Early solar system aqueous activity: K isotope evidence from Allende     

Yun Jiang  Piers Koefoed  Olga Pravdivtseva  Heng Chen  Chun‐Hui Li  Fang Huang  Li‐Ping Qin  Jia Liu  Kun Wang 《Meteoritics & planetary science》2021,56(1):61-76

The alkali element K is moderately volatile and fluid mobile; thus, it can be influenced by both primary processes (evaporation and recondensation) in the solar nebula and secondary processes (thermal and aqueous alteration) in the parent body. Since these primary and secondary processes would induce different isotopic fractionations, K isotopes could become a potential tracer to distinguish them. Using recently developed methods with improved precision (0.05‰, 95% confidence interval), we systematically measured the K isotopic compositions and major/trace elemental compositions of chondritic components (18 chondrules, 3 CAIs, 2 matrices, and 5 bulks) in the carbonaceous chondrite fall Allende. Among all the components analyzed in this study, CAIs, which formed initially under high‐temperature conditions in the solar nebula and were dominated by nominally K‐free refractory minerals, have the highest K₂O content (average 0.53 wt%) and have K isotope compositions most enriched in heavy isotopes (δ⁴¹K: ?0.30 to ?0.25‰). Such an observation is consistent with previous petrologic studies that show CAIs in Allende have undergone alkali enrichment during metasomatism. In contrast, chondrules contain lower K₂O content (0.003–0.17 wt%) and generally lighter K isotope compositions (δ⁴¹K: ?0.87‰ to ?0.24‰). The matrix and bulks are nearly identical in K₂O content and K isotope compositions (0.02–0.05 wt%; δ⁴¹K: ?0.62 to ? 0.46‰), which are, as expected, right in the middle of CAIs and chondrules. This strongly indicates that most of the chondritic components of Allende suffered aqueous alteration and their K isotopic compositions are the ramification of Allende parent‐body processing instead of primary nebular signatures. Nevertheless, we propose the small K isotope fractionations observed (< 1‰) among Allende components are likely similar to the overall range of K isotopic fractionation that occurred in nebular environment. Furthermore, the K isotope compositions seen in the components of Allende in this study are consistent with MC‐ICP‐MS analyses of the components in ordinary chondrites, which also show an absence of large (10‰) isotope fractionations. This is not expected as evaporation experiments in nebular conditions suggest there should be large K isotopic fractionations. Nevertheless, possible nebular processes such as chondrules back exchanging with ambient gas when they formed could explain this lack of large K isotopic variation.  相似文献   

Estimating masses of selected stars in the Pulkovo program by means of astrometry methods     

Natalia A.Shakht  Denis L.Gorshanov  Olga O.Vasilkova 《天文和天体物理学研究(英文版)》2018,(8)

Stars in the Pulkovo Observatory program are observed with a 65-cm refractor during many years to study their positions and movements. We present examples of two visual binary stars, for which orbits and masses of components were determined, and two astrometric stars, for which masses of their unseen companions were estimated. The first two stars are ADS 14636(61 Cygni) and ADS 7251,and the others are Gliese 623 and ADS 8035(Alpha UMa). Direct astrometric methods are used for estimation of mass-ratio and masses.  相似文献   

Hydrology models approach to estimation of the groundwater recharge: case study in the Bulgarian Danube watershed     

Olga Nitcheva 《Environmental Earth Sciences》2018,77(12):464

The groundwater (GW) makes an important part of a region runoff. GW bodies playing the role of accumulating reservoirs regulate the GW discharge enabling the river flow to have more uniform long-term distribution. Along with other important advantages, the GW offers the users stable water abstraction rate independent from the recharge rate. The GW recharge quantification belongs to the uneasy tasks in the water resource management. Applying the conventional methods needs multiyear observation records of the variation of the groundwater body (GWB) characteristics. The employment of hydrology models avoids that necessity but requires great amount of data related to the soil hydraulic properties, the land topography and cover of the GWB watershed and long-term records of the climatic effects. The paper presents an introduction of the mathematical model CLM3 into the GW recharge estimation problem. It is a complex and advanced model with adequate interpretation of the water-related processes in the soil and on the land surface under atmospheric effects. The input is available from NCEP/NCAR reanalysis atmosphere data and the International Geosphere-Biosphere Program (IGBP) data base. The model is applied to GW recharge assessment of the Bulgarian Danube district for the year 2013. The obtained monthly and yearly total district values and the areal distribution of the infiltration intensity are matched to the existing field observation-based estimates. The study shows that the CLM3 model approach leads to encouraging results. The method comes very useful with GWB lacking regime observation data as well as for GW recharge prognostic assessments under climatic scenarios.  相似文献   

