Deep-sea Sediments Research Articles

Cu Exists Predominantly as Kinetically Inert Complexes Throughout the Interior of the Equatorial and North Pacific Ocean

AbstractThe chemistry of copper (Cu) in seawater is well known to be dominated by complexation with organic ligands. The prevailing paradigm is that Cu forms strong but labile complexes. Recently, a novel procedure revealed that only a small fraction of dissolved Cu exists as labile complexes. The majority is present as a fraction that is relatively inert on timescales of weeks or more and probably does not participate in coordination exchange reactions, including biologically mediated processes. Samples collected from the 2018 GEOTRACES GP15 cruise show that throughout the interior of the Pacific Ocean, this inert fraction comprises about 90% of the dissolved Cu. Labile Cu accumulates in surface waters, probably arising from photochemical decomposition of the inert fraction. There is also a modest accumulation of labile Cu near deep sea sediments and along the Alaskan shelf and slope. The results have important implications for Cu transport and biological availability. Inert Cu may influence Cu transport throughout the water column and contribute to the linear increase in Cu with depth, a distribution which is hard to explain for a biologically active trace metal. The origins of inert Cu are unknown. It may be produced slowly within the water column on the timescale of meridional overturning circulation. In the Columbia River, between 92% and 98% of the dissolved Cu is in the inert fraction, suggesting a possible terrestrial source of inert Cu to the ocean.

Niche differentiation of microbial community shapes vertical distribution of recalcitrant dissolved organic matter in deep-sea sediments

Sedimentary organic matter provides carbon substrates and energy sources for microorganisms, which drive benthic biogeochemical processes and in turn modify the quantity and quality of dissolved organic matter (DOM). However, the molecular composition and distribution of DOM and its interactions with microbes in deep-sea sediments remain poorly understood. Here, molecular composition of DOM and its relationship with microbes were analyzed in samples collected from two sediment cores (∼40 cm below the sea floor), at depths of 1157 and 2253 m from the South China Sea. Results show that niche differentiation was observed on a fine scale in different sediment layers, with Proteobacteria and Nitrososphaeria dominating the shallow sediments (0–6 cm) and Chloroflexi and Bathyarchaeia prevailing in deeper sediments (6–40 cm), indicating correspondence of microbial community composition with both geographical isolation and the availability of organic matter. An intimate link between the DOM composition and microbial community further indicates that, microbial mineralization of fresh organic matter in the shallow layer potentially resulted in the accumulation of recalcitrant DOM (RDOM), while relatively low abundance of RDOM was linked to anaerobic microbial utilization in deeper sediment layers. In addition, higher RDOM abundance in the overlying water, as compared to that in the surface sediment, suggests that sediment might be a source of deep-sea RDOM. These results emphasize the close relation between the distribution of sediment DOM and different microbial community, laying a foundation for understanding the complex dynamics of RDOM in deep-sea sediment and water column.

Expansion of Armatimonadota through marine sediment sequencing describes two classes with unique ecological roles

Marine sediments comprise one of the largest environments on the planet, and their microbial inhabitants are significant players in global carbon and nutrient cycles. Recent studies using metagenomic techniques have shown the complexity of these communities and identified novel microorganisms from the ocean floor. Here, we obtained 77 metagenome-assembled genomes (MAGs) from the bacterial phylum Armatimonadota in the Guaymas Basin, Gulf of California, and the Bohai Sea, China. These MAGs comprise two previously undescribed classes within Armatimonadota, which we propose naming Hebobacteria and Zipacnadia. They are globally distributed in hypoxic and anoxic environments and are dominant members of deep-sea sediments (up to 1.95% of metagenomic raw reads). The classes described here also have unique metabolic capabilities, possessing pathways to reduce carbon dioxide to acetate via the Wood-Ljungdahl pathway (WLP) and generating energy through the oxidative branch of glycolysis using carbon dioxide as an electron sink, maintaining the redox balance using the WLP. Hebobacteria may also be autotrophic, not previously identified in Armatimonadota. Furthermore, these Armatimonadota may play a role in sulfur and nitrogen cycling, using the intermediate compounds hydroxylamine and sulfite. Description of these MAGs enhances our understanding of diversity and metabolic potential within anoxic habitats worldwide.

