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1.
A sulfur budget for the Black Sea anoxic zone   总被引：1，自引：0，他引：1  
A budget for the sulfur cycle in the Black Sea is proposed which incorporates specific biogeochemical process rates. The average sulfide production in the water column is estimated to be 30–50 Tg yr−1, occurring essentially in the layer between 500 and 2000 m. About 3.2–5.2 Tg sulfide yr−1 form during sulfate reduction in surface sediments of the anoxic zone. Total sulfur burial in anoxic sediments of 1 Tg yr−1 consists of 10–70% (ca. 40–50% is the average) water column formed (syngenetic) component, the rest being diagenetic pyrite. As a maximum, between 3 and 5 Tg yr−1 contribute sulfide to the bottom water or diffuse downward in the sediment. About 20–50 Tg yr−1 sulfide is oxidized mostly at the chemocline and about 10–20% of this amount (4.4–9.2 Tg yr−1) below the chemocline by the oxygen of the Lower Bosphorus Current. A model simulating the vertical distribution of sulfide in the Black Sea water column shows net consumption in the upper layers down to ca. 500 m, essentially due to oxidation at the chemocline, and net production down to the bottom. On the basis of the calculated budget anoxic conditions in the Black Sea are sustained by the balance between sulfide production in the anoxic water column and oxidation at the chemocline. On average the residence time of sulfide in the anoxic zone is about 90–150 yr, comparable to the water exchange time between oxic and anoxic zones. Hydrophysical control on the sulfur cycle appears to be the main factor regulating the extent of anoxic conditions in the Black Sea water column, rather than rates of biogeochemical processes.  相似文献   

2.
The report presents the results of the studies of the reduced sulfur species in the water of the anoxic zone of the Black Sea. The content of hydrogen sulfide was determined by means of spectrophotometry using dilution with oxygen-free distilled water. The detection limit of the H2S amounted to 0.3 μM with the method’s precision below 3%. The accuracy of the spectrophotometric determination was verified by iodometry after the fixation of the hydrogen sulfide in zinc acetate under the distillation with argon from the acidified seawater sample.  相似文献   

3.
The paper considers the thermohaline structure of Black Sea abyssal and near-bottom waters on the basis of exact measurements recorded in recent years under the HYDROBLACK and COMSBLACK international projects. The surface water mass (along with the cold mixed layer), the intermediate, abyssal, and near-bottom masses are identified. The upper boundary of deep waters is defined as a depth level where the density ratio decreases down to 0.1 This depth roughly corresponds to the 900–1100 m depth levels. Furthermore, the paper provides potential temperature and salinily values in the near-bottom layer, with an error of, respectively, 0.002°C and 0.002‰, at most. Translated by Vladimir A. Puchkin.  相似文献   

4.
New data are reported on the sulfur isotope composition and concentration of sulfide and sulfate in the upper part of the Black Sea anoxic zone as a function of the potential water density. The observations were performed at a station with the coordinates 44.489° N and 37.869° E three times a week every two days. A local negative deficiency in sulfate concentration up to 1.7% related to the sulfate reduction processes was recorded. This anomaly in sulfate concentration was short-lived and did not affect the sulfur isotope composition. In the upper part of the anaerobic zone, the δ34S(SO4) value varied from 21.2 to 21.5‰, which could have occurred from mixing of water masses from the oxic zone (21.1‰) and the Bottom Convective Layer (23.0 ± 0.2‰). The sulfur isotope composition of sulfide ranged from ?40.8% at a depth of 250 m to ?39.4‰ at the upper boundary of the anoxic zone with a H2S content of only 2.7 μM. Two models (mass balance and fractionation of sulfur isotopes using the Rayleigh equation) are considered to explain the differences in δ34S(H2S) values observed.  相似文献   

5.
The stable isotope ratio of sulfur (34S/32S) in dissolved sulfate and hydrogen sulfide was measured for 20 water samples from two deep hydrocasts from the south-central Black Sea. The isotope ratio of total reduced sulfur was also measured for surface sediment collected below each hydrocast. The range in the δ34S measurements for sulfate was +18.20 to +20.17‰ and for hydrogen sulfide ?38.71 to ?4.85‰. The distribution pattern for δ 34S in both sulfate and sulfide appears to be the result of in situ sulfate reduction.  相似文献   

