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Mesozooplankton spatial distribution and community structure in the South Adriatic Sea during two winters (2015, 2016) 
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下载免费PDF全文 Whereas the data on mesozooplankton in the epipelagic offshore Mediterranean Sea are extensive, less information is available about plankton in the deeper layers. The present study aims to describe the vertical and horizontal structure and distribution of mesozooplankton species and their associations down to 1,200 m in the water of the Southern Adriatic Sea. Zooplankton were sampled using a Nansen net of 200‐μm mesh size during two cruises in the winters of 2015 and 2016, extending from the coast to the open sea. In total, 203 zooplankton taxa were identified. The community was dominated by copepods, representing between 67% and 91% of the total abundance. The highest total densities were recorded in the upper layers where a high proportion (up to 36%) of appendicularians was also observed in the first sampled year. Five groups of samples were determined based on their community structure. In 2015 communities were distinct between the 0 and 50 m layer and the underlying one (50–100 m), whereas in 2016 epipelagic waters were inhabited by a more uniform mesozooplankton community. The mesopelagic and deep‐water fauna, especially copepods, showed a relatively stable composition in both sampling years Overall, our study confirms the oligotrophic character of the Southern Adriatic, with occasional density outbreaks of appendicularians under favourable conditions. 相似文献
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Magnitude transforms include magnitude magnetic anomalies (MMA), their gradients and Laplacians. They can be calculated from the total magnetic anomalies or other component anomalies. Magnitude magnetic anomalies have a space distribution different from that of the component anomalies. Their values are non‐negative and their respective patterns are similar to the positive gravity anomalies. Magnitude transforms are an effective tool for magnetic data analysis due to their simplified pattern and direct correlation with the space location of the source. They have advantages over the traditionally used reduction‐to‐the‐pole (RTP) transform, especially at low magnetic latitudes. The calculation of magnitudes of the anomalous field requires the total field data to be transformed into the component anomalies, while the reduction‐to‐the‐pole transform also includes a rotation of the magnetization vector, the orientation of which is usually assumed. For equal latitudes, the transfer functions of component‐component transforms in the frequency domain show better stability than the component‐component‐rotation transfer function. This is illustrated by a comparison of analytical expressions, and synthetic models of magnetic fields. The Dixon seamount case shows the possibilities for an improved data analysis and more confident source recognition at low latitudes using magnetic transforms. 相似文献
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Although there has been significant progress in the seismic imaging of mantle heterogeneity,the outstanding issue that remains to be resolved is the unknown distribution of mantle temperature anomalies in the distant geological past that give rise to the present-day anomalies inferred by global tomography models.To address this question,we present 3-D convection models in compressible and self-gravitating mantle initialised by different hypothetical temperature patterns.A notable feature of our forward convection modelling is the use of self-consistent coupling of the motion of surface tectonic plates to the underlying mantle flow,without imposing prescribed surface velocities(i.e.,plate-like boundary condition).As an approximation for the surface mechanical conditions before plate tectonics began to operate we employ the no-slip(rigid) boundary condition.A rigid boundary condition demonstrates that the initial thermally-dominated structure is preserved,and its geographical location is fixed during the evolution of mantle flow.Considering the impact of different assumed surface boundary conditions(rigid and plate-like) on the evolution of thermal heterogeneity in the mantle we suggest that the intrinsic buoyancy of seven superplumes is most-likely resolved in the tomographic images of present-day mantle thermal structure.Our convection simulations with a plate-like boundary condition reveal that the evolution of an initial cold anomaly beneath the Java-Indonesian trench system yields a long-term,stable pattern of thermal heterogeneity in the lowermost mantle that resembles the presentday Large Low Shear Velocity Provinces(LLSVPs),especially below the Pacific.The evolution of subduction zones may be,however,influenced by the mantle-wide flow driven by deeply-rooted and longlived superplumes since Archean times.These convection models also detect the intrinsic buoyancy of the Perm Anomaly that has been identified as a unique slow feature distinct from the two principal LLSVPs.We find there is no need for dense chemical ’piles’ in the lower mantle to generate a stable distribution of temperature anomalies that are correlated to the LLSVPs and the Perm Anomaly.Our tomography-based convection simulations also demonstrate that intraplate volcanism in the south-east Pacific may be interpreted in terms of shallow small-scale convection triggered by a superplume beneath the East Pacific Rise. 相似文献
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R.K. Zamanov G.Y. Latev K.A. Stoyanov S. Boeva B. Spassov S.V. Tsvetkov 《Astronomische Nachrichten》2012,333(8):736-743
We report simultaneous multicolour observations in 5 bands (UBVRI) of the flickering variability of the cataclysmic variable AE Aqr. Our aim is to estimate the parameters (colours, temperature, size) of the fireballs that produce the optical flares. The observed rise times of the optical flares are in the interval 220‐440 s. We estimate the dereddened colours of the fireballs as (U ‐B)0∼0.8‐1.4, (B ‐V)0∼0.03‐0.24, and (V ‐I)0∼0.26‐0.78. We find for the fireballs temperatures of 10000‐25000 K, masses of (7‐90)x1019 g, and sizes of (3‐7)x109 cm (using a distance of d = 86 pc). These values refer to the peak of the flares observed in the UBVRI bands. The data are available upon request from the authors (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Ruslan I. Kostov Christo Protochristov Chavdar Stoyanov Lszl Csedreki Alíz Simon Zita Szikszai Imre Uzonyi Bisserka Gaydarska John Chapman 《Geoarchaeology》2012,27(5):457-469
