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51.
This article presents a suite of long-term numerical simulations that investigate the dynamical mechanisms controlling the circulation in the South Brazil Bight (SBB). The overarching goal of these simulations is to quantify the relative contributions of local wind forcing and the Brazil Current (BC) to the upwelling of nutrient-rich slope water onto the shelf. The model results indicate that the water mass structure of the SBB is controlled by the synergy between wind-driven, inner-shelf upwelling and geostrophic, shelf-break upwelling. The later extends yearlong but the former peaks during the austral summer and decreases towards the winter. The interaction between the poleward flow of the BC and the bottom topography greatly influences the shelf circulation, particularly in the bottom boundary layer. Changes of the SBB coastline direction and shelf width modulate the along-shore pressure gradient and the magnitude of the shelf-break upwelling and downwelling. Thus, although the summer upwelling winds extend over large part of the SBB surface temperatures are warmer in the south because of the cooling effect of the shelf-break upwelling in the northern region. At difference with previous studies of shelf-break dynamics the shelf-break upwelling in our model is not controlled by the uplifting associated with the presence of instabilities of the boundary current or nonlinear accelerations under a variable shelf width. The proposed mechanism is relatively simple. As the boundary current flows along the continental slope, changes in the coastline orientation and along-shore bottom topography modify the along-shore pressure gradient which through geostrophy leads to inshore bottom flow and hence shelf-break upwelling. Such a mechanism can provide insight into upwellings on other western boundary current regions where similar topographic variations exist. 相似文献
52.
C Palma AI Lillebø C Borges M Souto E Pereira AC Duarte MP Abreu 《Marine pollution bulletin》2012,64(9):1884-1894
This study provides data concerning the hydrography and water chemistry of the Atlantic region between 29-38° N and 27-31° W, and establishes background values for dissolved Cu, Cd, Pb and As. Three water masses were identified: the Eastern North Atlantic Central Water (ENACW), the Mediterranean Water (MW) and the North Atlantic Deep Water (NADW). The ENACW exhibits a clear meridional gradient of temperature and salinity, with comparatively high values at the southern sites and lower values on the Azores platform. The ENACW, which includes the euphotic zone, also had comparatively high concentrations of oxygen and lower concentrations of nutrients and metals. The Cu, Cd and Pb results suggest that new background concentrations for OSPAR Region V (the Wider Atlantic) should be established as follows: 0.15-13nM for Cu, 0.05-1.4nM for Cd and 0.03-5nM for Pb. The background concentrations of As for OSPAR Region V should be 7-28nM. 相似文献
53.
Janaina Bezzerra Silva Mariana A. Giannotti Ana Paula C. Larocca José Alberto Quintanilha 《GeoJournal》2017,82(2):293-310
Spatial data have been used for the environmental monitoring of the consequences of accidents that involve the transportation of hazardous chemical products. This spatial data infrastructure (SDI), which was created for the sharing and use of spatial data, is limited by the absence of policies to support its establishment. The main objective of this study was to explore the use of social network analysis (SNA) as a tool to identify spatial data sharing between organizations involved in the management of accidents related to road transport of hazardous materials (RTHM). In addition, to discuss the existing policies and institutional agreements, and to initiate a conceptual SDI framework for RTHM sector. In this context, the institutions that are involved with RTHM were identified and information concerning their interest in the use and sharing of spatial data via a SDI was collected through interviews and consolidated. The interviews were at 39 institutions with representative employees. The interview data were tabulated and entered into the UCINET software (2000 version) to calculate metrics of centrality. From the SNA, the flow of data among the participating institutions was identified through the visual representation of the spatial data sharing and use networks. Subsequently, the existing institutional agreements for spatial data sharing were analyzed and discussed. The compiled results enabled the proposal of a conceptual SDI framework to support the management of disasters involving RTHM, based on the application of SNA theory, and the development of a methodology that supports the analysis of interactions among the various actors of an SDI. The purpose is to facilitate the formulation of policies for the sharing of spatial data for decision-making and preventive disaster management. The results indicate that the 39 institutions share spatial data, but this sharing is not always predetermined by formal agreements. Furthermore, there is a strong demand, by the institutions involved in the management of RTHM accidents, regarding legal mechanisms governing the sharing of data for the purpose of producing maps that help to describe actions of preparedness, prevention, management and immediate relief involving RTHM incidents. Finally, it was possible to propose a conceptual framework with data that is considered essential for creating an SDI for RTHM. 相似文献
54.
Mapping and monitoring net primary productivity with AVHRR NDVI time-series: statistical equivalence of cumulative vegetation indices 总被引：1，自引：0，他引：1
Carlo Ricotta Giancarlo Avena Alessandra De Palma 《ISPRS Journal of Photogrammetry and Remote Sensing》1999,54(5-6)
In the last two decades, numerous investigators have proposed cumulative vegetation indices (i.e., functions which encode the cumulative effect of NDVI maximum value composite time-series into a single variable) for net primary productivity (NPP) mapping and monitoring on a regional to continental basis. In this paper, we investigate the relationships among three of the most commonly used cumulative vegetation indices, expanding on the definition of equivalence of remotely sensed vegetation indices for decision making. We consider two cumulative vegetation indices as equivalent, if the value of one index is statistically predictable from the value of the other index. Using an annual time-series of broad-scale AVHRR NDVI monthly maximum value composites of the island of Corsica (France), we show that the pairwise linear association among the analysed cumulative vegetation indices shows coefficients of determination (R2) higher than 0.99. That is, knowing the value of one index is statistically equivalent to knowing the value of the other indices for application purposes. 相似文献
55.
