 × 10−3 to 2.78 × 10−1 and from –1.88 × 10−1 to 3.97 mmol m−2 d−1 at the sulfate‐methane‐transition‐zone (SMTZ) and sediment‐seawater interfaces, respectively. High methane fluxes tend to be associated with structural features, suggesting a strong structural control on the methane transport. A significant portion of ascending methane (>50%) is consumed by anaerobic oxidation of methane at the SMTZ at most sites, indicating effective biological filtration. Gas compositions and isotopes revealed a transition from the predominance of microbial methane in the passive margin to thermogenic methane at the upper slope of the active margin and onshore mud volcanoes. Methane production and consumption at shallow depths were nearly offset with a small fraction of residual methane discharged into seawater. The flux imbalance arose primarily due to the larger production of methane through deep microbial and thermogenic processes at a magnitude of 1512–43,096 Tg Myr−1 and could be likely accounted for by the sequestration of methane into hydrate forms, and clay absorption.

Sediment samples (213 sites) collected from the tectonic-active continental margin, offshore southwestern Taiwan were analyzed for grain sizes, organic carbon, nitrogen and carbon isotopic composition to obtain mass accumulation rate of terrestrial organic carbon and carbon budget to evaluate fate of terrestrial organic carbon from small mountainous rivers on the continental margin offshore southwestern Taiwan. Terrestrial organic carbon accumulation rates range from 0.29 to 45.6 g C m −2 yr −1 with a total accumulation budget of 0.063 Mt yr −1 , which accounts for less than 13% of total river particulate organic carbon loads exported from the adjacent rivers, the Gaoping (a.k.a., Kaoping), Erhjen and Tsengwen rivers. This low burial efficiency of terrestrial organic carbon demonstrated that a majority of river-borne particles together with organic materials was moved away from the study area. For the river-borne particles from the Gaoping river, a pair of depocenters in the upper slope flanking the Gaoping submarine canyon are the locations where the maximum TC org accumulation rate were observed which hold up to 45% (0.016 Mt yr −1 ) of the calculated accumulation found in the study region. On the other hand, the occurrence of higher-fraction terrestrial organic carbon in the upper and middle Gaoping submarine canyon suggests that a majority of particulate organic carbon of the Gaoping river was transported directly into the deep-sea basin through the Gaoping submarine canyon. Our results demonstrated that active margin with narrow shelf and slope is not an efficient sink for the large amount of terrigenous organic carbon supplied by the small rivers, but, a transient environment for these river derived particles.

Coastal water masses are inherently diverse, often with multiple water sources of different origins. Knowledge of characteristic salinity and temperature fingerprints can be very useful to differentiate between component water masses. For example, summertime river plumes carry relatively warm and less saline water into coastal waters, along with nutrients, clastic and organic sediments, and terrestrial-sourced biogenic particles. In an upwelling regime, relatively colder water carries marine-sourced nutrients and particles in water masses from deeper depths offshore. These two regimes are subject to biological-physical coupling that affects their size-differentiated particulate chlorophyll-a and organic carbon contents, and we show here how both regimes can be identified in these terms in the Taiwan Strait in summer. A close examination shows that microphytoplankton is the major contributor to chlorophyll-a concentrations in both regimes at all depths, and picophytoplankton is a minor contributor in the subsurface cold-water regime. The contribution from nanophytoplankton is relatively insignificant. Shipboard hydrographic profiling and water sampling was conducted over 28 h at a fixed location off the mouth of the Minjiang River in the northern Taiwan Strait, where the river plume and upwelling regimes overlap. Water samples were filtered onboard using a nested filtration system to separate suspended particles into >153, 63–153, 10–63, and 0.7–10 μm size classes. Our findings show that in the surface nepheloid layer, the river plume accounted for the physical process affecting large (>10 μm) terrestrial-sourced non-phytoplankton POC (organic debris), with an average C/N ratio of 92.2. The Upwelling regime accounted for the physical process affecting marine-sourced POC 10 μm) POC that contained fluorescence were either upwelling- or offshore-sourced, with an average C/N ratio of 8.5. In the benthic nepheloid layer, terrestrial- and marine-sourced POC containing fluorescence of all sizes were associated with river plume and upwelling regimes. Large (>63 μm) non-phytoplankton organic particles were also present, with an average C/N ratio of 10.2. Both spatial and temporal datasets point to strong three-dimensional coupling between biogenic particles and physical processes. The river plume and upwelling regimes further differentiate size-fractionated chlorophyll-a and POC.