Neolithic artifacts made of nephrite, □Ca2(Fe,Mg)5Si8O22(OH)2, are found at prehistoric settlements in Bulgaria. This study investigates these objects based on particle induced X‐ray emission using a scanning nuclear microprobe (micro‐PIXE technique). Seven nephrite artifacts from the Neolithic sites of Kovachevo, Bulgarchevo and Galabnik in southwest Bulgaria were analyzed to quantify their composition and to establish if a correlation exists between the distribution of major and trace elements, color, impurities, and texture. The nephrite artifacts are tremolite in composition, with a proposed ultrabasic origin. Based on the geochemical data obtained by micro‐PIXE, we divide the artifacts into Group 1 objects from the Kovachevo site and Group 2 objects from the Galabnik and Bulgarchevo sites. The analytical data and microprobe analyses are compared with geochemical data of nephrite from across the globe. The results are in a good agreement with previous electron microprobe and electron paramagnetic resonance (EPR) spectroscopy data. Our study provides a better understanding of the mineralogy and geochemistry of nephrite artifacts and helps to address questions regarding origin and the distribution of such materials in Bulgaria and other Balkan countries. 相似文献
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PetarMilanovi? 《中国岩溶》2009,28(2):123-134
Dinarides南部是世界上岩溶发育最强烈的地区之一,同时也是欧洲降水量最大的地区。区内碳酸盐岩沉积厚度大于300m,平均岩溶发育深度从250m 至350m,沿断裂发育的岩溶,甚至更深。地下水平均流速变化较大,从0.002 cm/s至55.2cm/s。地下水滞留时间很短,水位变化非常迅速,变幅高达312m。地下水位对强降雨的响应小于4小时。岩溶大泉的主要特征是管道出口深,最大最小流量变化大。区内发育的落水洞有成千上百个,其中一些落水洞排水能力超过100m3/s,规模巨大并被洪水暂时淹没的岩溶坡立谷闻名世界各地。泉水天然流量和野生动物生存环境的改变,特别是当地特有物种的破坏,已经成为新近许多岩溶工程项目的焦点议题。由于该区极其复杂的水文地理和政治环境,不同国度间的跨界含水层似乎是一个非常敏感的问题。 相似文献
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Magnetic field transforms with low sensitivity to the direction of source magnetization and high centricity 总被引：7，自引：0，他引：7
Magnetic data interpretation faces difficulties due to the various shapes of magnetic anomalies and the positions of their extrema with respect to the causative bodies for different directions of the source magnetization. The well‐known transforms — reduction to the pole, pseudogravity field, and analytic signal (total gradient) — help in reducing the problem. Another way to achieve the required effect is the transformation of magnetic data, ΔT or Z, into values of the anomalous magnetic intensity T. In this respect, we have found some transforms based on differential operators such as the gradient of T and its modulus R = |?T|, the Laplacian L = ?2T, the product T ?2T and its square root Q, and the Laplacian ?2(T2) and its square root E, to be useful. They are slightly sensitive to the magnetization orientation and their extrema occur above the sources. For a 2D anomaly of a homogeneous causative body, the proposed transforms do not depend on the inclination of magnetization. In the 3D case, such independence does not exist even for the elementary field of a point dipole. The influence of the magnetization direction is estimated by an integral coefficient of sensitivity. This coefficient takes values of up to 2.0 for ΔT or Z anomalies, while their transforms T, R, E, Q and L have values of less than 0.28, 0.29, 0.24, 0.16 and 0.07, respectively, i.e. on average, 10 times less. The estimation of the centricity is carried out using the relative deviation of the principal extremum of the anomaly or its transforms from the epicentre of the model body at a depth equal to 100 units. For a ΔT anomaly this deviation is up to 67%; for the L transform it is less than 8%; for Q, E, R and T it is less than 10%, 15%, 20% and 25%, respectively. The proposed transforms take only non‐negative values. With respect to their shape, the peripheral magnetic extrema are removed, the anomalous configuration is simplified and the resolution of complicated interference patterns is improved. Their calculation does not require additional data for the direction of magnetization, which is an essential advantage over the reduction‐to‐the‐pole and pseudogravity‐field transforms. A joint analysis of the measured field and its transforms T, E and L offers possibilities for more confident separation of the anomalous effects and direct correlation to their sources. The model tests performed and the 3D field applications to real magnetic data confirm the useful properties of the transforms suggested here. 相似文献
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Petar Milanović 《Environmental Geology》1990,15(1):5-11
The region of eastern Herzegovina and Dubrovnik coastal belt is one of the hydrogeologically and hydrologically most interesting regions of Yugoslavia karst. The main water course in the region is the Trebinjica river, the largest sinking river in Europe. All the poljes in the catchment area are temporary flooded, hydrologically separated, and closed karst entities. Enormous quantities of available water are not evenly disturbed neither in the time nor in the space. The Trebinjica Hydrosystem project uses the basic concept of total water regime organization and its multipurpose utilization. With the construction of seven dams, six artificial reservoirs, six tunnels (with total length, 57 km), and four canals (with total length 74 km) the natural regime of surface and underground waters has been completely changed.As a consequence of water regime disturbance, a lot of changes have been observed in the catchment area: changes in the karst aquifers; local changes of climate conditions; eolic erosion effect; influence on the karst underground and littoral belt; influence on the springs yield; influence on adjacent catchment area; pollution of karst aquifers and influence of storage reservoirs on seismicity—induced seismicity. This article presents influences observed after the first stage of hydrosystem construction. 相似文献