Occurrence and screening- flotation separation for the beneficiation of rare earth elements and yttrium (REY) in core sediments from the Pacific Ocean

Rare earth elements (REE) and yttrium (termed as REY), as a significant strategic resource, are recently found to be extremely enriched in deep-sea sediments, which is expected to be an important REY resource in the future. However, the efficient development and utilization of deep-sea REY-rich sediments are greatly limited by the current common beneficiation and metallurgy method. In this study, detailed grain size analysis, mineral identification and geochemical measurement aiming at deep-sea sediments collected from a station in the Central Pacific Basin were employed to determine the occurrence of deep-sea REY-rich sediments. Based on that, the Screening-flotation separation was adopted to achieve efficient enrichment of REY in the sediments. The ΣREY contents in the samples can reach 790 ppm, and sieve analysis reveal that bioapatite (fish teeth and bones) and Fe-Si-Mn oxide (oxyhydr) on the micro-nodule surface are the major REY carriers. About 87.27% REY was scavenged by bioapatite fossils. The REE patterns show distinct negative Ce/Ce* and slightly positive Eu/Eu* anomalies, similar to the Western and central North Pacific seawater, indicating a promising source of REY in the samples may be pore water in sediments, taking into account other studies as well. The grain size analysis suggests that REY enrichment can be achieved by removing the fine-grained particles (<15 μm). Screening-flotation separation, as a newly developed approach for the beneficiation, uses the pre-screening method to pre-detach the clay-size fraction (<15 μm), and combines flotation and magnetic separation, which further upgrades REY concentrate to achieve about 9 times enhancement of REY recovery from marine sediments. Although further research is needed, the study we determined can provide reference for industrial exploitation of rare earth resources in deep-sea REY-rich sediments.

Links between Ikaite Morphology, Recrystallised Ikaite Petrography and Glendonite Pseudomorphs Determined from Polar and Deep-Sea Ikaite

Petrography of recrystallised ikaite from Ocean Drilling Program material has been presented previously from Nankai Trough and Congo (ex-Zaire) deep-sea fan. This paper expands on the Nankai Trough ikaite observations, drawing on evidence from Laptev Sea, South Georgia, Okhotsk Sea, and coastal lagoon Point Barrow. However, even though many ikaite and glendonite sites occur at high latitudes, it cannot be that ikaite forms exclusively in polar environments, as demonstrated by the occurrences in the low latitude low temperature deep sea sediments offshore Gulf of Guinea (Angola Congo) and mid-latitude deep-sea trenches offshore Japan. Recrystallised ikaite occurs as mm large, zoned calcite crystals in all samples, along with secondary phases of calcite. Our data set is unique in that the origin, storage, and recrystallisation process of natural formed ikaite is recorded in detail and confirms that glendonite petrographic characteristics are a consequence of the structure and chemistry of recrystallising ikaite and not the physical or geochemical environment. The transformation of man-made ikaite to calcite as recorded in laboratory studies, is a process very similar to the one we have observed for natural ikaite. Most significant is that there is variation in the order of the calcite types within a single sample, leading to the conclusion that the variation is a consequence of impurities and geochemical variability in the ikaite, not the external environment. Morphological observations reveal similarities in ikaite and glendonite, this and the similarity in internal textures in glendonite and recrystallised ikaite confirms that glendonite may be used as an indicator of past presence of ikaite.

Discovery and verification of traction weakening effect between multi track shoe of deep-sea miner and sediment

The commercial exploitation of the deep-sea massive deep-sea polymetallic nodules depends on the excellent tractive performance of the deep-sea tracked miner. The walking safety and trafficability of the deep-sea tracked miner are greatly influenced by the traction of the crawler with multi track shoes. The total tractions generated from the two cases of failure surface under the uniformed pressure are deduced and analyzed based on the principle of virtual power. By substituting specified parameters, the traction weakening effect of multi track shoes is discovered, and then corresponding expression is put forward and verified by comparing the tested and theoretical traction relationships based on the traction test of multi track shoes. The research results show that the height and the distance should be considered into the design in a comprehensive way because of the existence of the weakening effect. The mechanism revealing of the source of the multi track shoe tractions could help to achieve the appropriate size of the track shoe and more traction according to the different track shoe distance.

