首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Natural marine gas hydrate was discovered in Korean territorial waters during a 2007 KIGAM cruise to the central/southwestern Ulleung Basin, East Sea. The first data on the geochemical characterization of hydrate-bound water and gas are presented here for cold seep site 07GHP-10 in the central basin sector, together with analogous data for four sites (07GHP-01, 07GHP-02, 07GHP-03, and 07GHP-14) where no hydrates were detected in other cores from the central/southwestern sectors. Hydrate-bound water displayed very low concentrations of major ions (Cl−, SO42−, Na+, Mg2+, K+, and Ca2+), and more positive δD (15.5‰) and δ18O (2.3‰) signatures compared to seawater. Cl– freshening and more positive isotopic values were also observed in the pore water at gas hydrate site 07GHP-10. The inferred sulfate–methane interface (SMI) was very shallow (<5 mbsf) at least at four sites, suggesting the widespread occurrence of anaerobic oxidation of methane (AOM) at shallow sediment depths, and possibly high methane flux. Around the SMI, pore water alkalinity was very high (>40 mM), but the carbon isotopic ratios of dissolved inorganic carbon (δ13CDIC) did not show minimum values typical of AOM. Moreover, macroscopic authigenic carbonates were not observed at any of the core sites. This can plausibly be explained by carbon with high δ13C values diffusing upward from below the SMI, increasing alkalinity via deep methanogenesis and eventually escaping as alkalinity into the water column, with minor precipitation as solid phase. This contrasts, but is not inconsistent with recent reports of methane-fuelled carbonate formation at other sites in the southwestern basin sector. Methane was the main hydrocarbon component (>99.85%) of headspace, void, and hydrate-bound gases, C1/C2+ ratios were at least 1,000, and δ13CCH4 and δDCH4 values were in the typical range of methane generated by microbial reduction of CO2. This is supported by the δ13CC2H6 signatures of void and hydrate-bound gases, and helps clarify some contradictory interpretations existing for the Ulleung Basin as a whole. In combination, these findings suggest that deep biogenic gas and pore waters migrate upward through pathways such as hydrofractures, and measurably influence the shallow carbon cycle. As a result, cation-adjusted alkalinity/removed sulfate diagrams cannot always serve to estimate the degree of alkalinity produced by sulfate reduction and AOM in high methane flux areas.  相似文献   

2.
The pore waters of CH4-containing sediments of the Håkon Mosby Mud Volcano were rich in NH+ 4, Br-, and I-; exhibited a high total alkalinity; but were poor in Cl-and SO2- 4. The geological evidence and our data suggest that organic matter decomposition in preglacial or early interglacial sediments took place during early diagenesis (bacterial processes) and during metamorphism (thermogenic processes under the 3100-m-thick layer of glacial sediments), accompanied by mud volcano fluid generation. It is argued that the CH4of the mud volcano sediments has a mixed, biogenic and thermogenic, origin.  相似文献   

3.
Transport between pore waters and overlying surface waters of Flamengo Bay near Ubatuba, Brazil, was quantified using natural and artificial geochemical tracers, 222Rn, Cl−, and SF6, collected from multi-level piezometers installed along a transect perpendicular to the shore. Eight sampling ports positioned along the length of the piezometers allowed sampling of pore waters at discrete depth intervals from 10 to 230 cmbsf (centimeters below seafloor). Small volume samples were collected from the piezometers using a peristaltic pump to obtain pore water depth profiles. Pore water 222Rn is deficient in shallow sediments, allowing application of a diffusion-corrected 222Rn exchange rate. This model estimates the magnitude of pore water exchange rates to be about 130–419 cm/day. An SF6-saturated fluorescein dye tracer was gently pumped into deep pore waters and exchange rates estimated from this method range from 29 to 185 cm/day. While absolute rates are higher using 222Rn than SF6, rates are of similar magnitudes and the trends with distance from shore are the same – flow is greatest 6 m from shore and decreases by more than 50% further offshore. A Cl− mass balance indicates the greatest fraction of fresh SGD occurs along an apparent preferential flow path in sediments within 5–7 m of the shoreline (87%). Recirculating bay waters through sediments dominate pore water advection at 10 m offshore where only 4% of the flow can be attributed to a freshwater source. Both fresh and marine sources combine to make up submarine groundwater discharge to coastal water bodies. The magnitude of fresh aquifer discharge is often a spatially variable and minor component of the total discharge.  相似文献   

