Strontium Isotope Compositions of Hydrothermal Barite from the Yonaguni IV: Insight into Fluid/Sediment Interaction and Barite Crystallization Condition

Hydrothermal barite is a typical low-temperature mineral formed during the mixing of hydrothermal fluid and seawater.Because of its extremely low solubility,barite behaves as a close system after crystallization and preserves the geochemical fingerprint of hydrothermal fluid.In this study,the elemental contents and Sr isotope compositions of hydrothermal barites from the Yonaguni IV were determined using electron microprobe and LA-MC-ICP-MS respectively.On these bases,the fluid/sediment interaction during the hydrothermal circulation and physicochemical condition of barite crystallization were discussed.Results show that the 87 Sr/86 Sr values of hydrothermal barites from the Yonaguni IV are apparently higher than those of the seawater and associated volcanic rocks,indicating the sufficient interaction between the hydrothermal fluid and overlying sediment.Monomineral Sr abundance shows large variations,reflecting the changes in barite growth rate during the fluid mixing.The mineralization condition in the Yonaguni IV was unstable.During the crystallization of barite,hydrothermal fluid and seawater mixed in varying degrees,with the pro-portions of hydrothermal fluid varied from 36%to 72%.The calculated crystallization temperatures range from 109 to 220℃.Sediment plays a critical role during the mineralization process in the Yonaguni IV and incorporation of sediment component into hydrothermal system was prior to barite crystallization and sulfide mineralization.     

Crystals of suspended marine barite in the eastern equatorial Pacific: processes of dissolution and effects on crystal morphology

Suspended paniculate substances were sampled in the eastern equatorial Pacific in water column from surface to near bottom in five stations in 2005,from which 868 barite crystals were recovered.The barite crystals were examined under scanning electron microscopy.About 61%of the total barites crystals contained detectable Sr by energy dispersive X-ray spectrometry.Barite crystals could be classified into four groups based on their morphology:1) bladed;2) ovoid or rounded;3) arrow-like;and 4) irregularly shaped.The arrow-like barite crystals in natural environment has never been reported before.In addition,about a half of the studied crystals showed features of dissolution as cavities or holes inside of the crystals or around their edges.We found that differential dissolution of barite crystals is consequence of heterogeneous Sr distribution in barite crystals.Our results would help in understanding the biogeochemical processes of marine barite formation and preservation in seawater and marine sediments.     

Distribution and generic composition of culturable marine actinomycetes from the sediments of Indian continental slope of Bay of Bengal

Actinomycetes population from continental slope sediment of the Bay of Bengal was studied. Samples were collected during two voyages of FORV Sagar Sampada in 2004 （May-June） and 2005 （July） respectively from 11 transects （each transect had ca. 200 m, 500 m, and 1 000 m depth stations）. The physicochemical parameters of overlying water, and sediment samples were also recorded. The actinomycete population ranged from 5.17 to 51.94 CFU/g dry sediment weight and 9.38 to 45.22 CFU/g dry sediment weight during the two cruises respectively. No actinomycete colony was isolated from stations in 1 000 m depth. Two-way analysis of variance showed significant variation among stations （ANOVA two-way, P〈0.05）, but no significance was found between the two cruises （ANOVA two-way, P〈0.05）. Populations in stations in 500 m depth in both cruises were higher than that of 200 m depth stations with statistically insignificant difference （ANOVA two-way, P〉0.05）. Three actinomycetes genera were identified. Streptomyces was found to be the dominating one in both the cruises, followed by Micromonospora, and Actinomyces. The spore of Streptomyces isolates showed the abundance in spiral spore chain. Spore surface was smooth. Multiple regression analysis revealed that the influencing physico-chemical factors were sediment pH, sediment temperature, TOC, porosity, salinity, and pressure. The media used in the present study was prepared with seawater. Thus, they may represent an autochthonous marine flora and deny the theory of land runoff carriage into the sea for adaptation to the salinity of the seawater and sediments.     

