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排序方式: 共有921条查询结果,搜索用时 15 毫秒
911.
Ma Carmen Ávila-López J. Martín Hernández-Ayón Víctor F. Camacho-Ibar Armando Félix Bermúdez Adan Mejía-Trejo Isaí Pacheco-Ruiz Jose M. Sandoval-Gil 《Estuaries and Coasts》2017,40(3):792-806
The present study examines the temporal variability of air–water CO2 fluxes (FCO2) and seawater carbonate chemistry in a Baja California coastal lagoon during an exceptionally warm anomaly that was developed in Northeast Pacific coasts during 2014. This oceanographic condition led to a summer-like season (weak upwelling condition) during the study period, which reached a maximum surface temperature anomaly of 2 °C in September 2014. San Quintín Bay acts as a source of CO2 to the atmosphere in 2014 (3.3 ± 4.8 mmol C m?2 day?1) with the higher positive fluxes mainly observed in summer months (9.0 ± 5.3 mmol C m?2 day?1). Net ecosystem production (NEP) switched seasonally between net heterotrophy and net autotrophy during the study period, with an annual average of 2.2 ± 7.1 mmol C m?2 day?1, which indicates that San Quintín Bay was a net autotrophic system during the atypical warm oceanographic condition in 2014. This pattern of seasonal variations in the carbon balance at San Quintín Bay appears to be linked to the life cycle of benthic communities, which play an important role in the whole-ecosystem metabolism. Under the limited input from external sources coupled with an increase in seawater temperatures, the recycled benthic carbon and nutrient fluxes play a major role to sustain water-column processes within the bay. Since the upwelling condition may influence the magnitude of the air–water CO2 fluxes, our results clearly indicated that San Quintín Bay is a net source of carbon to the atmosphere regardless of the adjacent oceanic conditions. Our study sheds light on the carbon dynamics and its metabolic implications in a shallow coastal ecosystem under a regional warm anomaly and contributes potentially relevant information in view of the likely future scenario of global climate change. 相似文献
912.
G. Asencio–Cortés S. Scitovski R. Scitovski F. Martínez–Álvarez 《Earth Science Informatics》2017,10(3):303-320
The prediction of earthquakes is a task of utmost difficulty that has been addressed in many different ways. However, an initial definition of the area of interest is needed, with adequate catalogs. In this work, different seismogenic zones proposals in the Republic of Croatia are studied, in terms of predictability. Such zones have been characterized with widely used seismicity parameters. Later, studies based on training and test sets properties as well as the quality of the data involved are carried out. The studies presented in this work analyze the prediction performance across the earthquake magnitude time series of the target seismogenic zones. Results show that specific prediction techniques could be used in some zones to improve earthquake magnitude prediction. 相似文献
913.
Ó. Pueyo Anchuela P. Frongia F. Di Gregorio A. M. Casas Sainz A. Pocoví Juan 《Environmental Earth Sciences》2017,76(5):230
Dispersion of pollutants from mining areas can result in risks to human health. The dynamic interaction of geological processes can generate complex situations that favor enrichment in toxic elements by sedimentary and diagenetic mechanisms. In order to explore the distribution of iron-rich minerals in coastal and river sediments, a geophysical campaign was performed along the outlet of the Piscinas and Naracauli Rivers that drain two abandoned mining areas in SW Sardinia. Both rivers flow into the Mediterranean Sea, a bay where fluvial, marine, and eolian processes interact. The geophysical campaign comprised magnetometry and ground-penetrating radar surveys. Magnetic properties were controlled by means of magnetic susceptibility measurements along the beach and dune areas, through sampling of surface sediments, natural outcrops and trenches, and considering different grain size intervals. Results indicate enrichment in ferromagnetic minerals at the leeside of dunes and berms. Sedimentological interpretation is supported by means of ground-penetrating radar. Due to both sedimentary and diagenetic processes, the 100- to 300-μm fraction of fine sands exhibits high susceptibility. Implied tenors of toxic elements in the magnetite may represent a serious hazard to environmental and health security. The results inferred from magnetic anomalies support the applicability of the geophysical approach in order to locate high concentrations of iron-rich particles both at surface and below ground and the usefulness of joint evaluation of magnetic susceptibility and ground-penetrating radar in order to characterize the sedimentary and geomorphology-controlled magnetite distribution. 相似文献
914.