The study collected water samples from three rivers in southern Taiwan to understand the temporal and spatial variations of major dissolved ions, including Na + , K + , Mg 2+ , Ca 2+ , Cl - , SO 4 2- -, HCO 3 - and H 4 SiO 4 , and to explore the relationships between chemical and physical weathering in an orogenic and tropical area. During 2006-2007, total dissolved solid discharge (TDS discharge) from the investigated rivers was calculated to be around 3.27 Mt/yr, and 60 % of dissolved ions were attributable to the outcrop of silicate. However, TDS discharge occupied just 3 % of total delivered material in the river water. Accordingly, physical transport plays a decisive role in weathering process with only a small fraction capable of going through chemical dissolution in reaching the river. The investigation results also show that the huge amount of water discharge in rainy seasons dilute ion concentrations, and that sea spray delivered by monsoon and compositions or properties of source rocks also induce spatial variations of dissolved ions. Additionally, areas with low strength rock have more dissolved material in the river water.

Following phylogenetic analysis based on 16S rRNA gene sequences, together with DNA G+C contents and differential chemotaxonomic and physiological characteristics, a new genus with the name Aliiglaciecola gen. nov. is proposed to more appropriately accommodate two recognized species of the genera Glaciecola and Aestuariibacter . Accordingly, [Glaciecola] lipolytica and [ Aestuariibacter] litoralis should be reassigned to the novel genus as Aliiglaciecola lipolytica comb. nov. (type strain, E3T = JCM 15139T = CGMCC 1.7001T) and Aliiglaciecola litoralis comb. nov. (type strain, KMM 3894T = JCM 15896T = NRIC 0754T), respectively. Aliiglaciecola lipolytica is proposed as the type species of this new genus. Physiologically, the combined characteristics of positive reactions for nitrate reduction and growth at 4 °C and 36 °C distinguish the new genus from the genera Aestuariibacter and Glaciecola by one to three traits. Moreover, the new genus is also distinguished from the genus Glaciecola by the fatty acid profile and distinguished from the genus Aestuariibacter by the differences of major isoprenoid quinone (MK-7 vs Q-8) and DNA G+C content (40.8–43.0 mol% vs 48.0–54.0 mol%).

Geochemical data (CH4, SO42−, I−, Cl−, particulate organic carbon (POC), δ13C-CH4, and δ13C-CO2) are presented from the upper 30 m of marine sediment on a tectonic submarine accretionary wedge offshore southwest Taiwan. The sampling stations covered three ridges (Tai-Nan, Yung-An, and Good Weather), each characterized by bottom simulating reflectors, acoustic turbidity, and different types of faulting and anticlines. Sulfate and iodide concentrations varied little from seawater-like values in the upper 1–3 m of sediment at all stations; a feature that is consistent with irrigation of seawater by gas bubbles rising through the soft surface sediments. Below this depth, sulfate was rapidly consumed within 5–10 m by anaerobic oxidation of methane (AOM) at the sulfate-methane transition. Carbon isotopic data imply a mainly biogenic methane source. A numerical transport-reaction model was used to identify the supply pathways of methane and estimate depth-integrated turnover rates at the three ridges. Methane gas ascending from deep layers, facilitated by thrusts and faults, was by far the dominant term in the methane budget at all sites. Differences in the proximity of the sampling sites to the faults and anticlines mainly accounted for the variability in gas fluxes and depth-integrated AOM rates. By comparison, methane produced in situ by POC degradation within the modeled sediment column was unimportant. This study demonstrates that the geochemical trends in the continental margins offshore SW Taiwan are closely related to the different geological settings.

