Water characteristics of abyssal and hadal zones in the southern Yap Trench observed with the submersible Jiaolong

Using observations in an applied cruise of the submersible Jiaolong, water characteristics, geostrophic transport, and turbulent mixing in abyssal and hadal zones of the southern Yap Trench were studied. The spatial structures of deep water show that the abyssal water is cold, saline, and oxygen rich. The hadal water has very small changes in potential temperature and potential density, and a little decrease in salinity and obvious decrease in oxygen. The isotherm, isopycnal, and isohaline are depressed in abyss over the central trench. The turbulent mixing is enhanced in the near-bottom zone and the hadal water on the trench slope, especially at the steep slope, the dissipation rate and diffusivity is strong, which weakens the stratification. The geostrophic flows move southward in the western region of the trench and northward in the eastern region, indicating cyclonic circulation. In the central region of the trench, the water transport is ~1.74 Sv southward. In the hadal zone, the northward and southward transports are balanced. Our analysis suggests that the abyssal water in the southern Yap Trench is from Lower Circumpolar Water (LCPW) and the hadal water seems to be of the isolated local water rather than LCPW.     

Impact of redox-stratification on the diversity and distribution of bacterial communities in sandy reef sediments in a microcosm

Relationships between microbial communities and geochemical environments are important in marine microbial ecology and biogeochemistry. Although biogeochemical redox stratification has been well documented in marine sediments, its impact on microbial communities remains largely unknown. In this study, we applied denaturing gradient gel electrophoresis (DGGE) and clone library construction to investigate the diversity and stratification of bacterial communities in redox-stratified sandy reef sediments in a microcosm. A total of 88 Operational Taxonomic Units (OTU) were identified from 16S rRNA clone libraries constructed from sandy reef sediments in a laboratory microcosm. They were members of nine phyla and three candidate divisions, including Proteobacteria (Alpha-, Beta-, Gamma-, Delta-, and Epsilonproteobacteria), Actinobacteria, Acidobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Firmicutes, Verrucomicrobia, Spirochaetes, and the candidate divisions WS3, SO31 and AO19. The vast majority of these phylotypes are related to clone sequences from other marine sediments, but OTUs of Epsilonproteobacteria and WS3 are reported for the first time from permeable marine sediments. Several other OTUs are potential new bacterial phylotypes because of their low similarity with reference sequences. Results from the 16S rRNA, gene clone sequence analyses suggested that bacterial communities exhibit clear stratification across large redox gradients in these sediments, with the highest diversity found in the anoxic layer (15–25 mm) and the least diversity in the suboxic layer (3–5 mm). Analysis of the nosZ, and amoA gene libraries also indicated the stratification of denitrifiers and nitrifiers, with their highest diversity being in the anoxic and oxic sediment layers, respectively. These results indicated that redox-stratification can affect the distribution of bacterial communities in sandy reef sediments.     

Distinct influence of trimethylamine N-oxide and high hydrostatic pressure on community structure and culturable deep-sea bacteria

Trimethylamine N-oxide(TMAO) is one of the most important nutrients for bacteria in the deep-sea environment and is capable of improving pressure tolerance of certain bacterial strains.To assess the impact of TMAO on marine microorganisms,especially those dwelling in the deep-sea environment,we analyzed the bacterial community structure of deep-sea sediments after incubated under different conditions.Enrichments at 50 MPa and 0.1 MPa revealed that TMAO imposed a greater influence on bacterial diversity and community composition at atmospheric pressure condition than that under high hydrostatic pressure(HHP).We found that pressure was the primary factor that determines the bacterial community.Meanwhile,in total,238 bacterial strains were isolated from the enrichments,including 112 strains a ffiliated to 16 genera of 4 phyla from the Yap Trench and 126 strains a ffiliated to 11 genera of 2 phyla from the Mariana Trench.Treatment of HHP reduced both abundance and diversity of isolates,while the presence of TMAO mainly af fected the diversity of isolates obtained.In addition,certain genera were isolated only when TMAO was supplemented.Taken together,we demonstrated that pressure primarily defines the bacterial community and culturable bacterial isolates.Furthermore,we showed for the first time that TMAO had distinct influences on bacterial community depending on the pressure condition.The results enriched the understanding of the significance of TMAO in bacterial adaptation to the deep-sea environment.     

Positive selection analysis reveals the deep-sea adaptation of a hadal sea cucumber (Paelopatides sp.) to the Mariana Trench

Journal of Oceanology and Limnology - The Mariana Trench, the deepest trench on the earth, is ideal for deep-sea adaptation research due to its unique characters, such as the highest hydrostatic...     