6.
We discuss the results of analysis of published data and field and laboratory investigations aimed at the solution of the problem of comparabilityof the results of detection of hydrogen sulfide in the Black Sea by spectrophotometric and iodometric methods. We show that the reproducibility of the results of spectrophotometric analysis is higher than hat of the iodometric method only in the case where the content of sulfide in a sample is less than 10–30 μMl−1. When larger concentrations are involved, the traditional iodometric analysis proves to be the most precise and reliable method for the detection of hydrogen sulfide in the Black-Sea waters. Translated by Peter V. Malyshev and Dmitry V. Malyshev  相似文献   

7.
Regularities of oxygen and hydrogen sulfide are examined, using the method of spatial isopycnic analysis. The contribution that ventilation of winter-time surface waters over the domes of cyclonic gyres makes to the transfer of O2 towards the upper boundary of the constant pycnocline and to the oxicline layer is demonstrated. The paper provides spatial scales of this phenomenon and indicates the areas where the upper boundary of the anoxic layer in the Black Sea, relative to the conventional density, is located much higher compared with the rest of the sea. The suboxic zone is shown to be a specific feature of the O2/H2S distribution in the Black Sea waters, typical, at least, of the northern part of the basin. Analysis of the suboxic spatial variability in the vertical has been conducted. Translated by Vladimir A. Puchkin.  相似文献   

8.
We make an attempt to answer the following question: how a natural stationary system formed by a layer and an interface “selects” a unique set of governing parameters from a great number of possible collections under the conditions of double-diffusion layer convection (e.g., for the bottom boundary layer in the Black Sea)? As the “rule of selection,” we use the principle of minimum entropy production for systems close to the state of thermodynamic equilibrium. In the process of solution of the problem, the system is regarded as a heat engine. The proposed approach is reduced to a simple procedure of application of the principle of minimum entropy production to the analyzed case. The combined analysis of the theoretical results, the data of deepwater field measurements in the Black Sea, and the results of laboratory experiments leads us to the conclusion that, most likely, the stationary system “selects” its governing parameters according to the Prigogine–Glansdorff principle. The density ratio (approximately equal to three for the stationary case) proves to be the key parameter of the system. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 16–25, January–February, 2009.  相似文献   

9.
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   

10.
To study the long-term variability of the thermohaline and dynamic characteristics of the Black Sea, we use three versions of climatic fields, namely, the fields reconstructed in the model according to the old (1903–1982) and new (1903–2003) hydrological climatic data arrays of temperature and salinity and according to the data of satellite altimetry. The analysis of the altimetry-based climatic fields confirms the distinctions (established earlier according to the old and new data arrays) in the seasonal variability of the integral characteristics of temperature and salinity and in the structures of hydrophysical fields in the sea. It is shown that, in the winter-spring season, the thermohaline fields reconstructed according to the new and altimetry data arrays are characterized by a small elevation of the halocline (pycnocline) and the upper boundary of the cold intermediate layer. In all seasons, the altimetry-based surface geostrophic currents contain numerous mesoscale eddies with different signs of rotation. Moreover, in all seasons, the Rim Current reconstructed according to the altimetry data is characterized by a narrower jet almost along the entire its length. This jet is especially intense near the coasts of West Anatolia. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 3–17, July–August, 2006.  相似文献   

11.
We compare the thermohaline and dynamic characteristics of the Black Sea reconstructed by using two versions of climatic temperature and salinity fields:old (1903–1982)and new (1903–2003). The fields are reconstructed with the help of continuous assimilation of the climatic temperature and salinity in the model. It is shown that the climatic thermohaline fields constructed with regard for the data of observations for the last 20 yr are characterized by an insignificant elevation of the halocline (pycnocline)in the winter-spring period and the elevation of the upper boundary of the cold intermediate layer in the spring-summer period. The intensity of surface geostrophic currents is greater than the same quantity computed on the basis of the old climatic data for the whole year. The horizontal currents in the sea computed according to the new climatic data are more intense. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 3, pp. 11–30, May–June, 2005.  相似文献   

