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1.
Iodate (IO3−) is the predominant dissolved species of iodine in the oxygenated waters of the Mediterranean Sea. Iodide (I−) is present in significant quantities (up to 65 nM) in oxygenated waters in the photic zone and near the interface above the anoxic and saline Bannock Basin. Lesser quantities of I− (< 10 nM) are found throughout the rest of the oxic water column. An additional unidentified dissolved iodine species is present immediately above the anoxic interface.Total dissolved iodine (ΣI) increases dramatically across the seawater/brine interface. Part of this increase is undoubtedly the result of the dissolution of iodine-rich evaporites during formation of the brine bodies at the Tyro and Bannock Basins. The vertical distribution of ΣI and other dissolved chemical species (particularly PO43−) in the Bannock Basin brine, however, suggests an additional, present-day, diagenetic source of dissolved iodine to the brine. Based on the increase in the concentration of the most soluble major ions across the seawater/brine interface, 5–7 μM of the 11.5-μM increase in ΣI concentration must be attributed to diagenesis.  相似文献   

2.
The Tyro and Bannock Basins, which are depressions in the eastern Mediterranean, contain hypersaline anoxic brines. These brines are of different composition: Tyro brine is primarily an early-stage halite (NaCl) brine, whereas Bannock brine includes the more soluble ions of late-stage evaporite minerals. Accordingly, the Bannock brine contains a much greater sulphate concentration than the Tyro Brine. This difference in sulphate concentration is reflected in the concentrations of ions such as Ca, Sr and Ba, which form sparingly soluble sulphate minerals.Equilibrium calculations using the Pitzer specific ion interaction model indicate that the brines in both basins are saturated with respect to gypsum (CaSO4-2H2O) and supersaturated to saturated with respect to dolomite (CaMg(CO3)2). The degree of saturation with respect to dolomite is greater in the Bannock Basin than it is in the Tyro Basin. Correspondingly, recent gypsum crystals and dolomite hardgrounds have been found in the Bannock Basin but not in the Tyro Basin.The Tyro brine is homogeneous in composition, whereas the Bannock brine demonstrates a clear two-layer brine structure. At the interface of the upper and the lower brine distinct positive anomalies occur in the total alkalinity and the concentration of phosphate, and negative anomalies occur in the concentrations of Mn2+ and the rare earth elements (REE). These anomalies and the observed association of gypsum/dolomite in the sediments are all consistent with a recent precipitation of dolomite and gypsum in the Bannock Basin. The brines in both basins are also saturated with respect to barite (BaSO4).The 87Sr/86Sr and δ34S ratios of the Bannock brines are amazingly consistent but differ dramatically from the values for modern or Messinian-age seawater. The Sr concentration and Sr and S isotope ratios in the gypsum crystals indicate that most of these crystals have resulted from precipitation/recrystallization from the brine and not from seawater. The observed variations between crystals are thought to reflect the recrystallization of (sub-) outcropping Messinian gypsum with a low 87Sr/86Sr ratio in the presence of seawater or brine fluids and with different extents of diagenesis.  相似文献   

3.
In the anoxic hypersaline Tyro and Bannock Basins of the eastern Mediterranean, extremely high concentrations of Co (0.015%), Cu (1.35%) and Zn (0.28%) were found in suspended matter collected at the sharp interface between seawater and the anoxic brine. The high particulate Co, Cu and Zn concentrations can be explained by the sharp increase in dissolved sulphide at these interfaces, and the resultant precipitation of metal sulphides. The particulate As, Sb and Mo concentrations also showed a sharp maximum at or close to the interface. However, the contributions of As, Sb and Mo contents in suspended matter to the total concentrations in the water column are small. Scanning electron microscopy-energy-dispersive X-ray analysis (SEM-EDAX) of suspended particulate matter from the Tyro Basin revealed spherical particles strongly enriched in Fe, Cu and Zn at the seawater-brine interface.  相似文献   

