Bottom water flows in the tropical fractures of the Northern Mid-Atlantic Ridge

The goal of this paper is to study the flows of Antarctic Bottom Water through the fracture zones in the northern part of the Mid-Atlantic Ridge based on the Conductivity-Temperature-Depth and Lowered Acoustic Doppler Current Profiler observations in 2014, 2015, and 2016. We measured the thermohaline properties and velocities and analyzed the flows of bottom water in the Strakhov, Bogdanov, nameless (07°28′N), Vernadsky, Doldrums, Arkhangelsky, Ten Degree, Vema, Marathon, Fifteen Twenty, and Kane fracture zones. These abyssal channels connect the deep basins of the East and West Atlantic. In addition to the known fact that the main portion of water propagates through the Vema Fracture Zone (11°N), we estimated that additionally a half of this volume propagates through the other fractures. Nevertheless, the pathway for the coldest water is located in the Vema Fracture Zone. Velocities of bottom currents in this fracture reach 45 cm/s. We found strong difference in the structure and transport through the Vema Fracture Zone based on four sections across the fracture occupied in 3 years from 2014 to 2016. The transport varies from 0.7 to 1.2 Sv. The core of maximum velocity in the main channel of this fracture changes its depth between 4000 m and the bottom at 4650 m. The total transport through the other fracture zones is as high as 0.48 ± 0.05 Sv.     

The Fifth Edition of the General Catalogue of Variable Stars:experiences in the constellation Centaurus

We have recently announced that the General Catalogue of Variable Stars enters the stage of its fifth, purely electronic edition(GCVS 5.1). We have included 1408 variable stars in the constellation Centaurus in this new version, GCVS 5.1. Working on this revision, we applied current possibilities from data mining, suggested new variability types for many variable stars and found new light elements for a large number of periodic variables. This paper describes the work completed during the preparation of GCVS 5.1 for Centaurus and discusses in detail a number of the most astrophysically significant cases.     

Representation of light pressure resultant force and moment as a tensor series

In this article, we address the problem of the determination of light pressure upon space structures with a complex geometric shape. For each surface element, we enforce a condition that it can interact with light only from its front side, a condition represented in the form of series of Chebyshev polynomials of the first kind. This Chebyshev expansion enables the use of a series of tensors of increasing rank for determination of the force and moment acting on the sail. We obtain expressions for the determination of light pressure on space structures of complex geometry, taking into account self-shadowing and reflections within the structure. We also give the expressions for tensor parametrization using the specularity coefficient in case of specular -diffuse reflection. For these expressions, we calculated the principal moment and force upon two-sided flat solar sail, spherical and cylindrical bodies, and approximated light pressure upon the proposed space-based observatory Millimetron. The proposed expressions can be used in the ballistic analysis of solar sails and other space objects significantly affected by radiation pressure. Also, these results can be used to analyze the dynamics of large-scale space structures around their center of gravity under light pressure.     

Freshening of near-bottom waters in Lake Baikal triggered by the Mw6.2 Kultuk earthquake of August 2008

In September 2008, freshening of near-bottom water and an increase in concentration of suspended particles were observed in the western part of southern Lake Baikal. The reduction in the content of total dissolved solids was about 0.4–0.7?mg/kg (0.7?%), and average suspended particle concentration increased strongly to 6–9?mg/l, the background value being 0.2?mg/l. The spatial distribution of these waters was virtually identical to the focal area of the M_w6.2 Kultuk earthquake that occurred on 27 August 2008. It is suggested that there was a causal relationship between these two phenomena. Freshening of a significant amount (about 20?km³) of near-bottom waters was plausibly caused by an input of poorly mineralized pore waters from bottom sediments as a result of dissociation of methane gas hydrates suspected to occur in the area. The energy radiated by the earthquake source was four orders of magnitude smaller than that needed to explain the observed freshening of near-bottom waters. This points to other mechanisms leading to seismic-induced sediment failure and possible subsequent hydrate dissociation in the case of the Kultuk earthquake.     

地球电磁法研究新进展——“第19届国际地球电磁感应学术研讨会”专辑

1 研讨会概况 地球电磁法是地球物理学的重要方法,它是通过观测自然的和人工产生的电场、磁场或电磁场研究自地表到地幔深处的电性结构和空间环境. 由IAGA I-2 工作组主办的两年一届的"国际地球电磁感应学术研讨会"的目的是展示和交流各种电磁方法的最新研究成果和前沿研究课题.每次研讨会的举办地点经过竞争和选举确定,1972年在Edinburgh, U.K.举行了第1届研讨会.     