We examined spatial patterns of sulfate utility and δ 34S signatures of sulfur species in sediments of a northern Taiwan subtropical estuary in December 2007. Results distinguished a sulfide-concentrated and freshwater-dominated site (called HR) in the upper estuary from two sulfate-concentrated and brackish-water-dominated sites (GR and GM) in the lower estuary. At the HR site, sulfide plays a crucial role in sulfur cycling. The δ 34S signature of sulfur species suggests two source pools: one with depleted 34S as seen in pyrite-S (−8.9‰), elemental sulfur (elemental-S, −8.6 ‰), and organic sulfur (organic-S, −7.5‰), and the other with enriched 34S as seen in acid-volatile sulfur (AVS, 6.9 ‰). These signatures greatly differed from those predicted in an environment in which sulfate (+21‰) is extremely limited, suggesting the relative importance of this isotopically light source. The two sites in the lower estuary were further differentiated: a mangrove-vegetated site (GM) had high elemental-S and pyrite-S concentrations, while a non-vegetated site (GR) had higher AVS and organic-S concentrations. These discrepancies may reflect the importance of mangrove vegetation in mediating sulfur speciation in estuarine sediments. At the GR and GM sites, the δ 34S signature became enriched with increasing depth because of sulfate limitation. δ 34S values of sulfur species in the deeper layer of the non-vegetated site varied with 34S enrichment, with remarkable enhancement to a value of 17.8‰ in AVS at a depth of 50 cm. Signatures of organic-S (9.8 ‰) and pyrite-S (−1.1 ‰) were also enriched. Such small fractionation, particularly in AVS, is likely to be associated with a sulfate deficiency in this lower estuarine area.

A dense seismic reflection survey with up to 250-m line-spacing has been conducted in a 15 × 15 km wide area offshore southwestern Taiwan where Bottom Simulating Reflector is highly concentrated and geochemical signals for the presence of gas hydrate are strong. A complex interplay between north–south trending thrust faults and northwest–southeast oblique ramps exists in this region, leading to the formation of 3 plunging anticlines arranged in a relay pattern. Landward in the slope basin, a north–south trending diapiric fold, accompanied by bright reflections and numerous diffractions on the seismic profiles, extends across the entire survey area. This fold is bounded to the west by a minor east-verging back-thrust and assumes a symmetric shape, except at the northern and southern edges of this area, where it actively overrides the anticlines along a west-verging thrust, forming a duplex structure. A clear BSR is observed along 67% of the acquired profiles. The BSR is almost continuous in the slope basin but poorly imaged near the crest of the anticlines. Local geothermal gradient values estimated from BSR sub-bottom depths are low along the western limb and crest of the anticlines ranging from 40 to 50 °C/km, increase toward 50–60 °C/km in the slope basin and 55–65 °C/km along the diapiric fold, and reach maximum values of 70 °C/km at the southern tip of the Good Weather Ridge. Furthermore, the local dips of BSR and sedimentary strata that crosscut the BSR at intersections of any 2 seismic profiles have been computed. The stratigraphic dips indicated a dominant east–west shortening in the study area, but strata near the crest of the plunging anticlines generally strike to southwest almost perpendicular to the direction of plate convergence. The intensity of the estimated bedding-guided fluid and gas flux into the hydrate stability zone is weaker than 2 in the slope basin and the south-central half of the diapiric fold, increases to 7 in the northern half of the diapiric fold and plunging anticlines, and reaches a maximum of 16 at the western frontal thrust system. Rapid sedimentation, active tectonics and fluid migration paths with significant dissolved gas content impact on the mechanism for BSR formation and gas hydrate accumulation. As we begin to integrate the results from these studies, we are able to outline the regional variations, and discuss the importance of structural controls in the mechanisms leading to the gas hydrate emplacements.