4.
Seawater and brine samples collected along vertical profiles above the Bannock and Tyro Basins (eastern Mediterranean), and gypsum samples collected by dredging and coring the anoxic section of the Bannock Basin, have been studied for their δ18O values. The following conclusions may be drawn from these data: (1) The water of the deep brines is isotopically slightly different from modern Mediterranean bottom water and might be a ‘fossil water’ possibly formed during a recent, climatically cooler stage or when the evaporation was slightly higher than nowadays. (2) The similarity between the δ18O values of the brine samples from the Bannock and Tyro Basins supports the possibility that the ages of the two basins are very close to each other. (3) Gypsum crystals on the bottom of the Bannock Basin are probably being formed by the dissolution and reprecipitation of sub-bottom (or outcropping) Messinian evaporites. This hypothesis is supported by the oxygen isotopic values exhibited by the gypsum crystallization water and by the oxygen and sulphur isotopic composition of gypsum. (4) The shells of pelagic organisms included in gypsum are probably very recent, but not contemporary, and may be referred to cooler environmental conditions.  相似文献   

5.
Polarographic techniques have been used to determine reduced inorganic sulphur speciation in recent anoxic marine sediments from two hypersaline basins, the Tyro and the Bannock Basins, in the Eastern Mediterranean. The following phases were determined: acid volatile sulphur (AVS), pyritic sulphur and zerovalent sulphur. The determination of AVS and pyrite was based respectively on the acidification and Cr(II) reduction of these sulphur components to H2S. H2S was collected in base and the sulphide concentration was measured by polarography. Standard Na2S and pyrite gave recoveries of 99.6% ± 3.9% and 97% ± 12% respectively. Total zerovalent sulphur in a sediment sample was measured by the reaction of sulphite with thiosulphate. Thiosulphate was measured directly by polarography.

Pyrite is the main phase of inorganic reduced sulphur in the sediments from the Tyro and the Bannock Basins, and it has about the same average level (125 υmoles per gramme dry weight) in the cores recovered from the two areas. However, the distribution of pyrite in the top 100 cm of the two cores differs significantly. In the Bannock Basin a sharp increase is observed with depth, whereas in the Tyro Basin there is a small decrease with depth.

The total amount of reduced inorganic sulphur is less than the total amount of sulphur in the sediments. This indicates that there must be additional sulphur-bearing phases. One of these phases may be gypsum, and indeed, gypsum crystals have been observed in the Bannock Basin.

In neither basin is there a significant correlation between reduced sulphur and organic carbon. The pyrite that occurs in these basins may have been formed syngenetically at the interface of the anoxic brine and oxic seawater. Diagenetic pyrite may have been formed within the sediments of the basins. AVS and total zerovalent sulphur are still observed at depth. We therefore suggest that this may be due to the incomplete transformation of AVS and zerovalent sulphur into pyrite.  相似文献   


6.
Elevated methane (CH4) concentrations (128–2692×103 nM) occur in the hypersaline anoxic brine pools of Bannock and Urania Basins, eastern Mediterranean Sea, compared to low concentrations (17–80×103 nM) in the sediments below the anoxic brines. The CH4 enrichment in the brines might be due to the long residence time of the brine in the Basin. An attempt is made to determine the sources for the enriched dissolved CH4 by considering the influence of hydrothermal activity, the occurrence of sapropel layers (biogenic) and dissolution of gas hydrates. Furthermore, it is suggested that the enriched CH4 in Bannock and Urania Basins is diffused and mixed with the overlying waters by local upward transport mechanisms that selectively move CH4 upward in these Basins.  相似文献   

7.
Peculiar pellicles have been recorded in the extant anoxic hypersaline basins of the Bannock area and the Western Strabo Trench (Eastern Mediterranean). Discrete layers of pellicles were found in 29 cores. They are oriented parallel to bedding planes or are folded within the sandy base of turbidites and within slumped sediments. In addition, similar pellicles occur at the surface of or interlocked within gypsum crystals recovered from the Bannock area.