Modelling the wave phenomena in acoustic and elastic media with sharp variations of physical properties using the grid‐characteristic method

This paper introduces a novel method of modelling acoustic and elastic wave propagation in inhomogeneous media with sharp variations of physical properties based on the recently developed grid‐characteristic method which considers different types of waves generated in inhomogeneous linear‐elastic media (e.g., longitudinal, transverse, Stoneley, Rayleigh, scattered PP‐, SS‐waves, and converted PS‐ and SP‐waves). In the framework of this method, the problem of solving acoustic or elastic wave equations is reduced to the interpolation of the solutions, determined at earlier time, thus avoiding a direct solution of the large systems of linear equations required by the FD or FE methods. We apply the grid‐characteristic method to compare wave phenomena computed using the acoustic and elastic wave equations in geological medium containing a hydrocarbon reservoir or a fracture zone. The results of this study demonstrate that the developed algorithm can be used as an effective technique for modelling wave phenomena in the models containing hydrocarbon reservoir and/or the fracture zones, which are important targets of seismic exploration.     

Research Note: First results of a low‐altitude unmanned aircraft system gamma survey by comparison with the terrestrial and aerial gamma survey data

In order to increase the efficiency of geological survey in difficult landscape‐morphological conditions, the authors have developed low‐altitude gamma technology surveys based on a multi‐rotor unmanned aircraft system, also known informally as Drones. These results have been compared against those from standard terrestrial and aerial gamma surveys. The successful results obtained at the reference site show that the developed methodology enables compilation of high‐quality data in difficult landscape conditions. These results yield the same level of information content as standard terrestrial gamma surveys. The exact unmanned aircraft system altitude over the earth must be maintained for carrying out high‐quality surveys. It was found that a CsI(Tl) detector with sizes 80 × 80 mm (vol. 0.4 dm³) enables obtaining of high‐quality radiometric data at altitudes of up to 70 m, at a speed of at least 20 km/h. The authors believe that low altitude ‘quasi‐terrestrial’ gamma surveys with a terrain drape may in the future replace terrestrial gamma surveys since they can offer better effectiveness at a lower cost.     

The cycling of Ni,Zn, Cu in the system “mine tailings–ground water–plants”: A case study

The comparative behaviour of Ni, Cu and Zn in the system “mine tailings–ground water–plants” has been investigated at the Ni–Cu mine site operated by INCO Ltd. Thompson Operations, Thompson, Manitoba. Oxidation of sulphide minerals causes the release of metals from exposed tailings containing Ni ∼2000 ppm, Cu ∼150 ppm and Zn ∼100 ppm to the ground water, which contains 350 mg/L Ni, 0.007 mg/L Cu, and 1.6 mg/L Zn. The metal concentration in the ground water is affected by the relative proportions of sulfide minerals, the rate of oxidation of sulphide minerals (Ni-bearing pyrrhotite > sphalerite > chalcopyrite), and the affinity of the metals for secondary Fe-phases (Ni > Zn > Cu).     

中国及境外天山铅锌成矿作用与找矿方向

中国及境外天山铅锌矿床多有发现,如哈萨克斯坦Tekeli、Shalkiya和Achisai,乌兹别克斯坦Kurgashinkan和Uchkulach,塔吉克斯坦Altyntopkan,中国新疆乌拉根、彩霞山、阿齐山、阿尔恰勒等大型—超大型铅锌矿床,构成了天山巨型铅锌成矿带.这些铅锌矿床形成于怎样的地球动力学背景?铅锌成...     

Tracking stormwater discharge plumes and water quality of the Tijuana River with multispectral aerial imagery

Spatial–temporal characteristics and environmental factors regulating the behavior of stormwater runoff from the Tijuana River in southern California were analyzed utilizing very high resolution aerial imagery, and time-coincident environmental and bacterial sampling data. Thirty nine multispectral aerial images with 2.1-m spatial resolution were collected after major rainstorms during 2003–2008. Utilizing differences in color reflectance characteristics, the ocean surface was classified into non-plume waters and three components of the runoff plume reflecting differences in age and suspended sediment concentrations. Tijuana River discharge rate was the primary factor regulating the size of the freshest plume component and its shorelong extensions to the north and south. Wave direction was found to affect the shorelong distribution of the shoreline-connected fresh plume components much more strongly than wind direction. Wave-driven sediment resuspension also significantly contributed to the size of the oldest plume component. Surf zone bacterial samples collected near the time of each image acquisition were used to evaluate the contamination characteristics of each plume component. The bacterial contamination of the freshest plume waters was very high (100% of surf zone samples exceeded California standards), but the oldest plume areas were heterogeneous, including both polluted and clean waters. The aerial imagery archive allowed study of river runoff characteristics on a plume component level, not previously done with coarser satellite images. Our findings suggest that high resolution imaging can quickly identify the spatial extents of the most polluted runoff but cannot be relied upon to always identify the entire polluted area. Our results also indicate that wave-driven transport is important in distributing the most contaminated plume areas along the shoreline.