The Mineral Composition and Sources of the Fine-Grained Sediments from the 49.6°E Hydrothermal Field at the SWIR

We used the X-ray diffraction method to determine systematically the mineral phases in bulk sediment samples and acid undissolved residuals of the fine-grained fraction of the surface sediments from the 49.6°E hydrothermal field at the Southwest Indian Ridge(SWIR)and discussed the mineral sources of the surface sediments.The results showed that the surface sediments in this region were composed of calcareous ooze,and calcite was the dominant mineral.The sediments also contained quartz,feldspar,clay minerals,pyroxene,sphalerite,barite,serpentine,and magnetite.The quartz,feldspar,and clay minerals were exogenous minerals that mainly originated from the Namib and Kalahari deserts in southern Africa.The pyroxene,serpentine,magnetite,sphalerite,calcite,and barite were endogenous minerals from weathering of seafloor basement rocks and seafloor hydrothermal activities.The sulfide particles in the sediments were mainly deposited from upwelling plumes.     

Formation of the modern current system in the East China Sea since the early Holocene and its relationship with sea level and the monsoon system

The Okinawa Trough is a natural laboratory for the study of air-sea interaction and paleoenvironmental change. It has been demonstrated that present offshore export of particles in the bottom nepheloid layer occur primarily with downwelling from the northeast winter monsoon, which is inhibited by a transverse circulation pattern in summer. This current system was very different during the Last Glacial Maximum owing to low sea level(-120 m) and exposure of a large shelf area. We collected sediment core Oki01 from the middle Okinawa Trough during 2012 using R/V K exue No. 1 to elucidate the timing and cause of the current system transition in the East China Sea. Clay mineral, dry density, and elemental(Ti, Ca) composition of core Oki01 was analyzed. The results indicate that clay minerals derived mainly from the Huanghe(Yellow) and the Changjiang(Yangtze) Rivers during 16.0–11.6 ka, and the modern current system in the East China Sea formed beginning in the early Holocene. Therefore, mixing of East China Sea continental shelf, Changjiang River and partially Taiwan Island sediment are the major contributors. The decrease of log(Ti/Ca) and alternating provenance since the early Holocene indicate less sediment from the East China in summer because of resistance of the modern current system, i.e., a "water barrier" and upwelling. Conversely, sediment delivery persists in winter and log(Ti/Ca) indicates the winter monsoon signal since the early Holocene. Our evidence also suggests that sediment from Taiwan Island could be transported by the Kuroshio Current to the middle Okinawa Trough, where it mingles with winter monsooninduced export of sediment from the Changjiang River and East China Sea continental shelf. Although the present research advances understanding of the evolutionary history of paleoenvironmental change in the Okinawa Trough, more sediment cores should be retrieved over wide areas to construct a larger scenario.     

TRANSFER OF ORGANIC POLLUTANTS DURING SEW AGE-SEAWATER MIXING

The transfer processes of organic pollutants during sewage - seawater mixing were simulated in three different mixing systems. The release rate of organic matter from sewage particles to seawater was found to be about 0.02-0.04d-1 . The release processes can be simulated by an exchange-equilibrium kinetic model. Degradation of COD was observed in all three mixing systems and can be described by a first order kinetic equation. The degradation rate constant k ranged between 0.04 and 0.07 d . These results have provided important parameters for estimation of environmental capacity.     

Benthic nutrient recycling in shallow coastal waters of the Bohai Sea

Sediment-water fluxes of N and P species in the Bohai Sea were investigated in September-October 1998 and April-May 1999. The benthic fluxes of nutrient species were determined by incubating sediment core samples with bottom seawater bubbled with air or nitrogen. NO^-2,NH4, dissolved organic nitrogen (DON) and phosphorus (DOP), total dissolved nitrogen (TDN) and phosphorus (TDP), and PO4^3- showed a net exchange flux from seawater to sediment, while NO^-3, dissolved inorganic nitrogen (DIN) and SiO3^2- were released from sediment to seawater in the Bohai Sea. Sediment-water nutrient exchange increases DIN and reduces the phosphorus load in the Bohai Sea. The release of silicate from sediment to overlying seawater reduces potential silicate limitation of primary production resulted from decrease of riverine discharge.The exchange flux of nutrients showed no obvious seasonal variation. The present study showed that the concentrations and composition of nutrients in the water column were affected by suspended sediment, and that not all the exchangeable phosphate in sediment could be released via sediment resuspension.     

