ENSO and solar activity signals from oxygen isotopes in diatom silica during late glacial-Holocene transition in Central Andes (18°S)     

Armand Hernández  Santiago Giralt  Roberto Bao  Alberto Sáez  Melanie J. Leng  Philip A. Barker 《Journal of Paleolimnology》2010,44(2):413-429

The late glacial-Holocene transition from the Lago Chungará sedimentary record in northern Chilean Altiplano (18°S) is made up of laminated sediments composed of light-white and dark-green pluriannual couplets of diatomaceous ooze. Light-white sediment laminae accumulated during short-term extraordinary diatom blooms whereas dark-green sediment laminae represent the baseline limnological conditions during several years of deposition. Diatom oxygen isotope ratios (δ¹⁸O_diatom) from 40 consecutive dark-green laminae, ranging from 11,990 to 11,450 cal year BP, show that a series of decadal-to-centennial dry–wet oscillations occurred. Dry periods are marked by relatively high isotope values whereas wet episodes are indicated by lower values. This interpretation agrees with the reconstructions of terrigenous inputs and regional effective moisture availability carried out in the lake but there is a systematic temporal disagreement between them owing to the non-linear response of the lacustrine ecosystem to environmental forcings. Furthermore, the δ¹⁸O_diatom record tracks effective moisture changes at a centennial scale. Three major phases have been established (11,990–11,800, 11,800–11,550, and 11,550–11,450 cal year BP). Each phase is defined by an increasing isotope trend followed by a sudden depletion. In addition, several wet and dry events at a decadal scale are superimposed onto these major trends. Spectral analyses of the δ¹⁸O_diatom values suggest that cycles and events could have been triggered by both El Niño-Southern Oscillation (ENSO) and solar activity. Significant ENSO frequencies of 7–9 years and 15–17 years, and periodicities of the solar activity cycles such as 11 years (Schwabe), 23 years (Hale) and 35 years (Brückner) have been recognised in the oxygen isotope time series. Time–frequency analysis shows that although solar and ENSO forcing were present at the onset of the Holocene, they were more intense during the late glacial period. The early Holocene might have been mainly governed by La Niña-like conditions that correspond to wet conditions over the Andean Altiplano.  相似文献   

Changes in the Diffuse CO2 Emission and Relation to Seismic Activity in and around El Hierro, Canary Islands     

Eleazar Padrón  Gladys Melián  Rayco Marrero  Dácil Nolasco  José Barrancos  Germán Padilla  Pedro A. Hernández  Nemesio M. Pérez 《Pure and Applied Geophysics》2008,165(1):95-114

Significant changes in the diffuse emission of carbon dioxide were recorded in a geochemical station located at El Hierro, Canary Islands, before the occurrence of several seismic events during 2004. Two precursory CO₂ efflux increases started thirteen and nine days before two seismic events of magnitude 2.3 and 1.7, which took place near El Hierro Island, Canary Islands, on March 23 and April 15, reaching a maximun value of 51.1 and 46.2 g m⁻² d⁻¹, respectively, five and eight days before the two seismic events. Other similar increases started thirteen and five days before the occurrence of two seismic events of magnitude 1.3 and 1.5 which took place on October 15 and 21 respectively, reaching the maximum values four and one day before the earthquakes. These changes were not related to variations in atmospheric or soil parameters. The Material Failure Forecast Method (FFM), which analyzes the rate of precursory phenomena, was successfully applied to forecast the first seismic event that took place in El Hierro Island in 2004.  相似文献   

Preliminary kinematical study of the solar neighbourhood from the CSI catalogue     

M. Hernández  J. Núñez 《Astrophysics and Space Science》1989,156(1-2):3-8

We present a kinematical study of low-velocity stars within a radius of less than 100 pc. The source is the CSI catalogue and we use the radial velocity equation of the second-order Ogorodnikov-Milne model in the computations.  相似文献   

An attempt to identify low l - low n solar acoustic modes     

M. Anguera Gubau  P. L. Pallé  F. Pérez Hernández  T. Roca Cortés 《Solar physics》1990,128(1):79-90

The low l solar acoustic spectrum has been measured with great accuracy (v/v 10^–4), for intermediate radial order modes, 11 n 34 (Jiménez et al., 1986; Grec, Fossat, and Pomerantz, 1983; Pallé et al., 1986). The measurement of the frequencies of modes of lower n, up to the fundamental one, are very important as they depart from asymptotic behaviour and, therefore, put more severe constraints on solar models. However, their amplitudes are very low (under 2 cm s^–1) and when compared to the solar velocity background noise (Jiménez et al., 1986), a S/N 1 is obtained. Taking advantage of the fact that lifetimes seem to be higher at lower frequencies (lower n values) (Jefferies et al., 1988; Elsworth et al., 1990), very long Doppler velocity measurements, obtained at Teide Observatory, have been used to increase S/N, therefore, providing the possibility to detect such modes. The frequencies observed are compared to those predicted by a solar model (Christensen-Dalsgaard, Däppen, and Lebreton, 1988), using the best equation of state yet computed (Mihalas, Däppen, and Hummer, 1988).  相似文献   

Hydrogen bonding and vibrational properties of hydroxy groups in the crystal lattice of dioctahedral clay minerals by means of first principles calculations     

V.?Botella  V.?Timon  E.?Escamilla-Roa  A.?Hernández-Languna  C.I.?Sainz-DíazEmail author 《Physics and Chemistry of Minerals》2004,31(8):475-486