The accretionary wedge of offshore southwestern Taiwan contains abundant deposits of gas hydrate beneath the sea floor. High concentrations of methane in pore waters are observed at several locations with little data concerning historical methane venting available. To understand temporal variation of methane venting in sediments over geologic time, a 23-m-long Calypso piston core (MD05-2911) was collected on the flank of the Yung-An Ridge. Pore water sulfate, dissolved sulfide, dissolved iron, methane, sedimentary pyrite, acid volatile sulfide, reactive iron, organic carbon and nitrogen as well as carbonate δ 13 C were analyzed. Three zones with markedly different pyrite concentration were found at the study site. Unit I sediments (>20 mbsf) were characterized with a high amount of pyrite (251–380 μmol/g) and a δ 13 C-depleted carbonate, Unit II sediments (15–20 mbsf) with a low pyrite (15–43 μmol/g) and a high content of iron oxide mineral and Unit III sediments ( The oscillation records of pyrite concentrations are controlled by temporal variations of methane flux. With an abundant supply of methane to Unit I and III, anaerobic methane oxidation and associated sulfate reduction favor diagenetic conditions conducive for significant pyrite formation. No AOM signal was found in Unit II, characterized by typical organically-limited normal marine sediments with little pyrite formation. The AOM induced pyrite formation near the SMI generates a marked pyrite signature, rendering such formation of pyrite as a useful proxy in identifying methane flux oscillation in a methane flux fluctuate environment.

Supplies of conventional natural gas and oil are declining fast worldwide, and therefore new, unconventional forms of energy resources are needed to meet the ever-increasing demand. Amongst the many different unconventional natural resources are gas hydrates, a solid, ice-like crystalline compound of methane and water formed under specific low temperature and high pressure conditions. Gas hydrates are believed to exist in large quantities worldwide in oceanic regions of continental margins, as well as associated with permafrost regions in the Arctic. Some studies to estimate the global abundance of gas hydrate suggest that the total volume of natural gas locked up in form of gas hydrates may exceed all known conventional natural gas reserves, although large uncertainties exist in these assessments. Gas hydrates have been intensively studied in the last two decades also due to connections between climate forcing (natural and/or anthropogenic) and the potential large volumes of methane trapped in gas hydrate accumulations. The presence of gas hydrate within unconsolidated sediments of the upper few hundred meters below seafloor may also pose a geo-hazard to conventional oil and gas production. Additionally, climate variability and associated changes in pressure-temperature regimes and thus shifts in the gas hydrate stability zone may cause the occurrence of submarine slope failures. Several large-scale national gas hydrate programs exist especially in countries such as Japan, Korea, Taiwan, China, India, and New Zealand, where large demands of energy cannot be met by domestic supplies from natural resources. The past five years have seen several dedicated deep drilling expeditions and other scientific studies conducted throughout Asia and Oceania to understand gas hydrates off India, China, and Korea. This thematic set of publications is dedicated to summarize the most recent findings and results of geo-scientific studies of gas hydrates in the marginal seas and continental margin of the Asia, and Oceania region.

We have conducted detailed hydrochemical surveys off the Pingtung Plain coast, SW Taiwan, using environmental isotope compositions (δ D , δ 18 O, δ 13 C DIC , tritium, and Δ 14 C) as the main tracers to investigate groundwater–seawater interactions in the region. The δ 18 O values of seawater in this area show significant variability with heavy isotope enrichment relatively to groundwater. The δ D and δ 18 O data also confirmed that submarine groundwater discharge (SGD) originated from meteoric water and were mixed with seawater. Due to an overdraft of groundwater, seawater has intruded inwardly through the offshore outcrops for both the unconfined and confined aquifers at a depth of 300 m. However, δ 18 O-depleted layer is found along deep parts of Kaoping Canyon. This result provides evidence for SGD in this region. This phenomenon is also reflected in depleted δ 13 C DIC and lower Δ 14 C values in deep canyon water than in adjacent seawater, and indicating that the discharge zone extends over a considerable distance to the offshore area (∼25 km). Based on these three parameters (δ 18 O, δ 13 C DIC and Δ 14 C), we used two end-member mixing model to estimate that fresh submarine groundwater constitute. The submarine fresh groundwater contributed about 3%, and the estimated submarine fresh groundwater discharge was calculated as 4.5 × 10 9 m 3 per year. This result is comparable with groundwater annual loss in the Pingtung Plain. As documented by the isotopic composition of the collected samples, detailed results show that SGD in the Pingtung coastal zone raises a potential environmental concern and provides implication for the management of groundwater resource in the region.