The Maribo CM2 meteorite fall—Survival of weak material at high entry speed     

Ji&#x;í Borovi ka  Olga Popova  Pavel Spurný 《Meteoritics & planetary science》2019,54(5):1024-1041

High entry speed (>25 km s^?1) and low density (<2500 kg m^?3) are the two factors that lower the chance of a meteoroid to drop meteorites. The 26 g carbonaceous (CM2) meteorite Maribo recovered in Denmark in 2009 was delivered by a bright bolide observed by several instruments across northern and central Europe. By reanalyzing the available data, we confirmed the previously reported high entry speed of (28.3 ± 0.3) km s^?1 and trajectory with slope of 31° to the horizontal. In order to understand how such a fragile material survived, we applied three different models of meteoroid atmospheric fragmentation to the detailed bolide light curve obtained by radiometers located in Czech Republic. The Maribo meteoroid was found to be quite inhomogeneous with different parts fragmenting at different dynamic pressures. While 30–40% of the (2000 ± 1000) kg entry mass was destroyed already at 0.02 MPa, another 25–40%, according to different models, survived without fragmentation up to the relatively large dynamic pressures of 3–5 MPa. These pressures are only slightly lower than the measured tensile strengths of hydrated carbonaceous chondrite (CC) meteorites and are comparable with usual atmospheric fragmentation pressures of ordinary chondritic (OC) meteoroids. While internal cracks weaken OC meteoroids in comparison with meteorites, this effect seems to be absent in CC, enabling meteorite delivery even at high speeds, though in the form of only small fragments.  相似文献   

Petrography of Late Cambrian to Middle Ordovician radiolarian chert in Kazakhstan with special reference to the emergence of benthic animals in the pelagic realm     

Yoshitaka Kakuwa  Olga I. Nikitina 《Sedimentology》2020,67(5):2764-2776

Upper Cambrian to Middle Ordovician radiolarian chert successions from Kazakhstan were studied to clarify the history of the emergence of benthic animals in ocean floor sediments. Radiolarian tests and clay were deposited for a period of 30 Myr without experiencing an influx of continent-derived coarse clastic materials. Red, grey and black cherts of the Upper Cambrian to the upper mid-Darriwilian are thinly laminated, and no trace of benthic animal activity is recognized in that time interval. Bioturbation structures and burrow traces in mid-Darriwilian stage red chert in Kazakhstan suggest that benthic animals colonized the location where radiolarian chert formed, but that there was a significant delay in colonization when compared with similar reported occurrences in Australia and Canada.  相似文献   

A multi-proxy reconstruction of spatial and temporal variations in Asian summer temperatures over the last millennium   总被引：1，自引：0，他引：1  

Feng?Shi  Quansheng?GeEmail author  Bao?Yang  Jianping?Li  Fengmei?Yang  Fredrik?Charpentier?Ljungqvist  Olga?Solomina  Takeshi?Nakatsuka  Ninglian?Wang  Sen?Zhao  Chenxi?Xu  Keyan?Fang  Masaki?Sano  Guoqiang?Chu  Zexin?Fan  Narayan?P.?Gaire  Muhammad?Usama?Zafar 《Climatic change》2015,131(4):663-676

