Volatiles in basalts and andesites from the Galapagos Spreading Center, 85° to 86°W     

Charles D Byers  David W Muenow  Michael O Garcia 《Geochimica et cosmochimica acta》1983,47(9):1551-1558

Glasses from submarine lavas recovered by the ALVIN submersible from the Galapagos Spreading Center (GSC) near 86°W have been analyzed by electron microprobe for major elements and by high-temperature mass spectrometry for volatiles. The samples studied range in composition from basalt to andesite and are more evolved than typical MORBs. Previous studies indicate that they are related to normal MORB by extensive crystal fractionation in small, isolated magma chambers. The H₂O, Cl and F contents of these lavas are substantially higher than any previously reported for MORBs. H₂O, Cl and F abundances increase linearly with P₂O₅ content, which is used as an indicator of the extent of crystal fractionation. The $\text{Fe}{}_2\text{O}{}_3\text{(FeO + Fe}{}_2\text{O}{}_3\text{)}$ ratios measured in the andesite glasses progressively decrease with increasing P₂O₅ content and are probably related to fractionation of Fe-Tioxides. Reduced carbon gas species, principally CH₄ and CO, were discovered in these glasses. The presence of reduced carbon species in GSC glasses may be indicative of a more reduced oxidation state of the upper mantle than is commonly assumed.  相似文献   

    

Antonio Garcia de Arangoa 《Journal of Geodesy》1955,29(2):8-12

  相似文献   

Application of the Mussel Watch concept in studies of the distribution of hydrocarbons in the coastal zone of the Ebro Delta     

Robert W Risebrough  Brock W De Lappe  Wayman Walker  Bernd R.T Simoneit  Joan Grimalt  Joan Albaiges  Jose Antonio Garcia Regueiro  Antoni Ballester Inolla  Manuel Mariño Fernandez 《Marine pollution bulletin》1983,14(5):181-187

The Mussel Watch concept was applied in a study of man-induced chemical changes in the Ebro Delta on the Catalonian coast to obtain a preliminary assessment of the distribution of synthetic organic compounds, petroleum and biogenic hydrocarbons in the local coastal zone. Mussels, oysters and clams were selected as the indicator organisms. Levels of petroleum accumulated by mussels were generally high, in the order of 100–800 μg^?1 dry weight, equivalent to those in mussels in the most polluted harbours and bays of California. The relative distributions of the steranes and pentacyclic triterpanes in the mussels were significantly different from those found in petroleum from a local field, indicating that local petroleum was not contributing to the present contamination. The composition of biogenic compounds was variable, probably reflecting differences in the composition of local plankton communities, PCB levels were high in relation to current levels in mussels from US sites, reflecting continuing PCB use in Spain. The Delta appears to be a point source of a number of organochlorine compounds, including HCB, the DDT compounds, endrin and γ-chlordane. Levels of the DDT compound o,p′-DDD, a pharmacologically active substance, were unexpectedly high; identification was confirmed by GS/MS. Many unidentified peaks were present on EC chromatograms, indicating a more complex pattern of contamination than might be suggested by printed summaries of data.  相似文献   

Trends in planetary science research in the Puna and Atacama Desert regions: Underrepresentation of local scientific institutions?     

A. Tavernier  G. A. Pinto  M. Valenzuela  A. Garcia  C. Ulloa  R. Oses  B. H. Foing 《Meteoritics & planetary science》2023,58(4):516-528

In 2019, while launching a multidisciplinary research project aimed at developing the Puna de Atacama region as a natural laboratory, investigators at the University of Atacama (Chile) conducted a bibliographic search identifying previously studied geographic points of the region and of potential interest for planetary science and astrobiology research. This preliminary work highlighted a significant absence of local institutional involvement in international publications. In light of this, a follow-up study was conducted to confirm or refute these first impressions, by comparing the search in two bibliographic databases: Web of Science and Scopus. The results show that almost 60% of the publications based directly on data from the Puna, the Altiplano, or the Atacama Desert with objectives related to planetary science or astrobiology do not include any local institutional partner (Argentina, Bolivia, Chile, and Peru). Indeed, and beyond the ethical questioning of international collaborations, Latin-American planetary science deserves a strategic structuring, networking, as well as a road map at national and continental scales, not only to enhance research, development, and innovation, but also to protect an exceptional natural heritage sampling extreme environmental niches on Earth. Examples of successful international collaborations such as the field of meteorites, terrestrial analogs, and space exploration in Chile or astrobiology in Mexico are given as illustrations and possible directions to follow to develop planetary science in South America. To promote appropriate scientific practices involving local researchers, possible responses at academic and institutional levels will eventually be discussed.  相似文献   