Abyssal Circulation in the Philippine Sea

The abyssal circulation in the Philippine Sea(PS)is investigated,with outputs from the Simple Ocean Data Assimilation version 2.2.4(SODA224).The deep-water currents in SODA224 are carefully evaluated,with sparse in situ observations in the North Pacific Ocean.In the upper deep layer(20003000 m)of the PS,a strong westward current,which originates from the Northeast Pacific Basin and enters the PS through the Yap-Mariana Junction,exists along 1114 N.This strong westward current bifurcates into two western boundary currents off the Philippines.The northward-flowing current flows out of the PS around 2021 N,whereas the southward-flowing current transports deep water from the northern hemisphere to the southern hemisphere.In the lower deep layer(30004500 m),the inflow water first flows northward to the east of the Western Mariana Basin and then turns westward at approximately 18 N.The inflow water mainly enters the Philippine Basin(PB),with a small part turning southward to constitute a weak cyclonic circulation.The water entering the PB mainly merges into a strong southward western boundary current in the south-ern PB.In the bottom layer(below 4500 m),both the northeast and northwest PB show single cyclonic gyres,whereas the south PB shows a single anticyclonic gyre.Moreover,comparisons with the observations indicate the possible existence of a cyclonic sense of circulation over the Philippine Trench.The current study provides the implications for future observations,which are needed to fur-ther investigate the temporospatial variations of the abyssal circulation in the PS on multiple scales.     

Diversity and community structure of eukaryotic microalgae in surface sediments in the central Bohai Sea,China, based on a metabarcoding approach

Sediment samples were collected at 17 stations in the central Bohai Sea, China, and the diversity and community structure of eukaryotic microalgae were assessed by metabarcoding the V4 region of 18S rDNA. A total of 930 operational taxonomic units (OTUs) were detected for microeukaryotes, including 98 algal OTUs. The algal communities comprised 42 genera belonging to 19 classes of six phyla, and they were dominated by chrysophytes and dinoflagellates. Dinoflagellates were also the most diverse microalgal group. The nano-sized dinoflagellates Biecheleria halophila and Azadinium trinitatum occurred abundantly in the study area; however, they have not been reported previously, as they may be overlooked or misidentified in light microscopy. Many pico-sized chlorophytes were detected in the sediment samples. Sixteen of the detected OTUs were assigned to potentially harmful and/or bloom-forming microalgae, suggesting some potential risks of harmful algal blooms in the central Bohai Sea. The capacity of metabarcoding to detect morphologically cryptic and small species makes this method a sufficiently sensitive means of detection for assessing eukaryotic microalgae in sediments.

     

Distribution characteristics of lipids in hadal sediment in the Yap Trench

In this study, cored sediment samples collected by the Jiaolong Submersible at 6 779 m depth from the hadal zone of the Yap Trench in May 2016 were sliced in 1-cm interval from top to bottom, and lipids in each sediment layer were quantitatively and qualitatively analyzed. The vertical distribution profiles of the lipids in the sediment sample, their main existing forms, and their possible sources were investigated. The results show that the concentration of lipid in the surface sediment was the highest with the carbon number from 12 to 27, dominated by medium and short-chain lipids. The total concentration of fatty acids in surface sediment was much higher than those in the offshore and deep-sea areas, being up to 325.77 μg/g due to the funnel effect caused by the “V” terrain of the trench. Fatty acid 18.0 was the most abundant lipids in the sediment sample. Abnormal high concentrations of fatty acid 18.ω7 and alkanes indicated the existence of hydrothermal fluids in the study area. In addition, saturated fatty acids and monounsaturated fatty acids existed mainly in free form, and polyunsaturated fatty acids existed mainly in bound form. Most of the alkanes were in bound form, and their major source was autochthounous input. The carbon number of alcohols in the sediment sample ranged from 12 to 20, mainly existed in bound form. The source of fatty acids was mainly autochthonous input, and the neutral lipids had both marine and terrestrial origin. This is the first study of lipids in hadal sediment of the Yap Trench. The results will promote deeper understanding of organic carbon cycle in marine environment.     