The contribution of trace elements from seawater to chimneys： a case study of the native sulfur chimneys in the sea area off Kueishantao, northeast of Taiwan Island

Hydrothermal fluid containing abundant matter erupts from seafloor, meets ambient cold seawater and forms chimneys. So the main matter origins of chimneys are seawater and matter which are taken by hydrothermal fluid from deep reservoir. However, because of seawater’s little contribution to the forming of chimneys, it is usually covered by the abundant matter which is taken by hydrothermal fluid. Therefore, chimneys formed in ordinary deep seawater hydrothermal activity, containing complex elements, cannot ...     

Origin and geochemistry of surface sediments in the mud deposit area offshore the Shandong Peninsula,China

The waters offshore the Shandong Peninsula separate the North Yellow Sea from the South Yellow Sea,and receive a large amount of terrestrial material from Chinese and Korean rivers,making it an ideal area for studying land-sea interactions.However,little attention has been given to measuring sediment transportation in most previous studies.Based on an analysis in composition of major and trace elements and particle size characteristics from 62 surface sediment samples from the northeastern region off Shandong Peninsula,the type,element composition,and controlling factors of the surface sediments were inve stigated.In addition,the transportation of sediments from source to sink was described from measured thermohaline data.The results show two types of surface sediments:sandy silt and silt.The sediments were mainly terrestrial;and marine carbonate had little effect on sediment composition.Shown on a binary diagram of Rb/Sc to Co/Sc,the Huanghe(Yellow) and Changjiang(Yangtze) rivers are the main sources of surface sediments in the study area.The component mixing model showed that the relative contribution of sediment from the Huanghe River was up to 92%,followed by the Changjiang River(8%).The Yellow Sea Warm Current and the North Shandong Peninsula Coastal Current met at ～3 7.7°N in the study area,and were the main forces carrying sediment from the two main river sources.However,there was a deficit of transported material into the study area in summer.The secondary distribution of sediment from the two river sources was controlled by tidal currents and waves.     

Sea surface temperature and salinity reconstruction based on stable isotopes and Mg/Ca of planktonic foraminifera in the western Pacific Warm Pool during the last 155 ka

Changes in sea surface temperature(SST), seawater oxygen isotope(δ 18 O sw), and local salinity proxy(δ 18 O sw-ss) in the past 155 ka were studied using a sediment core(MD06-3052) from the northern edge of the western Pacifi c Warm Pool(WPWP), within the fl ow path of the bifurcation of the North Equatorial Current. Our records reveal a lead-lag relationship between paired Mg/Ca-SST and δ 18 O during Termination II and the last interglacial period. Similarity in SST between our site and the Antarctic temperature proxy and in CO 2 profi le showed a close connection between the WPWP and the Antarctic. Values of δ 18 O sw exhibited very similar variations to those of mean ocean δ 18 O sw, owing to the past sea-level changes on glacial-interglacial timescale. Calculated values of δ 18 O sw-ss refl ect a more saline condition during high local summer insolation(SI) periods. Such correspondence between δ 18 O sw-ss and local SI in the WPWP may refl ect complex interaction between ENSO and monsoon, which was stimulated by changes in solar irradiance and their infl uence on the local hydrologic cycle. This then caused a striking reorganization of atmospheric circulation over the WPWP.     

Remote sensing retrieval of surface suspended sediment concentration in the Yellow River Estuary

Accurate assessment of surface suspended sediment concentration(SSSC) in estuary is essential to address several important issues: erosion, water pollution, human health risks, etc. In this study, an empirical cubic retrieval model was developed for the retrieval of SSSC from Yellow River Estuary. Based on sediments and seawater collected from the Yellow River and southeastern Laizhou Bay, SSSC conditions were reproduced in the laboratory at increasing concentrations within a range common to field observations. Continuous spectrum measurements of the various SSSCs ranging from 1 to 5700 mg/l were carried out using an Ava Field-3 spectrometer. The results indicated the good correlation between water SSSC and spectral reflectance(Rrs) was obtained in the spectral range of 726–900 nm. At SSSC greater than 2700 mg/L, the 740–900 nm spectral range was less susceptible to the effects of spectral reflectance saturation and more suitable for retrieval of high sediment concentrations. The best correlations were obtained for the reflectance ratio of 820 nm to 490 nm. Informed by the correlation between Rrs and SSSC, a retrieval model was developed(R2 = 0.992). The novel cubic model, which used the ratio of a near-infrared(NIR) band(740–900 nm) to a visible band(400–600 nm) as factors, provided robust quantification of high SSSC water samples. Two high SSSC centers, with an order of 103 mg/l, were found in the inversion results around the abandoned Diaokou River mouth, the present Yellow River mouth to the abandoned Qingshuigou River mouth. There was little sediment exchange between the two high SSSC centers due to the directions of the residual currents and vertical mixing.     