The pellicles are 0.5–3 mm thick and dark greenish-grey in colour. They foliate into very small (<1 mm) undulating and anastomosing microlaminae entrapping abundant biogenic and inorganic particles. The amorphous organic matter of the pellicles is most probably produced by bacterial masses linked to mineralization processes of the organic debris. Anaerobic sulphate-reducing bacteria (Desulphovibrio) are abundant and the presence of methane bacteria is likely.

Detailed analyses with the light microscope and scanning electron microscope yielded differences and similarities concerning ultrastructure, content, abundance and morphotypes of the bacterial pellicles from the Bannock area and the Western Strabo Trench. A consistently well-developed ultrastructure comprising thin microlaminae characterizes the Bannock pellicles, whereas the ultrastructure of the Tyro and Poseidon pellicles is usually not organized. Siliceous microfossils are abundant in samples from both sites, but centrate diatoms prevail in the Bannock pellicles whereas pennate diatoms are overwhelmingly dominant in the Tyro and Poseidon pellicles. Calcareous micro- and nannofossils, together with pyrite framboids, are more abundant in samples from the Bannock area. Bacteria are extremely abundant in samples from the Bannock area and three different morphological types have been distinguished. Only one type of bacteria was commonly observed in pellicles from the Western Strabo Trench basins.

Pellicles form at the normal seawater/brine interface, as substantiated by transmittance profiles and bacteriological investigations. Therefore, the term “deep mid-water bacterial mats” is proposed herein for these peculiar layers.

After bacterial mats grow at the interface, they are included within the sediments by following one of two different paths: (a) when pelagic sedimentation prevails, pellicles sink to the basin floor due to the increasing load of biogenic and inorganic detritus, and (b) under a tectonically active regime, turbidity currents and slumps can disrupt the interface and destroy the floating mats. In the latter case, fragments of pellicles are transported to the bottom within the gravity flows.  相似文献   


8.
Vertical gas profiles of N2, N2O and O2were obtained in intact sediment cores from a Tagus estuary salt marsh using membrane inlet mass spectrometry. This technique allows direct measurements of dissolved gas concentrations with minimal disturbance. O2concentrations decreased sharply with depth, becoming undetectable below 14mm. Denitrification products (N2and N2O) occurred in the surface layer of the sediment where O2was present. Diffusion of N2and N2O from the anaerobic zone, denitrification in anaerobic microsites and aerobic denitrification are possible explanations for this observation. N2was the sole product of denitrification in control sediment cores probably because of the great demand for electron acceptors in this sediment. The addition of NO3 − and CH3CO2 − increased the concentrations of N2and N2O in the sediment. Significantly higher concentrations in treated cores occurred between 1·5 and 2·0cm for N2and between 0·5 and 1·5cm for N2O. The peak in N2concentration occurred in the anaerobic zone of the sediment, close to the aerobic–anaerobic interface while the peak in N2O concentration occurred above this interface where concentrations of O2were approximately 10μM. This is indicative that, in this sediment, production of N2O is less sensitive to the presence of O2than reduction of N2O to N2.  相似文献   