4.
This study investigated the organic carbon accumulation rates (OCARs) and sulfate reduction rates (SRRs) in slope and basin sediments of the Ulleung Basin, East/Japan Sea. These sediments have high organic contents at depths greater than 2,000 m; this is rare for deep-sea sediments, except for those of the Black Sea and Chilean upwelling regions. The mean organic carbon to total nitrogen molar ratio was estimated to be 6.98 in the Ulleung Basin sediments, indicating that the organic matter is predominantly of marine origin. Strong organic carbon enrichment in the Ulleung Basin appears to result from high export production, and low dilution by inputs of terrestrial materials and calcium carbonate. Apparent sedimentation rates, calculated primarily from excess 210Pb distribution below the zone of sediment mixing, varied from 0.033 to 0.116 cm year−1, agreeing well with previous results for the basin. OCARs fluctuated strongly in the range of 2.06–12.5 g C m−2 year−1, these rates being four times higher at the slope sites than at the basin sites. Within the top 15 cm of the sediment, the integrated SRRs ranged from 0.72 to 1.89 mmol m−2 day−1, with rates approximately twice as high in the slope areas as in the basin areas. SRR values were consistently higher in areas of high sedimentation and of high organic carbon accumulation, correlating well with apparent sedimentation rates and OCARs. The sulfate reduction rates recorded in the basin and slope sediments of the Ulleung Basin are higher than those reported for other parts of the world, with the exception of the Peruvian and Chilean upwelling regions. This is consistent with the high organic carbon contents of surface sediments of the Ulleung Basin, suggesting enhanced organic matter fluxes.  相似文献   

5.
A Geographic Information System (GIS)-aided flow-tracking technique was adopted to investigate nutrient exchange rates between specific benthic communities and overlying seawater in a fringing reef of Ishigaki Island, subtropical Northwestern Pacific. Net exchange rates of NO3 −, NO2 −, NH4 +, PO4 3−, Total-N and Total-P were estimated from concentration changes along the drogue trajectories, each of which was tracked by the Global Positioning System and plotted on a benthic map to determine the types of benthic habitat over which the drogue had passed. The observed nutrient exchange rates were compared between 5 typical benthic zones (branched-coral (B) and Heliopora communities (H), seaweed-reefrock zone (W), bare sand area (S), and seagrass meadow (G)). The dependence of nutrient exchange rates on nutrient concentrations, physical conditions and benthic characteristics was analyzed by multiple regression analysis with the aid of GIS. The spatial correlation between nutrient exchange rates and benthic characteristics was confirmed, especially for NO3 − and PO4 3−, which were usually absorbed in hydrographically upstream zones B and W and regenerated in downstream zones H and G. NO3 − uptake in zones B and W was concentration-dependent, and the uptake rate coefficient was estimated to be 0.58 and 0.67 m h−1, respectively. Both nutrient uptake in zone W and regeneration in zone H were enhanced in summer. The net regeneration ratio of NO3 −/PO4 3− in zone H in summer ranged 5.2 to 34 (mean, 17.4), which was somewhat higher than previously measured NO3 −/PO4 3− for sediment pore waters around this zone (1.1–8.5). Nutrient exchanges in zone S were relatively small, indicating semi-closed nutrient cycling at the sediment-water interface of this zone. NH4 + efflux from sediments was suggested in zone G. The data suggest that the spatial pattern of nutrient dynamics over the reef flat community was constrained by zonation of benthic biota, and that abiotic factors such as nutrient concentrations and flow rates, influenced nutrient exchange rates only in absorption-dominated communities such as zones B and W.  相似文献   

