Hydrological and hydrochemical studies of the Middle and South Caspian Sea from the R/V Issledovatel’ Kaspia (September 2–17, 2006)

Sapozhnikov, V. V.; Azarenko, A. V.; Grashchenkova, O. K.; Кивва, К. К.

doi:10.1134/s0001437007020154

Cited by 10 publications

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“…In 2006, hypoxia was observed already at the depth of 400 m, and below the depth of 550 m the oxy gen content was close to the accuracy of the method. Then the concentration of hydrogen sulfide in the bot tom layer of the Middle Caspian was first reliably determined and amounted to 0.91 mg/L [12].…”

Section: The Resultsmentioning

confidence: 99%

Special features of the hydrochemical conditions variability in the deep water basins of the Caspian Sea

2015

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The features of the long term variability of the hydrochemical characteristics of deep water basins of the Caspian Sea are studied on the basis of information obtained during 18 year annual monitoring and supplemented with historical data. The effect of hypoxia and the hydrogen sulfide layer on the position of the nitrate maximum layer and the content of nitrates in it are shown. Studying the variability of the vertical dis tribution of the hydrochemical indicators revealed several factors that determine the removal of nutrients from the photic layer and their accumulation in the bottom layer. Among other things, the latest data revealed the unique features of the Caspian coastal upwelling. This will help to avoid underestimation of the produc tivity of the waters in the Middle Caspian Basin.

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Section: The Resultsmentioning

confidence: 99%

Special features of the hydrochemical conditions variability in the deep water basins of the Caspian Sea

2015

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“…Gypsum, calcite, Mg-calcite, and pyrite are the most common authigenic minerals in the Holocene deposits of the studied areas. The presence of these minerals both in the upper and in deeper layers of the sedimentary strata is associated with a combination of special geological, hydrological, and biogeochemical conditions prevailing in these areas [32,33,37,39,47].…”

Section: Authigenic Minerals and Features Of Their Formation In The Bottom Sediments Of The Derbent Basin And The South Caspian Basinmentioning

confidence: 99%

“…Regard must be paid to the presence of hydrogen sulfide recorded in the near-bottom waters of the Derbent and South Caspian Basins since the 1930s [28,37,47]. This phenomenon was observed alongside significant fluctuations in sea level, recorded since the 1950s [48] and is associated with both climatic changes and anthropogenic factors [37].…”

Section: Introductionmentioning

confidence: 99%

Authigenic Minerals of the Derbent and South Caspian Basins (Caspian Sea): Features of Forms, Distribution and Genesis under Conditions of Hydrogen Sulfide Contamination

2022

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This paper presents the results of complex lithological, mineralogical, and geochemical studies of bottom sediments of deep-water basins of the Caspian Sea (Derbent and South Caspian Basins) in areas contaminated by hydrogen sulfide. In the course of complex studies, numerous manifestations of authigenic mineral formation associated with the stage of early diagenesis have been established. Authigenic minerals belonging to the groups of sulfates (gypsum, barite), chlorides (halite), carbonates (calcite, low Mg-calcite; kutnohorite), and sulfides (framboidal pyrite), as well as their forms and composition, have been identified by a complex of analytical methods (X-ray diffractometry (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS); atomic absorption spectroscopy (AAS); coulometric titration (CT)); the nature of their distribution in bottom sediments has been assessed. Carbonates and sulfates are predominant authigenic minerals in the deep-water basins of the Caspian Sea. As a part of the study, differences have been established in the composition and distribution of associations of authigenic minerals in the bottom sediments in the deep-water basins. These are mineral associations characteristic of the uppermost part of the sediments (interval 0–3 cm) and underlying sediments. In the Derbent Basin, in sediments of the interval 3–46 cm, an authigenic association is formed from gypsum, calcite, magnesian calcite, siderite, and framboidal pyrite. An association of such authigenic minerals as gypsum and calcite is formed in sediments of the 0–3 cm interval. In the South Caspian Basin, in sediments of the interval 3–35 cm, an association of such authigenic minerals as gypsum, halite, calcite, magnesian calcite, and framboidal pyrite is formed. The association of such authigenic minerals as gypsum, halite, calcite, magnesian calcite, kutnohorite, and framboidal pyrite is characteristic of sediments of the 0–3 cm interval. We consider the aridity of the climate in the South Caspian region to be the main factor that determines the appearance of such differences in the uppermost layer of sediments of the basins. Judging by the change in the composition of authigenic associations, the aridity of the South Caspian increased sharply by the time of the accumulation of the upper layer of sediments (interval 0–3 cm). Taking into account lithological, mineralogical and geochemical data, the features of the processes of authigenic mineral formation in the deep-water basins of the Caspian Sea under conditions of hydrogen sulfide contamination have been determined. Analysis of the results obtained and published data on the conditions of sedimentation in the Caspian Sea showed that hydrogen sulfide contamination recorded in the bottom layer of the water column of the deep-water basins of the Caspian Sea may affect the formation of authigenic sulfides (framboidal pyrite), sulfates (gypsum), and carbonates (calcite and kutnohorite) associated with the activity of sulfate-reducing bacteria in reducing conditions.

