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991.
992.
Marcus Silva Moacyr Araujo Jacques Servain Pierrick Penven Carlos A.D. Lentini 《Ocean Modelling》2009,30(4):256-269
The southwestern tropical Atlantic (05°S–25°S/20°W–47°W), where part of the South Equatorial Current (SEC) enters at its eastern border, is of particular interest as it is fed by many western boundary currents along the eastern Brazilian continental shelf. However, the long-term variability of the dynamics in this region, which are also important as they contribute to the climate over northeastern Brazil, is largely unknown. We use the Regional Ocean Model System (ROMS) here for the first time in this area to simulate the ocean circulation with an isotropic horizontal grid resolution of 1/12° and 40 terrain-following layers. As a primary evaluation of the ROMS configuration, we explore surface and vertical thermal structures, the surface mixed layer, and mass transports within the upper levels. Interannual variability results are compared with the first two-year series of observed thermal profiles derived from the three PIRATA-SWE moorings. The simulated thermal structure in the upper ocean layers agrees well with in-situ data. ROMS simulations point out a broad and relatively weak SEC flow composed of a sequence of more or less defined near-surface cores. The westward SEC transport for the upper 400 m along the PIRATA-SWE section, calculated from the ROMS simulation for 2005–2007, shows an average volume transport of 14.9 Sv, with a maximum observed in JFM (15.7 Sv), and a minimum during MJJ (13.8 Sv). ROMS results indicate that the 2005–2007 seasonal near-surface westward SEC transport is modulated by the zonal wind variability. Three zonal sections extending from the American continent to the PIRATA buoy sites confirm that stronger northward NBUC transport and decreasing BC transport were achieved during May 2006 and May 2007, i.e. at the time the sSEC bifurcation reaches its southernmost position. On the other hand, the maximum southward BC flow was verified during January 2006, January 2007 and March 2007, with a minimum northward NBUC flow in December 2005 and October/December 2006, corresponding to the period when the sSEC bifurcation reaches its lowest latitude (OND). Sea Surface Height (SSH) and the surface Eddy Kinetic Energy (EKE) derived from simulations and AVISO Rio05 product point out the highest surface meso-scale activity (EKE 50 cm2 s−2) along the cSEC and NBUC/BC patches. Preliminary results provide additional ingredients in the complexity of the SEC divergence region and encourage us to conduct a more detailed exploration of the dynamics of this region using the ROMS. This also shows the need to continue, extend, and vertically upgrade the observational PIRATA-SWE array system, especially with more levels of salinity measurements and the installation of current measurements. 相似文献
993.
994.
Eduardo Teixeira da Silva Michael Ridd David Klumpp 《Marine environmental research》2009,67(4-5):177-182
Radiolabelled experiments were carried out to measure necessary parameters in the development of a biodynamic ecotoxicological simulation model of Cd accumulation in the barnacle biomonitor Balanus amphitrite. The Cd uptake rate constant from the dissolved phase, the Cd assimilation efficiency (AE) from suspended particulate matter (SPM) and the efflux rate constant were obtained using 109Cd. A Cd uptake rate constant from the dissolved phase (ku) of 0.0072 L g−1 h−1 was determined for the barnacle under environmentally realistic dissolved Cd concentrations (maximum of 400 ng L−1). Cd AE from SPM was determined from the barnacle feeding on SPM with low and high chl a concentrations, resulting in AEs of 39.0% and 48.7%, respectively, and an efflux rate of 0.0072 d−1. The difference between the AEs resulted from differences in chl a:SPM ratios suggesting a general tendency of higher AE when SPM is enriched with chl a. These results reinforce that the accuracy of ecotoxicological models for metal accumulation in organisms depends on how representative the selected food items are of the organism’s natural diet. 相似文献
995.
Ana I. Sousa Ana I. Lillebø Miguel A. Pardal Isabel Caçador 《Estuarine, Coastal and Shelf Science》2010
This study aimed to assess the contribution of different salt marsh halophytes (Spartina maritima, Scirpus maritimus, Halimione portulacoides, Sarcocornia fruticosa, and Sarcocornia perennis) to nutrient cycling and sequestration in warm-temperate salt marshes. Carbon, nitrogen and phosphorus concentration in plant organs and rhizosediment, as well as plant biomass were monitored every two months during one year. Results show that the C retained in the rhizosediment does not seem to be species or site specific. However, some halophytes seem to have a higher contribution to retain C from external sources, namely S. perennis and S. maritima. Regarding N, halophytes colonizing the upper and middle marsh areas had the highest NBPP (net belowground primary production) as well as the retention of N in the rhizosediment. Yet, excluding S. maritimus, all halophytes seem to contribute to the retention of N from external sources. The P retained in the rhizosediment does not seem to be species or site specific. Still, only S. maritima colonizing the lower marsh areas, which also had comparatively lower NBPP, seem to have a higher contribution to retain P from external sources. Additionally, it seems that there is no relation between plants sequestration capacity for nutrients and plant photosynthetic pathway. This work shows that nutrient cycling and accumulation processes by salt marsh halophytes contribute to reduce eutrophication (N and P retention) and also to reduce atmospheric CO2 (C retention), highlighting salt marsh ecosystems services and the crucial role of halophytes in maintaining ecosystem functions and health. 相似文献
996.
