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21.
Alexandre V. Andronikov Martin Novak Pavel Kram Ondrej Sebek Irina E. Andronikova Marketa Stepanova Hyacinta Vitkova Elena Antalova Arnost Komarek 《水文研究》2021,35(12):e14434
One pre-requisite for the construction of a global chromium isotope mass balance is detailed understanding of Cr isotope systematics in the critical zone where redox-processes can modify the isotope signature of geogenic Cr input into the hydrosphere. A Cr isotope inventory of bedrock, soil, and runoff was performed in a Central European headwater catchment underlain by amphibolite, situated in the vicinity of two previously studied catchments underlain by different bedrock types (serpentinite and leucogranite). Fresh bedrock in the amphibolite catchment NAZ contained ~300 mg/kg Cr, serpentinite at PLB contained ~800 mg/kg Cr, and leucogranite at LYS contained ~2 mg/kg Cr. Monthly hydrochemical monitoring at all three sites revealed higher Cr(VI) export fluxes in winter than in summer. NAZ was characterized by a distinct seasonality in the δ53Cr values, with minima during winter/spring snowmelts (−0.35‰) and maxima during dry summers (0.40‰). Similar seasonality in δ53Cr values had been reported from PLB and LYS. Bedrock at all three sites had similar Cr isotope composition close to −0.10‰, a value indistinguishable from the δ53Cr value of bulk silicate Earth (BSE). Positive mean δ53Cr value of NAZ runoff indicated Cr-isotope fractionations during weathering of geogenic Cr(III), combined with adsorption of the resulting Cr(VI) on soil particles during pedogenesis. However, the mass-weighted mean δ53Cr of NAZ runoff was lower (−0.08‰), indistinguishable from the Cr isotope signature of bedrock. The same pattern of lower mass-weighted mean δ53Cr values of runoff, compared to arithmetic mean δ53Cr values of runoff, were observed also at PLB and LYS. We suggest that elevated Cr runoff fluxes in winter remove some of the residual isotopically light Cr that accumulated in the soil during summer. Seasonality in runoff δ53Cr values appears to be a relatively widespread phenomenon, de-coupled from Cr availability for chemical weathering. 相似文献
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Anna Stepanova Ekaterina Taldenkova Henning A. Bauch 《Boreas: An International Journal of Quaternary Research》2012,41(4):557-577
Fossil ostracod assemblages were investigated in five AMS 14 C‐dated cores from various water depths of the Laptev and Kara seas ranging from the upper continental slope (270 m) to the present‐day shelf depth (40 m). Six fossil assemblages were distinguished. These represent the varying environmental conditions at the North Siberian continental margin since about 18 ka. In the cores from the shelf the ostracod assemblages reflect the gradual transition from an estuarine brackish‐water environment to modern marine conditions since 12.3 ka, as induced by the regional early Holocene transgression. The core from the upper continental slope dates back to c. 17.6 ka and contains assemblages that are absent in the shelf cores. The assemblage older than 10 ka stands out as a specific community dominated by relatively deep‐water Arctic and North Atlantic species that also contains euryhaline species. Such an assemblage provides evidence for past inflows of Atlantic‐derived waters from as early as c. 17.2 ka, probably facilitated by upwelling in coastal polynyas, and a considerable riverine freshwater influence with enhanced surface water stratification owing to the proximity of the palaeocoastline until early Holocene times. In all studied cores, relative increases in euryhaline species dominant in the inner‐shelf regions are recorded in the mid–late Holocene sediments (<7 ka), which otherwise already contain modern‐like ostracod assemblages with relatively deep‐water species. This observation suggests euryhaline species to be largely sea‐ice‐ and/or iceberg‐rafted and therefore may provide evidence for a climate cooling trend. 相似文献
23.
N. N. Mozgova Yu. S. Borodaev I. F. Gablina G. A. Cherkashev T. V. Stepanova 《Lithology and Mineral Resources》2005,40(4):293-319
The composition of ore minerals in MAR sulfide occurrences related to ultramafic rocks was studied using methods of mineragraphy, electron microscopy, microprobe analysis, and X-ray analysis. The objects are located at various levels of the maturity of sulfide mounds owing to differences in age, duration, and degree of activity of the following hydrothermal systems: generally inactive Logatchev-1 field (up to 66.5 ka old), inactive Logatchev-2 field (3.9 ka), and generally active Rainbow field (up to 23 ka). Relative to MAR submarine ore occurrences in the basalt substrate, mineralization in the hydrothermal fields mentioned above is characterized by high contents of Au, Cd, Co, and Ni, along with the presence of accessory minerals of Co and Ni. The studied mounds differ in quantitative ratios of major minerals and structural-textural features of ores that suggest their transformation. Ores in the Logatchev-1 field are characterized by the highest Cu content and the development of a wide range of multistage contrast exsolution structures of isocubanite and bornite. In the Logatchev-2 field, sphalerite-chalcopyrite and gold-arsenic exsolution structures are present, but isocubanite exsolution structures are less diverse and contrast. The Rainbow field is marked by the presence of homogenous isocubanite and the subordinate development of exsolution structures. We have identified four new phases in the Cu-Fe-S system. Phases X and Y (close to chalcopyrite and isocubanite, respectively) make up lamellae among isocubanite exsolution products in Logatchev-1 and Logatchev-2. Phase Y includes homogenous zones in zonal chimneys of the Rainbow field. Phases A and B are formed in the orange bornite domain at low-temperature alteration of chalcopyrite in the Logatchev-1 field. Mineral assemblages of the Cu-S system are most abundant and diverse in the Logatchev-1 field, but their development is minimal in the Logatchev-2 field where mainly Cu-poor sulfides of the geerite-covellite series have been identified. Specific features of mineral assemblages mentioned above reflect the maturity grade of sulfide mounds and can serve as indicators of maturity.__________Translated from Litologiya i Poleznye Iskopaemye, No. 4, 2005, pp. 339–367.Original Russian Text Copyright © 2005 by Mozgova, Borodaev, Gablina, Cherkashev, Stepanova. 相似文献
