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排序方式: 共有210条查询结果,搜索用时 15 毫秒
81.
Gaudenz Deplazes Anna Nele Meckler Larry C. Peterson Yvonne Hamann Beat Aeschlimann Detlef Günther Alfredo Martínez‐García Gerald H. Haug 《Sedimentology》2019,66(5):1967-1988
High‐resolution palaeorecords of climate are critical to improving current understanding of climate variability, its sensitivity and impact on the environment in the past and in the future. Sediments from the Cariaco Basin off the coast of Venezuela have proven to be sensitive recorders of tropical palaeoclimate variability down to an annual scale. However, the fingerprint of climate and sea level in the sediments of the last glacial period is still not completely understood. In this study, lamination analysis of sediments from the Cariaco Basin is extended to the last glacial period. Detailed sedimentological and geochemical analysis (laser ablation–inductively coupled plasma–mass spectrometry) reveals couplets of light‐coloured, terrigenous‐rich and dark‐coloured, biogenic opal‐rich laminae, which are interpreted to reflect the seasonal migration of the Intertropical Convergence Zone. In addition, a previously undescribed, nearly pure terrigenous lamina type is observed, which is referred to hereafter as a ‘C‐layer’. The C‐layers in the sedimentary sequence are interpreted as flood layers that originate from local rivers. The occurrence of these C‐layers is investigated for two core locations in the Cariaco Basin over the last 110 kyr by continuous X‐ray fluorescence scanning. Dansgaard–Oeschger oscillations are most clearly traced by proxies reflecting productivity and marine organic matter content of the sediment. In contrast, the abundance of terrigenous material differs at times between the two sites. On an interglacial to glacial timescale, the ability to record events causing C‐layers is likely to be influenced by changes in sea level and source proximity. On a millennial scale, both sediment cores contain more C‐layers during warmer interstadials compared with colder stadials during Marine Isotope Stage 3. This finding implies that interstadials were not only wetter than stadials, but probably also characterized by increased rainfall variability, leading to an enhanced frequency of flooding events in the hinterland of the Cariaco Basin. 相似文献
82.
Shallow structure beneath the Central Volcanic Complex of Tenerife from new gravity data: Implications for its evolution and recent reactivation 总被引:1,自引:0,他引:1
J. Gottsmann A.G. Camacho J. Martí L. Wooller J. Fernndez A. García H. Rymer 《Physics of the Earth and Planetary Interiors》2008,168(3-4):212-230
We present a new local Bouguer anomaly map of the Central Volcanic Complex (CVC) of Tenerife, Spain, constructed from the amalgamation of 323 new high precision gravity measurements with existing gravity data from 361 observations. The new anomaly map images the high-density core of the CVC and the pronounced gravity low centred in the Las Cañadas caldera in greater detail than previously available. Mathematical construction of a sub-surface model from the local anomaly data, employing a 3D inversion based on “growing” the sub-surface density distribution via the aggregation of cells, enables mapping of the shallow structure beneath the complex, giving unprecedented insights into the sub-surface architecture. We find the resultant density distribution in agreement with geological and other geophysical data. The modelled sub-surface structure supports a vertical collapse origin of the caldera, and maps the headwall of the ca. 180 ka Icod landslide, which appears to lie buried beneath the Pico Viejo–Pico Teide stratovolcanic complex. The results allow us to put into context the recorded ground deformation and gravity changes at the CVC during its reactivation in spring 2004 in relation to its dominant structural building blocks. For example, the areas undergoing the most significant changes at depth in recent years are underlain by low-density material and are aligned along long-standing structural entities, which have shaped this volcanic ocean island over the past few million years. 相似文献
83.
Subantarctic macrotidal flats, cheniers and beaches in San Sebastian Bay, Tierra Del Fuego, Argentina 总被引:6,自引:0,他引:6
San Sebastian Bay is a large, semicircular coastal embayment situated on the Atlantic coast of Tierra del Fuego, Argentina. It is a high-energy, subantarctic environment with a tidal range of 10.4 m, influenced by large waves of Atlantic and local origin and swept by constant, strong westerly winds. A 17 km long gravel spit protects the Northern part of the Bay giving rise to a gradient in sedimentary processes. From south to north, are seven distinct sedimentary environments. Coastal sedimentation started at least 5200 years before present (BP) and a rapid progradation related to a relative sea-level drop has infilled about 6 kilometres of the Bay with a sedimentary sequence 10–11 m thick. 14-C dating of unabraded shells in the Chenier ridges of the relict part of the complex allows for a precise reconstruction of the stages of the progradation, that has slowed from 2.35 m/year at 5000 years BP to 0.6 m/year at present. The possible causes of the sea-level drop are discussed. 相似文献
84.