12.
A five-year study of the interannual changes observed in May–June during the mass reproduction of coccolithophorids was carried out in the northeastern part of the Black Sea. The long-term dynamics were analyzed using the data on the phytoplankton collected during the last 40 years. The fraction of coccolithophorids represents either 20 or 60% of the total biomass of the algae and does not depend on either the previous winter conditions or the nitrogen content and the N: P ratio in the surface water layer. Our studies have revealed the dependency between the phosphate content and the size of the coccolythophorids’ fraction in the total phytoplankton biomass. The long-term population dynamics includes three periods. Until the mideighties, the coccolythophorid fraction in the Black Sea phytoplankton was insignificant (3%). The average biomass was equal to 8 μg/l. In the late eighties, the average biomass increased up to 106 μg/l. Since the midnineties, coccolythophorids often prevail in the number and mass among the other phytoplankton species. The general tendency for the growth of the coccolythophorid fraction in the phytoplankton cenoses coincides with the increase in the phosphate concentration in the near-surface water observed within the last 40 years. This fact corresponds to the experimental results, which demonstrate that the coccolythophorid development during May–June is phosphate-limited.  相似文献   

13.
Different methods of measuring low oxygen concentrations were compared in July 2008 in the Black Sea: the conventional Winkler method, electrochemical sensors (membrane and membrane-free), and two modifications of photoluminescence sensors. The membrane-free sensor used in the Black Sea since 1999 and the domestic photoluminescence sensor showed the best results: agreement of data, possibility of fine oxygen distribution resolution, and absence of the oxygen and hydrogen sulfide coexistence layer. The latter has good technical characteristics: high oxygen sensitivity and complete inertness to hydrogen sulfide, possibility of calibration in a gaseous environment, and a relatively low time constant (5–6 s). An equation was suggested for dynamic correction of data in the testing mode, which eliminates hysteresis of data on probe descent and ascent to a significant degree. It was shown that the oxygen concentration above the hydrogen sulfide layer in the subreductive zone of the Black Sea did not exceed 0.02 μM.  相似文献   

14.
Iodide oxidation to iodate in near-surface waters of the open oceans is an elusive process, and an unequivocal demonstration of it would simplify modelling of the marine iodine system. In the open ocean, the upward advection of iodate complicates any mathematical treatment of the problem. In this context, the high concentration (0.1 μM) of iodate in the Black Sea surface waters suggested that this Sea might be a place where oxidation might be demonstrated. Hydrologically, the surface waters of the Black Sea appear to be downstream of the deeper waters and, given the latter's anoxicity, the surface waters seemed likely to gain most of their iodine as iodide by upward advection. To test this further, prior to experimentation, an iodine budget for the near-surface waters, based upon the latest hydrological model of the Sea was prepared; this predicts a minimum oxidation flux of 3.89×10−4 mol I m−2 a−1. The chemistry of this oxidation is discussed in the light of existing knowledge of the sulfide system. It is argued that as the redox potential of the IO3−/I− and I2/I− couples at pHs typical of the Black Sea (7.75) are much higher than that of the sulfate–sulfide couple, iodide is probably oxidized in the near-surface domain. This contrasts with sulfide oxidation in the suboxic zone. The possible role of nitrifying bacteria in the oxidation is discussed.  相似文献   

15.
The energy characteristics of circulation in the Black Sea have been numerically analyzed for 2006. The annually and seasonally averaged integral components of the budget of both kinetic and potential energies are considered. It is shown that, over the period under study, wind forcing, buoyancy force, and friction are the main factors determining variations in the mechanical energy of the Black Sea. During the cold months, wind forcing maximally contributes to the kinetic energy. In spring, the contribution made by buoyancy force is dominant. The values of buoyancy force are maximum within the upper quasi-homogeneous layer during the warm season and on horizons, where the waters of the cold intermediate layer are concentrated, during the fall–winter season.  相似文献   

16.
To describe the phenomenon of cold surges in the Black Sea in winter, we study the problem of atmospheric response to a local heat source on the surface in two simple formulations. In the shallow-water model, the planetary boundary layer of the atmosphere is homogeneous with variable upper bound. In the second model, the boundary layer has a constant thickness and its stratification is homogeneous. In the one-dimensional problem, for a constant wind blowing perpendicularly to the sea coast, the atmospheric response is determined by a single dimensionless parameter called the Froude number. Depending on its value, there are two possible different modes of the response. The range Fr < 1 (subcritical mode) corresponds to gentle winds, strong stratifications, thick boundary layers, and high velocities of inertial gravitational waves. The range Fr > 1 (supercritical mode) corresponds to strong winds, weak stratifications, thin boundary layers, and low wave velocities. In the two-dimensional problem for a round sea, there are four qualitatively different types of response depending on the combination of two dimensionless parameters: the Froude number and the ratio of the radius of the sea to the radius of deformation. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 3–22, September–October, 2008.  相似文献   