9.
Chemical profiles of both oxidized (nitrate and sulfate) and reduced (ammonium, sulfide, acid-volatile sulfide [AVS], and pyrite) materials and the corresponding distribution of denitrifier microbial communities were measured at low tide in sediments at Guandu in the estuary of the Tanshui River, northern Taiwan in August 2002. Denitrifier strains were isolated for physiological and phylogenic analyses. Based on the distribution of nitrogenous compounds and denitrifier abundances, the vertical profile of Guandu sediments could be separated into four layers: a mixed layer (the top 1 cm of depth, respectively containing 0.82–2.37 and 535.9–475.0 μM of nitrate and ammonium), a nitrate-concentrated layer (1–5 cm in depth, 2.37–0.53 and 475.0–1192.1 μM, respectively), a denitrifier-aggregation layer (5–7 cm in depth, 0.53–0.72 and 1192.1–1430.1 μM, respectively), and an ammonium-enriched layer (7–12 cm in depth, 0.72–0.78 and 1430.1–2196.6 μM, respectively). Denitrifier strains were detected in all layers except for the mixed layer. A variety of metabolic processes by these strains may occur in different layers. Bacillus jeotgali-, Bacillus sphaericus-, and Bacillus firmus-related strains isolated from the nitrate-concentrated layer may be involved in the nitrification-denitrification coupling process due to the relatively low nitrate concentrations (maximum = 2.37 μM), and may contribute to denitrification not nitrification. Bacillus bataviensis- and B. jeotgali-related strains isolated from the denitrifier-aggregation layer comprised the predominant denitrifier population (3.64 × 104 cells/g of denitrifier abundance). They possess the ability of dissimilatory nitrate reduction to ammonium (DNRA). Bacillus jeotgali-related strains and two newly identified strains of GD0705 and GD0706 isolated from the ammonium-enriched layer possibly use fermentative processes as the main metabolic pathway instead of denitrification when nitrate is scarce, and this further supports the high ammonium concentrations (up to 2.20 mM) found in the Guandu sediments. In addition, spore formation also enhances the chance of survival of these strains in the face with such a nitrate-deficient environment.  相似文献   

10.
N2O Production, Nitrification and Denitrification in an Estuarine Sediment   总被引：1，自引：0，他引：1  
The mechanisms regulating N2O production in an estuarine sediment (Tama Estuary, Japan) were studied by comparing the change in N2O production with those in nitrification and denitrification using an experimental continuous-flow sediment–water system with15N tracer (15N-NO−3 addition). From Feburary to May, both nitrification and denitrification in the sediment increased (246 to 716 μmol N m−2 h−1and 214 to 1260 μmol N m−2 h−1, respectively), while benthic N2O evolution decreased slightly (1560 to 1250 nmol N m−2 h−1). Apparent diffusion coefficients of inorganic nitrogen compounds and O2at the sediment–water interface, calculated from the respective concentration gradients and benthic fluxes, were close to the molecular diffusion coefficients (0·68–2·0 times) in February. However, they increased to 8·8–52 times in May except for that of NO−2, suggesting that the enhanced NO−3 and O2supply from the overlying water by benthic irrigation likely stimulated nitrification and denitrification. Since the progress of anoxic condition by the rise of temperature from February to May (9 to 16 °C) presumably accelerated N2O production through nitrification, the observed decrease in sedimentary N2O production seems to be attributed to the decrease in N2O production/occurrence of its consumption by denitrification. In addition to the activities of both nitrification and denitrification, the change in N2O metabolism during denitrification by the balance between total demand of the electron acceptor and supply of NO−3+NO−2 can be an important factor regulating N2O production in nearshore sediments.  相似文献   

11.
It is shown that the data of Kremling (1983) for iron concentrations in sulphidic basin water fit to a solubility curve assuming reasonable constants for FeS in equilibrium with Fe2+, Fe(HS)2 and FeHS2−. Explanations are offered for the fact that the iron and manganese concentrations are considerably lower in the Framvaren bottom water with high sulphide concentrations (6–8 mM) than in the Gotland Deep with lower sulphide concentrations (0.001–0.052 mM). For other trace metals (Co, Ni, Cu, Zn, Cd, Hg and Pb) equilibrium conditions do not seem to exist.  相似文献   

12.
A brief review of the geological knowledge on the anoxic basins of the eastern Mediterranean is presented. Anoxic basins have been discovered in two different geological settings in the eastern Mediterranean. Bannock Basin belongs to the compressional style of the Mediterranean Ridge, and Tyro and Poseidon Basins belong to the transcurrent tectonic style of the Strabo Trench. The origin of the basins is subsurface salt dissolution triggered by tectonic deformation of the sediments on the Mediterranean Ridge, and tectonic subsidence (pull-apart mechanism) in the Strabo Trench. The onset of a deep-sea brine lake is always related to the outcrop of Messinian salts on the side-walls of the basin. The rate of basin subsidence controls the evolution of the brine lakes, which can also be completely diluted by bottom water circulation.  相似文献   

