Investigation of the ingrowth of radioactive daughters of in Mediterranean sapropels as a potential dating tool     

Silke Severmann  John Thomson   《Chemical Geology》1998,150(3-4)

Five different sapropels (S1, S3–S6) from two sites (2750 m and 3308 m water depth) in the eastern Mediterranean were analysed for C_org content and specific activities of , , and . Anoxia in the sapropel sediments during or shortly after deposition leads to U enrichment, and the observed excess of over activity is consistent with a seawater source for authigenic U. In certain cases, the U profile shape in and around the sappropels is interpreted to indicate that oxidation shortly after sapropel formation has caused a post-depositional downwards migration of both U isotopes. Systematic variability of the activity ratio across the sapropel units indicates that a different diagenetic process has also led to preferential relocation of produced in situ from the parent. The construction of quasi-isochrons in successively older sapropel units demonstrate that radioactive secular equilibrium is approached by a systematic ingrowth of over time from the marked initial disequilibrium between and the U isotopes. The effects of post-depositional diagenesis violate the isochron model boundary conditions, however, and lead to a deviation of the isochron ages from the expected stratigraphic ages. Following assessment of each data point, some improvements in the calculated ages were achieved in one case by exclusion from the calculations of those points most severely affected by open system behaviour.  相似文献   

Persistence of pre-metamorphic C and O isotopic signatures in marbles subject to Pan-African granulite-facies metamorphism and U–Th mineralization (Tranomaro, Southeast Madagascar)     

P. Boulvais  S. Fourcade  G. Gruau  B. Moine  M. Cuney 《Chemical Geology》1998,150(3-4):247-262

The status of fluid regimes during the Pan-African granulite-facies metamorphism in Southern Madagascar was examined by means of a mineralogical and stable isotope study of marble lithologies. In the granulitic Tranomaro area, which is made up of metasedimentary rocks (metapelitic, leptynitic (felsic) and calc–silicate metasediments) and intruded by syn-granulitic granitic bodies, syn-granulitic mineralization (Th–U) and metasomatic transformations (marbles→pyroxenites) demonstrate that fluid circulation has occurred. The Tranomaro marbles can be subdivided into two compositional groups, either Mg-poor or Mg-rich. This division reflects pre-metamorphic compositional differences rather than different histories. On a regional scale, the marbles display a large variation in (from +19 to +6.5‰ relative to SMOW) but have a more restricted range (from +1.4 to −2.5‰ relative to PDB). The lowest values are observed in magnesian marbles, whereas calcic ones do not have values lower than +13.5‰. Both initially low and high marbles may have locally been infiltrated by the syn-metamorphic fluid flow which gave rise to pyroxenites and Th–U ores (thorianite). values of carbonate in Mg-rich marbles evolve from +7 up to 8.5‰ towards the contact with a metasomatic pyroxenite in a meter-scale profile across an infiltration zone. The mineralogy, as well as the large and small-scale isotopic results argue for: (i) a pre-metamorphic origin for the isotopic variations, probably related to pre-granulitic dolomitization, (ii) a lack of pervasive fluid infiltration capable of erasing pre-metamorphic isotopic compositional differences, (iii) an absence of mantle-derived C-bearing fluids in the infiltrated zones. For the area as a whole, the present data are consistent with the decarbonation of impure siliceous limestones and dolostones coupled with fluid release from syn-metamorphic granitic intrusions.  相似文献   

A Modified Neural Network for Improving River Flow Prediction/Un Réseau de Neurones Modifié pour Améliorer la Prévision de L'Écoulement Fluvial     

《水文科学杂志》2013,58(2)

Abstract

Artificial neural network (ANN) models provide huge potential for simulating nonlinear behaviour of hydrological systems. However, the potential of ANN is yet to be fully exploited due to the problems associated with improving the model generalization performance. Generalization refers to the ability of a neural network to correctly process input data that have not been used for calibrating the neural network model. In the hydrological context, better generalization performance implies higher precision of forecasting. The primary objectives of this study are to explore new measures for improving the generalization performance of an ANN-based rainfall–runoff model, and to evaluate the applicability of the new measures. A modified neural network model (entitled goal programming (GP) neural network) for modelling the rainfall–runoff process has been developed, in which three enhancements are made as compared to the widely-used backpropagation (BP) network. The three enhancements are (a) explicit integration of hydrological prior knowledge into the neural network learning; (b) incorporation of a modified training objective function; and (c) reduction of network sensitivity to input errors. Seven watersheds across a range of climatic conditions and watershed areas in China were selected for examining the alternative networks. The results demonstrate that the GP consistently outperformed the BP both in the calibration and verification periods and three proposed measures yielded improvement of performance.  相似文献   