The structure, characterization and immunomodulatory potential of exopolysaccharide produced by Planococcus rifietoensis AP-5 from deep-sea sediments of the Northwest Pacific

Polysaccharides derived from microorganisms exhibit diverse structures and bioactivities, making them promising candidates for the treatment of various diseases. However, marine-derived polysaccharides and their activities are relatively little known. In this work, fifteen marine strains were isolated from surface sediments in the Northwest Pacific Ocean for screening of EPS production. Planococcus rifietoensis AP-5 produced a maximum yield of EPS at 4.80 g/L. The purified EPS (referred to as PPS) had a molecular weight of 51,062 Da and contained amino, hydroxyl, and carbonyl groups as its major functional groups. PPS primarily consisted of →3)-α-D-Galp-(1 → 4)-α-D-Manp-(1 → 2)-α-D-Manp-(1 → 4)-α-D-Manp-(1 → 4,6)-α-D-Glcp-(1 → 6)-β-D-Galp-(1→, with a branch consisting of T-β-D-Glcp-(1→. Additionally, surface morphology of PPS was hollow, porous, and sphere-like stack. PPS primarily contained C, N, and O elements, with a surface area of 33.76 m2/g, a pore volume of 0.13 cc/g, and a pore diameter of 1.69 nm, respectively. Based on the TG curve, the degradation temperature of PPS was measured to be 247 °C. Furthermore, PPS demonstrated immunomodulatory activity through dose-dependently upregulating the expression level of cytokines. It significantly enhanced the cytokine secretion at a concentration of 5 μg/mL. To sum up, this study offers valuable insights for screening marine polysaccharide-based immunomodulators.

A dataset of micro biodiversity in benthic sediment at a global scale

Microorganisms, occupying the largest biomass in deep sea, play essential roles in deep-sea ecosystem. It is believed that the microbes in deep-sea sediments are more representative of deep-sea microbial communities, the microbial composition of which is seldom affected by ocean currents. However, the community of benthic microbes on a global scale has not been adequately explored. Herein, we build a comprehensive global dataset determined by 16S rRNA gene sequencing to characterize the biodiversity of microorganisms in benthic sediment. The dataset comprised 212 records from 106 sites, included sequencing of bacteria and archaea for each site and yielded 4,766,502 and 1,562,989 reads, respectively. Through annotation, a total of 110,073 and 15,795 OTUs of bacteria and archaea were obtained, and 61 bacterial phyla and 15 archaeal phyla were identified, of which the dominant phyla were Proteobacteria and Thaumarchaeota in deep-sea sediment. Therefore, our findings provided a biodiversity data of microbial communities in deep-sea sediment at global-scale and laid a foundation to further reveal the structures of microorganism communities in deep sea.

Identification of the heterotrophic nanoflagellate Bilabrum latius in the southern Adriatic (Mediterranean Sea)

Heterotrophic flagellates (HF) represent an important protist group in marine ecosystem functioning. Characterised by high taxonomic diversity, identification and classification of HF is often difficult using classical methods of light microscopy (LM). Complementing LM with molecular methods, such as barcoding, enables reliable taxonomic identification of even small size nanoflagellates that share similar or unnoticeable morphological features. The order Bicosoecida is a group of heterotrophic nanoflagellates that are important part of protist plankton and benthic communities of the world oceans. Recently, on the basis of high-resolution light microscopy and barcoding, a new bicosoecid genus, Bilabrum, was described with B. latius sp. as a type species. Our study reports on identification of B. latius from co-culture with the diatom species Chaetoceros affinis isolated from fresh plankton samples collected in the southern Adriatic. This detection of the Adriatic B.latius represents first record of this species outside itś up to now known and described habitat (deep-sea sediment of the South - East Atlantic Ocean) and in diatom co-culture.

