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211.
Albert Palanques Mohamed El Khatab Pere Puig Pere Masqu Joan Albert S nchez-Cabeza Enrique Isla 《Marine Geology》2005,220(1-4):23-40
Three moorings equipped with sediment traps were deployed in the north-western Alboran continental margin to study downward particle fluxes in the Guadiaro submarine canyon depositional system. This area is located close to the Strait of Gibraltar and is influenced by the upwelling induced by the Atlantic Jet and by episodic flood events from the Guadiaro River. Sediment traps were installed in the Guadiaro Canyon, in the Guadiaro Channel and in the adjacent continental slope. The overall duration of the deployment was 12 months (from November 1997 to October 1998). Time-series of downward particle fluxes, major constituents (organic carbon, nitrogen, biogenic opal, calcium carbonate and lithogenics) and 210Pb were determined near the surface at mid-depths and near the bottom. Total mass fluxes (TMF) in this area fluctuated more than two orders of magnitude and showed an important seasonal variability with higher fluxes in winter. Increases in TMF and lithogenics together with decreases in 210Pb, organic carbon and opal were recorded in all traps coinciding with river floods, indicating a direct response of the system to these events and a rapid offshore transport of suspended matter affecting the entire water column. The channel site received similar particle fluxes to the western open slope site, indicating that this channel did not act as a preferential sediment conduit during the deployment period. In the Guadiaro Canyon, TMF were more than one order of magnitude higher, 210Pb concentration was lower (one half) and organic matter was more degraded than at the channel site during spring and summer, as a consequence of receiving particles resuspended by internal waves and occasionally by trawling activities. These particles were mainly retained in the canyon, which works as a trap. Also, during spring and summer, the opal and organic carbon percentages increased in all traps both in magnitude and variability, and peaks seem to be associated with biological blooms. 相似文献
212.
Joan D. Willey 《Marine Chemistry》1975,3(3):241-251
Amorphous silica can polymerize in distilled water, in 0.6 N NaCl solution and in seawater to form a colloidal suspension that contains approximately 200 ppm Si. Solid amorphous alumina can prevent this polymerization in seawater and in 0.6 N NaCl, and can inhibit but not prevent it in distilled water. This prevention of polymerization may be an important factor in authigenic mineral formation.The presence of solid amorphous alumina with solid silica in the same solutions causes the final concentrations of dissolved silica to be lower than those attained by solid silica in the absence of solid alumina. The effects are similar whether the final levels are approached from above or below the saturation concentration for amorphous silica. This indicates that the observed concentration of dissolved silica will be a function of available alumina as well as of the silica solubility.The presence of solid amorphous alumina with quartz in seawater, 0.6 N NaCl solution and distilled water causes dissolved silica levels to remain below 0.7 ppm Si for at least 38 days. The same systems in the absence of alumina approach the solubility levels of quartz within that time period. 相似文献
213.
Reports
Regional Seas Towards Sustainable Development 相似文献214.
We examine the question of whether or not the non-periodic variations in solar activity are caused by a white-noise, random process. The Hurst exponent, which characterizes the persistence of a time series, is evaluated for the series of14C data for the time interval from about 6000 BC to 1950 AD. We find a constant Hurst exponent, suggesting that solar activity in the frequency range from 100 to 3000 years includes an important continuum component in addition to the well-known periodic variations. The value we calculate,H 0.8, is significantly larger than the value of 0.5 that would correspond to variations produced by a white-noise process. This value is in good agreement with the results for the monthly sunspot data reported elsewhere, indicating that the physics that produces the continuum is a correlated random process and that it is the same type of process over a wide range of time interval lengths. 相似文献
215.
Leonardo Casini Matteo Maino Antonio Langone Giacomo Oggiano Stefania Corvò Joan Reche Estrada Montserrat Liesa 《Journal of Metamorphic Geology》2023,41(1):25-57
The Variscan high-grade metamorphic basement of northern Sardinia and southern Corsica record lower Carboniferous anatexis related to post-collisional decompression of the orogen. Migmatites exposed in the Punta Bianca locality (Italy) consist of quartz + biotite + plagioclase + K-feldspar orthogneisses, garnet and cordierite-bearing diatexite and metatexites, derived from metasediments. Field evidence, petrographic observations, ELA-ICP-MS zircon and monazite dating and pseudosection modelling suggest that anatexis was apparently episodic involving two main stages of partial melting. Using pseudosection modelling, we infer that the first stage of partial melting is in the upper amphibolite facies (~0.45 GPa at ~740°C). Cordierite overgrowths replacing sillimanite, combined with the composition of plagioclase and K-feldspar, suggest decompression followed cooling below the solidus at low pressures of ~0.3 GPa. The age of the first anatectic event is not precisely constrained because of extensive resetting of the isotopic systems during the second melting stage, yet few zircons preserve a lower Carboniferous age which is consistent with the regional dataset. This lower Carboniferous migmatitic fabric is offset by a network of pseudotachylyte-bearing faults suggestive of cooling to greenschist facies conditions. Garnet/cordierite-bearing diatexites incorporate fragments of pseudotachylite-bearing orthogneiss and metatexites. Pseudosection modelling indicates nearly isobaric re-heating up to ~750°C, followed by further cooling below the solidus. The inferred P–T path is consistent with decompression and cooling of the Variscan crust through post-collisional extension and collapse of the thickened orogenic crust, followed by nearly isobaric re-heating at low pressures (~0.3 GPa) yielding to a second melting stage under LP-HT conditions. U/Th-Pb monazite ages for diatexite migmatites indicate an upper bound of 310–316 Ma for the second melting stage, suggesting that the second melting stage is coincident with the regional phase of crustal shearing. The cause of the high geothermal gradient required for re-heating during the second melting stage is unknown but likely requires some heat source that was probably related to dissipation of mechanical work within crustal-scale shear zones. According to this interpretation, some upper Carboniferous peraluminous granite precursors of the Corsica–Sardinia Batholith could be the outcome rather than the cause of the late-Variscan high-T metamorphism. 相似文献
216.
