Sulfate reduction below the sulfate-methane transition in Black Sea sediments     

Lars Holmkvist  Alexey Kamyshny Jr.  Christoph VogtKyriakos Vamvakopoulos  Timothy G. FerdelmanBo Barker Jørgensen 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(5):493-504

A sudden increase in salinity about 7000 years ago caused a shift in the deposited sediments of the Black Sea from limnic to brackish-marine. Due to the development of an anoxic deep water basin and a relatively high sulfate concentration, organic matter is mineralized primarily through sulfate reduction in modern Black Sea sediments. Earlier studies showed that sulfate-reducing bacteria are abundant within the limnic sub-surface sediment in spite of extremely low concentrations of sulfate and organic carbon. A main objective of the present study was therefore to understand the depth distribution of sulfate reduction across the different sediment units, even deep below the sulfate-methane transition. Our study combined experimental measurements of sulfate reduction using ³⁵S radiotracer with analyses of sulfur and iron geochemistry in pore water and sediment. Potential sulfate reduction rates were measured with ³⁵S in sediment samples that were amended with sulfate and organic substrates and incubated in time-series up to 48 h. Sulfate reduction could thereby be detected and quantified at depths where concentrations of sulfate were otherwise too low to enable calculation of the rates. The results demonstrate that sulfate-reducing bacteria are active several meters below the sulfate-methane transition in Black Sea sediments. The cryptic sulfate reduction below the sulfate-methane transition may be driven by sulfate produced from re-oxidation of reduced sulfur species with oxidized iron minerals buried in the deep limnic sediment.  相似文献   

Assessment of the design displacement values at seismic fault crossings and of their excess probability     

STROM Alexander  IVASCHENKO Alexey  KOZHURIN Andrey 《山地科学学报》2011,8(2):228-233

Line structures such as pipelines that cross active faults should be designed to retain leak-tightness if the design displacement (Ddesign) occurs. Principal approaches to the Ddesign and rupture kinematics assessment are described. They are based on relationships between earthquake magnitude, rupture length and displacement, and on the detailed field data on a specific fault that crosses the pipeline route. Since the future offset at the crossing may exceed the design value, the probability of a displacement occurrence where the safety of the structure can not be ensured should be estimated. Assessment method on such event probability is described and exemplified through active fault studies carried out at several pipeline projects in Russia.  相似文献   

Palaeogeographic Changes at Lake Chokrak on the Kerch Peninsula,Ukraine, during the Mid‐ and Late‐Holocene     

Daniel Kelterbaum  Helmut Brückner  Vasiliy Dikarev  Stefanie Gerhard  Anna Pint  Alexey Porotov  Victor Zin'ko 《Geoarchaeology》2012,27(3):206-219

This project has reconstructed the palaeogeographic and environmental evolution of Lake Chokrak on the Kerch Peninsula, Ukraine, during the mid‐ and late‐Holocene. This record has been evaluated in association with a regional archaeological data set to explore human–environment interactions over this period. The results show major changes in the palaeogeographic setting of Lake Chokrak since the 3rd millennium B.C., when the postglacial marine transgression had started to fill the study area. Microfaunal analyses reveal the long persistence of an open marine embayment that only became separated from the Sea of Azov when a sand barrier developed during the late 2nd millennium B.C. When colonizing the Black Sea region after the 8th century B.C., the Greek settlers erected a fortification with a small settlement on a promontory that was by then a peninsula‐like headland extending into the lake. The colonists abandoned their settlement at the end of the 1st millennium B.C. when the depth of the surrounding lake decreased from 1.5 m to less than 1 m. Today, Lake Chokrak dries up completely during summer. A detailed relative sea level (RSL) curve for the northern coast of Kerch has been established. Sea level reached its highest position at the present day. Since the 3rd millennium B.C., sea level continuously rose, without any of the previously postulated regression/transgression cycles. The RSL curve indicates differential subsidence rates within short distances in relatively stable areas, exceeding 40 cm per 1000 years. © 2012 Wiley Periodicals, Inc.  相似文献   

On magnetic boundary conditions for non-spectral dynamo simulations     

Alexey Iskakov 《地球物理与天体物理流体动力学》2013,107(6):481-492

We address issues associated with non-local magnetic boundary conditions for non-spectral dynamo simulations. We introduce an integro-differential formulation for a domain bounded by an insulating outer domain. We show how to combine the flexibility of a local discretisation with a rigorous formulation of magnetic boundary conditions in arbitrary geometries. This formulation substantiates from mathematical point of view a new method for numerical solution of magnetohydrodynamic problems with non-local boundary conditions based on coupling finite volumes and boundary elements. Finally, we discuss practical efficiency of this new method.  相似文献   

Technological risk regulation of the subgrade base stability in permafrost areas     

S. Ya. Lutskiy  T. V. Shepitko  Alexey Y. Burukin 《寒旱区科学》2017,9(3):321-324

Maintenance and risk estimation of a weak roadbed condition during the construction period are described.Risk-management procedure for unstable,weak soils is proposed through adjusting the technological loads and real-time monitoring of their influence.The efficiency of implementing maximum allowable vibroloads and the drainage system for strengthening weak soils is shown in the example of the Northern Latitudinal Railway area.  相似文献   