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
85.
Alfredo Seritti David Pellegrini Elisabetta Morelli Corrado Barghigiani Romano Ferrara 《Marine Chemistry》1986,18(2-4)
Copper complexing capacity of cell exudates of Dunaliella salina in natural seawater culture medium was investigated in order to evaluate the influence of this organism on speciation of trace metals in seawater.Seawater samples were collected at 200 m and 2 miles off the coast and immediately filtered. Copper complexing capacity (CCCu) and stability constants (K′) of related cupric complexes were then measured. They were, respectively, 27.1 × 10−8 mol l−1 and 0.56 × 107 l mol−1 for the samples collected at 200 m and 12.8 × 10−8 mol l−1 and 6.10 × 107 l mol−1 for those collected 2 miles off the coast. A stock culture (20 ml, 106 cells ml−1) in log-phase was inoculated in 2 l of each sample of filtered natural seawater. The trend of cell influence was estimated on filtered culture medium by measuring CCCu and K′ after 1 h, 3 and 7 days. From the results it appears that CCCu increased with respect to time and this was related to the growth rate, indicating a certain relationship with cell metabolic activity.It can be concluded that a comparison between the culture referring to 200 m and 2 miles, respectively, shows that the former presents a CCCu two times higher than the latter while the K′ is ten times higher at 2 miles than that at 200 m. 相似文献
86.
Climate Dynamics - The atmospheric jet and blocking distributions, especially in the North Atlantic sector, have been challenging features for a climate model to realistically reproduce. This study... 相似文献
87.
88.
89.
José Alfredo Ramos-Leal B. López-Álvarez G. Santacruz-De León O. Almanza-Tovar J. Morán-Ramírez D. A. Padilla-Reyes Z. I. González-Acevedo 《Arabian Journal of Geosciences》2016,9(19):736
The paper evaluates the quality of groundwater for agricultural use in Tierra Nueva, San Luis Potosi, Mexico, where the agricultural productivity zone presents problems of salinity soil. Twenty groundwater samples and 11 soil samples at 2 depths at each point were collected and analyzed. In this type of water quality study, Wilcox classification diagram and the method of Salinity Laboratory United States for the quality of agricultural land were used. However, in some cases, these rankings do not reflect the actual condition, as in the case of Tierra Nueva, where the soil is classified as normal while water is classified at intermediate good. To analyze the real conditions of soil and water quality indicators of water for agricultural use risk of salinization, sodium adsorption ratio, adsorption ratio magnesium, permeability index, sodium percentage, soluble sodium percentage, residual sodium carbonate, and Kelly ratio were used. Sodicity rates including sodium adsorption ratio indicate no problem in soil extract. However, 25% of water samples are dangerous, with levels ranging from medium to high. For indexes of sodium percentage, residual sodium carbonate, and Kelly ratio, a distribution of classes ranging from questionable to inadequate was applied. Salinity levels show that effective salinity has good classification; potential salinity (PS) is conditional and therefore not recommended; and osmotic potential and electrical conductivity are classified as high in saline water, which is an increasingly important problem. The combination of different indices emphasized serious problems of salinity conditions, particularly sodicity. 相似文献
90.
Neil K. Ganju Mark J. Brush Brenda Rashleigh Alfredo L. Aretxabaleta Pilar del Barrio Jason S. Grear Lora A. Harris Samuel J. Lake Grant McCardell James O’Donnell David K. Ralston Richard P. Signell Jeremy M. Testa Jamie M. P. Vaudrey 《Estuaries and Coasts》2016,39(2):311-332
Numerical modeling has emerged over the last several decades as a widely accepted tool for investigations in environmental sciences. In estuarine research, hydrodynamic and ecological models have moved along parallel tracks with regard to complexity, refinement, computational power, and incorporation of uncertainty. Coupled hydrodynamic-ecological models have been used to assess ecosystem processes and interactions, simulate future scenarios, and evaluate remedial actions in response to eutrophication, habitat loss, and freshwater diversion. The need to couple hydrodynamic and ecological models to address research and management questions is clear because dynamic feedbacks between biotic and physical processes are critical interactions within ecosystems. In this review, we present historical and modern perspectives on estuarine hydrodynamic and ecological modeling, consider model limitations, and address aspects of model linkage, skill assessment, and complexity. We discuss the balance between spatial and temporal resolution and present examples using different spatiotemporal scales. Finally, we recommend future lines of inquiry, approaches to balance complexity and uncertainty, and model transparency and utility. It is idealistic to think we can pursue a “theory of everything” for estuarine models, but recent advances suggest that models for both scientific investigations and management applications will continue to improve in terms of realism, precision, and accuracy. 相似文献