The External Tanger Unit (Intrarif sub-Domain,External Rifian Zones,Morocco): an interdisciplinary study 总被引:1,自引:0,他引:1
Soufian Maaté Francisco Javier Alcalá Francesco Guerrera Rachid Hlila Alí Maaté Manuel Martín-Martín Giuliana Raffaelli Francisco Serrano Mario Tramontana 《Arabian Journal of Geosciences》2017,10(24):556
The External Tanger Unit represents one of the most complete Cretaceous-Miocene successions in the central areas of the Internal Intrarif sub-Domain (External Rif Zones, Morocco). An interdisciplinary study has been carried out to propose a new characterization of this unit which would allow a better comprehension of the confused and complex relationships among different units of the same sub-domain. The results achieved can be summarized as follows: (1) redefinition of the stratigraphic (litho-, bio-, and chrono-) record and introduction of a new, informal lithostratigraphic terminology; (2) recognition of two main depositional sequences (lower-middle Eocene p.p. and lower Oligocene p.p.-lower Miocene p.p.) separated by extended gaps (latest Cretaceous-early Eocene p.p. and middle Eocene p.p.-early Oligocene p.p.); (3) reconstruction of the evolution of the sedimentary realm, and of the relationships between tectonics and sedimentation; and (4) comparison between the upper Cretaceous-Miocene stratigraphic record and tectonic events of the Intrarif, which is located in the western external portion of the Maghrebian Flysch Basin, and the equivalent sedimentary record of the eastern portion of this basin in the Tunisian Tell. More in general, our results allowed (i) a first reconstruction of the Cretaceous-Miocene main tectono-sedimentary events; (ii) a more detailed location of the sedimentary suite in the external African Margin in the context of a wider palaeogeographic framework; and (iii) the definition of the main stages of the geological evolution of the area. 相似文献
915.
The aim of this study is to establish if the San Luis Potosi Plateau (SLPP), which is part of the southern edge of the Chihuahuan Desert, is generating desertification processes, indicating a progression of the desert toward the central part of Mexico. Therefore, we analyzed the temporal evolution of four environmental indicators of desertification: Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), Iron Oxides Index (IO) and Surface Temperature (ST). Landsat TM images are used to cover a period from 1990 to 2011. A new equation of total balance is proposed to generate an image of the overall evolution of each factor which is applied to get a probability map of desertification. The evolution of NDVI, NDWI and IO shows a behavior almost stable over the time. In contrast, the ST shows a slight increase. The outcomes of this study confirm periods of vegetation re-greening and 8.80% of the SLPP has the highest probability to develop desertification. The most affected area is the portion west of the region, and the east and south are the least affected areas. The results suggest a slight advance of the desert, although most of the area doesn’t have the necessary conditions to develop desertification. 相似文献
916.
Patricio Aceituno Maríadel del Rosario Prieto María Eugenia Solari Alejandra Martínez Germán Poveda Mark Falvey 《Climatic change》2009,92(3-4):389-416
At times when attention on climate issues is strongly focused on the assessment of potential impacts of future climate change due to the intensification of the planetary greenhouse effect, it is perhaps pertinent to look back and explore the consequences of past climate variability. In this article we examine a large disruption in global climate that occurred during 1877–1878, when human influence was negligible. The mechanisms explaining this global disturbance are not well established, but there is considerable evidence that the major El Niño episode that started by the end of 1876 and peaked during the 1877–1878 boreal winter contributed significantly to it. The associated regional climate anomalies were extremely destructive, particularly in the Northern Hemisphere, where starvation due to intense droughts in Asia, South-East Asia and Africa took the lives of more than 20 million people. In South America regional precipitation anomalies were typical of El Niño events, with rainfall deficit and droughts in the northern portion of the continent as well as in northeast Brazil and the highlands of the central Andes (Altiplano). In contrast, anomalously intense rainfall and flooding episodes were reported for the coastal areas of southern Ecuador and Northern Perú, as well as along the extratropical West coast of the continent (central Chile, 30° S–40° S), and in the Paraná basin in the southeast region. By far the most devastating impacts in terms of suffering and loss of life occurred in the semiarid region of northeast Brazil where several hundreds of thousands of people died from starvation and diseases during the drought that started in 1877. 相似文献
917.