Study on fluid inclusions and features of ore-forming fluids of Diakha gold deposit,Mali, West Africa

The Diakha gold deposit is located in the southeastern margin of the highly prospective/productive Paleoproterozoic( Birimian) Kédougou-Kéniéba Inlier. Gold mineralization is closely associated with a narrow,sub-vertical,NE-trending shear corridor. The corridor is to the east of a sinistrally reactivated D1 west-dipping fault,which emanated from SMSZ( D2 reverse-sinistral regional structure). The mineralization is hosted by fine-grained sandstone and breccias units associated with a moderate to strong hydrothermal alteration,which is dominated by albitization,carbonization,silicification,hematization,and chloritization. Diakha field data and laboratory analysis suggest the existence of two main stages of hydrothermal mineralization,namely stage I and stage II. Stage I is of a breccias type of mineralization and represents the major gold bearing stage. It isassociated with hematite + calcite + ankerite/dolomite and quartz pervasive alteration,controlled by the predominantly brittle-ductile NNE to NE-shearing structures of the main deformation event D2. Stage II is represented by the second minor hydrothermal episode,showing local quartz-tourmaline and tremolite alteration which is structurally controlled by the dipping S3 cleavage formed during D3 deformation. Petrographic and microthermometric studies of fluid inclusions from quartz veins reveal the presence of early dominant carbonic CO2-pure and aqueous-carbonic CO2-rich( LCO2+ VCO2± H2 O) in stage I. The exclusively aqueous H2 O + Na Cl ± CO2 fluid inclusions( L-type) are observed in stage II. Interpretation shows that the ore-forming fluids originated from a homogeneous H2 O-CO2 fluid during phase separation,with trapping temperatures of 250℃ to 280℃ and low salinity( 6 wt % Na Cl equiv),indicating an estimated trapping pressure for the deposit between 610 to 800 bars.     

Characteristics and sources of ore-forming fluids of South Narimalahei copper polymetallic deposit in East Kunlun,Qinghai

The South Narimalahei area is located on the north side of the Middle Kunlun fault in the eastern section of the East Kunlun composite orogenic belt. The ore body is veined and controlled by structures and se-condary fissures, which occurs in the structural alteration fracture zone in the Late Triassic granodiorite. In this deposit, copper mineralization is closely related to silicification and sericification. The formation process of the deposit includes hydrothermal mineralization and supergene oxidation. In this paper, the fluid inclusion minera-logy, microscopic temperature measurement and stable isotope studies have been carried out for ore of the main mineralization stage. The results show that the primary gas-liquid two-phase inclusions and a small amount of single-liquid inclusions are mainly developed in the quartz in the main mineralization stage. The results of microscopic temperature measurement show that the ore-forming fluid which has low temperature(151.7℃--205.8℃), low salinity(2.06 wt%--4.94 wt%NaCl), low density(0.86--0.92 g/cm~3) and shallow formation(1.5--3.0 km) is a hydrothermal solution of NaCl-H_2O system. Hydrogen and oxygen isotope results show that the ore-forming fluids mainly come from atmospheric precipitation, with a small amount of magmatic fluids participating. It is preliminarily determined that the South Narimalahei copper polymetallic deposit is a low-temperature hydrothermal vein deposit.     