6.
Macro- and meiofaunal communities were examined at four geomorphologically distinct sites with different gas- and oil-bearing fluid characteristics in the northern, central and southern basins of Lake Baikal. All sites had elevated concentrations of bicarbonate, nitrate, sulphate and chloride ions in pore fluids, with highest values at the Frolikha vent. Elevated levels of iron ions were found in pore waters of the St. Petersburg methane seep and the Gorevoy Utes oil seep. The chemical composition of pore waters at the Malenky mud volcano was similar to that reported in earlier work. Consistent with published data, the Frolikha vent (northern basin) and the St. Petersburg methane seep (central basin) were characterised by methane of mixed genesis (thermogenic + biogenic), whereas the methane source was mainly thermogenic at the Gorevoy Utes oil seep (central basin) and biogenic at the Malenky mud volcano (southern basin). In contrast to marine seep ecosystems, the macrofauna was dominated only by amphipods, giant planarians and oligochaetes, whereas bivalves were absent; the meiofauna was similar to its marine counterpart, being dominated by nematodes, cyclops, harpacticoids and ostracods. A statistically significant positive relationship was revealed between faunal abundance and the availability of bacterial mats on seep sediments. Moreover, ANOVA tests showed significant increases in both meiozoobenthic and macrozoobenthic densities at “hot spot” vent/seep sites relative to discharge-free reference sites. The isotopic composition of carbon and nitrogen at various trophic levels of these benthic vent/seep communities was found to differ markedly from that reported by earlier studies for the pelagic and other benthic food webs in Lake Baikal. As in marine seeps, the macrofauna had variable isotopic signatures. Light δ13C and δ15N values suggest the utilization of chemosynthetically fixed and/or methane-derived organic matter. By contrast, the heavy δ13C signatures of some mobile amphipods likely reflect consumption of photosynthetically derived carbon. These findings would at least partly explain why Lake Baikal is a notable outlier in global temperature–biodiversity patterns, exhibiting the highest biodiversity of any lake worldwide but at an extremely cold average temperature.  相似文献   

7.
The Arcachon lagoon is a 156 km2 temperate mesotidal lagoon dominated by tidal flats (66% of the surface area). The methane (CH4) sources, sinks and fluxes were estimated from water and pore water concentrations, from chamber flux measurements at the sediment–air (low tide), sediment–water and water–air (high tide) interfaces, and from potential oxidation and production rate measurements in sediments. CH4 concentrations in waters were maximal (500–1000 nmol l−1) in river waters and in tidal creeks at low tide, and minimal in the lagoon at high tide (<50 nmol l−1). The major CH4 sources are continental waters and the tidal pumping of sediment pore waters at low tide. Methanogenesis occurred in the tidal flat sediments, in which pore water concentrations were relatively high (2.5–8.0 μmol l−1). Nevertheless, the sediment was a minor CH4 source for the water column and the atmosphere because of a high degree of anaerobic and aerobic CH4 oxidation in sediments. Atmospheric CH4 fluxes at high and low tide were low compared to freshwater wetlands. Temperate tidal lagoons appear to be very minor contributor of CH4 to global atmosphere and to open ocean.  相似文献   

8.
We report some main results of multidisciplinary investigations carried out within the framework of the Indian National Gas Hydrate Program in 2002–2003 in the Krishna–Godavari Basin offshore sector, east coast of India, to explore indicators of likely gas hydrate occurrence suggested by preliminary multi-channel seismic reflection data and estimates of gas hydrate stability zone thickness. Swath bathymetry data reveal new evidence of three distinct geomorphic units representing (1) a delta front incised by several narrow valleys and mass flows, (2) a deep fan in the east and (3) a WNW–ESE-trending sedimentary ridge in the south. Deep-tow digital side-scan sonar, multi-frequency chirp sonar, and sub-bottom profiler records indicate several surface and subsurface gas-escape features with a highly resolved stratification within the upper 50 m sedimentary strata. Multi-channel seismic reflection data show the presence of bottom simulating reflections of continuous to discrete character. Textural analyses of 76 gravity cores indicate that the sediments are mostly silty clay. Geochemical analyses reveal decreasing downcore pore water sulphate (SO4 2−) concentrations (28.7 to <4 mM), increasing downcore methane (CH4) concentrations (0–20 nM) and relatively high total organic carbon contents (1–2.5%), and microbial analyses a high abundance of microbes in top core sediments and a low abundance of sulphate-reducing bacteria in bottom core sediments. Methane-derived authigenic carbonates were identified in some cores. Combined with evidence of gas-escape features in association with bottom simulating reflections, the findings strongly suggest that the physicochemical conditions prevailing in the study area are highly conducive to methane generation and gas hydrate occurrence. Deep drilling from aboard the JOIDES Resolution during 2006 has indeed confirmed the presence of gas hydrate in the Krishna–Godavari Basin offshore.  相似文献   