Characterization of microbial communities in sediments of the South Yellow Sea

Illumina sequencing and quantitative PCR(qPCR) based on the 16 S ribosomal RNA(rRNA) gene were conducted to characterize the vertical distribution of bacterial and archaeal communities in the sediments of two sites from the South Yellow Sea. Both bacterial and archaeal communities showed a clear stratified distribution with sediment depth. The microbial communities in the upper layers were distinct from those in the deeper layers; the relative abundances of sequences of Thaumarchaeota, Gammaproteobacteria, and Actinobacteria were higher in the upper than in the deeper sediments, whereas the sequences of Bathyarchaeia, Lokiarchaeota, Euryarchaeota, Chloroflexi, and Deltaproteobacteria were relatively more abundant in the deeper sediments. Sediment depth and total organic carbon(TOC) can significantly influence both the bacterial and archaeal communities. Furthermore, bacterial and archaeal groups potentially involved in nitrogen, sulfur, and methane metabolism were detected in both sites. In our study, both ammonia-oxidizing bacteria( Nitrospira) and ammonia-oxidizing archaea( Candidatus Nitrosopumilus) were responsible for ammonia oxidization. Additionally, sulfur-reducing bacteria SEEP-SRB1 forming consortia with anaerobic methane-oxidizing archaea ANME-2 a-2 b were capable of anaerobic methane oxidation(AOM) in the 3400-02 sediment samples.     

南三河沉管工程基槽开挖对海域水环境的影响

南三河沉管是鉴江供水枢纽工程中的一处跨海管道工程,管道基槽开挖会对周围海域水质产生影响。基于建立的二维非稳态水环境数学模型,利用同步水文水质监测数据对模型参数进行率定,并反演得到SS源强浓度,继而预测施工期SS对海域水环境的影响范围及程度。结果表明:距基槽中心50 m范围的SS源强浓度达到70 mg/L;SS会对基槽中心线上下游各700 m范围内的水域产生影响(增量≥10 mg/L),影响程度以挖槽为中心线向两侧递减。     

侧孢短芽孢杆菌对铜绿微囊藻藻际微生物群落的影响

【目的】探究铜绿微囊藻(Microcystis aeruginosa)藻际微生物群落组成以及与溶藻细菌侧孢短芽孢杆菌(Brevibacillus laterosporus)Bl-zj共培养对藻际微生物群落的影响。【方法】将侧孢短芽孢杆菌Bl-zj与铜绿微囊藻共培养4 d后(BL组),收集样品,以单独培养的铜绿微囊藻(BG组)为对照,提取样品总基因组DNA后进行16S rDNA扩增、构建文库、测序及生物信息学分析,比较BL组与BG组间藻际微生物群落的差异。【结果】测序平均获得高质量序列85390条,946个OUT(Operational Taxonomic Unit),BL组特有OTU 339个。物种组成分析显示,BG组微生物群落主要以微囊藻属(Microcystis)为主,其余相对丰度由高到低分别为假单胞菌属(Pseudomonas)、中慢生根瘤菌属(Mesorhizobium)、短芽孢杆菌属(Brevibacillus)和红杆菌属(Rhodobacter)。BL组微生物群落主要以短芽孢杆菌属(Brevibacillus)为主。BL组的微生物多样性相较于BG组显著下降(P<0.05)。经预测,BG组微生物功能集中在能量代谢与外源生物降解与代谢,BL组微生物功能集中在碳水化合物代谢和氨基酸代谢功能。【结论】侧孢短芽孢杆菌Bl-zj与铜绿微囊藻共培养,打破了铜绿微囊藻藻际微生物群落的平衡,与Bl-zj的溶藻进程有关。     

Archaeal community structure in sediments from a seamount in the Mariana Volcanic Arc

Seamounts are subsurface mountains in the ocean.Examination of the abundance and distribution of Archaea in seamount ecosystems may provide a better understanding of their ecological functions.Most studies of marine archaeal assemblages in seamount area have focused on hydrothermal vents or ferromanganese crusts.We investigated the archaeal communities from a seamount of the Mariana Volcanic Arc,in the tropical western Pacific Ocean by using high-throughput sequencing.Thaumarchaeota was dominant in the sediments of all sample stations.Community diversity and species richness were greatest at stations near the top of the seamount,and lowest at the deepest station.One sample station on the steep southeast slope that faced the Yap-Mariana trench had a unique composition of Archaea.In summary,depth has an important influence on archaeal community structure,and the geographic properties and sediment characteristics may explain the unique distribution patterns of Archaea in this seamount.This study provides a foundation for future research on Archaea in seamounts.     