When microplastics are not plastic: Chemical characterization of environmental microfibers using stimulated Raman microspectroscopy

The abundance of anthropogenic debris dispersed in the environment is exponentially growing, raising concerns about marine life and human exposure to microplastics. Microfibers are the most abundant microplastic type in the environment. However, recent research suggests that most microfibers dispersed in the environment are not made of synthetic polymers. In this work, we systematically tested this assumption by determining the man-made or natural origin of microfibers found in different environments, including surface waters, sediments at depths >5000 m and highly sensitive habitats like mangroves and seagrass, and treated water using stimulated Raman scattering (SRS) microscopy. Our findings show that ¾th of analyzed microfibers are of natural origin. One plastic fiber is estimated per every 50 L in surface seawater, every 5 L in desalinated drinking water, every 3 g in deep sea sediments and every 27 g in coastal sediments. Synthetic fibers were significantly larger in surface seawaters compared to organic fibers due to higher resistance to solar radiation. These results emphasize the necessity of using spectroscopical methods to assess the origin of environmental microfibers to accurately estimate the abundance of synthetic materials in the environment.

Mid-Pleistocene links between Asian dust, Tibetan glaciers, and Pacific iron fertilization

Increasing Asian dust fluxes, associated with late Cenozoic cooling and intensified glaciations, are conventionally thought to drive iron fertilization of phytoplankton productivity in the North Pacific, contributing to ocean carbon storage and drawdown of atmospheric CO2. During the early Pleistocene glaciations, however, productivity remained low despite higher Asian dust fluxes, only displaying glacial stage increases after the mid-Pleistocene climate transition (~800ka B.P.). We solve this paradox by analyzing an Asian dust sequence, spanning the last 3.6 My, from the Tarim Basin, identifying a major switch in the iron composition of the dust at ~800ka, associated with expansion of Tibetan glaciers and enhanced production of freshly ground rock minerals. This compositional shift in the Asian dust was recorded synchronously in the downwind, deep sea sediments of the central North Pacific. The switch from desert dust, containing stable, highly oxidized iron, to glacial dust, richer in reactive reduced iron, coincided with increased populations of silica-producing phytoplankton in the equatorial North Pacific and increased primary productivity in more northerly locations, such as the South China Sea. We calculate that potentially bioavailable Fe2+ flux to the North Pacific was more than doubled after the switch to glacially- sourced dust. These findings indicate a positive feedback between Tibetan glaciations, glaciogenic production of dust with enhanced iron bioavailability, and changes in North Pacific iron fertilization. Notably, this strengthened link between climate and eolian dust coincided with the mid-Pleistocene transition to increased storage of C in the glacial North Pacific and more intense northern hemisphere glaciations.

Complete genome sequence of Pseudoalteromonas sp. PS1M3, a psychrotrophic bacterium isolated from deep-sea sediment off the Boso Peninsula, Japan Trench.

Herein, we report the complete genome sequence of Pseudoalteromonas sp. PS1M3 (= NCBI 87791), which is a psychrotrophic bacterium that inhabits in seabed off the Boso Peninsula, Japan Trench. Analysis of the genomic sequence revealed that PS1M3 possesses 2 circular chromosomal DNAs and 2 circular plasmid DNAs. The genome of PS1M3 had a total size of 4,351,630bp, an average GC content of 39.9%, and contained a total of 3811 predicted protein coding sequences, 28 rRNAs, and 100 tRNAs. The Kyoto Encyclopedia of Genes and Genomes (KEGG) was utilized to annotate the genes and KofamKOALA within KEGG assigned a gene cluster involved in glycogen biosynthesis and metabolic pathways with regard to heavy metal resistance (copper; cop and mercury; mer), indicating that PS1M3 can potentially use a stored glycogen as an energy source under oligotrophic environment and cope with multi-heavy metal contamination. To assess available genome relatedness indices, whole-genome average nucleotide identity analysis was examined using the complete genome sequences of Pseudoalteromonas spp., showing that 67.29-97.40% sequence similarity with PS1M3. This study may be useful in understanding the roles of a psychrotrophic Pseudoalteromonas in cold deep-sea sediment adaptation mechanisms.

