Solar influence and hydrological variability during the Holocene from a speleothem annual record (Molinos Cave,NE Spain)   总被引：1，自引：0，他引：1       下载免费PDF全文

Arsenio Muñoz  Miguel Bartolomé  Alicia Muñoz  Carlos Sancho  Ana Moreno  John C. Hellstrom  Mª Cinta Osácar  Isabel Cacho 《地学学报》2015,27(4):300-311

We present a multi‐proxy approach to reconstructing Holocene climate conditions in northeastern Spain based on an excellent correlation among the lamina thickness, colour parameters and isotope (δ¹⁸O and δ¹³C) variations recorded in a speleothem. An age model constructed from five U/Th dates and annual lamina counting suggests that the uppermost 14.7 cm of the MO‐7 stalagmite grew between 7.2 and 2.5 ka before present but experienced a growth hiatus from 4.9 to 4.3 ka. Three spectral analysis methods were applied to 11 time series. The results reveal common solar periodicities on decennial (Gleissberg cycle) and centennial (De Vries‐Suess cycle) scales. The onset of Holocene carbonate precipitation in the MO‐7 stalagmite appears to be associated with a cold, wet period, whereas the hiatus and the end of growth are related to warm, dry periods. This environmental trend fits well within the regional Holocene climate.  相似文献   

The application of diffusion–reaction mixed model to assess the best experimental conditions for bark chemical activation to improve copper(II) ions adsorption     

G. Montes-Atenas  F. Valenzuela  S. Montes 《Environmental Earth Sciences》2014,72(5):1625-1631

Natural sorbents have been thoroughly assessed to determine their adsorption capabilities to remove pollutants from industrial wastewaters. Among them, pine bark has demonstrated potential for carrying out the removal of contaminants, particularly heavy metals, at the level of traces present in dissolved state. Nevertheless, to move towards the wastewater treatment implementation at large scale, the handling and processing requirements of pine bark to optimise the adsorption of heavy metals must be fully assessed. This research study presents a new mathematical model to evaluate the impact of acid pre-treatment of pine bark on heavy metals adsorption at different pine bark-aqueous solution pulp densities. A diffusion–reaction mixed model was developed and applied to the case study of copper(II) adsorption onto pine bark. The low binding energy inferred from analysing the adsorption isotherms suggested that a diffusive mechanism is governing the whole process. The mixed diffusion–reaction kinetic model indicated that the activation increases the rate at which metal ions are adsorbed, but it reduces the maximum achievable adsorption which in turn restricts its usefulness to relatively high pulp densities (above 10 g/L). The latter constitutes the first step towards optimising the use of bark pine for treating wastewater polluted with heavy metals and for establishing rules for scaling-up the process.  相似文献   

Millennial-scale variations in western Sierra Nevada precipitation during the last glacial cycle MIS 4/3 transition     

Jessica L. Oster  Isabel P. Montañez  Regina Mertz-Kraus  Warren D. Sharp  Greg M. Stock  Howard J. Spero  John Tinsley  James C. Zachos 《Quaternary Research》2014

Dansgaard–Oeschger (D–O) cycles had far-reaching effects on Northern Hemisphere and tropical climate systems during the last glacial period, yet the climatic response to D–O cycles in western North America is controversial, especially prior to 55 ka. We document changes in precipitation along the western slope of the central Sierra Nevada during early Marine Oxygen Isotope Stages (MIS) 3 and 4 (55–67 ka) from a U-series dated speleothem record from McLean's Cave. The timing of our multi-proxy geochemical dataset is coeval with D–O interstadials (15–18) and stadials, including Heinrich Event 6. The McLean's Cave stalagmite indicates warmer and drier conditions during Greenland interstadials (GISs 15–18), signified by elevated δ¹⁸O, δ¹³C, reflectance, and trace element concentrations, and less radiogenic ⁸⁷Sr/⁸⁶Sr. Our record extends evidence of a strong linkage between high-latitude warming and reduced precipitation in western North America to early MIS 3 and MIS 4. This record shows that the linkage persists in diverse global climate states, and documents the nature of the climatic response in central California to Heinrich Event 6.  相似文献   