9.
Two sites of the Deep Sea Drilling Project in contrasting geologic settings provide a basis for comparison of the geochemical conditions associated with marine gas hydrates in continental margin sediments. Site 533 is located at 3191 m water depth on a spit-like extension of the continental rise on a passive margin in the Atlantic Ocean. Site 568, at 2031 m water depth, is in upper slope sediment of an active accretionary margin in the Pacific Ocean. Both sites are characterized by high rates of sedimentation, and the organic carbon contents of these sediments generally exceed 0.5%. Anomalous seismic reflections that transgress sedimentary structures and parallel the seafloor, suggested the presence of gas hydrates at both sites, and, during coring, small samples of gas hydrate were recovered at subbottom depths of 238m (Site 533) and 404 m (Site 568). The principal gaseous components of the gas hydrates wer methane, ethane, and CO2. Residual methane in sediments at both sites usually exceeded 10 mll?1 of wet sediment. Carbon isotopic compositions of methane, CO2, and ΣCO2 followed parallel trends with depth, suggesting that methane formed mainly as a result of biological reduction of oxidized carbon. Salinity of pore waters decreased with depth, a likely result of gas hydrate formation. These geochemical characteristics define some of the conditions associated with the occurrence of gas hydrates formed by in situ processes in continental margin sediments.  相似文献   

10.
An analysis is presented of data on chlorophyll a concentrations of the total and the netplankton (>10 μm), determined either in April to June or in August to September from 48°N to 15°S along 175°E in the Pacific Ocean during 6 years by the NOPACCS (Northwest Pacific Carbon Cycle Study). Particular attention was given to the variability of absolute concentrations of the netplankton chlorophyll a and their percentage shares of the total chlorophyll a concentration. Below 0.2 μg l−1 of surface total chlorophyll a, the netplankton chlorophyll a showed low percentage shares (such as 12.7% on average) with a large variation, but above 0.2 μg l−1 it was 35.9% on average with less variation, showing an accelerated increase at high total chlorophyll a concentrations. High netplankton chlorophyll a concentrations in surface waters were observed at high latitudes, in waters having high chlorophyll a concentrations at sub-surface depth, and in equatorial upwelling. The percentage shares of netplankton in the total chlorophyll a in the euphotic zone were 8.5% and 25.9% above and below 0.2 μg l−1, respectively, although the data points scattered over a wide range (from 7.2% to 53.8%) depending on differences in water masses, depths and seasons. High chlorophyll a concentrations and high percentage shares of netplankton corresponded to high ambient nitrate plus nitrite concentrations. Integrated netplankton chlorophyll a concentrations in the euphotic zone varied from 0.7 to 19.5 mg m−2 in waters below 0.2 μg l−1 of surface total chlorophyll a, and from 2.0 to 29.5 mg m−2 above 0.2 μg l−1, and the percentage shares of netplankton for the former were 7.4% on average and 23.7% for the latter. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
Experiments with a set of electrolyte solutions have been carried out to investigate the effects of pore water composition changes on the stability conditions of methane hydrate in marine sediments. The results reveal that (1) SO42− and Cl− concentration changes can affect hydrate stability slightly, (2) the changes in both the type and the concentration of cations, which occur in normal diagenetic processes, do not exert a significant influence on the methane hydrate stability conditions, and (3) the shift of hydrate stability in pore water can be expressed as a function of the Cl− concentration only. Based on the results above, an empirical equation ΔT (K)=0.00206 Cl− (mmol/dm3) has been obtained for estimating the shift in the equilibrium temperature of methane hydrate in pore water at a given pressure.  相似文献   

12.
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 δ13C 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 δ13C-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 (<10 mbsf) by a present-day sulfate–methane interface (SMI) at 5 m with a high amount of pyrite (84–221 μmol/g) and a high concentration of dissolved sulfide.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.  相似文献   

13.
Copper concentrations have been measured in more than 200 samples collected from an Alaskan fjord and continental shelf and slope regions in the northwestern Gulf of Alaska. Concentrations were lowest (2·1 nmol kg−1) at depths of 400–1000 m in the continental slope waters of the Gulf of Alaska. Copper increased systematically with decreasing salinities shoreward to concentrations >30 nmol kg−1 in fjord surface waters during summer months of high freshwater runoff. Copper concentrations increased with depth at an inner fjord station where deep basin waters have restricted circulation, and these data together with surface (<5 cm) pore water copper concentrations (mean=122 nmol kg−1) about an order of magnitude higher than bottom water copper concentrations are indicative of a flux of copper across the sediment-seawater interface. This latter was estimated at 32±12 nmol cm−2 annually, and represented less than 20% of the annual input to fjord surface water (228–411 nmol cm−2) added during summer months. Mass balances in bottom waters indicate a vigorous recycling of copper with a residence time estimated at 21±11 days. Most copper that is remobilized in surface sediments is returned to bottom waters and little (3%) is removed by subsequent diagenetic reaction in the buried sediments. However, an estimate of copper accumulating in anoxic fjord sediments was comparable with copper added to fjord surface waters suggesting that input-removal reactions rather than internal cycling controls copper geochemistry in this estuary.  相似文献   

