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181.
Paola Del Negro Mauro Celussi Erica Crevatin Alessandro Paoli Fabrizio Bernardi Aubry Alessandra Pugnetti 《Marine Ecology》2008,29(3):375-386
The prokaryotic community, both in terms of abundance and activity (exoenzymatic hydrolysis of proteins, polysaccharides and phosphorylated molecules and leucine uptake), was investigated seasonally for a 3‐year period (2004–2006) in the Gulf of Venice (northern Adriatic Sea). By focusing on spatial and temporal variability, the prokaryote dynamics showed significant variations on a horizontal and seasonal scale, but no substantial differences were observed among years. The basin‐scale variability was mainly influenced by allochthonous inputs from the Po river and the Venice Lagoon, which were the main source of nutrients, acting as a ‘bottom up’ control on prokaryotes. On a seasonal scale, all the microbial parameters (except the polysaccharide degradation) showed significant variations following the temperature fluctuations. The annual rate of change was very low for all the chemical, physical and biological parameters and only the abundance and phosphatase activity of the prokaryotes differed significantly among years. 相似文献
182.
Paola Mameli Giovanni Mongelli Giacomo Oggiano Enrico Dinelli 《International Journal of Earth Sciences》2007,96(5):887-902
Bauxite deposits are widespread in NW Sardinia. They formed during the middle Cretaceous, in consequence of a period of emergence of the Mesozoic carbonate shelf. In the Nurra area the geometries derived by the Middle Cretaceous tectonic phases controlled the ore typologies. Two bauxite profiles, laying on different bedrocks, were sampled. The bauxitization proceeded from the surface downward, with the accumulation of Al2O3 and residual ‘immobile’ elements (Al, Ti, HFSE), and corresponding mobility and loss of SiO2 and Fe2O3. Epigenetic kaolinite formed close to faults and joints, probably as a result of silicification, introduced by low temperature hydrothermal solutions. Rare earth elements, especially LREE, are concentrated in Fe-rich bauxite horizons, probably due to scavenging by goethite. REE-enrichment is not observed in the boehmite-rich horizons. Very high REE contents are observed in a Fe-depleted horizon due to the occurrence of REE accessory minerals, probably of the bastnäsite group. Conservative indices, including TiO2/Al2O3 and Ti/Cr ratios, and Eu anomalies (Eu/Eu*), suggest that the deposits formed by weathering of sediments derived from mafic rocks of the Hercynian basement. This, in turn, implies that the basement was exposed during middle Cretaceous. 相似文献
183.
The forced and free response of the South China Sea to the large-scale monsoon system 总被引:1,自引:0,他引:1
Non-tidal sea level anomalies (SLAs) can be produced by many different dynamical phenomena over many time scales, and they can induce serious damages in coastal regions especially during extreme events. In this work, we focus on the SLAs in the South China Sea (SCS) to understand whether and how they can be related to the large-scale, seasonal monsoon system which dominates the SCS circulation and dynamics. We have two major objectives. The first one is to understand whether the NE (winter) and SW (summer) monsoons can be responsible for the persistent SLAs, both positive and negative, observed at the SCS ends along the main monsoon path. The second objective is to understand the SCS response as a free system upon onset/relaxation or sudden changes in the forcing wind. It is well known that sudden changes in the forcing mechanism induce free oscillations, or seiches, in closed, semi-enclosed basins and harbors, and we want to identify the possible seiche modes of the SCS. To our knowledge, these two objectives have not been previously addressed. We address these objectives both through observational analysis and modeling simulations. Multi-year tide-gauge data from stations along the coastal regions of the SCS are analyzed examining their spatial correlations. Strong negative correlations are found between the northeast and southwest stations at the two ends of the SCS under the path of the NE/SW monsoons. They correspond to wind-induced positive/negative sea level set-ups lasting for the entire monsoon season and changing sign from winter to summer. Short periods of negative correlations are also found between the SLAs at eastern and western stations during El Niño years in which the monsoons are weaker and have an enhanced E/W component inducing corresponding sea level set-ups. The tide-gauge station at Tanjong Pagar at the southwest SCS end near Singapore is chosen to study four extreme SLAs events in the observational record during 1999. Modeling simulations are carried out to reproduce them. The observed and modeled extreme SLAs agree quite well, both in the amplitude of the highest peak and in phase. Three main peaks are identified in the observational energy spectrum of the de-tided SLAs at the same station in 1999. Using Merian’s formula to evaluate the periods of seiches in idealized basins Wilson (Adv Hydrosci 8:1–94, 1972) the first two peaks (24.4 h and 11.9 h) are found to correspond to the first two seiche modes in the direction of the main, longer axis of the SCS. The third peak (8.5 h) is found to correspond to the seiche in the transversal, shorter axis. Finally, modeling simulations are carried out by suddenly dropping a circular bump of water in the quiescent basin at different locations to excite the seiches. The periods of the modeled peaks agree quite well with the observational ones, the first two periods being actually identical. 相似文献
184.