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“…It is important to note that since 1930 the unstable presence of hydrogen sulfide was recorded in bottom waters in the Southern Caspian [Ambrosimov et al, 2014;Ivanov et al, 2013;Sapozhnikov et al, 2007]. The first data on the presence of small concentration of hydrogen sulfide were recorded in 1933-1934[Bruevich, 1937.…”

Section: Es6003mentioning

confidence: 99%

“…Regular monitoring studies of the Caspian Sea were renewed by VNIRO scientist in 1995. In 2006, a sharp decrease in the oxygen content and the smell of hydrogen sulfide in the bottom waters of the South Caspian Basin were discovered [Sapozhnikov et al, 2007]. In 2011, scientists of VNIRO discovered hydrogen sulfide in the near-bottom horizons of the water column (at a depth of 900 m) in the central part of the South Caspian Basin.…”

Section: Es6003mentioning

confidence: 99%

Framboidal pyrite formation in the bottom sediments of the South Caspian Basin under conditions of hydrogen sulfide contamination

Kozina¹,

Reykhard²,

Dara³

et al. 2018

Russ. J. Earth Sci.

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Structural features and distribution of framboidal pyrite were studied during lithological, mineralogical and geochemical studies of sediments in the South Caspian Basin. The lithological and geochemical parameters affecting the intensity of the formation of authigenic pyrite in sediments of the South Caspian Basin under conditions of hydrogen sulfide contamination were determined. According to X-ray diffraction (XRD), the content of pyrite in pelitic ooze reaches 4%. Microscopic studies have shown that pyrite formation occurs intensively in sediments with a high content of biogenic mineral components, such as opal diatom frustules and calcite plates of coccolithophores. Scanning electron microscopy (SEM) has demonstrated the presence of spherical pyrite framboids, as well as individual pyrite crystallites and their disordered clusters of various shapes. The diameter of the framboids varies from 3 to 10 microns. Pyrite crystallites have subspherical, complicated polyhedral, prismatic, octahedral, pentagonal dodekahedron shapes. The crystallite sizes range from 0.5 to 3 microns. Based on geochemical data, there is no direct correlation between the intensity of pyrite formation and the high content of such components as Fe and C org in bottom sediments. We assume that the formation of authigenic framboid pyrite in surface sediments (including the fluffy layer) is most likely due to the presence of hydrogen sulfide contamination in the near bottom water of the South Caspian Basin. Framboidal pyrite in the deeper layers (up to a depth of 35 cm) is the result of diagenetic processes that occur in accordance with the classical scheme of vertical zonality of diagenetic transformations in sediments.

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Hydrological and hydrochemical studies of the Middle and South Caspian Sea from the R/V Issledovatel’ Kaspia (September 2–17, 2006)

Cited by 10 publications

References 0 publications

Special features of the hydrochemical conditions variability in the deep water basins of the Caspian Sea

Special features of the hydrochemical conditions variability in the deep water basins of the Caspian Sea

Authigenic Minerals of the Derbent and South Caspian Basins (Caspian Sea): Features of Forms, Distribution and Genesis under Conditions of Hydrogen Sulfide Contamination

Framboidal pyrite formation in the bottom sediments of the South Caspian Basin under conditions of hydrogen sulfide contamination

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