Dintwe Tumelo K. M. Sasaoka Takashi Shimada Hideki Hamanaka Akihiro Moses Dyson N. Peng Ma Fanfei Meng Liu Seifei Ssebadduka Ronald Onyango Joan A. 《Geotechnical and Geological Engineering》2022,40(4):2213-2229
Geotechnical and Geological Engineering - Crown pillars provide regional and local support by isolating the ground surface from underground mine workings. Topography above the underground mine may... 相似文献
217.
Joaquín Torres-Sospedra Joan Avariento David Rambla Raúl Montoliu Sven Casteleyn Mauri Benedito-Bordonau 《International journal of geographical information science》2015,29(11):1955-1968
A Smart City relies on six key factors: Smart Governance, Smart People, Smart Economy, Smart Environment, Smart Living and Smart Mobility. This paper focuses on Smart Mobility by improving one of its key components: positioning. We developed and deployed a novel indoor positioning system (IPS) that is combined with an outdoor positioning system to support seamless indoor and outdoor navigation and wayfinding. The positioning system is implemented as a service in our broader cartography-based smart university platform, called SmartUJI, which centralizes access to a diverse collection of campus information and provides basic and complex services for the Universitat Jaume I (Spain), which serves as surrogate of a small city. Using our IPS and based on the SmartUJI services, we developed, deployed and evaluated two end-user mobile applications: the SmartUJI APP that allows users to obtain map-based information about the different facilities of the campus, and the SmartUJI AR that allows users to interact with the campus through an augmented reality interface. Students, university staff and visitors who tested the applications reported their usefulness in locating university facilities and generally improving spatial orientation. 相似文献
218.
Biodegradation of riverine dissolved organic carbon in five estuaries of the southeastern United States 总被引:1,自引:0,他引:1
The biological turnover of riverine dissolved organic carbon (DOC) discharged into five southeastern United States estuaries was examined in long-term respiration bioassays. Measures of bacterial oxygen consumption indicated surprisingly large differences in the inherent biodegradability of DOC among the five estuaries, despite their close geographic proximity. Differences of up to 13-fold in biodegradation rates were also found temporally within a single estuary. For most of the southeastern United States estuaries, measured rates of riverine DOC biodegradation were low relative to rates reported for other freshwater and marine environments. This was particularly true for the coastal plain (“blackwater”) rivers that contribute about 35% of the riverine DOC exported to coastal marine environments in this region; extrapolation of biodegradation rates to the adjacent continental shelf predict biodegradation of a maximum of 11% of exported blackwater DOC within the estuary-shelf system (with transit times of up to 140 d). DOC from Piedmont rivers was more biologically labile, with maximum losses of 30% predicted within the estuary and adjacent shelf. Short exposures to natural sunlight increased the lability of the riverine DOC and enhanced biodegradation rates by over 3-fold in some cases, although significant inter-estuary differences in susceptibility of riverine DOC to photolysis were also evident. *** DIRECT SUPPORT *** A01BY085 00007 相似文献
219.
220.
Aliphatic hydrocarbons (AHs), sterols (ST), and lipid classes were determined in suspended particles collected in the Catalan Sea, northwestern Mediterranean. Principal Component Analysis of the data set revealed a clustering of samples depending on the sources of organic matter, i.e., coastal influenced, open sea and frontal zone. Terrestrial inputs were recognized in particles collected in the surface waters, at the vicinities of river outflow (i.e., Rhône and Ebro), by a predominance of C29 and C31 n-alkanes, 24-ethylcholest-5-en-3β-ol (S12), and the anthropogenic 5β(H)-cholestan-3β-ol, coprostanol (S1). Phytoplanktonic molecular markers (n-C17, 27-nor-24-methylcholesta-5,22E-dien-3β-ol, cholesta-5,22-dien-3β-ol and 24-methylcholest-5-en-3β-ol) were widespread but relatively more apparent in the open sea and frontal zones. A similar distribution was observed for lipid classes, with higher concentrations of phospholipids, and an enrichment in free fatty acids in the areas influenced by river discharges. Total sterol, the unresolved complex mixture of hydrocarbons and the pristane–phytane ratio were highest at a persistent frontal zone, possibly reflecting the combination of a higher primary productivity and fossil hydrocarbon absorption on to suspended particles. Moreover, vertical profiles exhibited a subsurface concentration maximum at 20–30 m water depth, concurrently with the chlorophyll. 相似文献