13.
Potentiometric titrations of deep Black Sea water give reasonably precise values of sulphide in the concentration range 30–300 μmol l−1 and a strong indication of thiols in the concentration range 10–30 μmol l−1. Organic analysis of Black Sea water should therefore include the search for compounds containing SH groups. A simple stoichiometric model indicates that sulphur-containing proteins might be the main source of thiols after hydrolysis and deamination. The alkalinity and total sulphide are simply related by At = 3287 ± 30 + (3.84 ± 0.10) [H2 S]t μmol kg−1. The slope of 3.84 instead of the stoichiometric slope of 2.31 indicates a lack of reduced sulphate in the form of hydrogen sulphide.  相似文献   

14.
Atmospheric and oceanic pCO2 were measured continuously along an Atlantic Meridional transect (50°N–50°S) in September–October 1995 and 1996 (U.K. to the Falklands Islands) and in April–May 1996 (Falklands Islands to the UK). The Atlantic ocean was a net sink for atmospheric CO2 for all 3 transects. The largest sinks were located at high latitudes, in regions of high wind speed, where strong CO2 undersaturations, associated with high biological activity, were observed. In these regions the partial pressure difference between the ocean and the atmosphere reached −110 μatm. A CO2 source occurred in the equatorial region between 0° and 10°S, where ΔpCO2 of up to 40 μatm was found. Another source was in the northern subtropical gyre where its extension varied according to the season. Along the whole transect the October cruises exhibited similar pCO2 distributions suggesting a dominance of the seasonal variability and small year to year changes.  相似文献   

15.
β-dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) concentrations were recorded from September 1999 to September 2000 in two geographically close ecosystems, differently affected by eutrophication: the Little Bay of Toulon and the Niel Bay (N.W. Mediterranean Sea, France). Little Bay had higher nutrient levels ([NO3−]max. = 30.3 μM; [PO43−]max. = 0.46 μM) and higher chlorophyll a concentrations ([chl a]mean = 2.4 μg/L) compared to Niel Bay ([NO3−]max. = 19.7 μM; [PO43−]max. = 0.17 μM; [chl a]mean = 0.4 μg/L). In the two sites, we measured dissolved (DMSPd < 0.2 μm) and particulate DMSP (DMSPp > 0.2 μm) concentrations. The DMSPp was particularly analysed in the 0.2–5, 5–90 and > 90 μm fractions. In the eutrophicated Little Bay, DMSPd concentrations showed a clear seasonality with high values from January to March (124–148 nM). The temporal profile of the DMSPp concentrations was similar, peaking in February–March (38–59 nM). In the less eutrophic Niel Bay, DMSPp concentrations were much lower (6–9 nM in March–April), whereas DMSPd concentrations were relatively high (110–92 nM in February–March). DMS concentrations were elevated from the end of the winter to the spring in Little Bay, ranging from 3 nM in October to 134 nM in March. In the less eutrophic Niel Bay, lower DMS levels were observed, generally not exceeding 20 nM. Each particulate fraction (0.2–5; 5–90; > 90 μm) contained less DMSP in Niel Bay than in Little Bay. At both sites, the 5–90 μm fraction made up most of the DMSPp. This 5–90 μm fraction consisted of microphytoplankton, principally Dinophyceae and Bacillariophyceae. The 5–90 μm biomass calculated from cell biovolumes, was more abundant in Little Bay where the bloom at the end of the winter (165 μg/L in March) occurred at the same time as the DMSP peaks. The estimated DMSPp to biomass ratio for the 5–90 μm fraction was always higher in Little Bay than in Niel Bay. This suggests that the high DMSP levels recorded in Little Bay were not only due to a large Dinophyceae presence in this ecosystem. Indeed, the peak of DMSPp to biomass ratio obtained from cell biovolumes (0.23 nmol/μg in March) was consistent with the proliferation of Alexandrium minutum. This Dinophyceae species may account for between 50% (2894 cells/L) and 63% (4914 cells/L) of the total phytoplankton abundance in the Little Bay of Toulon.  相似文献   