Radiological and geochemical characteristics of an ultramafic massif (NE Portugal) regarding the site aptness to host a near surface repository for low and intermediate level radwaste     

Pedro Duarte  Lídia Silva  António Mateus  M. Fátima Araújo  Mário Reis  Romão Trindade  Isabel Paiva 《Environmental Earth Sciences》2013,68(2):547-557

The search for suitable sites to install near-surface repositories for low to intermediate level radioactive wastes has increased in the recent years, reflecting both the continuous rise in radioactive materials applications by the society and the increasing awareness of public perception regarding radwaste management. International recommendations towards the application of higher safety standards to low and intermediate level waste disposal sites being developed by the International Atomic Energy Agency (IAEA), and the European Commission decision that each Member State must safely dispose its own radwaste in its territory, according to national radwaste management plans, has leading to new soundly scientific studies. In Portugal, possible locations for that purpose are under study since 2006, following the pre-requisites indicated by IAEA. One of these sites overlaps a significant portion of an ultramafic massif, corresponding to an allochthonous and metamorphosed ophiolite complex. In the surveyed area of this massif, the prevailing rock type consists of (serpentinised) peridotites, occasionally containing irregular bodies of (amphibolitised) gabbros, over which an irregular/ill-developed regolith exists. The activities of ⁴⁰K, ¹³⁷Cs, ²¹⁰Pb, ²²⁶Ra and ²³²Th measured in samples representing three consecutive levels of the regolith upper portion in 13 stations confirm the heterogeneity put in evidence through in situ γ-ray surveys previously performed. The available dataset also demonstrates that radionuclide contents decrease prominently with depth, becoming closer to the bedrock values (up to ca. 41 Bq kg^?1 for ⁴⁰K in flaser-gabbros and near zero for all the remaining cases) but never reaching them. Therefore, the low/moderate radionuclide activity in the regolith upper portion reflect the contribution of sources that are independent of the lithological background; i.e. they indicate external and miscellaneous contributions to the “soil”-forming components, most of them coming from (dry or wet) atmospheric deposition. The chemical composition of the (serpentinised) peridotites and (amphibolitised) gabbros in the surveyed area, as well as their alteration products included in regolith, is homogeneous enough to be used as a faithful reference in monitoring studies of any kind. In addition, the significant ¹³⁷Cs activities measured in some top “soil” samples (up to 92 Bq kg^?1) strongly suggest that there are mineralogical specificities of the peridotite-derived regolith able to fix that radionuclide. This particular feature reinforces the existing criteria that favour the peridotites of Morais as a suitable host for a near surface repository of low to intermediate level radwaste.  相似文献   

Lavras do Sul: A New Equilibrated Ordinary L5 Chondrite from Rio Grande do Sul,Brazil     

M. E. Zucolotto  L. L. Antonello  M. E. Varela  R. B. Scorzelli  Isabel P. Ludka  P. Munayco  E. dos Santos 《Earth, Moon, and Planets》2012,108(2):139-150

The new Brazilian chondrite, Lavras do Sul, was found in 1985 at Lavras do Sul, Rio Grande do Sul State-Brazil (33°30′48″S; 53°54′65″W). It consists of a single mass weighing about 1 kg, covered by a black fusion crust with grayish interior. Four polished thin sections were prepared from a slice weighing 67 g on deposit at the Museu Nacional/UFRJ. It consists mostly of chondrules and chondrule fragments dispersed in a recrystallized matrix. Most chondrules are poorly defined and range in size from 300 to 2,000 μm, although some of them show distinct outlines, particularly when viewed under cross-polarized transmitted and reflected light. The texture of chondrules varies from non-porphyritic (e.g., barred-olivine, radial-pyroxene) to porphyritic ones (e.g., granular olivine as well as olivine-pyroxene). The meteorite contains mainly olivine (Fa_24.9), low-Ca pyroxene (Fs_22.6) and metal phases, with minor amounts of plagioclase, chromite and magnetite. Mössbauer Spectroscopy studies indicate that the metal phase is kamacite, tetrataenite and antitaenite. Veins of secondary iddingsite crosscut the thin section and some ferromagnesian silicates. The chemical composition indicates that Lavras do Sul is a member of the low iron L chondrite group. The poorly delineated chondritic texture with few well-defined chondrules, the occurrence of rare clinopyroxene and plagioclase (and maskelynite) with apparent diameters ranging from 5 to 123 μm led us to classify Lavras do Sul as an equilibrated petrologic type 5. The shock features of some minerals suggest a shock stage S3, and the presence of a small amount of secondary minerals such as iddingsite and goethite, a degree of weathering W₁. The meteorite name was approved by the Nomenclature Committee (Nom Com) of the Meteoritical Society (Meteoritic Bulletin Nº99).  相似文献   