The green–blue swing: plasticity of plankton food‐webs in response to coastal oceanographic dynamics          下载免费PDF全文

Domenico D'Alelio  Maria Grazia Mazzocchi  Marina Montresor  Diana Sarno  Adriana Zingone  Iole Di Capua  Gayantonia Franzè  Francesca Margiotta  Vincenzo Saggiomo  Maurizio Ribera d'Alcalà 《Marine Ecology》2015,36(4):1155-1170

The internal organization of plankton communities plays a key role in biogeochemical cycles and in the functioning of aquatic ecosystems. In this study, the structure of a marine plankton community (including both unicellular and multicellular organisms) was inferred by applying an ecological network approach to species abundances observed weekly at the long‐term ecological research station MareChiara (LTER‐MC) in the Gulf of Naples (Tyrrhenian Sea, Mediterranean Sea) in the summers of 2002–2009. Two distinct conditions, characterized by different combination of salinity and chlorophyll values, alternated at the site: one influenced by coastal waters, herein named ‘green’, and the other reflecting more offshore conditions, named ‘blue’. The green and blue ‘phases’ showed different keystone biological elements: namely, large diatoms and small‐sized flagellates, respectively. Several correlations amongst species belonging to different trophic groups were found in both phases (connectance ~0.30). In the green phase, several links between phytoplankton and mesozooplankton and within the latter were detected, suggesting matter flow from microbes up to carnivorous zooplankton. A microbial‐loop‐like sub‐web, including mixo‐ and heterotrophic dinoflagellates and ciliates, was present in the green phase, but it was relatively more important in the blue phase. The latter observation suggests a more intense cycling of matter at the microbial trophic level in the blue phase. These results show that different modes of ecological organization can emerge from relatively small changes in the composition of aquatic communities coping with environmental variability. This highlights a significant plasticity in the internal structure of plankton webs, which should be taken into account in predictions of the potential effects of climatic oscillations on aquatic ecosystems and biogeochemical cycles therein.  相似文献   

North and South Hemispheric Solar Activity for Cycles 21 – 23: Asymmetry and Conditional Volatility of Plage Region Areas     

E. Gonçalves  N. Mendes-Lopes  I. Dorotovič  J. M. Fernandes  A. Garcia 《Solar physics》2014,289(6):2283-2296

We study the dynamic evolution of the time series describing the plage regions areas observed daily at the Observatório Astronómico da Universidade de Coimbra, in each one of the solar hemispheres during solar cycles 21?–?23. The classical ARMA model has proven to be insufficient to describe the time variations seen in the data because of the strong conditional variability. We found that the data are well fitted by ARMA mixed with power-δ TGARCH error models. The power index δ is non-integer; this property has recently been introduced in the literature on time-series analyses and indicates the presence of strong volatility and long memory in the data series. We also detected dynamic asymmetry in the plage region areas observed in the two hemispheres when two different temporal models were obtained to fit them. The finding of a dynamic asymmetry is also supported by the dynamic evolution of the daily difference (north–south) time series, which is significantly different from white noise. This statistical modeling of time series, taking into account new and different characteristics of the solar activity, will be very useful in subsequent forecast developments.  相似文献   

Earthquake imprints on a lacustrine deltaic system: The Kürk Delta along the East Anatolian Fault (Turkey)          下载免费PDF全文

Aurélia Hubert‐Ferrari  Meriam El‐Ouahabi  David Garcia‐Moreno  Ulaş Avşar  Sevgi Altınok  Sabine Schmidt  Nathalie Fagel  M. Namık Çağatay 《Sedimentology》2017,64(5):1322-1353