Although native aluminum (Al°) has been reported to occur in various geological settings for more than 20 locations but its mechanism of formation still remains to be elucidated. We report the occurrence and characterization of Al° particles recovered from the surface sediment (CF4) and a short core sediment (ROV-G, 37 cm length) obtained at cold seeps in the northeastern continental slope (NCS) of the South China Sea (SCS). X-ray diffraction analysis shows that the collected particles are metallic aluminum with the unit cell edge a of 4.059 ± 0.005 A (CF4#2) and 4.029 ± 0.004 A (T26–28#2, ROV-G). The Al° particles occur as spherules, irregular plates and elongated forms with typical lamellar structures. Their chemical compositions are 95.07–99.84% Al (the average values is 98.42%) with very small amounts of Si, Fe, Ti, S, Zn, Mg, Ca, K, Na, Cu, Co and P, and are similar to Al° particles from the East Pacific Rise and the Central Indian Basin but differ markedly to those from other locations. After ruling out several possibilities of Al° sources and mechanism of formation, an alternative cold seep mechanism is proposed for the origin of Al° in the SCS. During the processes of anaerobic oxidation of methane (AOM) and pyrite formation, high H2S and H2 partial pressures result in strong reducing micro-environments, under which Al ( OH ) 4 - is reduced to its metallic state by the microbial-bacterial processes.

A large number of sediment cores collected during 2005–2010 from the Taiwan Strait were analyzed for radionuclides ( 210 Pb, 137 Cs and 7 Be) to elucidate sedimentation dynamics in this all-important gateway linking two largest marginal seas in the western Pacific (namely, the South China Sea and the East China Sea). Apparent sediment accumulation rates derived from 210 Pb and 137 Cs profiles vary from 2 cm/yr, averaging ∼0.4 cm/yr and showing a spatial pattern closely related to hydrodynamics and sediment source-to-sink pathways. Spatial-temporal variation of 7 Be activity in surface sediments off Taiwan’s west coast indicates episodic deposition of flood layers and their mobility from river estuaries toward the north. In conjunction with particle size distribution in surface sediments and the structure of sediment strata revealed by sub-bottom echo images; the radionuclide data can be used to outline three different sediment source-to-sink dispersal systems. Based on sediment loads of surrounding rivers and the distribution of sediment accumulation rates, lateral transport is required to account for the budget and size distribution of sediments in the strait.

We have conducted detailed hydrographic surveys off the Pingtung Plain coast, SW Taiwan, using environmental isotope and trace element compositions (δ 18 O, Δ 87 Sr, and Ba) as the main tracers to investigate submarine groundwater discharge (SGD) in the region. The δ 18 O values of seawater in this area show significant variability with heavy isotope enrichment relatively to groundwater, and two δ 18 O-depleted layers are found at depths of 400-700 m and 1200 m along deep parts of Kaoping Canyon. Assuming two end-member mixing model, we estimate that fresh submarine groundwater may constitute a few percent of the total SGD in the canyon. This is reflected in lower salinity, higher Δ 87 Sr values and Ba concentrations in deep canyon water than in adjacent seawater. Pore water samples collected from the canyon floor have light δ 18 O values and low chloride concentrations, consistent with the overlying δ 18 O-depleted water. Elsewhere, seabed pore waters have normal seawater compositions. The results of this study indicate that the deep SGD in the Pingtung Plain coastal zone is mainly fed by recirculating seawater with some admixture of fresh groundwater in canyon area (down to ~ 1200 m). Areas with notable SGD are located a long distance from the shoreline (~ 25 km), and the ‘deep’ SGD may be widespread off southern Taiwan. This discharge must be considered as a significant source of trace elements and other chemical constituents to the coastal ocean.