F. Valero M. Y. Luna M. L. Martín A. Morata F. González-Rouco 《Climate Dynamics》2004,22(2-3):307-323
The variability of autumn precipitation in the western Mediterranean and its relationship to the large-scale atmospheric variability during the period 1948 to 1989 is assessed. A singular value decomposition analysis is used to establish modes of coupled variability between regional precipitation and geopotential height (Z300), zonal (U-wind) and meridional (V-wind) wind components at the 300 hPa level. The Z300/precipitation coupling, which accounts for 52% of the total squared covariance, is strong during the autumn. The first Z300 coupled mode, in its positive phase, is characterised by a dipole structure with negative anomalies over Scandinavia and positive anomalies over the Iberian Peninsula in the Z300 and negative precipitation anomalies in the western Mediterranean. In its negative phase, a coupled pattern is found showing a high-over-low block and positive precipitation anomalies over the Mediterranean area. The coupling depicted by the second mode is weaker than that found in the first mode. The second coupled mode (21% of the total squared covariance) is characterised by negative anomalies in the eastern North Atlantic and positive ones over North Africa and the central Mediterranean in the Z300 and negative anomalies in the regional precipitation. Consistent with the results of the two first modes mentioned, the coupled patterns of either U-wind/precipitation or V-wind/precipitation are found to be coherent with those for Z300/precipitation. Composite maps were obtained to give a representation of the average circulation associated with coherent precipitation variability in the western Mediterranean. The regional impacts of both modes are investigated and the large-scale dynamic patterns presented are important modes of variability. Taking into account data for the whole of the twentieth century, results show that the first singular mode is responsible for the decadal trends and long term changes in precipitation. The late 1970s and 1980s is shown as the drier period and the late 1950s and early 1960s as the wettest years of the century. 相似文献
918.
J. Bedia S. Herrera D. San Martín N. Koutsias J. M. Gutiérrez 《Climatic change》2013,120(1-2):229-247
The effect of climate change on wildfires constitutes a serious concern in fire-prone regions with complex fire behavior such as the Mediterranean. The coarse resolution of future climate projections produced by General Circulation Models (GCMs) prevents their direct use in local climate change studies. Statistical downscaling techniques bridge this gap using empirical models that link the synoptic-scale variables from GCMs to the local variables of interest (using e.g. data from meteorological stations). In this paper, we investigate the application of statistical downscaling methods in the context of wildfire research, focusing in the Canadian Fire Weather Index (FWI), one of the most popular fire danger indices. We target on the Iberian Peninsula and Greece and use historical observations of the FWI meteorological drivers (temperature, humidity, wind and precipitation) in several local stations. In particular, we analyze the performance of the analog method, which is a convenient first choice for this problem since it guarantees physical and spatial consistency of the downscaled variables, regardless of their different statistical properties. First we validate the method in perfect model conditions using ERA-Interim reanalysis data. Overall, not all variables are downscaled with the same accuracy, with the poorest results (with spatially averaged daily correlations below 0.5) obtained for wind, followed by precipitation. Consequently, those FWI components mostly relying on those parameters exhibit the poorest results. However, those deficiencies are compensated in the resulting FWI values due to the overall high performance of temperature and relative humidity. Then, we check the suitability of the method to downscale control projections (20C3M scenario) from a single GCM (the ECHAM5 model) and compute the downscaled future fire danger projections for the transient A1B scenario. In order to detect problems due to non-stationarities related to climate change, we compare the results with those obtained with a Regional Climate Model (RCM) driven by the same GCM. Although both statistical and dynamical projections exhibit a similar pattern of risk increment in the first half of the 21st century, they diverge during the second half of the century. As a conclusion, we advocate caution in the use of projections for this last period, regardless of the regionalization technique applied. 相似文献
919.
Influence of transient storage on stream nutrient uptake based on substrata manipulation 总被引:3,自引:0,他引:3
Alba Argerich Eugènia Martí Francesc Sabater Roy Haggerty Miquel Ribot 《Aquatic Sciences - Research Across Boundaries》2011,73(3):365-376
Quantification of the transient storage zone (As) has become critical in stream biogeochemical studies addressed to examine factors controlling nutrient uptake. It is expected
that higher As may enhance the interaction between nutrients and biota and thus, increase nutrient uptake. However, results from the literature
are controversial. We hypothesized that besides of the size of As, the intrinsic physical and biological characteristics of stream structures that generate As are also relevant for nutrient uptake. We performed 24 additions of phosphate, ammonium, and chloride in four reaches of
a man-made channel where we introduced three types of naturally colonized substrata packs (mud, sand and cobbles) to modify
As. We estimated ammonium and phosphate uptake coefficients in both the main channel and As using a solute transport model (OTIS-P) and compared the results among reaches with different substrata types. The introduction
of substrata packs decreased water velocity and increased As similarly among treatments. Nutrient uptake coefficients in the main channel were similar among reaches with different type
substrata packs; however, nutrient uptake coefficients measured in As differed among them as well as the ratio between ammonium and phosphorus uptake coefficients in As, which were 1.6 in reaches with mud packs and 0.02 in reaches with sand or cobble packs. Results obtained in this study suggest
that the contribution of As in nutrient uptake not only depends on the size of As but on the type of materials used to increase As, and thus, have biogeochemical implications on restoration projects aimed to modify channel morphology. 相似文献
920.