INTERNAL WAVE EIGENMODES AND THEIR WEAK NONLINEAR RESONANT INTERACTION IN A NONLINEARLY STRATIFIED FLUID- A PRELIMINARY THEORETICAL AND EXPERIMENTAL STUDY

A preliminary theoretical and experimental study was conducted on internal wave modes and their weak nonlinear resonant interaction in a nonlinearly stratified fluid . An asymptotical solution of the modes and a dispersion relation of internal waves in a stratified fluid with density profile similar to that in our experiment were obtained theoretically . The resonant-interaction mechanism to 2nd order approximation is also discussed . The resonant interaction of the 3rd and 4th mode internal waves excited by the unstable 1st mode wave is analyzed on the basis of data obtained by conductivity probes. The resonant-interaction condition, , is examined . It is shown that the resonant instability increases with pycnocline thickness and wave maker driving frequency .     

The Origin and Preservation of Suspended Barites near the 90°E Ridge in the Northeastern Indian Ocean

Suspended particulate barite crystals were detected in the water columns at four different stations near the 90°E ridge in the Indian Ocean. Four distinct morphological types of marine barites were distinguished: euhedral-subhedral crystals, oval or round crystals, rhombic crystals, and irregular crystals. The barite crystals in the study area are typically fine, with a dominant size of 1 – 3μm. The vertical distribution of barites is significantly affected by the formation and sedimentation pro...     

Distribution and Ecological Risk Assessment of HCHs and DDTs in Surface Seawater and Sediment of the Mariculture Area of Jincheng Bay,China

The distribution of hexachlorocyclohexanes(HCHs) and dichlorodiphenyltrichloroethanes(DDTs) in the surface seawater and sediment of Jincheng Bay mariculture area were investigated in the present study. The concentration of total HCHs and DDTs ranged from 2.98 to 14.87 ng L-1 and were 0.032 ng L-1, respectively, in surface seawater, and ranged from 5.52 to 9.43 and from 4.11 to 6.72 ng g-1, respectively, in surface sediment. It was deduced from the composition profile of HCH isomers and DDT congeners that HCH residues derived from a mixture of technical-grade HCH and lindane whereas the DDT residues derived from technical-grade DDT and dicofol. Moreover, both HCH and DDT residues may mainly originate from historical inputs. The hazard quotient of α-HCH, β-HCH, γ-HCH and δ-HCH to marine species was 0.030, 0.157, 3.008 and 0.008, respectively. It was estimated that the overall probability of adverse biological effect from HCHs was less than 5%, indicating that its risk to seawater column species was low. The threshold effect concentration exceeding frequency of γ-HCH, p,p'-DDD, p,p'-DDE and p,p'-DDT in sediment ranged from 8.3% to 100%, and the relative concentration of the HCH and DDT mixture exceeded their probable effect level in sediment. These findings indicated that the risk to marine benthos was high and potentially detrimental to the safety of aquatic products, e.g., sea cucumber and benthic shellfish.     

Abundance and Distribution of Fatty Acids in Sediments of the South Mid-Atlantic Ridge

Sediment samples obtained from the South Mid-Atlantic Ridge were studies by gas chromatography-mass spectrometer(GC-MS) for the abundance and distributions of total fatty acids(TFAs). Approximately 34 fatty acids were identified, with the chain-lengths ranging from C12 to C30. The total concentrations of TFAs(∑TFA) ranged from 7.15 to 30.09 μg g-1 dry sediment, and ∑TFA was weakly correlated with bitumen content(R2 = 0.69). The ∑TFA of samples around hydrothermal areas were significantly higher than that of samples away from hydrothermal areas, indicating intense primary production and large biomass in the hydrothermal areas, and suggesting a close relationship between hydrothermal activity and ∑TFA of samples. The characteristics of the TFA composition in the present study are rich in monounsaturated fatty acids and lacking in polyunsaturated fatty acids, and the ratios between the concentrations of monounsaturated fatty acids and ΣTFAs in samples close to the hydrothermal areas, are about 0.8, but for samples far from the hydrothermal areas, they are only about 0.5. Several fatty acids(e.g., a/i C15:0 and C16:1ω7), which are signature biomarkers for sulfur-metabolizing bacteria, show the same distribution trend as ∑TFA of samples, further highlighting the close relationship between fatty acid content and hydrothermal activity and/or hydrothermal communities. The metabolic activities of hydrothermal communities, especially those of microorganisms, are likely the main source of fatty acids in samples.     