First geophysical and shallow ice core investigation of the Kazbek plateau glacier,Caucasus Mountains     

Stanislav S. Kutuzov  Vladimir N. Mikhalenko  Alexi M. Grachev  Patrick Ginot  Ivan I. Lavrentiev  Anna V. Kozachek  Victoria V. Krupskaya  Alexey A. Ekaykin  Levan G. Tielidze  Pavel A. Toropov 《Environmental Earth Sciences》2016,75(23):1488

First-ever ice core drilling at Mt. Kazbek (Caucasus Mountains) took place in the summer of 2014. A shallow ice core (18 m) was extracted from a plateau at ~4500 m a.s.l. in the vicinity of the Mt. Kazbek summit (5033 m a.s.l.). A detailed radar survey showed that the maximum ice thickness at this location is ~250 m. Borehole temperature of ?7 °C was measured at 10 m depth. The ice core was analyzed for oxygen and deuterium isotopes and dust concentration. From the observed seasonal cycle, it was determined that the ice core covers the time interval of 2009–2014, with a mean annual snow accumulation rate of 1800 mm w. eq. Multiple melt layers have been detected. δ¹⁸O values vary from ?25 to ?5‰. The dust content was determined using a particle sizing and counting analyzer. The dust layers were investigated using scanning electron microscopy and X-ray diffraction analysis. Dust can be separated into two categories by its origin: local and distant. Samples reflecting predominantly local origin consisted mainly of magmatic rocks, while clay minerals were a characteristic of dust carried over large distances, from the deserts of the Middle East and Sahara. The calculated average dust flux over three years at Kazbek was of 1.3 mg/cm² a^?1. Neither δ¹⁸O nor dust records appear to have been affected by summer melting. Overall, the conditions on Kazbek plateau and the available data suggest that the area offers good prospects of future deep drilling in order to obtain a unique environmental record.  相似文献   

An Asthenospheric Upwelling Beneath Central Mongolia — Implications for Intraplate Surface Uplift and Volcanism     

Matthew J. COMEAU  Michael BECKEN  Alexey V. KUVSHINOV  GRAYVER  Johannes K?UFL  Erdenechimeg BATMAGNAI  Shoovdor TSERENDUG  Sodnomsambuu DEMBEREL 《《地质学报》英文版》2021,95(Z1):70-72

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Grad–Shafranov Reconstruction of Magnetic Clouds: Overview and Improvements     

A.?IsavninEmail author  E.?K.?J.?Kilpua  H.?E.?J.?Koskinen 《Solar physics》2011,273(1):205-219

The Grad–Shafranov reconstruction is a method of estimating the orientation (invariant axis) and cross section of magnetic flux ropes using the data from a single spacecraft. It can be applied to various magnetic structures such as magnetic clouds (MCs) and flux ropes embedded in the magnetopause and in the solar wind. We develop a number of improvements of this technique and show some examples of the reconstruction procedure of interplanetary coronal mass ejections (ICMEs) observed at 1 AU by the STEREO, Wind, and ACE spacecraft during the minimum following Solar Cycle 23. The analysis is conducted not only for ideal localized ICME events but also for non-trivial cases of magnetic clouds in fast solar wind. The Grad–Shafranov reconstruction gives reasonable results for the sample events, although it possesses certain limitations, which need to be taken into account during the interpretation of the model results.  相似文献   

Local stability and estimation of uncertainty for solutions to inverse problems     

Alexey I. Yaremchuk  Maxim I. Yaremchuk  Jens Schröter  Martin Losch 《Ocean Dynamics》2001,52(2):71-78

 We present a method for studying local stability of a solution to an inverse problem and evaluate the uncertainty in determining true values of particular observables. The investigation is done under the assumption that only the Gaussian part of fluctuations about the local minimum of the cost (likelihood) function is essential. Our approach is based on the spectral analysis of the Hessian operator associated with the cost function at its extremal point, and we put forward an effective iterative algorithm suitable for numerical implementation in the case of a computationally large problem. Received: 16 May 2001 / Accepted: 22 October 2001  相似文献   

The Mitigation of Multipath Errors by Strobe Correlators in GPS/GLONASS Receivers     

Victor A. Veitsel  Alexey V. Zhdanov  Mark I. Zhodzishsky 《GPS Solutions》1998,2(2):38-45

An effective method of decreasing multipath errors in GPS or GPS/GLONASS receivers by changing delay lock loop correlator reference signal is discussed. Unlike other approaches, this method does not lead to apparatus complication, power comsumption increase, or augmentation of digital processor load. This method eliminates the multipath error completely if the difference in delays of direct and reflected signal is more than 30 m, and decreases this error for smaller delays. The cost of such decrease is that the noise error is decreased. However, the noise error is much less dangerous than the multipath one because of its smaller value and much shorter correlation interval. Calculated and experimental data for the method are given for multipath and noise errors. ? 1998 John Wiley & Sons, Inc.  相似文献