Depth of faulting and ancient heat flows in the Kuiper region of Mercury from lobate scarp topography     

Isabel Egea-González  Javier Ruiz  Carlos Fernández  Jean-Pierre Williams  Álvaro Márquez  Luisa M. Lara 《Planetary and Space Science》2012,60(1):193-198

Mercurian lobate scarps are interpreted to be the surface expressions of thrust faults formed by planetary cooling and contraction, which deformed the crust down to the brittle–ductile transition (BDT) depth at the time of faulting. In this work we have used a forward modeling procedure in order to analyze the relation between scarp topography and fault geometries and depths associated with a group of prominent lobate scarps (Santa Maria Rupes and two unnamed scarps) located in the Kuiper region of Mercury for which Earth-based radar altimetry is available. Also a backthrust associated with one of the lobate scarps has been included in this study. We have obtained best fits for depths of faulting between 30 and 39 km; the results are consistent with the previous results for other lobate scarps on Mercury.The so-derived fault depths have been used to calculate surface heat flows for the time of faulting, taking into account crustal heat sources and a heterogeneous surface temperature due to the variable insolation pattern. Deduced surface heat flows are between 19 and 39 mW m^?2 for the Kuiper region, and between 22 and 43 mW m^?2 for Discovery Rupes. Both BDT depths and heat flows are consistent with the predictions of thermal history models for the range of time relevant for scarp formation.  相似文献   

Fluid-driven low-grade metamorphism in polydeformed rocks of Avalonia (Arisaig Group, Nova Scotia, Canada)   总被引：1，自引：0，他引：1  

Isabel Abad  Fernando Nieto  Gabriel Gutiérrez-Alonso  J. Brendan Murphy  James A. Braid  Alejandro B. Rodríguez-Navarro 《Swiss Journal of Geoscience》2012,105(2):283-297

The Lower Silurian??Lower Devonian Arisaig Group (Antigonish Highlands) in the Canadian Appalachians is a sequence of shallow marine strata deposited after the accretion of Avalonia to Baltica during the closure of the Iapetus Ocean. Deformation of the strata is widely attributed to the Devonian Acadian orogeny and produced shallowly plunging regional folds and a cleavage of varying penetrativity. Phyllosilicate minerals from the finest-grained rocks exhibit very low-grade (diagenetic-anchizone) metamorphic conditions. X-ray diffraction study reveals that the sampled rocks contain quartz, K-white mica, chlorite, and feldspars; illite?Csmectite and chlorite?Csmectite mixed-layers are common but Na?CK mica and kaolinite occur only in some samples. The identification of illite?Csmectite mixed-layers in diagenetic samples, with Kübler Index >0.50 ??°2?? and the highly heterogeneous b-cell dimension of the K-white micas are in agreement with the variable chemical composition of dioctahedral micas, which present low illitic substitution and variable phengitic content. The spatial variation in the above crystal-chemical parameters was plotted along a NW?CSE composite cross section across the regional folds. No correlation was found between the metamorphic conditions and either the stratigraphic depth or the strain values measured by phyllosilicates orientation analyses, as a function of the penetrativity of the cleavage. However, the metamorphic grade generally increases towards the Hollow Fault, and is highest in samples located within a 1?km corridor from the fault surface. Incipient cleavage is observed in the anchizonal samples located in the vicinity of the Hollow Fault and in some of the diagenetic samples, indicating cleavage development under low temperatures (<200?oC). These relationships, together with regional syntheses, suggest low-grade metamorphism post-dated regional folding and was coeval with Late Carboniferous dextral movement along the Hollow Fault. Fluid circulation associated with movement along this major fault may be the driving mechanism for the increasing metamorphism towards it.  相似文献   

