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51.
Piazza R Giuliani S Bellucci LG Mugnai C Cu NH Nhon DH Vecchiato M Romano S Frignani M 《Marine pollution bulletin》2010,60(12):2303-2310
Samples from nine Central Vietnam coastal lagoons, together with three soils and sediments collected in two freshwater reservoirs of the Thua Thien-Hué province, were analysed for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Total concentrations are low, from 192 to 2912 pg g−1 and depth profiles in Tam Giang-Cau Hai (TG-CH) sediment cores show only minor changes over time in PCDD/F input and composition. Octachloro dibenzo-p-dioxin (OCDD) is the prevailing congener (approximately 90%), indicating combustion as the main PCDD/F source to these coastal systems, whereas natural formation might be partly responsible for the presence at depth. 2,3,7,8-Tetrachloro dibenzo-p-dioxin (TCDD), largely sprayed together with Agent Orange over the study areas during the war (1961–1971), is absent or very low. This result supports the hypothesis of strong degradation soon after spraying. Multivariate statistical analyses account for the presence of local, short-range sources as observed in the northern part of the TG-CH lagoon. 相似文献
52.
The Vrancea subcrustal earthquakes of August 30,1986 and May 30,1990 are the two most recent seismic events that have occurred in Romania with moment magnitudes M W ≥ 6.9.The spectral analysis of the strong ground motions recorded in Bucharest reveals that despite small differences in magnitude between the 1986 and 1990 earthquakes,their frequency contents are very different,sometimes even opposing.The main focus of this study is to conduct a comparative analysis of the response spectra in terms of the bi-normalized response spectra(BNRS) proposed by Xu and Xie(2004 and 2007) for strong ground motions recorded in Bucharest during these two seismic events.The mean absolute acceleration and relative velocity response spectra for the two earthquakes are discussed and compared.Furthermore,the mean bi-normalized absolute acceleration and normalized relative velocity response spectra with respect to the control period T C are computed for the ground motions recorded in Bucharest in 1986 and 1990.The predominant period T P is also used in this study for the normalization of the spectral period axis.Subsequently,the methodology proposed by Martinez-Perreira and Bommer(1998) is applied in order to estimate the seismic intensity of the two events.The results are discussed and several conclusions regarding the possibility of using the bi-normalized response spectra(BNRS) are given. 相似文献
53.
54.
Cristian Suteanu 《Surveys in Geophysics》2014,35(5):1215-1242
The goal of this paper is to provide an overview of recent progress regarding the acquisition and processing of surface air temperature data in the Arctic. It highlights potential methodological contributions to the identification and characterization of pattern change, focusing on spatial and temporal correlations and scale-symmetry properties of time series. The presented methods include L-moments, climate network analysis, detrended fluctuations analysis, and Haar wavelet analysis. New results concerning data from high-latitude Arctic stations illustrate some of the presented methodological aspects. 相似文献
55.
We analyze minimum and maximum daily temperature records from weather stations situated in the Canadian Arctic area and investigate scaling properties and their change over time. Detrended fluctuation analysis is applied to the entire available records, as well as to successive non-overlapping temporal windows. Scaling is found for intervals of 1–2?months to 5–8?years, with most exponents in the range 0.70?±?0.05. Exponents are subject to temporal change that is found significant when compared with 95?% confidence intervals. Patterns of change are shared by groups of stations in spite of the distances separating their locations. Defining regions characterized by similar patterns of change may be possible, but such a classification should not be expected to be constant: region boundaries shift over time. 相似文献
56.
