Analysis of meteorological drought episodes in Paraguay   总被引：3，自引：0，他引：3  

Julián Báez Benitez  Roger Monte Domecq 《Climatic change》2014,127(1):15-25

This paper analyzes the meteorological drought events in Paraguay in the period of 1964 to 2011, using the Standardized Precipitation Index (SPI). The objective is to determine if the frequency and/or severity of droughts has increased or decreased in the last years, in response of climate change. They The southernmost parts of the country are affected by severe droughts producing damage to soybean and corn crop during the rainy season (October–March) especially during the summer of 2008–2009. The years of 1967, 1968, 1978, 1979, 2000 and 2008 was identified as severe to extreme drought events and coincides with La Niña event. However, the relationship between all drought events, especially those agricultural droughts and La Niña is not clear, suggesting the necessity of new research, focusing on new drivers to explain the cause of the droughts. The economy of Paraguay, based for good part on agriculture, is clearly vulnerable to droughts. Even though no undeniable increasing trend in drought frequency/severity was detected, contingency plans to diminish drought impacts ought to be elaborated.  相似文献   

The impact of soil moisture–atmosphere coupling on daily maximum surface temperatures in Southeastern South America     

Coronato  Tanea  Carril  Andrea F.  Zaninelli  Pablo G.  Giles  Julián  Ruscica  Romina  Falco  Magdalena  Sörensson  Anna A.  Fita  Lluis  Li  Laurent Z. X.  Menéndez  Claudio G. 《Climate Dynamics》2020,55(9-10):2543-2556

Based on a series of experiments conducted by two regional climate models (RCA4 and LMDZ) with and without soil moisture-atmosphere coupling, we investigate the role of soil moisture on the occurrence of surface air temperature extremes and its persistence in Southeastern South America. Our analysis reveals that both factors, soil moisture-atmosphere coupling and relatively drier soil conditions, enhance the temperature extremes. In addition, the existence of soil-atmosphere coupling and the associated soil moisture variability is crucial for the development of the extremes in SESA. The key role of soil-atmosphere coupling is also reflected in the intrinsic persistence of hot days, which is greater in simulations with interactive soil moisture than in those with prescribed soil conditions. In the absence of soil-atmosphere coupling, the imprint of the anomalous dry (and also wet) soil conditions on the intensity and persistence of hot days is weaker.

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考洲洋海水营养盐分布及其与浮游植物的关系     

甘居利  林钦  李纯厚  黄洪辉  贾晓平 《广东海洋大学学报》2002,22(6):32-37

根据 1998年的现场调查资料 ,分析考洲洋海水无机营养盐与浮游植物生物量的平面分布及其相互关系。结果表明二者的关系很密切 :浮游植物量在枯水期 (2月 )与无机氮、无机磷、硅酸盐显著正相关 ,相关系数分别为 0 779、0 94 6和 0 876 (n =12 ) ;在丰水期 (8月 )与无机氮和硅酸盐负相关、与磷酸盐正相关 ,相关系数分别为 - 0 6 5 5、- 0 84 5和 0 5 84 (n =11)。从浮游植物对营养盐的一般需要量和N、P、Si的原子比分析 ,2月N、P显得紧缺 ,8月N、P、Si均过量  相似文献   

南海北部渔场表层沉积物中的硫化物   总被引：1，自引：0，他引：1  

甘居利  李纯厚  贾晓平  王增焕  蔡文贵  吴洽儿 《广东海洋大学学报》2001,21(2):44-47

为了给南海北部渔场的资源和环境保护提供基础数据,用碘量法测定了南海北部陆架区表层沉积物中硫化物含量.结果表明,全部28份样品中硫化物含量为3.3～42.2mg/kg(干重,下同),平均为12.1mg/kg,符合外海含量低的一般规律,明显低于沿岸海湾的含量,远低于日本渔业环境质量标准(200mg/kg)和安全下限值(400mg/kg).硫化物含量在测站间和不同区域间存在一定差异,南北方向呈近岸(13.1mg/kg)略高于离岸(12.1mg/kg)、离岸略高于远岸(11.1mg/kg)的梯度分布,但梯度差异不显著(p＞0.10);东西方向的分布特点是粤西海域(23.7mg/kg)＞海南岛以东(15.3mg/kg)＞台湾浅滩(9.4mg/kg)≈粤东海域(8.7mg/kg)≈珠江口外海域(8.6mg/kg).空间分布不太均匀主要是受沉积物类型的影响,与陆源硫化物输入的关系不大.  相似文献   

New Archaeomagnetic Data from Tunisia: Dating of Two Kilns and New Archaeointensities from Three Ceramic Artifacts     

