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1.
The characteristic pattern of multiple colored layers in coastal stratified lakes in the process of separation from the White Sea 总被引：1，自引：1，他引：0
Krasnova Elena D. Matorin Dmitry N. Belevich Tatiana A. Efimova Ludmila E. Kharcheva Anastasiia V. Kokryatskaya Natalia M. Losyuk Galina N. Todorenko Daria A. Voronov Dmitry A. Patsaeva Svetlana V. 《中国海洋湖沼学报》2018,36(6):1962-1977
An unusual feature of the saline stratified lakes that were formed due to ongoing postglacial uplift on the White Sea coast is the presence of several differently colored thin layers in the zone with sharp gradients. Colored layers in five lakes at various stages of separation from the sea were investigated using optical microscopy, spectrophotometry, spectrofluorimetry, and photobiology. The upper greenish colored layer located in the aerobic strata of all lakes near the compensation depth of 1% light penetration contains green algae. In the chemocline, another layer, brightly green, red or pink, is dominated by mixotrophic flagellates. Despite the very low light intensities and the presence of H 2 S, active photosynthesis by these algae appears to be occurring, as indicated by high values of the maximum quantum yield of primary photochemistry, electron transport activity, photosynthetic activity of photosystem II, the fraction of active centers, and low values of heat dissipation. In the reduced zone of the chemocline, a dense green or brown suspension of anoxygenic phototrophs(green sulfur bacteria) is located. 相似文献
2.
R. A. J. TROUW L. S. A. SIMÕES & C. S. VALLADARES 《Journal of Metamorphic Geology》1998,16(4):475-490
A subduction complex composed of ocean floor material mixed with arc-derived metasediments crops out in the Elephant Island group and at Smith Island, South Shetland Islands, Antarctica, with metamorphic ages of 120–80 Ma and 58–47 Ma, respectively. Seven metamorphic zones (I–VII) mapped on Elephant Island delineate a gradual increase in metamorphic grade from the pumpellyite–actinolite facies, through the crossite–epidote blueschist facies, to the lower amphibolite facies. Geothermometry in garnet–amphibole and garnet–biotite pairs yields temperatures of about 350 °C in zone III to about 525 °C in zone VII. Pressures were estimated on the basis of Si content in white mica, Al2O3 content in alkali amphibole, NaM4/AlIV in sodic-calcic and calcic amphibole, AlVI/Si in calcic amphibole, and jadeite content in clinopyroxene. Mean values vary from about 6–7.5 kbar in zone II to about 5 kbar in zone VII. Results from the other islands of the Elephant Island group are comparable to those from the main island; Smith Island yielded slightly higher pressures, up to 8 kbar, with temperatures estimated between 300 and 350 °C. Zoned minerals and other textural indications locally enable inference of P–T –t trajectories, all with a clockwise evolution. A reconstruction in space and time of these P–T –t paths allows an estimate of the thermal structure in the upper crust during the two ductile deformation phases (D1 & D2) that affected the area. This thermal structure is in good agreement with the one expected for a subduction zone. The arrival and collision of thickened oceanic crust may have caused the accretion and preservation of the subduction complex. In this model, D1 represents the subduction movements expressed by the first vector of the clockwise P–T–t path, D2 reflects the collision corresponding to the second vector with increasing temperature and decreasing pressure, and D3 corresponds to isostatic uplift accompanied by erosion, under circumstances of decreasing temperature and pressure. 相似文献
3.
桐柏碰撞造山带及其邻区变形特征与构造格局 总被引：3，自引：2，他引：1
桐柏碰撞造山带及其邻区可以划分为九个大地构造单元,自北向南分别是:华北克拉通南缘岩石构造单元——宽坪岩群、具弧后盆地性质的二郎坪岩石构造单元、具岛弧性质的秦岭杂岩单元、龟山岩组和南湾岩组构成的俯冲前缘楔构造带、构造混杂岩带、桐柏北部高压岩片单元、桐柏核部杂岩单元、桐柏南部高压岩片单元以及随州构造变形带。根据详细的构造解析以及新的地质年代学资料,本文将中生代以来的构造变形划分为五幕,前两幕变形主要发育在构造混杂岩带以南的各个岩石构造单元中,之后的三幕变形则波及整个研究区。第一幕变形的时间约为255～238Ma,以发育区域上透入性的片理及北西西向的拉伸线理为主,并导致了高压岩片早期自西向东的挤出。第二幕变形的时间约为230～215Ma,以自北向南的逆冲推覆构造为主,使得高压岩片进一步垂向抬升。第三幕变形应早于下侏罗统,以近北西西向的宽缓褶皱为主要特征,该幕变形期间桐柏核部杂岩及其两侧高压岩片单元发生同步的抬升。第四幕变形大致发生在140～130Ma之间,主要表现为桐柏核部杂岩两侧走滑型韧性剪切带的活动,桐柏核部杂岩表现出向东的挤出。第五幕变形发生在120～80Ma,表现为北西向及北东向的脆性断裂活动,并切割以上所有构造形迹。桐柏高压岩片的抬升剥露受多幕变形控制,呈阶段性的抬升。 相似文献
4.