We developed a new methodology to determine CO2 fluxes in intertidal and shallow subtidal plant communities, namely seagrasses, both when the plants are submerged and when they are air-exposed. The apparatus comprises closed incubation chambers and a gas exchange column, designed to remove carbon dioxide from the water. Different types of incubation chambers were designed and built to adapt the system to distinct environments and incubation requirements. The methodology was tested under a comprehensive range of situations and its advantages and limitations are discussed. Overall, the method provides precise measurements of community carbon dioxide fluxes, through a fast and non-intrusive process, allowing repeatable in situ measurements of carbon uptake both in submerged and air-exposed conditions. As the experimental apparatus is identical, directly comparable measurements of air-exposed and submerged community production may be obtained, allowing sound estimates of daily carbon budgets of intertidal and shallow subtidal communities. 相似文献
997.
Cheila Almeida Rui CoelhoMarco Silva Luís BentesPedro Monteiro Joaquim RibeiroKarim Erzini Jorge M.S. Gonçalves 《Estuarine, Coastal and Shelf Science》2008
The faunal communities of four intertidal habitats namely sand, mud, seagrass (Zostera noltii) and seagrass patches (mixSM) of a temperate coastal lagoon, Ria Formosa (southern Portugal), were sampled. A total of 47 species were taken in 428 bottomless drop sampler samples, with the highest number of species and the more commonly occurring species belonging to the Mollusca phylum. The dominance of these gastropod species underlines the importance of the grazing food chain in these habitats. Bittium reticulatum was the most abundant species, being especially abundant in the seagrass habitat. The most frequent and highest biomass species in the community was Carcinus maenas, a predator that makes use of the available resources and that is adapted to the highly variable intertidal environment. Pomatoschistus microps was the most abundant fish species, with highest densities in the mud habitat, which demonstrates an ability to occupy a low depth area. The seagrass habitat had the highest diversity, abundance and biomass, followed by the mixSM habitat and was different from all the others. Assemblages were highly influenced by the presence of vegetation, providing forage and refuge from predation. A well defined summer group was identified in all habitats. These results highlight the importance of seagrass beds and the idea that their decrease implies the decrease of lagoon production through the impoverishment of the trophic structure of the lagoon. 相似文献
998.
Luciana Gnio Ana Sousa Nuno Vaz Joo M. Dias Carlos Barroso 《Journal of Sea Research》2008,59(3):133-143
The effect of low salinity on the survival of recently hatched veliger of the gastropod Nassarius reticulatus (L.) was studied under laboratory conditions at 17 °C ± 1 °C. Significant mortality occurred for salinities ≤ 17 psu and the LS50 (salinity that causes 50% mortality) varied from 14.5 psu to 17.2 psu for exposures between 1 h and 48 h, respectively. The results were included in a mathematical model in order to estimate the mortality of N. reticulatus veliger in Ria de Aveiro under different salinity scenarios determined by numerical simulation. The model predicts a massive mortality of veliger immediately after their eclosion (1 h) in Ria de Aveiro during spring tide when the river input reaches its expected maximum — a situation that has been observed occasionally and may overlap a massive eclosion of veliger in the water. Except in this extreme situation, the mortality in Ria de Aveiro is generally restricted to the upstream limits of the channels. The results indicate that N. reticulatus recruitment in estuaries may strongly depend on the prevailing salinity regime. 相似文献
999.
将分数阶傅氏变换引入地震数据空间预测滤波中,研究滤波效果与信号保真的最佳折衷.利用分数阶傅氏变换把信号旋转变换到任意1个角度时"频"平面,运用奇异值分解(SVD)方法求取空间预测滤波算子,实现预测滤波;通过数据相关系数和相对误差能量曲线评价滤波效果.研究结果表明,可以找到1个合适的分数阶域,使得分数阶域空间预测滤波能够在压制噪声和保留信号特征两方面达到最佳折衷,较一般f-x域预测滤波具有更大灵活性. 相似文献
1000.
基于局域波分解的地震信号时频属性提取 总被引:1,自引:0,他引:1
局域波分解可以得到有意义的频率并可以抑制时频分布交叉项,是1种新的自适应信号分解方法.在局域波分解基本原理的基础上,研究基于局域波分解的地震信号分频谱及频率属性的提取方法.将局域波分解与传统时频分析结合,进行有效数值实现与对比分析,通过模型地震数据与实际2D地震数据试算验证方法的正确性和有效性.研究表明:基于局域波分解的Wigner时频分布分频谱,具有较高的时频分辨率,交叉项得到简单有效的抑制;基于局域波分解的时频分析方法计算提取的频率属性,避免无意义的负频率,物理意义明确,为在地震储层研究和油气检测中的正确应用奠定基础. 相似文献