To investigate climate variability in Asia during the last millennium, the spatial and temporal evolution of summer (June–July–August; JJA) temperature in eastern and south-central Asia is reconstructed using multi-proxy records and the regularized expectation maximization (RegEM) algorithm with truncated total least squares (TTLS), under a point-by-point regression (PPR) framework. The temperature index reconstructions show that the late 20th century was the warmest period in Asia over the past millennium. The temperature field reconstructions illustrate that temperatures in central, eastern, and southern China during the 11th and 13th centuries, and in western Asia during the 12th century, were significantly higher than those in other regions, and comparable to levels in the 20th century. Except for the most recent warming, all identified warm events showed distinct regional expressions and none were uniform over the entire reconstruction area. The main finding of the study is that spatial temperature patterns have, on centennial time-scales, varied greatly over the last millennium. Moreover, seven climate model simulations, from the Coupled Model Intercomparison Project Phase 5 (CMIP5), over the same region of Asia, are all consistent with the temperature index reconstruction at the 99 % confidence level. Only spatial temperature patterns extracted as the first empirical orthogonal function (EOF) from the GISS-E2-R and MPI-ESM-P model simulations are significant and consistent with the temperature field reconstruction over the past millennium in Asia at the 90 % confidence level. This indicates that both the reconstruction and the simulations depict the temporal climate variability well over the past millennium. However, the spatial simulation or reconstruction capability of climate variability over the past millennium could be still limited. For reconstruction, some grid points do not pass validation tests and reveal the need for more proxies with high temporal resolution, accurate dating, and sensitive temperature signals, especially in central Asia and before AD 1400.  相似文献   

Radionuclides and mercury in the salt lakes of the Crimea     

Natalya Mirzoyeva  Larisa Gulina  Sergey Gulin  Olga Plotitsina  Alexandra Stetsuk  Svetlana Arkhipova  Nina Korkishko  Oleg Eremin 《中国海洋湖沼学报》2015,33(6):1413-1425

90 Sr concentrations,resulting from the Chernobyl NPP accident,were determined in the salt lakes of the Crimea(Lakes Kiyatskoe,Kirleutskoe,Kizil-Yar,Bakalskoe and Donuzlav),together with the redistribution between the components of the ecosystems.The content of mercury in the waters of the studied reservoirs was also established.Vertical distributions of natural radionuclide activities( 238 U,232 Th,226 Ra,210 Pb,40 K) and anthropogenic 137 Cs concentrations(as radiotracers) were determined in the bottom sediments of the Koyashskoe salt lake(located in the south-eastern Crimea) to evaluate the longterm dynamics and biogeochemical processes.Radiochemical and chemical analysis was undertaken and radiotracer and statistical methods were applied to the analytical data.The highest concentrations of 90 Sr in the water of Lake Kiyatskoe(350.5 and 98.0 Bq/m 3) and Lake Kirleutskoe(121.3 Bq/m 3) were due to the discharge of the Dnieper water from the North-Crimean Canal.The high content of mercury in Lake Kiyatskoe(363.2 ng/L) and in seawater near Lake Kizil-Yar(364 ng/L) exceeded the maximum permissible concentration(3.5 times the maximum).Natural radionuclides provide the main contribution to the total radioactivity(artificial and natural combined) in the bottom sediments of Lake Koyashskoe.The significant concentration of 210 Pb in the upper layer of bottom sediments of the lake indicates an active inflow of its parent radionuclide—gaseous 222 Rn from the lower layers of the bottom sediment.The average sedimentation rates in Lake Koyashskoe,determined using 210 Pb and 137 Cs data,were 0.117 and 0.109 cm per year,respectively.  相似文献   

The droughts of 1997 and 2005 in Amazonia: floodplain hydrology and its potential ecological and human impacts     

Javier Tomasella  Patrícia F. Pinho  Laura S. Borma  José A. Marengo  Carlos A. Nobre  Olga R. F. O. Bittencourt  Maria C. R. Prado  Daniel A. Rodriguez  Luz A. Cuartas 《Climatic change》2013,116(3-4):723-746