Complete genome sequence of Bacillus cereus 2-6A, a marine exopolysaccharide-producing bacterium isolated from deep-sea hydrothermal sediment of the Pacific Ocean

Bacillus cereus 2-6A, was isolated from the sediments in the hydrothermal area of the Pacific Ocean with a water depth of 2628m. In this study, we report the whole genome sequence of strain 2-6A and analyze that to understand its metabolic capacities and biosynthesis potential of natural products. The genome of strain 2-6A consists of a circular chromosome of 5,191,018bp with a GC content of 35.3mol% and two plasmids of 234,719bp and 411,441bp, respectively. Genomic data mining reveals that strain 2-6A has several gene clusters involved in exopolysaccharides (EPSs) and polyhydroxyalkanoates (PHAs) production and complex polysaccharides degradation. It also possesses a variety of genes for allowing strain 2-6A to cope with osmotic stress, oxidative stress, heat shock, cold shock and heavy metal stress, which could play a vital role in the adaptability of the strain to hydrothermal environments. Gene clusters for secondary metabolite production, such as lasso peptide and siderophore, are also predicted. Therefore, genome sequencing and data mining provide insights into the molecular mechanisms of Bacillus in adapting to hydrothermal deep ocean environments and can facilitate further experimental exploration.

Ichnological characterization of deep-sea muddy deposits: Macrobenthic communities revealing palaeoenvironmental conditions within turbidite systems

Traditionally, studies on turbiditic systems were mostly focused on sedimentological features, but later some other features as bioturbation have been included. Ichnological analysis is probed as a powerful tool for deep-sea sediments studies, revealing accurate information about palaeoenvironmental conditions during deposition. For the first time, a detailed ichnological and sedimentological integrative analysis focused on Miocene muddy turbiditic deposits from the westernmost Mediterranean at the Tabernas Basin (SE Spain) is here presented. The representative Rambla de Tabernas section has been selected to identify dominant palaeoenvironmental conditions before the deposition of the well-known Gordo megabed. The ichnological content reveals a trace fossil association comprising 26 ichnospecies, belonging to 14 ichnogenera ascribed to the Nereites ichnofacies in an overall stable and well oxygenated environment dominated by low-energy conditions. The distribution, and abundance of trace fossils, integrated with sedimentological information, allow to characterize variation in depositional conditions within the turbiditic system. Before deposition of the Gordo megabed, the turbiditic system in the lower part of the studied area had generalized low energy conditions. These conditions are probably linked to distal depositional areas, characterized by the record of the Paleodictyon ichnosubfacies in interbedded sandstones-mudstones, with a common occurrence of Tab/Tabc Bouma intervals. In contrast, higher energy conditions and deposition prevailed in proximal settings (e.g., channels and proximal lobes) in the upper part. They arecharacterized by the Ophiomorpha rudis ichnosubfacies in interbedded sandstones-mudstones with dominant Tab Bouma intervals. Additionally, the low ichnodiversity in comparison with similar deposits from other worldwide areas, is probably caused by the influence of local environmental conditions in the studied basin.

The patterns of marine microbial communities in composts with high lignocellulose content

More eco-efficient and high-performance disposal or conversion approaches for practical biomass applications have become a sought-after craze. In this study, microbial communities derived from deep-sea sediments were used in organic compost consisting of more than 50% lignocellulose. The results showed that deep-sea microorganisms did possess the ability to dissolve lignocellulose, and their patterns in composting exhibited specificity. The temperature of the system quickly exceeded 40 °C from the 5th day and the peak was over 60 °C, and then went through the whole period within 17 days. The pH of the system increased from 5 to 9, along with a reduction in moisture content to around 19%. Bacterial diversity increased with composting, while fungal diversity showed a downward trend. Significant temperature-driven variability in bacterial communities was observed, while differences in fungal communities at high-temperature stages and later stages were not pronounced. The system ended up with a 47% reduction in cellulose and an almost 30% reduction in hemicellulose. This study demonstrated the different digestion pathways of bacteria and fungi in response to high lignocellulose environments and the great potential of microbial communities from marine as important candidates for lignocellulose treatment.