14.
The petrophysical properties of sediment drill core samples recovered from the Sardinian margin and the abyssal plain of the Southern Tyrrhenian Basin were used to estimate the downhole change in porosity and rates of deposition and mass accumulation. We calculated how the deposited material has changed its thickness as a function of depth, and corrected the thickness for the compaction. The corresponding porosity variation with depth for terrigenous and pelagic sediments and evaporites was modelled according to an exponential law. The mass accumulation rate for the Plio-Quaternary is on average 4.8×104 kg m−2 my−1 on the Sardinian margin and for the Pliocene in the abyssal plain. In the latter area, the Quaternary attains its greatest thickness and a mass accumulation rate of 11–40×104 kg m−2 my−1. The basement response to sediment loading was calculated with Airy-type backstripping. On the lower part of the Sardinian margin, the basement subsidence rate due to sediment loading has decreased from a value of 300 m my−1 in the Tortonian and during the Messinian salinity crisis (7.0–5.33 Ma) to about 5 m my−1 in the Plio-Quaternary. In contrast, on the abyssal plain this rate has changed from 8–50 m my−1 during the period 3.6–0.46 Ma, to 95–130 m my−1 since 0.46 Ma, with the largest values in the Marsili Basin. The correlation between age and the depth to the basement corrected for the loading of the sediment in the ocean domain of the Tyrrhenian Basin argues for a young age of basin formation.  相似文献   

15.
We investigated the molecular composition (methane, ethane, and propane) and stable isotope composition (methane and ethane) of hydrate-bound gas in sediments of Lake Baikal. Hydrate-bearing sediment cores were retrieved from eight gas seep sites, located in the southern and central Baikal basins. Empirical classification of the methane stable isotopes (δ13C and δD) for all the seep sites indicated the dominant microbial origin of methane via methyl-type fermentation; however, a mixture of thermogenic and microbial gases resulted in relatively high methane δ13C signatures at two sites where ethane δ13C indicated a typical thermogenic origin. At one of the sites in the southern Baikal basin, we found gas hydrates of enclathrated microbial ethane in which 13C and deuterium were both highly depleted (mean δ13C and δD of –61.6‰ V-PDB and –285.4‰ V-SMOW, respectively). To the best of our knowledge, this is the first report of C2 δ13C–δD classification for hydrate-bound gas in either freshwater or marine environments.  相似文献   

16.
We have developed, deployed, and tested a novel probe for study of the geochemistry of sediment pore waters based upon Raman spectroscopy. The Raman technique has already been used successfully for in situ measurements of targets of scientific interest including gas and hydrothermal vents and complex gas hydrates, but sediment geochemistry has so far been an intractable problem since the sediments themselves are strongly fluorescent and typically only very small sample volumes are obtainable. The 35 cm long probe extracts pore fluids through a 10 μm sintered metallic frit and draws the sample through a 2 mm diameter channel into a sapphire windowed optical cell within which the laser beam is focused and the spectrum recorded. The dead volume of the system is ～1 ml and the instrument is ROV deployable with activation of probe insertion and sample withdrawal under direct operator control. The unique features of this mode of detection include observation of the sulfate gradient in marine pore waters as an indicator of diagenesis, direct measurement of the dissolved sulfide species H2S and HS?, and measurement of dissolved methane; all of which are of primary geochemical interest. Quantitative analysis is achieved by area ratio to known water peaks and from standard calibration curves with a precision of ±5%. We find only very small fluorescence from pore waters measured in situ, but observe rapid increases in fluorescence from cores returned to the surface and exposed to oxygen.  相似文献   