This work presents the refractory black carbon(rBC)results of a snow and firn core drilled in West Antarctica(79°55'34.6"S,94°21'13.3"W)during the 2014?15 austral summer,collected by Brazilian researchers as part of the First Brazilian West Antarctic Ice Sheet Traverse.The core was drilled to a depth of 20 m,and we present the results of the first 8 m by comparing two subsampling methods—solid-state cutting and continuous melting—both with discrete sampling.The core was analyzed at the Department of Geological Sciences,Central Washington University(CWU),WA,USA,using a single particle soot photometer(SP2)coupled to a CETAC Marin-5 nebulizer.The continuous melting system was recently assembled at CWU and these are its first results.We also present experimental results regarding SP2 reproducibility,indicating that sample concentration has a greater influence than the analysis time on the reproducibility for low rBC concentrations,like those found in the Antarctic core.Dating was carried out using mainly the rBC variation and sulfur,sodium and strontium as secondary parameters,giving the core 17 years(1998?2014).The data show a well-defined seasonality of rBC concentrations for these first meters,with geometric mean summer/fall concentrations of 0.016μg L^?1 and geometric mean winter/spring concentrations of 0.063μg L^?1.The annual rBC concentration geometric mean was 0.029μg L^?1(the lowest of all rBC cores in Antarctica referenced in this work),while the annual rBC flux was 6.1μg m^?2 yr^?1(the lowest flux in West Antarctica records so far). 相似文献
5.
Hagen-Thorn V. A. Troitskaya Yu. V. Hagen-Thorn E. I. Troitsky I. S. Savchenko S. S. Arharov A. A. Efimova N. V. Klimanov S. K. Volkov E. V. 《Astronomy Reports》2019,63(5):378-390
The results of multicolor photometric and polarization observations of the blazar 4C 38.41 (Q 1633+382) performed at St. Petersburg State University, the Pulkovo Astronomical Observatory of the Russian Academy of Sciences, Boston University, and Steward Observatory in 2006–2017 are analyzed. Separate variable sources responsible for the observed activity are distinguished, whose power-lawspectra and high degree of polarization confirm their synchrotron nature. The observed color variability of the object (redder when brighter) can be explained by an increase in the contribution to the total emission of a red component with variable flux and a constant relative spectral energy distribution. A close correlation between the optical and gamma-ray light curves is identified, suggesting the same location of the variable sources responsible for the radiation in these bands.
相似文献6.
V. D. Mats D. Yu. Shcherbakov I. M. Efimova 《Stratigraphy and Geological Correlation》2011,19(4):404-423
Independent methods of geological and molecular-biological chronologies have made it possible to define generally corresponding
stages in the geological and biological evolution of the environments and communities of Lake Baikal since the Late Cretaceous,
i.e., during the last 70 myr. All the abiotic elements drastically changed during geological evolution, with destruction of
existing and formation of new natural complexes. Nevertheless, some specific zones retained relicts of former settings. The
resulting present-day natural complex includes elements of different ages and geneses. Similar to different natural zones
of the present-day Earth, which are populated by different biocoenoses, stages in the development of abiotic elements are
also characterized by different faunal and floral assemblages. Some taxa were replaced by others, and the resulting aqueous
biota of Lake Baikal includes different-age and ecologically different elements. The oldest groups of Baikal organisms appeared
approximately 70 Ma ago, although the largest proportion of the lake biota started forming 4–3 Ma ago in response to the most
drastic changes in the abiotic elements of the environment. The youngest taxa appeared 1.8 to 0.15 Ma ago, i.e., during the
period when superdeep lake environments and mountainous glaciations were developing. The chronological coincidence of main
stages in development of abiotic and biotic elements of the nature indicates their relationships. Particular transformations
of abiotic elements and the probable mechanism of their influence on the evolution of living communities are also considered. 相似文献
7.
Transport of crustal microparticles from Chilean Patagonia to the Antarctic Peninsula by SEM-EDS analysis 总被引：2，自引：0，他引：2
8.
9.
V. P. Grinin O. Yu. Barsunova S. G. Sergeev A. A. Arkharov S. Yu. Shugarov A. O. Semenov N. V. Efimova 《Astronomy Reports》2018,62(10):677-688
The results of many-year photometric observations of the weak-line T Tauri star V715 Per in the optical (V RI) and infrared (JHK) photometric bands are presented. The period of the star’s lowamplitude brightness variations in the V RI bands detected earlier, 5.23d, is confirmed. This period persists during the entire 14-year time interval of the observations, but its amplitude varies with time. The same period was found in the variations of JHK infrared fluxes, with the brightness variations in the two ranges being almost synchronous. The most probable origin of these variations is periodic eclipses of the star by its own disk, perturbed by its interaction with the magnetosphere (AA Tau-type variations). In addition to the periodic brightness variations, the star also displayed sporadic Algol-like minima characteristic of UX Ori stars during several years (2005–2011). The amplitude of these variations increasedmonotonically, reaching approximately 1m in the V band by the end of 2010, after which the deep fadings ended. During this entire time interval, the amplitude of the periodic variations was observed to decrease. After 2011, the periodic component began to become stronger again. These changes of the photometric activity of V715 Per can be explained by an increasing rate of gas accretion onto the star, decreasing the radius of warped regions of the disk and leading to accompanying Algol-like fadings. This model assumes a low inclination of the circumstellar disk in V715 Per to the line of sight. 相似文献
10.
A. I. Tikhonov A. F. Ivanov N. E. Mironova V. P. Tikhonov S. V. Efimova 《Water Resources》2013,40(7):761-766
An integrated study with the use of uranium-isotope and microelement hydrogeochemical methods showed the possibility of studying changes in the dynamics and geoenvironmental condition of groundwater in an urban area by the indicator modeling of groundwater formation and circulation, as well as interaction of waters from different horizons, including water ingress from deeper aquifers. 相似文献