A new model of lithosphere deformation beneath the Okinawa Trough based on gravity data

The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal subduction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deformation at the collision front, while the oblique subduction in the southern part gives rise to a smaller accretion with small deformation than that in the northern part. The mechanisms that cause distinction between these two types have been analysed and calculated by using gravity data based on the lithosphere rheology and the stress state of the lithosphere in the subduction boundary. The two types of subduction model are associated with the internal extension in the southern Okinawa Trough and the small extension in the northern part. The difference of the stress state between the two types of subduction model is also manifested in other tectonic features, such as topography, volcanic activity and crust movement. Modeling bathymetric and gravity data from this area suggests that the oblique subduction of low angle, together with smooth geometry of the overlying plate crust, results in small stress released on the south of the trench by the subduction plate. The intraplate faults in the southern Okinawa Trough behind the trench stand in surplus intensive stress. On the other hand, the normal subduction of high angle, together with strong undulation geometry of the overlying crust, results in more intensive stress released in the northern Ryukyu Trench than that in the south. The intraplate faults in the northern Okinawa Trough behind the northern Ryukyu Trench stand in small stress.     

Characteristics of nitrogen forms in the surface sediments of southwestern Nansha Trough,South China Sea

The area of the southwestern Nansha Trough is one of the most productive areas of the southern South China Sea.It is a typical semi-deep sea area of transition from shoal to abyssal zone.To understand distributions and roles of nitrogen forms involved in biogeochemical cycling in this area,contents of nitrogen in four extractable forms:nitrogen in ion exchangeable form(IEF-N),nitrogen in weak acid extractable form(WAEF-N),nitrogen in strong alkali extractable form(SAEF-N) and nitrogen in strong oxidation extractable form(SOEF-N),as well as in total nitrogen content(TN) in surface sediments were determined from samples collected from the cruise in April-May 1999.The study area was divided into three regions(A,B and C) in terms of clay sediment(<4 μm) content at <40%,40%-60% and >60%,respectively.Generally,region C was the richest in the nitrogen of all forms and region A the poorest,indicating that the finer the grain size is,the richer the contents of various nitrogen are.The burial efficiency of total nitrogen in surface sediments was 28.79%,indicating that more than 70% of nitrogen had been released and participated in biogeochemical recycling through sediment-water interface.     

Microbial ecological associations in the surface sediments of Bohai Strait

Microbial communities play key roles in the marine ecosystem. Despite a few studies on marine microbial communities in deep straits, ecological associations among microbial communities in the sediments of shallow straits have not been fully investigated. The Bohai Strait in northern China(average depth less than 20 m) separates the Bohai Sea from the Yellow Sea and has organic-rich sediments. In this study, in the summer of 2014, six stations across the strait were selected to explore the taxonomic composition of microbial communities and their ecological associations. The four most abundant classes were Gammaproteobacteria, Deltaproteobacteria, Bacilli and Flavobacteriia. Temperature, total carbon, depth, nitrate, fishery breeding and cold water masses influenced the microbial communities, as suggested by representational dif ference and composition analyses. Network analysis of microbial associations revealed that key families included Flavobacteriaceae, Pirellulaceae and Piscirickettsiaceae. Our findings suggest that the families with high phylogenetic diversity are key populations in the microbial association network that ensure the stability of microbial ecosystems. Our study contributes to a better understanding of microbial ecology in complex hydrological environments.     

Bacterial diversity and community structure in the East China Sea by 454 sequencing of the 16S rRNA gene

The 454 sequencing method was used to detect bacterial diversity and community structure in the East China Sea. Overall, 149 067 optimized reads with an average length of 454 nucleotides were obtained from 17 seawater samples and five sediment samples sourced in May 2011. A total of 22 phyla, 34 classes, 74 orders, 146 families, and 333 genera were identified in this study. Some of them were detected for the first time from the East China Sea. The estimated richness and diversity indices were both higher in the sediment samples compared with in the seawater samples. All the samples were divided by their diversity indices into four regions. Similarity analysis showed that the seawater samples could be classified into six groups. The groups differed from each other and had unique community structure characteristics. It was found that different water masses in the sampling areas may have had some influence on the bacterial community structure. A canonical correspondence analysis revealed that seawater samples in different areas and at different depths were affected by different environmental parameters. This study will lay the foundation for future research on microbiology in the East China Sea.     

Talc-beating serpentinized peridotites from the southern Mariana forearc： implications for aseismic character within subduction zones

The serpentinized peridotites overlying the subducted zones in the Izu-Bonin-Mariana (IBM) arc system have been interpret as the cause of the low-velocity layer identified beneath the IBM froearc, in turn few earthquakes occurred along the plate boundary. Chrysotile, which is a low temperature and highly hydrated phase of serpentine with low frictional strength, has been suggested as the low velocity material in the serpentinized peridotites, besides, brucite is inferred to be likely conducive to stable sliding. However, such idea encounters challenging in our serpentinized peridotites from the southern Mariana forearc, which absent both the above minerals. The presence of talc, which characterized by its weak, low-friction and inherently stable sliding behavior, provides new clue. Here we report the occurrence of talc in serpentinized peridotites collected from the landward trench slope of the southern Mariana forearc. We infer that talc is mainly forming as a result of the reaction of serpentine minerals with silica-saturated fluids released from the subducting slab, and talc also occurs as talc veins sometimes. Due to its unique physical properties, talc may therefore play a significant role in aseismic slip in the IBM subduction zone.