17.
A shallow hydrothermal brine seep located off the Greek island of Milos in the Aegean Sea was studied. The brine fluid outcropped as a pool of water in a seabed depression and was detected in the surrounding pore-waters of sediments colonised by the sulphur bacterium Achromatium volutans. The seep fluid was highly saline and sulphidic, depleted in Mg2+ and SO42−, but enriched over seawater in Na+, Ca2+, K+, Cl−, SiO2, reduced species and dissolved gases. The high concentrations of Na+, Ca2+ and K+ were consistent with the Milos tectonic setting. Na-K and Na-K-Ca geothermometers predicted a reservoir temperature of 300–325 °C for the most concentrated seep samples. The deep geothermal reservoir within the metamorphic basement of Milos island has already been located and studied and may represent the source of the seep fluid. Faunal diversity was lowest in seep-influenced sediments, but a sulphide-intolerant species was found in areas of the bacterial mat where salinity and temperature were much lower. Pressure-induced variations in the vertical depth of the brine interface may be occurring in the sediment.  相似文献   

18.
Dissolved and particulate concentrations of silver in Tokyo Bay estuarine waters and Japanese rivers were determined in this study. The dissolved silver concentrations in the surface water of Tokyo Bay range from 5.9 to 15.1 pmol kg−1, which is comparable to those in the surface water of the Japan Sea, but two or three times higher than those in the surface water of the open ocean. However, elevated concentrations of dissolved silver are not found in Tokyo Bay compared with those in other highly urbanized estuaries, such as San Francisco Bay (20∼243 pmol kg−1). In the Tokyo Bay estuary, silver typically exhibits non-conservative mixing behavior, which is a common feature in the other estuaries reported previously. Dissolved silver concentrations decrease with salinity from the rivers to the mouth of Tokyo Bay. Silver is efficiently scavenged by suspended particulates, as evidenced by the high conditional distribution coefficients for silver throughout the estuary (log Kd > 5.0 ± 0.6). The silver fluxes into Tokyo Bay via inflowing rivers and atmospheric deposition were estimated as 83 kg y−1 and 15 kg y−1, respectively. A simple budget calculation shows that the silver supplied from rivers and atmosphere must be rapidly scavenged within the Tokyo Bay estuary.  相似文献   

19.
The concentrations of Cu, Ni and Cd were determined in Funka Bay during a spring phytoplankton bloom, consisting of diatoms. Just after the bloom, both dissolved Cd and nutrients were removed in the euphotic zone. However, the removal ratio of Cd to phosphate was very different from that in seawater. The removal of Cd took place at a Cd/phosphate ratio of 0.07×10−3, which was lower than in seawater before the bloom (0.25×10−3), leading to an increase in this ratio in seawater exceeding 0.7×10−3 at the end of the bloom. Elevated concentrations of Cd and phosphate were observed in the deeper layer after the bloom due to the decomposition of detrital materials produced in the bloom. The ratio of Cd/phosphate in the regeneration step was 0.24×10−3 which was different from the removal ratio of 0.07×10−3. These observations suggest that the high Cd/phosphate ratio in the regeneration would reflect a relatively high regeneration rate of Cd than that of phosphate. No significant decrease in Cu and Ni concentrations was observed during the development of the bloom, suggesting that biological removal of these metals was not so significant during the spring bloom. The concentrations of Cd, Cu and silicate in surface waters increased after the bloom with decreasing salinity due to the influence of a spring thaw.  相似文献   

20.
The results of microbiological, biogeochemical, and isotope geochemical studies in the Kara Sea are described. The samples for these studies were obtained during the 54th voyage of the research vessel Akademik Mstislav Keldysh in September 2007. The studied area covered the northern, central, and southwestern parts of the Kara Sea and the Gulf of Ob. The quantitative characteristics of the total bacterial population and the activity of the microbial processes in the water column and bottom sediments were obtained. The total population of the bacterioplankton (BP) varied from 250000 cells/ml in the northern water area to 3000000 cells/ml in the Gulf of Ob. The BP population depended on the content of the water suspension. The net BP production was minimal in the central water area, amounting to 0.15–0.2 μg C/(l day), and maximal (0.5–0.75 μg C/(l day)) in the Gulf of Ob. The organic material at the majority of the stations in the Ob transect predominantly contained light carbon isotopes (−28.0 to −30.18‰) of terrigenous origin. The methane content in the surface water layer varied from 0.18 to 2.0 μl CH4/l, and the methane oxidation rate changed in the range of 0.1–100 nl CH4/(l day). The methane concentration in the upper sediment layer varied from 30 to 300 μl CH4/dm3; the rate of the methanogenesis was 44 to 500 nl CH4/(dm3 day) and that of the methane oxidation, 30 to 2000 nl CH4/(dm3 day). The rate of the sulfate reduction varied from 4 to 184 μg S/(dm3 day).  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号