J. J. Kasper‐Zubillaga H. Zolezzi‐Ruíz A. Carranza‐Edwards P. Girón‐García G. Ortiz‐Zamora M. Palma 《地球表面变化过程与地形》2007,32(4):489-508
Sedimentological, compositional and geochemical determinations were carried out on 54 desert and coastal dune sand samples to study the provenance of desert and coastal dunes of the Altar Desert, Sonora, Mexico. Grain size distributions of the desert dune sands are influenced by the Colorado River Delta sediment supply and wind selectiveness. The desert dune sands are derived mainly from the quartz‐rich Colorado River Delta sediments and sedimentary lithics. The dune height does not exert a control over the grain size distributions of the desert dune sands. The quartz enrichment of the desert dune sands may be due to wind sorting, which concentrates more quartz grains, and to the aeolian activity, which has depleted the feldspar grains through subaerial collisions. The desert dune sands suffer from little chemical weathering and they are chemically homogeneous, with chemical alteration indices similar to those found in other deserts of the world. The desert sands have been more influenced by sedimentary and granitic sources. This is supported by the fact that Ba and Sr concentration values of the desert sands are within the range of the Ba and Sr concentration values of the Colorado River quartz‐rich sediments. The Sr values are also linked to the presence of Ca‐bearing minerals. The Zr values are linked to the sedimentary sources and heavy mineral content in the desert dunes. The Golfo de Santa Clara and Puerto Peñasco coastal dune sands are influenced by long shore drift, tidal and aeolian processes. Coarse grains are found on the flanks whereas fine grains are on the crest of the dunes. High tidal regimens, long shore drift and supply from Colorado Delta River sediments produce quartz‐rich sands on the beach that are subsequently transported into the coastal dunes. Outcrops of Quaternary sedimentary rocks and granitic sources increase the sedimentary and plutonic lithic content of the coastal dune sands. The chemical index of alteration (CIA) values for the desert and coastal dune sands indicate that both dune types are chemically homogeneous. The trace element values for the coastal dune sands are similar to those found for the desert dune sands. However, an increase in Sr content in the coastal dune sands may be due to more CaCO3 of biogenic origin as compared to the desert dune sands. Correlations between the studied parameters show that the dune sands are controlled by sedimentary sources (e.g. Colorado River Delta sediments), since heavy minerals are present in low percentages in the dune sands, probably due to little heavy mineral content from the source sediment; grain sizes in the dune sands are coarser than those in which heavy minerals are found and/or the wind speed might not exert a potential entrainment effect on the heavy mineral fractions to be transported into the dune. A cluster analysis shows that the El Pinacate group is significantly different from the rest of the dune sands in terms of the grain‐size parameters due to longer transport of the sands and the long distance from the source sediment, whereas the Puerto Peñasco coastal dune sands are different from the rest of the groups in terms of their geochemistry, probably caused by their high CaCO3 content and slight decrease in the CIA value. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
56.
I. R. Paladino A. C. Sokolowski J. Irigoin H. Rodriguez M. C. Gagey M. B. Barrios J. De Grazia S. Debelis J. Wolski A. Bujan 《Environmental Earth Sciences》2018,77(11):411
The south of the green belt of Buenos Aires is one of the most important producers of fresh vegetables in the province. Only few of the horticultural farmers receive professional agronomic advice. For this reason, an excess of supplies are being used, irrigation water quality is unknown and soils are not analyzed. The aim of this work was to evaluate chemical and physico-chemical characteristics of soils from Florencio Varela, Buenos Aires Argentina, which have not been cultivated for over 20 years (NC), under open-Fields Cultivation systems (FC) and under Greenhouses Cultivation systems (GC). The variables analyzed were: pH in water (pH), Electrical Conductivity (EC), Total Nitrogen (TN), Extractable Phosphorus (EP), Total Oxidizable Carbon (TOC), Oxidizable Carbon associated to Mineral fraction (MOC) and Particulate Oxidizable Carbon (POC). The results showed excess of EP, high pH and loss of oxidizable carbon for FC and GC with respect to NC. Furthermore, an incipient salinity was found in GC. Under FC, EC and TN were lower than GC, probably associated with leaching due to rain. Overfertilization is common in horticultural farming in the green belt, where the worst-case scenario is represented by phosphorus due to its low mobility and high residuality. The problems detected show the need for chemical analysis on soils and irrigation water. This will avoid imbalances due to overfertilization and the use of unsuitable water, thereby preventing soil degradation and aquifer contamination. 相似文献
57.