Lluís Casas  Boutheina Fouzai  Marta Prevosti  Nejia Laridhi‐Ouazaa  Ramon Jrrega  Siwar Baklouti 《Geoarchaeology》2016,31(6):564-576

Two isolated kilns of unknown age and three well‐dated artifacts from Tunisia have been investigated using archaeomagnetic techniques. Dating has been attempted for the kilns and archaeomagnetic intensities have been obtained for the artifacts. The kilns lack datable artifacts although one of them (Sidi Zahruni) could be related to a nearby late Roman site. Comparison with the SCHA.DIF.3K regional geomagnetic model suggests for both kilns two possible periods of last use, either Roman or Medieval. Three archaeomagnetic intensities were obtained for the well‐dated ceramic artifacts adding to scarce archaeomagnetic data from Africa. The new data along with recently published archaeointensities from other Tunisian sites have been compared with the regional model SCHA.DIF.3K, its updated version, and the global ARCH3k.1 geomagnetic model. The models show relatively good agreement with the new archaeointensities and with previously published intensities. The uncertainty of the experimental data tends to increase for older artifacts, and their agreement with the geomagnetic models diminishes. The observed trend of the intensity models to underestimate values in the Tunisian area for the Roman period could be overcome by adding new data from well‐dated artifacts from North African, particularly from pre‐Roman and Roman sites.  相似文献   

Relationship between bedload and suspended sediment in the sand-bed Exu River,in the semi-arid region of Brazil     

Jose Ramon B. Cantalice  Moacyr Cunha Filho  Borko D. Stosic  Victor Casimiro Piscoya  Sergio M. S. Guerra  Vijay P. Singh 《水文科学杂志》2013,58(8):1789-1802

Abstract

Suspended sediment and bedload discharges in sand-bed rivers shape semi-arid landscapes and impact sediment delivery from these landscapes, but are still incompletely understood. Suspended sediment and bedload fluxes of the intermittent Exu River, Brazil, were sampled by direct measurements. The highest suspended sediment concentration observed was 4847.4 mg L^-1 and this value was possibly associated with the entrainment of sediment that was deposited in the preceding year. The bedload flux was well related to the stream power and the river efficiently transported all available bedload with a mean rate of 0.0047 kg m^-1 s^-1, and the percentage of bedload to suspended sediment varied between 4 and 12.72. The bed sediment of Exu River was prone to entrainment and showed a proclivity for transport. Thus, sand-bed and gravel-bed rivers of arid environments seem to exhibit the same mobility in the absence of armour layer.

Editor D. Koutsoyiannis; Associate editor B. Touaibia

Citation Cantalice, J.R.B., Cunha Filho, M., Stosic, B.D., Piscoya, V.C., Guerra, S.M.S., and Singh, V.P., 2013. Relationship between bedload and suspended sediment in the sand-bed Exu River, in the semi-arid region of Brazil. Hydrological Sciences Journal, 58 (8), 1789–1802.  相似文献   

Deep incision in an Aptian carbonate succession indicates major sea‐level fall in the Cretaceous     

Telm Bover‐Arnal  Ramon Salas  Joan Guimerà  Josep Anton Moreno‐Bedmar 《Sedimentology》2014,61(6):1558-1593

Long‐term relative sea‐level cycles (0·5 to 6 Myr) have yet to be fully understood for the Cretaceous. During the Aptian, in the northern Maestrat Basin (Eastern Iberian Peninsula), fault‐controlled subsidence created depositional space, but eustasy governed changes in depositional trends. Relative sea‐level history was reconstructed by sequence stratigraphic analysis. Two forced regressive stages of relative sea‐level were recognized within three depositional sequences. The first stage is late Early Aptian age (intra Dufrenoyia furcata Zone) and is characterized by foreshore to upper shoreface sedimentary wedges, which occur detached from a highstand carbonate platform, and were deposited above basin marls. The amplitude of relative sea‐level drop was in the order of tens of metres, with a duration of <1 Myr. The second stage of relative sea‐level fall occurred within the Late Aptian and is recorded by an incised valley that, when restored to its pre‐contractional attitude, was >2 km wide and cut ≥115 m down into the underlying Aptian succession. With the subsequent transgression, the incision was backfilled with peritidal to shallow subtidal deposits. The changes in depositional trends, lithofacies evolution and geometric relation of the stratigraphic units characterized are similar to those observed in coeval rocks within the Maestrat Basin, as well as in other correlative basins elsewhere. The pace and magnitude of the two relative sea‐level drops identified fall within the glacio‐eustatic domain. In the Maestrat Basin, terrestrial palynological studies provide evidence that the late Early and Late Aptian climate was cooler than the earliest part of the Early Aptian and the Albian Stage, which were characterized by warmer environmental conditions. The outcrops documented here are significant because they preserve the results of Aptian long‐term sea‐level trends that are often only recognizable on larger scales (i.e. seismic), such as for the Arabian Plate.  相似文献   