Habitat heterogeneity effects on microbial communities of the Gulf of Maine

Many biological and physical variables influence microbes at the sediment-water interface, whose response to those variables affects the overall fate and residence time of organic matter (OM) in the marine environment. In addition to the many ecological roles microbes play in deep-sea sediments, further studies are needed to address microbial community diversity and its influence on seafloor organic matter remineralization rates. We explored microbial diversity, distribution, and associated organic matter remineralization among contrasting habitats and following 24-h experimental phytodetrital enrichment of sediments from Canyon, Inter-Canyon, and Channel habitats of the Gulf of Maine, Northwest Atlantic. Based on multivariate analyses of community composition we found that habitat heterogeneity influenced microbial community composition but not microbial diversity. Similarly, the phytodetrital addition did not translate to significant differences in microbial diversity but altered nitrate flux in Inter-canyon sediments and phosphate flux in Channel sediments. Bacteria were dominant over Archaea and, of the environmental variables we measured, quantity and quality of organic matter best explained overall microbial community variation. Proteobacteria, Bacteroidae, Acidobacteriota, Planctomycetota, and NB1-J Deltaproteobacteria dominated all habitats, but variation in the microbial community at our study sites explained only 7% of nutrient fluxes. Our exploratory study did not suggest a strong contribution of microbial community composition to OM remineralization variation both among contrasting habitats and in response to phytodetrital addition, and thus to this aspect of deep-sea ecosystem functioning, at least over short-term incubations.

Preliminary Study of Accretion Complexes of Mangilu Area, Pangkep Ragency South Sulawesi

The exposure of Mesozoic rocks in the Mangilu area, both as a result of tectonic deformation in the form of mélange, low-high degree metamorphism and deep-sea sediments (flysch, radiolarian cherts, and sediment flow in the form of olistostrome), which formed in the subduction zone indicates complex accretionary rocks. The purpose of this study is to identify and study the accretionary complex trace rocks of the Mesozoic era. The method used in this study was field observation, including collection of geological data, tectonic deformation, rock groups and laboratory analysis (petrography). In general, the accretion complex is divided into 2 categories, namely a). oceanic volcanic groups and sediments of the oceanic crust; b). terigenous sediments from continents with sialic beds. The oceanic volcanic group consists of gabbro, diabase, dolerite, pillow and hyaloclastic lava, and oceanic sediments consist of radiolarian chert and mali limestone. The terigen sedimentary group consists of flysch type sandstones and olistostrome flow sediments with components in the form of granite, granodiorite, dacite and diabase. Other components found in autoclastic breccia rocks in the Mangilu area consist of metaperidotite, serpentinite, quartzite and metachert. Based on the Oceanic Plate Stratigraphy (OPS) arrangement, the autoclastic breccia rocks in the Mangilu area consist of bottom up, namely ultramafic/serpentinite, gabbro, diabase, pillow basaltic lava, hyaloclastic, radiolarian chert, mali limestone and flysch sediments. The mixing of rocks originating from oceanic plates with continental plates in autoclastic breccias indicates that the Mesozoic accretion complex in the Mangilu area has experienced strong deformation in the form of thurst in the Tertiary era.

Contrasting benthic ecological functions in deep-sea canyon and non-canyon habitats: Macrofaunal diversity and nutrient cycling

