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71.
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
72.
Giorgio Rivalenti Maurizio Mazzucchelli Vicente Antonio Vitorio Girardi Giancarlo Cavazzini Cristina Finatti Maria Adelaide Barbieri Wilson Teixeira 《Lithos》1998,43(4):235-265
Paleoproterozoic basaltic, andesitic and rhyolitic dykes crosscut the Archaean Carajás basement. Basalts are distinguished into a high and a low TiO2 group (HTi and LTi), each group consisting of geochemically distinct NE- and NW-trending swarms. The HTi dykes are evolved transitional basalts having essentially EMORB-type geochemistry. The LTi basalts are tholeiites (NE-trending swarm) and high-Al basalts (NW-trending swarm) displaying incompatible trace elements patterns with variably negative Nb anomaly, enrichment in Rb, Ba, K (LILE) and La, Ce and Nd (LREE) and positive Sr anomaly. With respect to orogenic analogues, andesites have lower Al2O3, CaO and Ni, higher FeO, LILE, LREE, Nb, Zr and Ti and negative Sr anomaly. Rhyolites have geochemical characteristics comparable with those of A-type granites. At 1.8 Ga,
ranges from 0.700 to 0.705 in the HTi basalts and from 0.700 to 0.704 in the LTi group. Andesites define an isochron of 1874±110 Ma (Sro=0.7038±0.0010). Rhyolites from Southern and Northern Carajás define two isochrons of 1802±130 Ma (Sro=0.7062±0.0046) and 1535±82 Ga (Sro=0.7625) respectively, the younger date being interpreted as resetting of the Rb–Sr isotopic system. We propose a petrogenetic model relating LTi basalts with melting of lithospheric mantle metasomatized by acid melts derived from incipient melting of eclogites, representing in turn the subsolidus product of basaltic batches trapped in the mantle. The HTi basalts are explained by melting of the lithospheric mantle containing the complementary residual eclogite. Andesite petrogenesis is consistent with crystal fractionation from a high-Mg andesite parent derived from a mantle source more extensively metasomatized by eclogite-derived melts. Rhyolite composition is consistent with low melting degree of the basement rocks. The basalt–andesite–rhyolite dykes may represent the effects of crustal extension and arching in Carajás, which produced the anorogenic acid to intermediate magmatism (Uatumã group) and affecting a large part of the Amazon craton between 1.85 and 1.7 Ga. 相似文献
73.
Abstract. The morphological variability of the common West Indian loggerhead sponge, Spheciospongia vesparium, is examined in light of the latest morphological and ecological information and new biochemical criteria, that is, composition and concentration of fatty acids. A typical and a yellow ecophenotypical form are distinguished. Comparing this species with its next relatives in the same zoogeographical region it is found that S. othella, first described from Bermuda, cannot be maintained as a separate species. S. cuspidifera, previously misinterpreted as "Xestospongia tier-neyi", is confirmed as a distinct species of Spheciospongia, whereas "Prianos" tierneyi is considered a morphological variant of S. vesparium. 相似文献
74.
In this paper, we use distance-based methods, specifically a slight variation of Ripley’s K function and a bivariate generalisation of this function, to explore the detailed location pattern of the Spanish manufacturing industry, the scope of localisation and the tendency towards colocalisation between horizontally and vertically linked industries. To do so, we use micro-geographic data, considering a narrowly defined industry classification. Our results show heterogeneous location patterns, but with a significant tendency towards localisation. The sectoral scope is very sensitive to the degree of homogeneity of the activities in each sector. The more homogeneous the activities in a specific sector are, the more similarities we find in the spatial location patterns among its industries. Finally, although the patterns of colocalisation detected are sensitive to the counterfactuals used, between 20 and 48% of the pairs of industries with strong input–output linkages considered in this study show a significant tendency to colocalisation, and among them 74% are vertically linked industries. 相似文献
75.
Pablo?L.?AnticoEmail authorView authors OrcID profile Vicente?R.?Barros 《Theoretical and Applied Climatology》2017,129(1-2):171-176
Long-term variability of El Niño (EN) cycle has been the topic of several studies, mainly because of its impacts on climate around the globe. This variability has been mainly described by changes in the intensity and frequency of EN events. In this study, interdecadal changes in the zonal evolution of EN-related sea surface temperature anomalies (SSTA) and their possible link with a well-known mode of Pacific interdecadal variability are analyzed. EN events are classified according to the sense of zonal propagation of SSTA along the equatorial Pacific during the period 1900–2012. As a result, two types of EN are defined: eastward-directed and westward-directed EN. It is found that EN-related SSTA preferably evolves to the east (west) during the warm (cold) phase of the Pacific Decadal Oscillation. Hence, this study offers new insights into the possible causes of long-term EN changes. 相似文献
76.
On the Urban Heat Island Effect Dependence on Temperature Trends 总被引:2,自引:0,他引:2
For U.S., Argentine and Australian cities, yearly mean urban to rural temperature differences (Tu-r) and rural temperatures (Tr) are negatively correlated in almost every case, suggesting that urban heat island intensity depends, among other parameters on the temperature itself. This negative correlation is related to the fact that interannual variability of temperature is generally lower in urban environments than in rural areas. This seems to hold true at low frequencies leading to opposite trends in the two variables. Hence, urban stations are prone to have lower trends in absolute value than rural ones. Therefore, regional data sets including records from urban locations, in addition to urban growth bias may have a second type of urban bias associated with temperature trends. A bulk estimate of this second urban bias trend for the contiguous United States during 1901–1984 indicates that it could be of the same order as the urban growth bias and of opposite sign. If these results could be extended to global data, it could be expected that the spurious influence of urban growth on global temperature trends during warming periods will be offset by the diminishing of the urban heat island intensity. 相似文献
77.