Impact of Human Activities on Depositional Process of Tidal Flat in Quanzhou Bay of China

As a very important component of a coastal system,tidal flats come to be a focus of the studies on land-ocean interaction in the coastal zone because those areas are subjected to intense human activities and are highly sensitive to the global change.The Quanzhou Bay,located along the middle part of Fujian coast of China,covers about 136.4km2,and the area of coastal wetland in the entire bay from intertidal to subtidal with 6m of water depth accounts for 96% of the total area.Seven short cores were collected and divided in situ with the interval of 5cm on the coastal wetlands of Quanzhou Bay on April 19,2006.The sediment samples were scattered and the grain sizes were measured by using Mastersizer 2000.Human beings' activities on tidal flat have disturbed the vertical distribution of sediments in stratigraphic sequence and accelerated the sedimentation rates.Grain size analysis results show that the grain size diameters increase and sediment becomes worse sorted towards the sea under the strong human disturbance;Spartina alterniflora can play a role of trapping the fine sediment;but near the bank,the sediment becomes coarse and there are two peak values on frequency curve influenced by the sandpile.The trough formed by human activities along the coastline changes the transport path of water and suspended sediment.The sediments are transported through the trough and deposit in it during the flood;the ebb flow is retarded by the flow output through the adjacent trough,and the deposited sediment can not be re-suspended;then,the sedimentation rate increases.In situ observation show that the sedimentation rate is about 8-10cm/yr.     

Summertime freshwater fractions in the surface water of the western Arctic Ocean evaluated from total alkalinity

As a quasi-conservative tracer, measures of total alkalinity （TA） can be utilized to trace the relative fractions of freshwater and seawater. In this study, based on the TA and related data collected during the third Chinese National Arctic Research Expedition （JulySeptember 2008, 3rd CHINARE-Arctic） and the fourth Chinese National Arctic Research Expedition （JulySeptember 2010, 4th CH1NARE-Arctic）, fractions of sea-ice meltwater, river runoff, and seawater within the surface water of the western Arctic Ocean were determined using salinil~~ and TA relationships. The largest fraction of seeL-ice meltwater was found around 75~N within the Canada Basin during both surveys, which is located at the ice edge. Generally, it was found that the frac- tion of river runoff was less than that of sea-ice meltwater. The river runoff, composed mainly of contributions from the Yukon River carried by Bering inflow water and the Mackenzie River, was influenced by the currents, leading to two peak areas of its fraction. Our results show that the dilution effect of freshwater carried by Bering inflow water during the 3rd CH1NARE-Arctic in 2008 expedition period may be stronger than that during the 4th CH1NARE-Arctic in 2010 expedition period. The peak area of sea-ice meltwater fraction during the 4th CH1NARE-Arctic was different from that of the 3rd CHINAR-E-Arctic, corresponding to their sea-ice condition.     

Three tropical seagrasses as potential bio-indicators to trace metals in Xincun Bay, Hainan Island, South China

Concentrations of the trace metals Cu,Cd,Pb,and Zn were measured in seawater,rhizosphere sediments,interstitial water,and the tissues of three tropical species of seagrasses (Thalassia hemprichii,Enhalus acoroides and Cymodocea rotundata) from Xincun Bay of Hainan Island,South China.We analyzed different environmental compartments and the highest concentrations of Pb and Zn were found in the interstitial and seawater.The concentrations of Cd and Zn were significantly higher in blades compared with roots or rhizomes in T.hemprichii and E.acoroides,respectively.A metal pollution index (MPI) demonstrated that sediment,interstitial water,and seagrasses in the sites located nearest anthropogenic sources of pollution had the most abundant metal concentrations.There was obvious seasonal variation of these metals in the three seagrasses with higher concentrations of Cu,Pb and Zn in January and Cd in July.Furthermore,the relationships between metal concentrations in seagrasses and environmental compartments were positively correlated significantly.The bioconcentration factors (BCF) demonstrated that Cd from the tissues of the three seagrasses might be absorbed from the sediment by the roots.However,for C.rotundata,Zn is likely to be derived from the seawater through its blades.Therefore,the blades of T.hemprichii,E.acoroides and C.rotundata are potential bio-indicators to Cd content in sediment,and additionally Zn content (C.rotundata only) in seawater.