Understanding ecosystem functioning and stability of continental slope environments requires assessing the effects of habitat heterogeneity (canyon and non-canyon habitats) on benthic macrofaunal communities and ecosystem functioning. We evaluated the importance of habitat heterogeneity and phytodetrital enrichment in canyon, channel, and inter-canyon habitats of the Gulf of Maine, Northwest Atlantic. Using an ROV, we collected sediment cores at five seafloor sites in the Gulf of Maine (663–969 m depth). Over ∼24 h, we incubated ∼6 cores per site, three of which were enriched with the diatom Chaetoceros muelleri. For all core treatments, we measured macrofaunal composition, functional diversity indices (functional richness, evenness, and divergence), and benthic nutrient fluxes (ammonium, nitrate, phosphate, and silicate), as well as oxygen consumption. We also dedicated two non-incubated cores to quantifying sedimentary and chemical-physical characteristics. We found that benthic communities differed among the three habitats, but these differences and our phytodetrital additions did not translate to significant differences in rates of benthic fluxes among habitats., expect for nitrate and phosphate fluxes. Total organic carbon and chlorophyll-a explained most of the variation in oxygen consumption, which was similar in enriched and control cores. We conclude that large-scale habitat heterogeneity contributes to variation in benthic community composition, but with no consistent effect on nutrient fluxes. These results also suggest that phytodetrital deposition influences oxygen consumption but plays a lesser role in short-term nutrient cycling in deep-sea heterogeneous habitats, perhaps masked by other environmental variables. Moreover, sediments with high functional richness and relatively high functional divergence may sometimes lack the specific trait types that rapidly enhance nutrient regeneration and thus contribute to ecosystem functioning of deep-sea sediments.

Sulfur metabolism in subtropical marine mangrove sediments fundamentally differs from other habitats as revealed by SMDB

Shotgun metagenome sequencing provides the opportunity to recover underexplored rare populations and identify difficult-to-elucidate biochemical pathways. However, information on sulfur genes, including their sequences, is scattered in public databases. Here, we introduce SMDB (https://smdb.gxu.edu.cn/)—a manually curated database of sulfur genes based on an in-depth review of the scientific literature and orthology database. The SMDB contained a total of 175 genes and covered 11 sulfur metabolism processes with 395,737 representative sequences affiliated with 110 phyla and 2340 genera of bacteria/archaea. The SMDB was applied to characterize the sulfur cycle from five habitats and compared the microbial diversity of mangrove sediments with that of other habitats. The structure and composition of microorganism communities and sulfur genes were significantly different among the five habitats. Our results show that microorganism alpha diversity in mangrove sediments was significantly higher than in other habitats. Genes involved in dissimilatory sulfate reduction were abundant in subtropical marine mangroves and deep-sea sediments. The neutral community model results showed that microbial dispersal was higher in the marine mangrove ecosystem than in others habitats. The Flavilitoribacter of sulfur-metabolizing microorganism becomes a reliable biomarker in the five habitats. SMDB will assist researchers to analyze genes of sulfur cycle from the metagenomic efficiently.

Theoretical evaluation of utilizing rock physics inversion for hybrid models of gas-hydrate distribution in deep water sediments of Oman sea

Most of the hydrate assessment methods are developed based on relating the elastic properties to the hydrate saturation via establishment of robust and calibrated rock physics models and among them the most practical one is Effective Medium Theory (EMT) with four models of gas hydrate distributions. Generally, considering only one of these models in hydrate characterization could be an unrealistic assumption and therefore, rock physics inversion may cause erroneous assessments (over- or under-estimation).In this paper, hybrid models of hydrate distributions have been introduced for different combinations of two possible classical models by applying some modifications in the EMT workflow. Then, based on the modified EMT for hybrid models, a statistical rock physics inversion approach has been developed for estimation of gas hydrate saturations along with porosity, simultaneously. The result shows that theoretically it is possible to combine two models of distribution in both rock physics modeling and inversion processes. This developed approach was applied on a 2-D marine pre-stack time migrated (PSTM) seismic line passing through an anticlinal-ridge type structure in deep Oman sea sediment. For comparison, this approach was applied for single hydrate distribution as well. The results recommend to use the hybrid models of cementing and non-cementing distributions in the characterization to simultaneously consider all changes on the elastic properties of the host sediment imposed by hydrate presence. The results showed even in an un-explored area (without well information), this method can provide reliable robust result for porosity (independent of hydrate distribution assumption) and qualitative output for hydrate sweet-spots detection. Finally and after drilling the first exploration well, by having well log data in hydrate zone, along with possibility of validations and parameters calibrations for hybrid models, more reliable quantification could be achieved with this method; as the in-situ data increases the certainty of the determined elastic properties in model-based inversion process and also accuracy of defined mineralogical compositions.