Evaluating TCE Abiotic and Biotic Degradation Pathways in a Permeable Reactive Barrier Using Compound Specific Isotope Analysis     

Paulo Lojkasek‐Lima  Ramon Aravena  Orfan Shouakar‐Stash  Shaun K. Frape  Massimo Marchesi  Stephanie Fiorenza  John Vogan 《Ground Water Monitoring & Remediation》2012,32(4):53-62

A pilot‐scale zero valent iron (ZVI) Permeable Reactive Barrier (PRB) was installed using an azimuth‐controlled ‐vertical hydrofracturing at an industrial facility to treat a chlorinated Volatile Organic Compound (VOC) plume. Following ZVI injection, no significant reduction in concentration was observed to occur with the exception of some multilevel monitoring wells, which also showed high levels of total organic carbon (TOC). These patterns suggested that the zero valent iron was not well distributed in the PRB creating leaky conditions. The geochemical data indicated reducing conditions in these areas where VOC reduction was observed, suggesting that biotic processes, associated to the guar used in the injection of the iron, could be a major mechanism of VOC degradation. Compound‐Specific Isotope Analysis (CSIA) using both carbon and chlorine stable isotopes were used as a complementary tool for evaluating the contribution of abiotic and biotic processes to VOC trends in the vicinity of the PRB. The isotopic data showed enriched isotope values around the PRB compared to the isotope composition of the VOC source confirming that VOC degradation is occurring along the PRB. A batch experiment using site groundwater collected near the VOC source and the ZVI used in the PRB was performed to evaluate the site‐specific abiotic isotopic fractionation patterns. Field isotopic trends, typical of biodegradations were observed at the site and were different from those obtained during the batch abiotic experiment. These differences in isotopic trends combined with changes in VOC concentrations and redox parameters suggested that biotic processes are the predominant pathways involved in the degradation of VOCs in the vicinity of the PRB.  相似文献   

Dynamical parameter analysis of continuous seismic signals of Popocatépetl volcano (Central Mexico): A case of tectonic earthquakes influencing volcanic activity     

Marta Tárraga  Servando De La Cruz-Reyna  Ana T. Mendoza-Rosas  Roberto Carniel  Alicia Martínez-Bringas  Alicia García  Ramon Ortiz 《Acta Geophysica》2012,60(3):664-681

The continuous background seismic activity contains information on the internal state of a volcanic system. Here, we report the influence of major regional tectonic earthquakes (M > 5 in most cases) on such state, reflected as changes in the spectral and dynamical parameters of the volcano continuous seismic data. Although changes do not always occur, analysis of five cases of earthquake-induced variations in the signals recorded at Popocatépetl volcano in central México reveal significant fluctuations following the tectonic earthquakes. External visible volcanic activity, such as small to moderate explosions and ash emissions, were related to those fluctuations. We briefly discuss possible causes of the variations. We conclude that recognition of fluctuations in the dynamical parameters in volcano monitoring seismic signals after tectonic earthquakes, even those located in the far field, hundreds of kilometers away, may provide an additional criterion for eruption forecasting, and for decision making in the definition of volcanic alert levels.  相似文献   

Climate signal in varve thickness: Lake La Cruz (Spain), a case study   总被引：1，自引：0，他引：1  

Lidia Romero-Viana  Ramon Julià  Antonio Camacho  Eduardo Vicente  Maria Rosa Miracle 《Journal of Paleolimnology》2008,40(2):703-714

Lake La Cruz is a meromictic, karstic lake with annually laminated sediment formed by summer pulses of calcite deposition. The aim of this study was to explore the potential use of the laminated sediment from Lake La Cruz as a quantitative climate proxy, by calibrating lamina thickness against instrumental climate data. Statistical analysis of the relation between lamina thickness and the meteorological dataset indicated a high correlation between calcium carbonate lamina thickness and rainfall from December to March (r  = 0.725, P < 0.01, n = 35). Winter rainfall anomalies in the area are, in turn, highly negatively correlated with the North Atlantic Oscillation index (NAO, r = −0.832; P < 0.01; n = 53). We propose a regression model to infer past winter rainfall from calcium carbonate laminae thickness. These results highlight new possibilities for paleoenvironmental research using calcite laminated sediment records as climate proxies, especially to study past rainfall variability.  相似文献