Diffusion of landfill leachate through compacted natural clays containing small amounts of carbonates and sulfates   总被引：1，自引：0，他引：1  

Isabel S. De Soto  Ana I. Ruiz  Carlos Ayora  Rosario García  Mercedes Regadio  Jaime Cuevas 《Applied Geochemistry》2012

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Organotin levels in Nazaré canyon (west Iberian Margin, NE Atlantic) and adjacent coastal area   总被引：1，自引：0，他引：1  

Sousa AC  Oliveira IB  Laranjeiro F  Takahashi S  Tanabe S  Cunha MR  Barroso CM 《Marine pollution bulletin》2012,64(2):422-426

Organotin compounds (OTs) are ubiquitous in the marine environment and high concentrations (μg g(-1) range) in sediments from different coastal areas around the world have been reported. However, few reports have described the OTs contamination status in the offshore and deep sea environment. This work investigated organotin levels in Nazaré canyon for the first time. Levels of monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), diphenyltin (DPT), triphenyltin (TPT), dioctyltin (DOT) and trioctyltin (TOT) were quantified in sediment samples from the upper flanks of the canyon and from the adjacent coastal area. TBT levels detected in the canyon flanks are about two to three orders of magnitude lower than those found in the coastal area. Nevertheless, when quantifiable, TBT levels in the canyon samples were higher than the Environmental Assessment Criteria set for TBT in sediments by the OSPAR Commission indicating that at those locations negative ecological impacts are likely to occur.  相似文献   

Distribution and thickness of sedimentary facies in the coastal dune, beach and nearshore sedimentary system at Maspalomas, Canary Islands   总被引：1，自引：1，他引：0  

Angela Fontán Bouzas  Javier Alcántara-Carrió  Isabel Montoya Montes  Andrés Barranco Ojeda  Silvia Albarracín  Jorge Rey Díaz de Rada  Jorge Rey Salgado 《Geo-Marine Letters》2013,33(2-3):117-127

Numerous studies have shown that most beaches and coastal dune systems of the world are currently eroding but very few have investigated the combined sediment budgets of subaerial and nearshore submarine systems. In the case of the dune field of the Maspalomas Natural Special Reserve (in the south of Gran Canaria), the adjacent Maspalomas and El Inglés beaches and the adjacent submarine platform, the sediment budgets have been severely affected by erosion over the past few decades. The objectives of this study were to investigate the availability of sand within the modern sedimentary system, including the coastal dunes, the beaches and the submerged shelf, but also to assess local sediment sinks. An isopach map generated on the basis of topo-bathymetric data and seismic-reflection profiles revealed that sediment thickness varies from 0–22 m in the study area. Expanses of relatively low sediment thickness were identified in the south-western sector of the coastal dune field along Maspalomas beach, and in the nearshore region to the south of this beach. These localized sediment-deficit areas earmark Maspalomas beach as the most vulnerable shore strip threatened by erosion. The shallow seismic data also revealed that the submarine platform south of Maspalomas represents a marine terrace cut into an ancient alluvial fan, thus documenting an influence of the geomorphological heritage on the present-day morphodynamics. A side-scan sonar mosaic of this nearshore platform enabled the delimitation of areas covered by rock, boulders and gravel, vegetated sand patches and a mobile sand facies, the latter including ripple and megaripple fields. The megaripple field in a valley close to the talus of the marine terrace has been identified as a major sediment sink of the Maspalomas sedimentary system. It is fed by south-westerly storm-wave events. The sediment deficit in the coastal dune field and along Maspalomas beach can therefore only be explained by a currently faster loss of sediment to an offshore sink than can be compensated by the supply of sand from outside the system.  相似文献