Aggregational behavior of the blue mussels Mytilus edulis and Mytilus trossulus: a potential pre‐zygotic reproductive isolation mechanism     

Guangxu Liu  Erin Stapleton  David Innes  Raymond Thompson 《Marine Ecology》2011,32(4):480-487

The blue mussels Mytilus edulis and Mytilus trossulus occur sympatrically and are able to hybridize in populations on the eastern coast of Newfoundland, Canada, presenting an opportunity to study their aggregational behavior. Aggregation behavior may therefore provide insight into post‐settlement interactions and pre‐zygotic reproductive isolation between the species. Three treatments were designed using M. edulis and M. trossulus to investigate their intraspecific and interspecific spatial distribution patterns. With Ripley’s K‐function and Monte Carlo simulation analysis, we found that in the single‐species treatment, M. edulis aggregated significantly but not M. trossulus. Based on results of two‐way ANOVAs, both the number of aggregations and the moving distance were significantly affected by the treatments (single‐species or mixed‐species treatment) and times (24, 48, 72 and 96 h). In further pairwise comparisons using Tukey’s test, M. edulis aggregated differently with or without M. trossulus occupying the same tank, suggesting that the aggregational behavior of M. edulis could be driven by species‐specific chemical cues. The result that M. edulis aggregates intraspecifically may increase the probability of intraspecific fertilization of the spawned gametes and thus function as a pre‐zygotic reproductive isolation mechanism maintaining the blue mussel hybrid zone.  相似文献   

Impacts of CO₂-driven seawater acidification on survival, egg production rate and hatching success of four marine copepods   总被引：1，自引：0，他引：1  

ZHANG Dajuan  LI Shaojing  WANG Guizhong  GUO Donghui 《海洋学报(英文版)》2011,30(6):86-94

Ecological experiments were conducted to examine the effects of seawater containing elevated par- tial pressure of carbon dioxide (p CO2 800 × 10 -6 , 2 000 × 10 -6 , 5 000 × 10 -6 and 10 000 × 10 -6 ) on the survival and reproduction of female Acartia pacifica, Acartia spinicauda, Calanus sinicus and Centropages tenuiremis, which are the dominant copepods in the southern coastal waters of China. The results show that the effects of elevated p CO2 on the survival rates of copepods were species-specific. C. sinicus, which was a macro-copepod, had a higher survival rate (62.01%-71.96%) than the other three species (5.00%-26.67%) during the eight day exposure. The egg production rates of C. sinicus, A. spinicauda and C. tenuiremis were significantly inhibited by the increased p CO2 and the exposure time duration. There were significantly negative impacts on the egg hatching success of A. spinicauda and C. tenuiremis in the p CO2 2 000 × 10 -6 and 10 000 × 10 -6 groups, and, in addition, the exposure time had noticeably impacts on these rates too. This study indicates that the reproductive performances of copepods were sensitive to elevated p CO2 , and that the response of different copepod species to acidified seawater was different. Furthermore, the synergistic effects of seawater acidification and climate change or other pollutant stresses on organisms should be given more attention.  相似文献   

The reproductive biology of a shallow water morid (Salilota australis Günther, 1878), around the Falkland Islands     

Paul Brickle  Vladimir LaptikhovskyAlexander Arkhipkin 《Estuarine, Coastal and Shelf Science》2011,94(1):102-110

The reproductive biology of a shelf morid, red cod (Salilota australis) was investigated in the Falkland Islands, in order to expand our knowledge of the reproductive strategy of this relatively unstudied family of fishes. Red cod spawn to the south and south-west of West Falkland between August and October. Length frequency and sex ratio data suggest that females arrive at the spawning grounds first. The greatest spawning activity occurred in early evening and this timing may be an adaptation to reduce predation on eggs. Ripe egg size varied from 0.95 to 1.26 mm and was not dependant on female size. There was no regulative atresia during maturation and the formation of fecundity and fecundity increased with increasing fish total length (L_T) from 300,000 (42-45 cm L_T) to 4.5-9.0 million eggs (75-83 cm L_T). The fecundity of most of the population was between 2 and 5 million eggs. Red cod releases small batches of eggs over the spawning period. Batch size ranged from 30,000-90,000 (39-42 cm L_T) in smaller animals to 400,000-800,000 (>75 cm L_T) in larger animals and the batch size of first spawners was significantly higher than for advanced spawners. The study allows us to discuss the evolutionary relationships between the Gadiformes.  相似文献   