Sediment supply: The main driver of shelf-margin growth 总被引:1,自引:0,他引:1
Despite the obvious importance of sediment supply to shelf-margin architecture and to the potential of margins to contain and bypass deep-water sands, the role of supply in shelf-margin growth has received limited attention. High cross-shelf sediment flux is critically important for the occurrence of deep-water sands, not least on Greenhouse or rapidly subsiding margins where the impact of eustatic sea-level fall may be insufficient to drive sediment delivery out across the shelf into deep-water areas. To draw greater attention to the supply parameter we review a number of shelf margins that have grown chiefly through supply by shelf-edge deltas and associated sediment-gravity flows. Based on structural style and water depth, we recognize two broad types of shelf-margin. Moderately deep-water margins produce clinoforms < 1000 m high and show rates of shelf-edge progradation < 60 km/My and aggradation < 270 m/My, and consequently, infill their basins relatively rapidly, and develop more progradational architectures with morphologically smooth and relatively undeformed slopes. Very deep-water margins produce clinoforms > 1000 m high and generally show rates of shelf-edge progradation < 40 km/My and aggradation < 2500 m/My, and therefore infill their basins more slowly and develop more aggradational architectures with much gravity-driven slope deformation, proneness to failure and ponded architectures (salt or shale driven). On both margin types, long-term (> 1 My) rates of shelf-edge progradation of several tens of km/My tend to be linked to the delivery of relatively large volumes of sand into the deep-water basin. Delivery of this sand beyond the shelf-edge happens despite Greenhouse conditions and is likely recurrent and periodic (delivery cycles in the order of 100′s ky). Such prominent margin growth is a strong indication that sediment influx was relatively high and we refer to these margins as “supply-dominated” shelf margins. The Gulf of Mexico margin is a well-known and data-rich example of a “supply-dominated” shelf-margin during certain times (e.g., Paleocene). In contrast, on both margin types, low rates of shelf-edge progradation are linked to diminished (or even non-existent) and less frequently recurrent deep-water sediment delivery suggestive of relatively low sediment influx. Occurrence of deep-water sand delivery under low sediment influx probably requires fall of relative sea level. The differences between rapidly and slowly prograding margins indicate that sediment supply (and not sea level) is likely to be the key limiting factor on the growth of shelf margins and that sediment supply, as interpreted through progradation rate, can therefore be used to make a first-order prediction of relative amounts of sand passed to deep-water areas. 相似文献
57.
Tectonic implications of paleomagnetic research into Upper Cretaceous magmatic rocks in the Apuseni Mountains, Romania 总被引:1,自引:0,他引:1
The paleomagnetism of Upper Cretaceous magmatic rocks from 47 collecting sites (172 samples, 692 specimens) in the Apuseni Mountains was studied. After AF cleaning, characteristic magnetizations were identified for various collecting areas in the study zone, which defined a few spatial and temporal units for which paleomagnetic poles could be derived statistically. At 21 sampling sites the paleomagnetic directions showed a high level of intrasite and intersite consistency, with a mean direction of If = −38° and Df = −100°, with 95 = 6°. The paleomagnetic results show that to reach their present-day position the Apuseni Mountains moved to the north, around 14° with respect to Europe, or around 25° with respect to the geographic poles, between the Campanian and, probably, Late Miocene, while a clockwise rotation, of around 80°, was taking place. 相似文献
58.
Sergio Caetano-Filho Pierre Sansjofre Magali Ader Gustavo M.Paula-Santos Cristian Guacaneme Marly Babinski Carolina Bedoya-Rueda Matheus Kuchenbecker Humberto L.S.Reis Ricardo I.F.Trindade 《地学前缘(英文版)》2021,12(1):203-218
Carbon isotope compositions of both sedimentary carbonate and organic matter can be used as key proxies of the global carbon cycle and of its evolution through time,as long as they are acquired from waters where the dissolved inorganic carbon(DIC)is in isotope equilibrium with the atmospheric CO2.However,in shallow water platforms and epeiric settings,the influence of local to regional parameters on carbon cycling may lead to DIG isotope variations unrelated to the global carbon cycle.This may be especially true for the terminal Neoproterozoic,when Gondwana assembly isolated waters masses from the global ocean,and extreme positive and negative carbon isotope excursions are recorded,potentially decoupled from global signals.To improve our understanding on the type of information recorded by these excursions,we investigate the pairedδ^13Ccarb andδ^13Corg evolution for an increasingly restricted late Ediacaran-Cambrian foreland system in the West Gondwana interior:the basal Bambui Group.This succession represents a 1~(st)-order sedimentary sequence and records two majorδ^13Ccarb excursions in its two lowermost lower-rank sequences.The basal cap carbonate interval at the base of the first sequence,deposited when the basin was connected to the ocean,hosts antithetical negative and positive excursions forδ^13Ccarb andδ^13Corg,respectively,resulting inΔ^13C values lower than 25‰.From the top of the basal sequence upwards,an extremely positiveδ^13Ccarb excursion is coupled toδ^13Corg,reaching values of+14‰and-14‰,respectively.This positive excursion represents a remarkable basin-wide carbon isotope feature of the Bambui Group that occurs with only minor changes inΔ^13C values,suggesting change in the DIC isotope composition.We argue that this regional isotopic excursion is related to a disconnection between the intrabasinal and the global carbon cycles.This extreme carbon isotope excursion may have been a product of a disequilibria between the basin DIC and atmospheric CO2 induced by an active methanogenesis,favored by the basin restriction.The drawdown of sulfate reservoir by microbial sulfate reduction in a poorly ventilated and dominantly anoxic basin would have triggered methanogenesis and ultimately methane escape to the atmosphere,resulting in a^13C-enriched DIC influenced by methanogenic CO2.Isolated basins in the interior of the Gondwana supercontinent may have represented a significant source of methane inputs to the atmosphere,potentially affecting both the global carbon cycle and the climate. 相似文献
59.