Widely distributed bottom simulating reflectors (BSRs) imply the potential existence of gas hydrates offshore southwestern Taiwan. To compare the distribution of methane concentrations along passive and active margins in the region, bottom waters and cored sediments were collected during four cruises from 2005 to 2006. The results reveal that sites with high methane concentrations are predominantly distributed in the active margin and site GS5 is the only site that contains very high methane concentrations in the passive margin of studied area. Anomalously high methane fluxes still can be obtained from the calculation of diffusive methane flux, although there might be some gas leakage during or after sampling procedures. The profiles of methane and sulfate concentration reveal very shallow depths of the sulfate–methane interface (SMI) at some sites. There is evidence that sulfate reduction is mainly driven by the process of anaerobic methane oxidation. Thus, sulfate fluxes can be used as a proxy for methane fluxes through the use of diffusion equations; and the results show that the fluxes are very high in offshore southwestern Taiwan. The depths of the SMI are different at sites GH6 and C; however, both methane profiles reveal parallel methane gradients below the SMI. This might be because of methane migration to surface sediments from the same reservoir with the same diffusion rates. Although BSRs are widely distributed both in the active margin and in the passive margin, most sites with high methane concentrations have been found in the active margin. Therefore, the specific tectonic settings in offshore SW Taiwan might strongly control the stability of gas hydrates, and thus affect the methane concentrations and fluxes of the sediments and sea waters. Furthermore, the carbon isotopic composition of methane shows that a biogenic gas source is dominant at shallower depth; however, some thermogenic gases might be introduced through the fracture/fault zones from deeper source in the active region of studied area.

Article history: 210 Pb, 137 Cs and 7 Be) to elucidate sedimentation rates and processes, and for the calculation of a sediment budget. The study area is located at an active collision marginwith a narrow shelf and a submarine canyon extending essentially into the river's mouth. The results indicate fairly constant hemipelagic sedimentation in much of the open margin and for most of the time except in the inner shelf and along the axis of the canyon where sediment transport is more dynamic and is controlled by tidal current and wave activities constantly, and by fluvial floods or gravity-driven flows episodically. Sedimentation rates in the study area derived from 210 Pb

A high-resolution seismic reflection survey was conducted over submarine mounds on continental slope ridges in passive margin offshore southwestern Taiwan during the NT07-05 cruise in March 2007. The continental slope ridges were formed by an erosion system in which submarine canyons incise the continental slope and control ridge formations. The seismic survey revealed the geologic structure of continental slope ridges where there are target locations, site F and site G, of submarine mounds. Site F corresponds to the southern peak of the Formosa Ridge, where sedimentary strata are generally flat lying. On the Formosa Ridge, methane hydrate BSR (bottom simulating reflector) was widely observed, but it is chopped off just below site F. There is also a vertical narrow reflection blanking between the cut of the BSR and site F on the seafloor. SeaBat multibeam echo sounder detected a gas plume rising from the mound of site F. ROV Hyper-Dolphin discovered very large and dense chemosynthetic communities at the top of the mound. Site G is also a small submarine mound in another continental slope ridge. The mound is thought to be a mud volcano. There is no clear BSR, but there are high-amplitude beds below the mound. The high-amplitude beds peak just below site G, and there is also a vertical, high amplitude zone between the peak and the submarine mound of site G. Thus, the geologic structures in sites F and G have morphologically similar characteristics. It can be considered that the BSR in the Formosa Ridge should act as a good cap for trapping gassy fluid, and the narrow blanking just below site F is a fluid conduit where strata have been disturbed. On the other hand, in site G, the high-amplitude beds acts in the same way as BSR in site F, and the vertical high-amplitude zone just below site G is considered also to be the mark of a conduit from the peak of the high-amplitude beds to the submarine mound, where remnant gas components in the conduit may have emphasized partial acoustic impedance, although the Hyper-Dolphin could not find any present activity on the mound. We found the cold seep site at the top of site F in the Formosa Ridge. By integrating bathymetric characters and seismic reflection data, we can have a better understanding of the fluid circulation system in the cold seep site. In site F, the BSR that forms a trap as a gas reservoir is shallower than the canyon floors on either side of the ridge. We suggest that this reservoir configuration may enable a thermal pump system in the ridge and the surrounding cold seawater to enter the fluid system, and form a notable fluid circulation and unusual chemosynthetic communities.