湛江地区光裸星虫的生殖细胞发育和生殖周期   总被引：2，自引：0，他引：2  

王庆恒  杜晓东  黄洪艳  秦红贵 《广东海洋大学学报》2005,25(1):5-9

采用活体观察和常规石蜡切片技术对湛江地区光裸星虫生殖周期、生殖细胞的发育及形态结构进行研究。结果表明:星虫雌雄异体,无肉眼可见生殖腺结构,原生殖细胞在体腔液中发育;雌性生殖细胞根据其卵膜的形成和卵黄积累情况可以分为4个发育阶段,小生长期、大生长期、成熟前期和成熟期;雄性生殖细胞也分为增殖期、生长期、成熟期和变态期4个阶段;成熟的生殖细胞经肾管排出体外。生殖季节为5~9月,其中7~8月为高峰期。  相似文献   

Reproductive morphology ofEucheumagelatinae (Esper) J. Agardh (Solieriaceae,Gigartinales, rhodophyta)     

Kuang Mei  Xia Bang-mei 《中国海洋湖沼学报》1996,14(1):31-35

Eucheuma gelatinae (Esper) J. Agardh has vegetative and reproductive features distinguishing it from other species ofEucheuma. The occurrence of reproductive nemathecia containing carpogonial branches, auxiliary cells and post-fertilization stages including gonimoblast and pericarp initiation, fusion cell formation stages and carposporophyte development are described and ilustrated for the first time for this species. Contribution No. 2380 of the Institute of Oceanology, Chinese Academy of Sciences.  相似文献   

廉州湾红树蚬的繁殖生物学研究     

周浩郎  张俊杰  杨明柳  邢永泽  吴斌  阎冰 《海洋科学》2014,38(12):34-39

2011年8月至2012年7月,采集广西北海廉州湾红树蚬(Polymesoda erosa)的周年样品进行了性腺发育、生殖周期和胚胎发育研究。结果表明,红树蚬雌雄异体,性别可通过成熟生殖腺颜色区分;1年1个生殖周期,性腺发育可分为增殖期、生长期、成熟期、排放期和休止期5个阶段,性腺发育两性同步;繁殖期从6月延续到11月,其中7月和10月为繁殖高峰期;肥满度指数最高为5.19%(5月份),最低为1.98%(2月份);繁殖方式为非孵育型,沉性卵,外被一层厚的胶质卵膜,水温26℃时,D形幼虫孵出时间约为27h。  相似文献   

Impact of brine acidification on hatchability,survival and reproduction of Artemia parthenogenetica and Artemia franciscana in salt ponds,Bohai Bay,China   总被引：1，自引：0，他引：1  

隋丽英  邓元告  王婧 《中国海洋湖沼学报》2014,32(1):81-87

We studied the effect of pH(pH 5, 6, 7 and 8) on the hatching percentage, survival and reproduction of Artemia strains in Bohai Bay salt ponds. Strains included parthenogenetic Artemia from Bohai Bay(BHB), Artemia franciscana from San Francisco Bay, and A. franciscana artifi cially produced in salt ponds in Vietnam. The latter was included as a potential inoculum for biological management of salt ponds. The hatching percentage of cysts after 24 h and the survival rate of the tested Artemia strains were signifi cantly reduced when exposed to a culture medium at pH 5 for 18 d( P 0.05). The tolerance of Artemia to 48 h acid exposure varied with developmental stage, increasing in the following order: juvenile, nauplii, pre-adult, with maximum tolerance in adults. All strains of Artemia tested could not reproduce at pH 5. At pH levels from pH 6–8, a higher pH generally resulted in a shorter brood interval and enhanced ovoviviparity. Hence, we suggest that brine acidifi cation has a negative impact on Artemia populations in the Bohai Bay saltworks. Inoculation of Artemia with either local parthenogenetic Artemia or exotic A. franciscana should be feasible at pH 7–8.  相似文献