Bruny Baret Imre Bartos Boutayeb Bouhou Alessandra Corsi Irene Di Palma Corinne Donzaud Vronique Van Elewyck Chad Finley Gareth Jones Antoine Kouchner Szabolcs Mrka Zsuzsa Mrka Luciano Moscoso Eric Chassande-Mottin Maria Alessandra Papa Thierry Pradier Peter Raffai Jameson Rollins Patrick Sutton 《Astroparticle Physics》2011,35(1):1-7
We derive a conservative coincidence time window for joint searches of gravitational-wave (GW) transients and high-energy neutrinos (HENs, with energies ?100 GeV), emitted by gamma-ray bursts (GRBs). The last are among the most interesting astrophysical sources for coincident detections with current and near-future detectors. We take into account a broad range of emission mechanisms. We take the upper limit of GRB durations as the 95% quantile of the T90’s of GRBs observed by BATSE, obtaining a GRB duration upper limit of ∼150 s. Using published results on high-energy (>100 MeV) photon light curves for 8 GRBs detected by Fermi LAT, we verify that most high-energy photons are expected to be observed within the first ∼150 s of the GRB. Taking into account the breakout-time of the relativistic jet produced by the central engine, we allow GW and HEN emission to begin up to 100 s before the onset of observable gamma photon production. Using published precursor time differences, we calculate a time upper bound for precursor activity, obtaining that 95% of precursors occur within ∼250 s prior to the onset of the GRB. Taking the above different processes into account, we arrive at a time window of tHEN − tGW ∈ [−500 s, +500 s]. Considering the above processes, an upper bound can also be determined for the expected time window of GW and/or HEN signals coincident with a detected GRB, tGW − tGRB ≈ tHEN − tGRB ∈ [−350 s, +150 s]. These upper bounds can be used to limit the coincidence time window in multimessenger searches, as well as aiding the interpretation of the times of arrival of measured signals. 相似文献
58.
The phytoplankton distribution and composition in Lisbon bay was studied, at a short time scale based on a weekly sampling, during one year (April 2004 – May 2005), using microscopic examination and pigment analysis with high-performance liquid chromatography (HPLC). This work is a contribution to the knowledge on species succession and ecology of coastal communities. The frequency of the sampling permitted monitoring peak blooming and decaying, a process which frequently occurred within 1 –2 weeks. 相似文献
59.
Alain Duran Thomas C. Adam Laura Palma Shalimar Moreno Ligia Collado‐Vides Deron E. Burkepile 《Marine Ecology》2019,40(4)
Feeding behavior of coral reef fishes often determines their species‐specific ecological roles. We studied the two most common Caribbean surgeonfishes (Acanthurus coeruleus and Acanthurus tractus) to examine their species‐specific grazing rates and feeding preferences and how these differed with environmental context. We quantified the feeding activity of both surgeonfishes at four spur and groove reefs in the Florida Keys, USA, that varied in fish abundance, rugosity, algal community composition, and sediment loading. Overall, A. tractus fed twice as fast as A. coeruleus. Both species selected for turf algae but avoided feeding on turf algae that had become laden with sediment. Selectivity for upright macroalgae was more complex with A. tractus targeting Dictyota spp., while A. coeruleus avoided Dictyota spp. relative to the alga's abundance. Both species selected for epiphytes growing on other organisms such as macroalgae and sponges. However, several of these feeding patterns changed with ontogeny. For example, larger individuals of both species fed more frequently on long, sediment‐laden algal turf and less frequently on Dictyota spp. compared to smaller sized individuals. In addition, A. tractus also increased its preference for upright calcareous algae as they attained larger sizes. Overall, the disparity in feeding preferences of surgeonfishes likely indicates subtle differences in species‐specific ecological roles. Both A. coeruleus and A. tractus likely prevent development of turf algae and thus maintain algal communities in the early stages of succession. Additionally, A. tractus may also help reduce macroalgal abundance by targeting common macroalgal species. 相似文献
60.
As part of a long‐term project to determine abundances and astrophysical properties of evolved red stars in open clusters, we present high‐precision DDO photoelectric observations for a sample of 33 red giant candidates projected in the fields of nine Galactic open clusters. These data are supplemented with UBV photoelectric photometry of 24 of these stars as well as with CORAVEL radial‐velocity observations for 13 red giant candidates in four of the clusters. We also present Washington photoelectric photometry of a small sample of red giant candidates of the open cluster Ruprecht 97. The likelihood of cluster membership for each star photometrically observed and for 23 additional red giant candidates with UBV and DDO data available in the literature, is evaluated by using two independent photometric criteria. Nearly 82% of the analysed stars are found to have a high probability of being cluster giants. Photometric membership probabilities show very good agreement with those obtained from CORAVEL radial velocities. While E (B –V) colour excesses were determined from combined B – V and DDO colours, calibrations of the DDO system were used to derive MK spectral types, effective temperatures and metallicities. The derived DDO metallicities range between values typical of moderately metal‐poor clusters ([Fe/H] = –0.19) to moderately metal‐rich ([Fe/H] = 0.25) ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献