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O. Luízar M. V. Stepanova J. M. Bosqued E. E. Antonova R. A. Kovrazhkin 《Annales Geophysicae》2000,18(11):1399-1411
Multiple inverted-V structures are commonly observed on the same auroral zone crossing by a lowaltitude orbiting satellite. Such structures appear grouped and apparently result from an ionospheric and/or magnetospheric mechanism of stratification. More than two years of AUREOL-3 satellite observations were analyzed to study their properties and their formation in the framework of the ionosphere-magnetosphere coupling model proposed by Tverskoy. This model predicts some natural periodicity in the electrostatic potential profile (and subsequently in the field-aligned current profiles) that could account for oscillations experimentally observed in the auroral zone, such as successive inverted-Vs. Experimental results obtained during quiet or moderately active periods demonstrate that the number of structures observed within a given event is well described by a scaling parameter provided by the hot plasma stratification theory and expressed in terms of the field-aligned current density, the total width of the current band, the plasma sheet ion temperature, and the height-integrated Pedersen conductivity of the ionosphere. The latitudinal width, in the order of 100/200 km at ionospheric altitudes, is relatively independent of the current density, and is determined not only by the existence of a potential difference above the inverted-Vs, but also by basic oscillations of the ionosphere-magnetosphere coupling system predicted by Tverskoy. The large number of cases studied by the AUREOL-3 satellite provides reliable statistical trends which permits the validation of the model and the inference that the multiple structures currently observed can be related directly to oscillations of the magnetospheric potential (or the pressure gradients) on a scale of 1000/2000 km in the near-Earth plasma sheet. These oscillations arise in the Tverskoy model and may naturally result when the initial pressure gradients needed to generate a large-scale field-aligned current have a sufficiently wide equatorial scale, of about 1 RE or more. 相似文献
26.
N. N. Mozgova Yu. S. Borodaev T. V. Stepanova G. A. Cherkashev E. A. Zhirnov 《Lithology and Mineral Resources》2000,35(1):1-18
Primary sulfides from cores of holes 957M, 957C, and 957H drilled during the ODP Leg 158 on the active hydrothermal TAG mound
(Mid-Atlantic Ridge, 26°08′ N) were examined for the concentration of several elements. Based on 262 microprobe analyses,
it has been established that the sulfides are characterized by an extremely heterogeneous distribution of noble metals (Au,
Ag, Pt, and Pd) and several associated elements (Hg, Co, and Se). Noble metals are arranged in the following order in terms
of decreasing abundance, i.e., concentration level above the detection limit (the number of analyses containing the specific
element is given in parentheses): Au (65), Ag (46), Pt (21), and Pd (traces). The associated trace elements make up the following
series: Co (202), Hg (132), and Se (49). Main carriers of the “invisible” portion of noble metals are represented by pyrite
(Au, Hg), marcasite and pyrite (Ag, Co), sphalerite and chalcopyrite (Pt, Pd), and chalcopyrite (Se). The noble metal distribution
in sulfides reveals a lateral zonality: the maximal concentration and abundance of Au in chalcopyrite (or Pt and Ag in chalcopyrite
and pyrite) increase from the periphery (Hole 957H) to the center (holes 957C and 957M) of the hydrothermal mound, while the
Au distribution in pyrite displays a reversed pattern. The Co distribution increases with depth. This work discusses the vertical
zonality in the distribution of elements mentioned above and their response to the evolution of ore genesis. 相似文献
27.
E. A. Gusev N. Yu. Anikina L. G. Derevyanko T. S. Klyuvitkina L. V. Polyak E. I. Polyakova P. V. Rekant A. Yu. Stepanova 《Oceanology》2014,54(4):465-477
The molluscan shells from three drill and two piston cores obtained in the southern Russian sector of the Chukchi Sea are dated by the AMS 14C measurement method back to 0.8–3.5 and 9.2–10.5 ka. The period of 9–10 ka was marked by increased sedimentation rates related to the transgression onset. The fossils in the lower Holocene section exhibit the successive upward replacement of brackish-water organisms by their marine counterparts. After the opening of the Bering Strait in the middle Holocene, the sedimentation was under influence of the increased bioproductivity of the waters. The climatic optimum in the Chukotka region corresponds to the early Holocene, while the late Holocene was characterized by the wider development of the ice cover on the shelf. 相似文献
28.
V. Pinto M. Stepanova E.E. Antonova J.A. Valdivia 《Journal of Atmospheric and Solar》2011,73(11-12):1472-1477
We have studied the turbulent processes in the central plasma sheet using the tailward alignments of THEMIS satellites. Fluctuations of the plasma bulk velocity and corresponding eddy-diffusion coefficients were calculated using the simultaneous data obtained by THEMIS satellites situated inside the central plasma sheet between approximately 5 and 30 Earth's radii. The instantaneous profiles of eddy-diffusion coefficients show an increase with distance from the Earth in the tailward direction. This result agrees with previous statistical studies, and it is relevant for the understanding of the dynamics of the turbulent plasma sheet. 相似文献
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Izvestiya, Physics of the Solid Earth - A method for the solution of inverse geophysical problems for finding the shape of an anomalous body by analyzing the dispersionless Toda hierarchy chain is... 相似文献