article i nfo High-resolution CHIRP sonar profiles across the Taiwan Strait reveal a large silt-sand-dominated deltaic clinoform, up to 50-m thick, overlying the postglacial transgressive sea floor across the southeastern, central, and northern strait. Delta-like configuration and internal depositional sequences indicate a northwestward progradation from western Taiwan, primarily from the Choshui (Zhuoshui) River. Grain-size and mineral data confirm the sediment's Taiwanese derivation. The CHIRP profiles, together with existing radiocarbon and geomagnetic dates, suggest that the clinoform has formed over the past 10 kyr. The estimated volume of 375 km 3 of sediment (mainly sand and silt) suggests a mean annual accumulation of 60×10 6 t/yr. Presumably much of fine mud delivered by Taiwanese rivers has been washed away by the local currents, and escaped either northeastward into the Southern Okinawa Trough or southward into the South China Sea. Numerous shallow borings onshore over the central western Taiwan coastal plain reveal an additional 350 km 3

A mesophilic, hydrogenotrophic methanogen, strain CYW4T, was isolated from deep-sea sediment obtained by the Ocean Researcher I cruiser, ORI-961, in 2011. The sediment was from the deformation front area offshore of south-western Taiwan. Here, seismic reflections indicated that methane hydrates were abundant. The methanogenic substrates utilized by strain CYW4Twere formate and H2/CO2, but not acetate, secondary alcohols, methylamines, methanol and ethanol. Cells of strain CYW4Twere non-motile, irregular cocci and 0.6–1.5 µm in diameter. The S-layer protein had anMrof 112 000. The optimum growth conditions were at 37 °C, pH 8.1 and 0.08 M NaCl. Growth of the strain was stimulated by acetate. The G+C content of the chromosomal DNA of strain CYW4Twas 61 mol%. Phylogenetic analysis revealed that strain CYW4Twas most closely related toMethanoculleus marisnigriJR1T(96.82 % 16S rRNA gene sequence similarity). Based on the morphological, phenotypic and phylogenetic characteristics presented here, it is evident that strain CYW4Trepresents a novel species of the genusMethanoculleus, and the nameMethanoculleus taiwanensissp. nov. is proposed. The type strain is CYW4T( = BCRC AR10043T = NBRC 110782T). The optical density of cultures of strain CYW4Tdropped abruptly upon entering the stationary growth phase. During this time numerous particles of approximately 50 nm in diameter were observed on and around the cells. This suggests that strain CYW4Tharbours a lytic virus that is induced in the stationary phase, which is of interest because only a few lytic viruses have been reported in methanogens.

Particulate aerosol was sequentially extracted by citrate/dithionite/bicarbonate and acetic acid/sodium acetate buffers so as to isolate phosphorus associated with oxides/hydroxides (Fe-P) and Acet-P, respectively. Total phosphorus (TP) and total inorganic phosphorus (TIP) contents were analyzed separately and the difference between them used to calculate the organic phosphorus (OP) content. The difference between TIP and the sum of Fe-P and Acet-P was assumed to be the detrital apatite (Det-P). The results of this study indicate that phosphorus species show a clear monthly variability that is related to the source strengths of the crustal weathering and biological blooming in winter and spring, respectively. There are highly significant covariations between the TP, TIP and Det-P, which suggests that these derive from similar sources and share transport mechanisms. The percentage concentrations of OP show that phosphorus tends to be associated with organic particles in warm periods when biological activity is greatest.