Deltas contain sedimentary records that are not only indicative of water‐level changes, but also particularly sensitive to earthquake shaking typically resulting in soft‐sediment‐deformation structures. The Kürk lacustrine delta lies at the south‐western extremity of Lake Hazar in eastern Turkey and is adjacent to the seismogenic East Anatolian Fault, which has generated earthquakes of magnitude 7. This study re‐evaluates water‐level changes and earthquake shaking that have affected the Kürk Delta, combining geophysical data (seismic‐reflection profiles and side‐scan sonar), remote sensing images, historical data, onland outcrops and offshore coring. The history of water‐level changes provides a temporal framework for the depositional record. In addition to the common soft‐sediment deformation documented previously, onland outcrops reveal a record of deformation (fracturing, tilt and clastic dykes) linked to large earthquake‐induced liquefactions and lateral spreading. The recurrent liquefaction structures can be used to obtain a palaeoseismological record. Five event horizons were identified that could be linked to historical earthquakes occurring in the last 1000 years along the East Anatolian Fault. Sedimentary cores sampling the most recent subaqueous sedimentation revealed the occurrence of another type of earthquake indicator. Based on radionuclide dating (¹³⁷Cs and ²¹⁰Pb), two major sedimentary events were attributed to the ad 1874 to 1875 East Anatolian Fault earthquake sequence. Their sedimentological characteristics were determined by X‐ray imagery, X‐ray diffraction, loss‐on‐ignition, grain‐size distribution and geophysical measurements. The events are interpreted to be hyperpycnal deposits linked to post‐seismic sediment reworking of earthquake‐triggered landslides.  相似文献   

Disaster education for landslide risk reduction: an experience in a public school in Rio de Janeiro State,Brazil     

Marcos Barreto de Mendonca  Adriana Sobreira Valois 《Natural Hazards》2017,89(1):351-365

Public policies for reducing the disaster risk associated with landslides in Brazil, based almost solely on the implementation of engineering works to stabilise hillsides, have proved ineffective, with this type of disaster becoming more common and more severe. There is therefore an urgent need to form a culture that encourages the public to participate directly in disaster management and develops community capacity, which requires a broad disaster education programme on formal, non-formal and informal levels. Given the recent approach to the topic, this study aims to contribute to the development of a disaster education methodology for landslides, based on an experience that was coordinated by the authors within formal education. The experience was implemented in a state school in the city of Niterói (Rio de Janeiro State, Brazil) which is recurrently affected by disasters associated with landslides. The issue of disasters associated with landslides was addressed in a one-semester course, using the theory of meaningful learning and a range of pedagogical tools in both theory and practical classes, for a total period of 16 h. The educational activities were preceded by a landslide risk perception survey and teacher training. The study concluded that the course promoted interactive and participatory learning, a connection to the real problem in the field and an affective relationship with the issue.  相似文献   

Paradigm shifts in community ecology: Open versus closed units,challenges and limits of connectivity studies          下载免费PDF全文

Adriana Giangrande  M. Cristina Gambi  M. Flavia Gravina 《Marine Ecology》2017,38(6)

Due to the presence of the complex life cycles involving a benthic adult and a pelagic larval phase, the study of benthic community dynamics cannot ignore investigations of the processes occurring in the water column. Current investigations focus mainly on larval dispersal from an evolutionary and a biogeographic perspective, taking into account also population connectivity, conservation planning and coastal management. In the present paper we underline the need to improve knowledge of the main traits of marine invertebrate life cycles, highlighting the limits and challenges of current approaches. Firstly, we summarized the changing approaches within community studies, following the paradigm shifts found in recent marine ecological research, from supply‐side ecology to connectivity, and involving the concepts of open and closed populations. Secondly, we analysed the main larval traits influencing dispersal, paying particular attention to pelagic larval duration in light of the few available data for connectivity studies. The difficulty in estimating many of the main traits of larval ecology make numerical simulation fundamental for a better understanding of the relationship between propagule dispersal and seawater dynamics, both being highly variable. We conclude that some essential biological information is still lacking for the proper integration of the modeling approaches. Thus it is necessary to further investigate the life‐cycle traits and physiological and ecological characteristics of each species, an approach known as autecology or natural history. All too frequently modern ecologists ignore such reductionist approaches, although they are essential for a full understanding of processes, such as connectivity and metapopulation dynamics.  相似文献   

Duality rotations and type D solutions of Einstein-Born-Infeld theory     

H. Salazar  A. Garcia D.  J. F. Plebanski 《Astronomische Nachrichten》1986,307(5):327-333

Within the non-linear electrodynamics of Born-Infeld type, constrained by the condition that admits the freedom of the duality rotations the explicit type D solutions, which generalize the charged Taub-NUT metric with cosmological constant, are constructed. The obtained type D solution exhausts all solutions within the considered class, assumed that the real eigenvectors of the electromagnetic field are aligned along the geodesic and shear-free principa null directions.  相似文献