Valentin R. Troll Frances M. Deegan Steffi Burchardt Kirsten Zaczek Juan‐Carlos Carracedo Fiona C. Meade Vicente Soler Mario Cachao Jorge Ferreira Abigail K. Barker 《Geology Today》2015,31(4):137-145
The origin of volcanism in the Canary Islands has been a matter of controversy for several decades. Discussions have hinged on whether the Canaries owe their origin to seafloor fractures associated with the Atlas Mountain range or to an underlying plume or hotspot of superheated mantle material. However, the debate has recently come to a conclusion following the discovery of nannofossils preserved in the products of the 2011–2012 submarine eruption at El Hierro, which tell us about the age and growth history of the western‐most island of the archipelago. Light coloured, pumice‐like ‘floating rocks’ were found on the sea surface during the first days of the eruption and have been shown to contain fragments of pre‐island sedimentary strata. These sedimentary rock fragments were picked up by ascending magma and transported to the surface during the eruption, and remarkably retained specimens of pre‐island Upper Cretaceous to Pliocene calcareous nannofossils (e.g. coccolithophores). These marine microorganisms are well known biostratigraphical markers and now provide crucial evidence that the westernmost and youngest island in the Canaries is underlain by the youngest sediment relative to the other islands in the archipelago. This finding supports an age progression for the onset of volcanism at the individual islands of the archipeligo. Importantly, as fracture‐related volcanism is known to produce non‐systematic age‐distributions within volcanic alignments, the now‐confirmed age progression corroberates to the relative motion of the African plate over an underlying mantle plume or hotspot as the cause for the present‐day Canary volcanism. 相似文献
78.
Alfredo Aparicio Colombo C.G. Tassinari Roberto García Vicente Araña 《Journal of Volcanology and Geothermal Research》2010,189(1-2):143-150
The lavas produced by the Timanfaya eruption of 1730–1736 (Lanzarote, Canary Islands) contain a great many sedimentary and metamorphic (metasedimentary), and mafic and ultramafic plutonic xenoliths. Among the metamorphosed carbonate rocks (calc-silicate rocks [CSRs]) are monomineral rocks with forsterite or wollastonite, as well as rocks containing olivine ± orthopyroxene ± clinopyroxene ± plagioclase; their mineralogical compositions are identical to those of the mafic (gabbros) and ultramafic (dunite, wherlite and lherzolite) xenoliths. The 87Sr/86Sr (around 0.703) and 143Nd/144Nd (around 0.512) isotope ratios of the ultramafic and metasedimentary xenoliths are similar, while the 147Sm/144Nd ratios show crustal values (0.13–0.16) in the ultramafic xenoliths and mantle values (0.18–0.25) in some CSRs. The apparent isotopic anomaly of the metamorphic xenoliths can be explained in terms of the heat source (basaltic intrusion) inducing strong isotopic exchange (87Sr/86Sr and 143Nd/144Nd) between metasedimentary and basaltic rocks. Petrofabric analysis also showed a possible relationship between the ultramafic and metamorphic xenoliths. 相似文献
79.
This work presents a new design of disc infiltrometer, which, associated with a microflowmeter (MF) and a solenoid valve set, makes it possible to automate the infiltration rate (Q) measurements at different soil pressure heads (ψ). The MF consists of a 13·8‐cm long and 1·5 mm i.d. pipe, with a pressure transducer connecting the two ends of the MF, inserted in a water‐flow pipe that connects the Mariotte tube and the water‐supply reservoir of the disc infiltrometer. Water flow is calculated from the head losses in the MF. Changes in ψ in the bubble tower, automatically affected when the infiltration rate reaches steady state, are controlled by a datalogger connected to four solenoid valves. The new design was tested in laboratory and field conditions, and the results showed that the MF allows the soil water infiltration rates to be correctly estimated for different soil characteristics. The solenoid valve set plus datalogger system satisfactorily monitored the changes in ψ and allowed the measurement time to be optimized. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
80.
Eugenio Molina-Navarro Antonio Sastre-Merlín Rosa Vicente Silvia Martínez-Pérez 《Hydrogeology Journal》2014,22(5):1115-1129
A small calcareous basin in central Spain was studied to establish the role of groundwater in the Pareja Limno-reservoir. Limno-reservoirs aim to preserve a constant water level in the riverine zone of large reservoirs to mitigate the impacts arising from their construction. Groundwater flow contribution (mean 60 %) was derived by recharge estimation. In situ measurements (spring discharge, electrical conductivity and sulfate) were undertaken and spring discharge was compared with a drought index. Twenty-eight springs were monitored and three hydrogeological units (HGUs) were defined: a carbonate plateau (HGU1), the underlying aquitard (HGU2), and the gypsum-enriched HGU3. HGU1 is the main aquifer and may play a role in the preservation of the limno-reservoir water level. Hydrogeochemical sampling was conducted and the code PHREEQC used to describe the main geochemical processes. Weathering and dissolution of calcite and gypsum seem to control the hydrogeochemical processes in the basin. Water progresses from Ca2+–HCO3 – in the upper basin to Ca2+–SO4 2– in the lower basin, where HGU3 outcrops. A clear temporal pattern was observed in the limno-reservoir, with salinity decreasing in winter and increasing in summer. This variation was wider at the river outlet, but the mixing of the river discharge with limno-reservoir water buffered it. 相似文献