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171.
José Alfredo Ramos-Leal Janete Morán-Ramírez José Teodoro Silva-García Rosa María Fuentes-Rivas Gustavo Cruz-Cárdenas Salvador Ochoa-Estrada Francisco Estrada-Godoy 《Arabian Journal of Geosciences》2018,11(15):422
The present study characterized the hydrogeochemical processes of the aquifer of Ciénega de Chapala in Michoacán, Mexico. The dominant water families contained bicarbonate magnesium and sodium. In the region, water infiltrates into a fractured volcanic environment exposed in the surrounding mountains and is transmitted to the volcano-sedimentary units of the ciénega, where silicate alteration and ion exchange processes occur in the clays of the subsoil. The Gibb diagrams confirm that the main evolutionary processes in the aquifer are rock-water interactions in the local flow and evaporation in the intermediate and regional flows. The molar ratios of HCO3/Na and Ca/Na are congruent with the type of volcano-sedimentary environment present in the area. Ternary mixing processes associated with three end members were also identified and were related to the flow systems in the area. The local flow contributes 77% of water to the system, and the intermediate and regional flows contribute 16% and 7%, respectively. 相似文献
172.
Margaret M. Hurwitz Natalia Calvo Chaim I. Garfinkel Amy H. Butler Sarah Ineson Chiara Cagnazzo Elisa Manzini Cristina Peña-Ortiz 《Climate Dynamics》2014,43(12):3367-3376
The seasonal mean extra-tropical atmospheric response to El Niño/Southern Oscillation (ENSO) is assessed in the historical and pre-industrial control CMIP5 simulations. This analysis considers two types of El Niño events, characterized by positive sea surface temperature (SST) anomalies in either the central equatorial Pacific (CP) or eastern equatorial Pacific (EP), as well as EP and CP La Niña events, characterized by negative SST anomalies in the same two regions. Seasonal mean geopotential height anomalies in key regions typify the magnitude and structure of the disruption of the Walker circulation cell in the tropical Pacific, upper tropospheric ENSO teleconnections and the polar stratospheric response. In the CMIP5 ensembles, the magnitude of the Walker cell disruption is correlated with the strength of the mid-latitude responses in the upper troposphere i.e., the North Pacific and South Pacific lows strengthen during El Niño events. The simulated responses to El Niño and La Niña have opposite sign. The seasonal mean extra-tropical, upper tropospheric responses to EP and CP events are indistinguishable. The ENSO responses in the MERRA reanalysis lie within the model scatter of the historical simulations. Similar responses are simulated in the pre-industrial and historical CMIP5 simulations. Overall, there is a weak correlation between the strength of the tropical response to ENSO and the strength of the polar stratospheric response. ENSO-related polar stratospheric variability is best simulated in the “high-top” subset of models with a well-resolved stratosphere. 相似文献
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174.
Interpretation of bulk‐sediment geochemistry is one of several approaches for determining sediment provenance. This study investigates the value added by bulk‐sediment geochemical analysis in interpreting provenance in a passive margin clastic basin, the Upper Jurassic–Lower Cretaceous deltaic sediments of the Scotian Basin. Provenance studies in this basin are challenging because source tectonic terranes are parallel to the basin margin and polycyclic sediment sources are abundant. More than 400 samples of mudstone and sandstone representing the geographical and stratigraphic range of interest were analysed for 57 elements. Diagenetic processes added calcium to many samples and removed potassium in rocks buried below 3 km, thus impacting principal component analysis and published weathering indices. However, multiple geochemical approaches to assessing the degree of weathering showed climatically controlled changes in weathering in the Tithonian and Barremian, and changes in supply from major tectonic events, such as the top‐Aptian uplift in the Labrador rift. Covariance of elements in heavy minerals demonstrates the varying magnitude of polycyclic supply and stratigraphic changes in sources. Geochemical analyses revealed a previously unsuspected Tithonian alkali volcanic sediment source, characterized by high niobium and tantalum. The lack of highly contrasting sources means that geochemistry alone is inadequate to determine sediment provenance. Published discrimination diagrams are of limited value. Statistical analysis of geochemical data is strongly influenced by diagenetic processes, episodic volcanic inputs and polycyclic concentration of resistant heavy minerals in sandstones. Single indicator elements for particular sources are generally lacking. Nevertheless, careful consideration of geochemical variability on a case by case basis, integrated with detrital mineral studies, provides new insights into palaeoclimate, sediment provenance and, hence, regional tectonics. Although there is no simple template for such analysis, this study demonstrates an approach that can be used for other basins. 相似文献
175.
Mauro de Melo Júnior Leonardo K. Miyashita Naira J. Silva Salvador A. Gaeta Rubens M. Lopes 《Marine Ecology》2013,34(3):363-372
We investigated the reproductive biology of the planktonic harpacticoid copepod Euterpina acutifrons, including morphometric data, egg production rates (EPR) and viability, and weight‐specific egg production. Experiments were carried out during 1 year in an inner‐shelf area off Ubatuba (SE Brazil), a site seasonally influenced by bottom intrusions of the relatively cold and nutrient‐rich South Atlantic Central Water (SACW). We hypothesized that E. acutifrons attain higher reproductive rates when SACW penetrates in this region. Live females were incubated individually in cell culture plates during two periods of 24 h each, under controlled temperature and light conditions. Euterpina acutifrons carried on average 16.9 ± 6.9 eggs·sac?1, ranging between 10.8 ± 5.7 and 30.8 ± 7.4 eggs·sac?1. Estimated EPRs ranged from 6.3 ± 3.4 to 13.6 ± 4.2 eggs·female?1·day?1, with mean weight‐specific egg production rates of 0.06 ± 0.04 and 0.17 ± 0.08 per day. Euterpina acutifrons was not directly influenced by SACW intrusions, but body length and clutch size were positively related to temperature and chlorophyll content. Egg hatching time was clearly dependent on water temperature, as a 2 °C increase resulted in a decrease of 15 h in egg hatching time. This shows that even a small variation in temperature may considerably affect E. acutifrons population dynamics. Reproductive traits of this pelagic harpacticoid seem, therefore, to be controlled by the trade‐offs between increased food supply and the metabolic demands at low temperatures associated with SACW bottom intrusions toward this coastal area. 相似文献
176.
177.
Carlos Alberto Galaz-Samaniego M. Cristina Peñalba Francisco Abraham Paz-Moreno Iván Rosario Espinoza-Encinas Kinardo Flores-Castro Rogelio Monreal Carlos Lizárraga-Celaya 《第四纪科学杂志》2023,38(1):76-91
During the last glacial termination, the climate system experienced intense global variations whose causes and impacts are not fully defined, particularly for low latitudes. The northwestern Mexico Sky Islands present a climate-sensitive ideal setting to record palaeoecological and palaeoclimatic changes due to their physiographic complexity and location in the ecotone between temperate and tropical ecosystems. High-resolution pollen analysis and a detailed sedimentological study were conducted at the Ciénega Tonibabi tropical thorn scrub site. The 15 540–0 cal a bp nearly continuous record shows that the North Atlantic Ocean did have a cold and humid climatic influence during the glacial stages of the end of the Pleistocene, including a sharp pulse during the Younger Dryas. However, a shift to the Pacific Ocean influence occurred during the Holocene, which led to the development of the El Niño conditions prevailing today. Colder and warmer phases follow one another with higher or lower winter precipitation, including a sharp Bølling–Allerød and development and intensification of the North American monsoon. They are reflected in hydrological changes as well as in the advances, retreats and intermingling of coniferous forests and tropical thorn scrub. 相似文献