Eduardo?Andrade-InesEmail author Cristian?Beaugé Tatiana?Michtchenko Philippe?Robutel 《Celestial Mechanics and Dynamical Astronomy》2016,126(4):405-432
We analyse the secular dynamics of planets on S-type coplanar orbits in tight binary systems, based on first- and second-order analytical models, and compare their predictions with full N-body simulations. The perturbation parameter adopted for the development of these models depends on the masses of the stars and on the semimajor axis ratio between the planet and the binary. We show that each model has both advantages and limitations. While the first-order analytical model is algebraically simple and easy to implement, it is only applicable in regions of the parameter space where the perturbations are sufficiently small. The second-order model, although more complex, has a larger range of validity and must be taken into account for dynamical studies of some real exoplanetary systems such as \(\gamma \) Cephei and HD 41004A. However, in some extreme cases, neither of these analytical models yields quantitatively correct results, requiring either higher-order theories or direct numerical simulations. Finally, we determine the limits of applicability of each analytical model in the parameter space of the system, giving an important visual aid to decode which secular theory should be adopted for any given planetary system in a close binary. 相似文献
60.
Georgeta?Bandoc Remus?Pr?v?lieEmail author Cristian?Patriche Elena?Dragomir Maria?Tomescu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(4):1113-1129
The analysis of phenological changes in vegetation is essential for the assessment of the response and adaptation of ecosystems/agro-ecosystems to climate change. This study analyses spatial and temporal changes in phenological events (phenophases) and in the climatic growing season in southern and south-eastern Romania, based on mean monthly temperature values recorded between 1961 and 2010 at 24 weather stations, spread out uniformly in the study area. By using the histophenogram method for extracting the mean phenophases length (eight in total, i.e. growing season onset, budding–leafing, flowering, fruiting, maturing, dissemination, start of leaf loss and end of leaf loss) and that of the overall growing season, this paper aims to analyse current phenological changes (in three periods, 1991–2000, 2001–2010 and 1991–2010) in relation to 1961–1990, which is the reference interval in various global climatic studies. Following the analysis of the theoretical phenology length, based on the temperature thresholds (between 5 and 25 °C) that differentiate biological cycles of vegetation, results showed an overall increase in phenological activity (especially in the past decade, 2001–2010), except for two phenophases (fruiting and dissemination), for which largely dominant length decreases were identified. Quantitatively, increases (and null changes, in a few cases) in phenological length generally range between 0–5 days/0–10% (e.g. in the budding–leafing phenophase) and 11–15 days/10.1–20% (maturing), considering the absolute changes or percentages in the three periods, compared to the reference interval 1961–1990. For the most part, the current decrease in the fruiting and dissemination phenophases falls in the interval ?1 to ?5 days/?10.1 to ?20%, compared to the reference period. At the same time, it was noticed that the entire growing season has been expanding, especially in the past decade, when numerous increase instances of up to 15 days were recorded, corresponding to a dominant interval of 0–10% from the period 1961–1990. The results can be particularly useful for adapting the different types of crops to future climate changes, considering that the study area has a high agro-ecological importance. 相似文献