A hydrogeological study of the Nossana Spring (Val Seriana, Bergamo, Italy) is presented with the aim of assessing the spring’s depletion risk. In the last few years, the discharge of the Nossana Spring showed a decreasing trend, similar to the trend of many other springs in the Prealpine Region. The study was carried out using a groundwater flow model to simulate the depletion curve of the spring in different recharge conditions. The simulations have shown that the depletion curve of the Nossana Spring depends on the recharge during the previous season. As a result, a negative exponential relation giving the spring depletion curve as a function of the recharge was obtained. This relation was also used to statistically calculate the actual probability of the occurrence of a deficiency in water resources, which for the present day is equal to 2%. Finally, the effect of climate change was considered, showing in the next 100 years a flat decline of about 40% in the average spring discharge and a considerable shortening of the critical length (the time to reach the critical discharge at which supply problems occur) in the dry season, which will be halved by the end of the century. 相似文献
185.
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187.
Earthquake catalogues for Romania supply for 11th–15th century earthquakes located in the region of Vrancea records that consist
of a complete set of parameters, including magnitude and depth. Scope of this paper is to verify the reliability and consistency
of these parameters with the informative background as explicitly referenced by the catalogues. After retrieving the original
sources they mention, the set of data appeared to be related almost exclusively to the Russian plain and too poor to be at
the very origin of the parameter assessment. Data for 19th–20th century earthquakes, such as instrumental locations and CMT
solutions, added to the understanding of the macroseismic response of the Russian plain to Vrancea earthquakes. On the one
hand, the investigation and analysis of historical earthquake records for the fourteen events listed by the catalogues in
the 11th–15th centuries has shown that for three earthquakes (1022, 1038, 1258) no primary sources could be traced, and three
more earthquakes (1091, 1170 and 1328) are attested only by scarcely reliable records and had to be classified as doubtful,
and one (1473) is simply a duplication of the 1471 event. On the other hand, the availability of data on recent earthquakes
that may be compared to historical ones in terms of macroseismic effects allowed the authors to agree with the previous catalogue
compilers’ solution with regard to both magnitude and depth of the past earthquakes for which do exist reliable primary historical
records. 相似文献
188.
Claudio Faccenna Michele Soligo Andrea Billi Luigi De Filippis Renato Funiciello Claudio Rossetti Paola Tuccimei 《Global and Planetary Change》2008,63(4):299-308
The depositional and erosional history of the Lapis Tiburtinus endogenic travertine located circa 25 km to the east of Rome, Central Italy, near the Colli Albani quiescent volcano, is interpreted through three-dimensional stratigraphy and uranium-series geochronology. Analyses of large exposures located in active quarries and of cores obtained from 114 industrial wells reveal that the travertine deposit is about 20 km2 wide and 60 m thick on average. The travertine thickness is over 85 m toward its western N–S-elongated side, where thermal springs and large sinkholes occur aligned over a seismically-active N-striking fault. The travertine age was calculated using the U/Th isochron method. Results constrain the onset and conclusion of travertine deposition at about 115 and 30 ka, respectively. The three-dimensional study of the travertine shows that this deposit is characterized by a succession of depositional benches grown in an aggradational fashion. The benches are separated by five main erosional surfaces, which are associated with paleosols, conglomerates, and karstic features. This evidence shows that the travertine evolution was mostly controlled by water table fluctuations. Chronological correlations between travertine evolution and paleoclimate indicators suggest that the travertine deposition was partly modulated by climate conditions. Other influencing factors may have been fault-related deformation and volcanic events. 相似文献
189.
High frequency quasi-periodic oscillations (HFQPOs) have been detected in microquasars and neutron star systems. The resonance model suggested by Kluźniak and Abramowicz (2000, 2001) explains twin QPOs as two weakly coupled nonlinear resonant epicyclic modes in the accretion disk. Although this model successfully explains many features of the observed QPOs, it still faces difficulties and shortcomings. Here we summarize the aspects of the theory that remain a puzzle and we briefly discuss likely developments. 相似文献
190.
Izaskun Jiménez-Serra Jesús Martín-Pintado Arturo Rodríguez-Franco Paola Caselli Serena Viti Tom Hartquist 《Astrophysics and Space Science》2008,313(1-3):159-163
We present the first C-shock and radiative transfer model that calculates the evolution of the line profiles of neutral and
ion species like SiO, H13CO+ and HN13C for different flow times along the propagation of the shock through the unperturbed gas. We find that the line profiles
of SiO characteristic of the magnetic precursor stage have very narrow linewidths and are centered at velocities close to
the ambient cloud velocity, as observed toward the young shocks in the L1448-mm outflow. Consistently with previous works,
our model also reproduces the broad SiO emission detected in the high velocity gas in this outflow, for the downstream postshock
gas in the shock. This implies that the different velocity components observed in L1448-mm are due to the coexistence of different
shocks at different evolutionary stages. 相似文献