It is well known that most of the severe droughts in Amazonia, such as that of 1997, are El Niño-related. However, in 2005, the Amazon was affected by a severe drought that was not El Niño-related, as most of the rainfall anomalies that have happened in southwestern Amazonia are driven by sea surface temperature anomalies in the tropical North Atlantic. Earlier studies have analyzed both droughts in terms of their meteorological causes and impacts in terra firme (non-flooded) forests. This study compares the hydrological effects of both droughts on the Amazonian floodplain and discusses their potential ecological and human impacts based on an extensive literature review. The results revealed that the effects of the 2005 drought were exacerbated because rainfall was lower and evaporation rates were higher at the peak of the dry season compared to the 1997 drought. This induced a more acute depletion of water levels in floodplain lakes and was most likely associated with higher fish mortality rates. Based on the fact that the stem growth of many floodplain species is related to the length of the non-flooded period, it is hypothesized that the 1997 drought had more positive effects on floodplain forest growth than the 2005 drought. The fishing community of Silves in central Amazonia considered both droughts to have been equally severe. However, the 2005 drought was widely broadcasted by the press; therefore, the governmental mitigation efforts were more comprehensive. It is suggested that the availability of new communication technology and greater public awareness regarding environmental issues, combined with the new legal framework for assessing the severity of calamities in Brazil, are among the primary factors that explain the difference in societal response between the two droughts.  相似文献   

Geochemical and microbiological characteristics of sediments near the Malenky mud volcano (Lake Baikal, Russia), with evidence of Archaea intermediate between the marine anaerobic methanotrophs ANME-2 and ANME-3   总被引：1，自引：1，他引：0  

Tamara I. Zemskaya  Tatiayna V. Pogodaeva  Olga V. Shubenkova  Svetlana M. Сhernitsina  Olga P. Dagurova  Savelii P. Buryukhaev  Bair B. Namsaraev  Oleg M. Khlystov  Aleksandr V. Egorov  Aleksei A. Krylov  Gennadii V. Kalmychkov 《Geo-Marine Letters》2010,30(3-4):411-425

Detailed lithological, biogeochemical and molecular biological analyses of core sediments collected in 2002–2006 from the vicinity of the Malenky mud volcano, Lake Baikal, reveal considerable spatial variations in pore water chemical composition, with total concentrations of dissolved salts varying from 0.1 to 1.8‰. Values of methane δ¹³С in the sediments suggest a biogenic origin (δ¹³С_min. ?61.3‰, δ¹³С_max. ?72.9‰). Rates of sulphate reduction varied from 0.001 to 0.7 nmol cm^?3 day^?1, of autotrophic methanogenesis from 0.01 to 2.98 nmol CH₄ cm^?3 day^?1, and of anaerobic oxidation of methane from 0 to 12.3 nmol cm^?3 day^?1. These results indicate that methanogenic processes dominate in gas hydrate-bearing sediments of Lake Baikal. Based on clone libraries of 16S rRNA genes amplified with Bacteria- and Archaea-specific primers, investigation of microbial diversity in gas hydrate-bearing sediments revealed bacterial 16S rRNA clones classified as Deltaproteobacteria, Gammaproteobacteria, Chloroflexi and OP11. Archaeal clone sequences are related to the Crenarchaeota and Euryarchaeota. Baikal sequences of Archaea form a distinct cluster occupying an intermediate position between the marine groups ANME-2 and ANME-3 of anaerobic methanotrophs.  相似文献   

Adaptation strategy of bivalve Modiolus modiolus from upwelling regions of the Kuril Islands shelf (Sea of Okhotsk) to heavy metal effects     

Victor Ya. Kavun  Olga V. Podgurskaya 《Continental Shelf Research》2009

Cd, Cu, Fe, Mn, Ni, Pb, Zn concentration in the organs (muscle, gonads, mantle, gills, digestive gland, kidney) of mussel Modiolus modiolus was studied. Mussels were collected from shelf upwelling sites of Kuril Is. Sea of Okhotsk (104 and 85 m) and, for comparison, coastal high contaminated and clean sites (Peter the Great Bay, Sea of Japan). It was found that mussels from shelf upwelling regions accumulated unusually high Cd concentration in studied organs, excepting digestive gland. Shelf mussels have evolved passive adaptation to elevated level of ambient heavy metals (distribution of heavy metal load between all organs, especially, muscle). In contrast, mussels from high contaminated sites have evolved active adaptation (strong regulation of metal concentration in the organs at the maximal permissible concentration due to increased kidney function). We supported that under natural condition, passive adaptation of aquatic organisms to increased ambient metal level have been evolved only under constant low-water temperature.  相似文献