17.
Three cores of marine sediments from the Shenhu area in the northern part of the South China Sea were analyzed by XANES analysis for sulfur speciation. The area has been investigated for the presence of hydrocarbons and potential gas hydrate formations. Cored samples of site 4B showed a specific profile of sulfur speciation with sharp and frequent variations in relative contents of sulfate and sulfide, which differed greatly from the profiles obtained for the sediments taken at sites 5B and 6A. The upper part of core 4B (of 0–95 cm) was soft and rich in pore water, containing mainly coarse silt sand. The lower part of the core (i.e., depth > 95 cm) was relatively dryer and darker in color, and dominated by silts and clay resembling sediments from mud volcanoes. The sulfur speciation results revealed that sulfate makes up almost 100 percent of all sulfur species in the upper part of the core 4B, which indicates strong oxidizing conditions, whereas the lower part of the same core has high relative contents of sulfide, sometimes close to 100% S2−. In the lower part of the core, the relative content of sulfide and sulfate changes rapidly and frequently, indicating rapid changes of oxidizing and reducing conditions. On the other hand, the vertical profiles of sulfur species for the cores from sites 5B and 6A are relatively consistent with lower sulfide contents indicative of stable and weaker reducing conditions. We hypothesize that the frequent and sharp variations in the ratios of sulfide to sulfate at site 4B may indicate some intermittent eruption of methane with clay from petroleum reservoirs underneath the sea floor over a relatively short period of time.  相似文献   

18.
Concentrations of dissolved sulfate and sulfur isotopic ratios of dissolved sulfide in surface sediments of the Peru shelf and upper slope indicate that the sediments can be divided into two depth intervals based on the dominant biogeochemical reactions. Although rates of bacterial sulfate reduction are high throughout Peru surface sediments, chemistry of the upper interval (<10–20 cm) is dominated by chemoautotrophic oxidation of dissolved sulfide and elemental sulfur, while the lower interval (>10–20 cm) is dominated by dissimilatory sulfate reduction. In three of the four cores examined here, pore water concentrations of sulfate in the top 10 cm of the sediment are significantly higher than those of the overlying seawater. Peak sulfate concentrations in pore water (37–53 mmol/l) are ∼1.3–1.9 times that of seawater sulfate and are located 1–6 cm below the sediment/water interface (SWI). The excess sulfate is most likely produced by oxidation of elemental sulfur coupled to reduction of nitrate, a reaction mediated by a facultative chemoautotrophic sulfide-oxidizing bacterium, Thioploca spp. Numerical simulations demonstrate that the anomalously high concentrations of dissolved sulfate can be produced by steady-state or non-steady-state processes involving high rates of bacterial oxidation of elemental sulfur. If bacterial sulfur oxidation is a transient phenomenon, then it is probably triggered by seasonal or El Niño-induced changes in water-column chemistry of the Peru undercurrent.  相似文献   

19.
Vertical distributions of sulfate, hydrogen sulfide, and iron (II) concentrations in interstitial waters and of sulfur content in sediment have been studied in a sediment core (73 cm long) from a meromictic lake, Lake Suigetsu, which changed from fresh-water to brackish conditions in 1664 A.D. The diatom assemblage of the sediment has also been analyzed. A boundary between high (>1.5%) and low (<0.2%) sulfur contents is found at a depth of 52 cm in the core. In the high sulfur layer (above 52 cm), the maximum sulfur content is 6.8% at 35 to 37 cm. The diatom assemblage, however, indicates that the boundary between fresh-water and brackish sediments lies at 40 cm. The hydrogen sulfide and iron (II) profiles in the interstitial waters indicate a sink for these chemical species near a depth of 40 cm. The discrepancy between the chemically-defined boundary at 52 cm and the paleontologically-defined boundary at 40 cm seems to be due to the downward migration of hydrogen sulfide and deposition of iron sulfide after the lake became brackish.  相似文献   

20.
The influence of the winter atmospheric forcing on the interannual variability of the Black Sea’s active layer’s thermohaline structure during 1982–2008 is investigated. The results are based on the combined analysis of the hydrological measurements from a ship, satellite measurements of the sea’s surface temperature (SST), and the NCEP/NCAR reanalysis data for the surface air temperature (SAT). A high correlation between the variability of the winter mean SST/SAT and the thermohaline characteristics of the active layer during the following warm season was found. It is shown that the winter atmospheric forcing significantly affects the variability of the temperature, salinity, and density down to the 150–200 m depth, and this has to be considered in the analysis of the interannual and long-term variability of the Black Sea’s active layer.  相似文献   

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