16.
The degree of atmospheric saturation for O2, Ar, and N2 gases in water can be determined to accuracies of ±0.1–0.3% using mass spectrometry to determine the gas ratios and Winkler titrations for oxygen analysis. We describe methods used to obtain this level of accuracy and precision. Oxygen accuracy of ±0.1% can be obtained by careful attention to standardization using KIO3 standards that have been corrected for impurities. Accurate O2/Ar and O2/N2 gas ratios (±0.1–0.2%) are obtainable by measuring the mass ratios against the atmosphere if the effect of different gas concentrations on the performance of the mass spectrometer are taken into account. Oxygen and argon saturation values have been determined previously to accuracies of less than or equal to ±0.1%, but published estimates of the saturation value for nitrogen differ by more than 1%. We have redetermined the N2 saturation value at 19°C and zero salinity to be 0.92% greater than the results reported in the work of Weiss (1970).  相似文献   

17.
Iron-rich concretions are frequently found around plant roots in Tagus estuary (Portugal) where radial delivery of O2 takes place. Salt marsh sediments exhibit cracks that are an additional feature to introduce O2 and other solutes in the upper sediments. Metal concentrations in salt marsh sediments are clearly above the background levels reflecting the anthropogenic sources from a large city with 2.5 million inhabitants, and several industrial centres. In order to evaluate how both oxidised structures influences the redistribution of redox sensitive elements in salt marsh sediments, concretions were collected from roots of Halimione portucaloides below the oxygenated zone. These tubular cylindrical structures were analysed for Fe, Al, Mn, As, and P along 1-cm radial transect in a millimetre scale from the inner part to the adjacent anoxic sediment. In addition, oxidised cracks were analysed for the same spatial resolution, from the sediment–water interface to anoxic layers (2-cm transept). The parallelism between Fe, As, and P concentrations at this microscale is the most noticeable aspect. Iron and As presented very high concentrations in the 4-mm concretions (3.4 mmol g−1 and 3.1 μmol g−1, respectively) and decreased sharply to the host sediment. Oxygen released from roots oxidise the solid sulphides, and the reduced Fe and As are transported towards the root by both diffusion and pore water flow associated with the root water uptake. Subsequently, Fe(III) precipitates and As is retained by sorption and/or coprecipitation. These elements are also enriched in the first 2-mm of oxidised cracks, but in lower concentrations (50% and 30%, respectively). Manganese concentrations in concretions were low (11.8 μmol g−1), indicating that Fe dominates the sediment chemistry. Phosphorus and iron concentrations in the ascorbate fraction were higher in the oxidising surfaces of concretions (10.7 μmol g−1 and 1.6 mmol g−1, respectively) and of cracks (5.1 μmol g−1 and 0.47 mmol g−1). The parallelism of Fe and As distributions includes not only their similar redox chemistries, but also that to phosphate, including control by coprecipitation of the host iron phases. The mechanisms involved in the mobilisation of As and P are however different, whereas As comes from the oxidation of iron sulphides; dissolved P derives from reduction of ferri-hydroxide phases.  相似文献   