     

Distribution characteristics of polychlorinated biphenyls （PCBs） in coastal areas of Okinawa Island, Japan

Surface sediment and seawater samples were collected from coastal areas around Okinawa Island from September 2001 to May 2002. The samples were analyzed for total polychlorinated biphenyl (PCB) levels and homolog composition. The results show that total PCB levels ranged from 0.32 to 128.7 ng/g (dry wt.) in sediment and 1.59 to 2.48 ng/L in seawater. The levels exceed the Environmental Quality Standard (EQS) for water pollution of Japan. The distribution of PCB homolog showed different patterns in the sediments and seawaters. Penta-chlorobiphenyls (CBs) comprised the main congener group in seawater, while hexa-CBs were more abundant homologs in the sediments. The heavily contaminated sites featured higher CBs, including penta-CBs, hexa-CBs, and hepta-CBs, than those in less contaminated sites where tri-CBs dominated. This study provides current distribution and geochemical behavior of PCBs in the coastal areas around Okinawa Island.     

The Sources and Transport Patterns of Modern Sediments in Hangzhou Bay: Evidence from Clay Minerals

Clay mineral compositions of 199 offshore surface sediment samples collected from the Hangzhou Bay have been analyzed. The clay minerals in the sediments from the Hangzhou Bay are dominated by illite(58.7%, on average), followed by chlorite(20.3%), kaolinite(16.9%) and smectite(4.1%). Two provinces were classified by Q-mode cluster analysis. Class Ⅰ with relatively low amounts of illite and smectite is widely distributed in the Hangzhou Bay, especially concentrated in the top and mouth of the bay, and the northern and southern nearshore areas. Class Ⅱ with comparatively high amounts of illite and smectite is mainly concentrated in the central part of the bay with the water depth of 8–10 m. By comparing clay mineral compositions with the neighbouring regions, we can find that the sediments in the Hangzhou Bay are mainly influenced by the resuspension and repeated deposition of particles from the Yangtze River due to the strong dynamic environment. In particular, the clay fraction of Class Ⅰ is mainly supplied by the Yangtze River, while the sediments of Class Ⅱ are mixture of the clay minerals carried by the Yangtze River and Qiantang River. In general, the distributions of clay minerals in the northern bay are affected by Yangtze River runoff, coastal current and flood tide together, and in the southern they are mainly affected by the Qiantang River runoff and ebb tide.     

Vertical variations and composition of dissolved free amino acid in the seawater of the Yap Trench in the western Pacific Ocean

The composition and concentration of dissolved free amino acid (DFAA) of seawater samples collected in May 2016 from the surface to the hadal zone of the northern region of the Yap Trench were analyzed by pre-column derivatization of o-phthalaldehyde. Results show that the average concentration of DFAA in the study area was 0.47±0.36 µmol/L. In different sampling stations, the concentrations of DFAA with water depth showed complex variation patterns. At the sediment-seawater interface, the concentrations of DFAA in the western side of the trench were obviously higher than that in its eastern side. In the study area, there were no significant correlations between the concentrations of DFAA and the environmental parameters such as concentrations of chlorophyll a (Chl a), dissolved oxygen (DO), pH, and dissolved inorganic nitrogen (DIN), indicating that the concentrations of DFAA in seawater of the trench are affected by many factors, such as photosynthesis, respiration, temperature, pressure, illumination, and circulation. The dominant DFAA are similar in different water layers of sampling stations, including aspartic acid (Asp), glutamic acid (Glu), glycine (Gly), and serine (Ser). The composition of different amino acids, and the relative abundance of acidic, basic, and neutral amino acids might be related to the sources and consumption of various amino acids. Nine pairs of amino acids in the DFAA showed significantly positive relationship by correlation matrix analysis, suggesting that they might share similar biogeochemical processes. The degradation index (DI) of the DFAA in seawater of the Yap Trench could reflect the degradation, source, and freshness of DFAA in the trench to some extents. This is a preliminary study of amino acids from sea surface to hadal zone in the ocean, more works shall be done in different trenches to reveal their biogeochemical characteristics in extreme marine environments.