18.
The seasonal dynamics of inorganic nutrients and phytoplankton biomass (chlorophyll a), and its relation with hydrological features, was studied in the NW Alboran Sea during four cruises conducted in February, April, July and October 2002. In the upper layers, the seasonal pattern of nutrient concentrations and their molar ratios (N:Si:P) was greatly influenced by hydrological conditions. The higher nutrient concentrations were observed during the spring cruise (2.54 μM NO3−, 0.21 μM PO43− and 1.55 μM Si(OH)4, on average), coinciding with the increase of salinity due to upwelling induced by westerlies. The lowest nutrient concentrations were observed during summer (<0.54 μM NO3−, 0.13 μM PO43− and 0.75 μM Si(OH)4, on average), when the lower salinities were detected. Nutrient molar ratios (N:Si:P) followed the same seasonal pattern as nutrient distribution. During all the cruises, the ratio N:P in the top 20 m was lower than 16:1, indicating a NO3− deficiency relative to PO43−. The N:P ratio increased with depth, reaching values higher than 16:1 in the deeper layers (200–300 m). The N:Si ratio in the top 20 m was lower than 1:1, excepting during spring when N:Si ratios higher than 1:1 were observed in some stations due to the upwelling event. The N:Si ratio increased with depth, showing a maximum at 50–100 m (>1.5:1), which indicates a shift towards Si-deficiency in these layers. The Si:P ratio was much lower than 16:1 throughout the water column during the four cruises. In general, the spatial and seasonal variation of phytoplankton biomass showed a strong coupling with hydrological and chemical fields. The higher chlorophyll a concentrations at the depth of the chlorophyll maximum were found in April (2.57 mg m−3 on average), while the lowest phytoplankton biomass corresponded to the winter cruise (0.74 mg m−3 on average). The low nitrate concentrations together with the low N:P ratios found in the upper layers (top 20 m) during the winter, summer and autumn cruises suggest that N-limitation could occur in these layers during great part of the year. However, N-limitation during the spring cruise was temporally overcome by nutrient enrichment caused by an intense wind-driven upwelling event.  相似文献   

19.
The esterification of two model vertebrate steroid hormones – estradiol (E2) and dehidroepiandrosterone (DHEA) – was studied in the oyster Crassostrea virginica. The activity of acyl-CoA:steroid acyltransferase was characterized in microsomal fractions isolated from oyster digestive glands. The apparent Km and Vmax values changed with the fatty acid acyl-CoA used (C20:4, C18:2, C18:1, C16:1, C18:0 or C16:0), and were in the range of 9–17 μM, and 35–74 pmol/min/mg protein for E2, and in the range of 45–120 μM, and 30–182 pmol/min/mg protein for DHEA. Kinetic parameters were also assessed in gonadal tissue. The enzyme saturated at similar concentrations, although conjugation rates were lower than in digestive gland. Preliminary data shows that tributyltin (TBT) in the low μM range (1–50) strongly inhibits E2 and DHEA esterification, the esterification of E2 being more sensitive to inhibition than that of DHEA. Overall, results indicate that apolar conjugation occurs in oysters, in both digestive gland and gonads, at a very similar rate to mammals, suggesting that this is a well conserved conjugation pathway during evolution. Esterification, together with other mechanisms, can modulate endogenous steroid levels in C. virginica, and might be a target for endocrine disrupters, such as TBT.  相似文献   

20.
We present evidence for strong hydrothermal activity in the eastern Manus Basin (depth: 1700–2100 m), the existence of large scale triple-layered buoyant plumes at depths of 1100 m (“shallow plume”), 1700 m (“deep plume”), and 1400 m (“middle plume” with less extent than the other two plumes) that were revealed from water column anomalies of CH4, Mn, Al and pH observed in November to December 1990. Judging from the horizontal distribution of these parameters, the deep plume seems to originate from two distinct hydrothermal sites (eastern and western sites) in the research area, the eastern site being visually ascertained with deep-tow observations at the same time. The CH4/Mn ratio (mol mol−1) of the deep plume (0.02–0.05) is the lowest yet observed in hydrothermal plumes. The order of magnitude difference of CH4/Mn ratios between the shallow plume and the deep plume suggests that different kinds of fluid-rock interaction occurred to make the hydrothermal end members for the deep and shallow plumes. The shallow plume, which had an areal extent of more than 50 km, may be an episodic “megaplume”, because it was not recognized in the previous CH4 profiles in 1986, and because it has a similar CH4/Mn ratio as the megaplume observed in the North Fiji Basin. We found that the eastern deep plume is characterized by enormously high aluminium concentrations (0.6– 1.5 μmol kg−1), pH anomalies (0.1) and high Al/Mn ratios (10–17). The endmember fluid for the eastern deep plume may have an unusually low pH value to dissolve this much aluminum during fluid-rock interaction, or this plume may originate from an eruption-influenced fluid.  相似文献   

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