The hydroxy groups of the crystal lattice of dioctahedral 2:1 phyllosilicates were investigated by means of quantum-mechanical calculation. The standard Kohn-Sham self-consistent density functional theory (DFT) method was applied using the generalized gradient approximation (GGA) with numerical atomic orbitals and double-zeta polarized functions as basis set. Isomorphous cation substitution of different cations in the octahedral and tetrahedral sheet was included along with several interlayer cations reproducing experimental crystal lattice parameters. The effect of these substitutions and the interlayer charge on the hydroxyl group properties was also studied. These structures represent different cation pairs among Al³⁺, Fe³⁺ and Mg²⁺ in the octahedral sheet of clays joined to OH groups. The geometrical disposition of the OH bond in the crystal lattice and the hydrogen bonds and other electrostatic interactions of this group were analyzed. The frequencies of different vibrational modes of the OH group [(OH), (OH) and (OH)] were calculated and compared with experimental data, finding a good agreement. These frequencies depend significantly on the nature of cations which are joined with, and the electrostatic interactions with, the interlayer cations. Besides, hydrogen-bonding interactions with tetrahedral oxygens are important for the vibrational properties of the OH groups; however, also the electrostatic interactions of these OH groups with the rest of tetrahedral oxygens within the tetrahedral cavity should be taken into account. The cation substitution effect on the vibration modes of the OH groups was analyzed reproducing the experimental behaviour.Dr. V. Botella passed away last February  相似文献   

Ocean basins near the Scotia–Antarctic plate boundary: Influence of tectonics and paleoceanography on the Cenozoic deposits     

A. Maldonado  F. Bohoyo  J. Galindo-Zaldívar  J. Hernández-Molina  A. Jabaloy  F. J. Lobo  J. Rodríguez-Fernández  E. Suriñach  J. T. Vázquez 《Marine Geophysical Researches》2006,27(2):83-107

The distribution of seismic units in deposits of the basins near the Antarctic–Scotia plate boundary is described based on the analysis of multichannel seismic reflection profiles. Five main seismic units are identified. The units are bounded by high-amplitude continuous reflectors, named a to d from top to bottom. The two older units are of different age and seismic facies in each basin and were generally deposited during active rifting and seafloor spreading. The three youngest units (3 to 1) exhibit, in contrast, rather similar seismic facies and can be correlated at a regional scale. The deposits are types of contourite drift that resulted from the interplay between the northeastward flow of Weddell Sea Bottom Water (WSBW) and the complex bathymetry in the northern Weddell Sea, and from the influence of the Antarctic Circumpolar Current and the WSBW in the Scotia Sea. A major paleoceanographic event was recorded by Reflector c, during the Middle Miocene, which represents the connection between the Scotia Sea and the Weddell Sea after the opening of Jane Basin. Unit 3 (tentatively dated ∼Middle to Late Miocene) shows the initial incursions of the WSBW into the Scotia Sea, which influenced a northward progradational pattern, in contrast to the underlying deposits. The age attributed to Reflector b is coincident with the end of spreading at the West Scotia Ridge (∼6.4 Ma). Unit 2 (dated ∼Late Miocene to Early Pliocene) includes abundant high-energy, sheeted deposits in the northern Weddell Sea, which may reflect a higher production of WSBW as a result of the advance of the West Antarctic ice-sheet onto the continental shelf. Reflector a represents the last major regional paleoceanographic change. The timing of this event (∼3.5–3.8 Ma) coincides with the end of spreading at the Phoenix–Antarctic Ridge, but may be also correlated with global events such as initiation of the permanent Northern Hemisphere ice-sheet and a major sea level drop. Unit 1 (dated ∼Late Pliocene to Recent) is characterized by abundant chaotic, high-energy sheeted deposits, in addition to a variety of contourites, which suggest intensified deep-water production. Units 1 and 2 show, in addition, a cyclic pattern, more abundant wavy deposits and the development of internal unconformities, all of which attest to alternating periods of increased bottom current energy.  相似文献   

Winter water mass distributions in the western Gulf of Mexico affected by a colliding anticyclonic ring     

Victor M. V. Vidal  Francisco V. Vidal  Abel F. Hernández  Eustorgio Meza  Lorenzo Zambrano 《Journal of Oceanography》1994,50(5):559-588

The winter water mass distributions in the western Gulf of Mexico, affected by the collision of a Loop Current anticyclonic ring, during January 1984 are analyzed. Two principal modes of Gulf Common Water (GCW) formation, arising from the dilution of the Caribbean Subtropical Underwater (SUW), are identified. Within the western gulf continental slope to the east of Tamiahua, the GCW is formed by the collision of anticyclonic rings. During these collision events, the SUW, entrapped at the core (200 m depth) of these features, is diluted by low salinity (36.1S36.3) water from the uppermost layer of the main thermocline. The end product of this mixture is GCW, which is further diluted by low salinity coastal water within the western gulf continental shelf. The second GCW formation mode is associated to the northerly wind stress which propagates over the western gulf during winter. During January, 1984, this wind stress gave rise to a 175 m mixed layer. This convective mixing destroyed the static stability of the summer thermocline and allowed for the partial dilution of the SUW with low salinity (S36.3) water from the western gulf continental shelf. Within the western gulf's upper 2000 m, the following water masses were identified to be present: GCW, SUW, Tropical Atlantic Central Water and associated dissolved oxygen minimum stratum, Antarctic Intermediate Water remnant, a mixture of the Caribbean Intermediate Water and the upper portion of North Atlantic Deep Water (NADW), and the NADW itself. The topographic distribution of these water masses' strata was dictated by the cyclonic-anticyclonic baroclinic circulation that evolved from the anticyclone's collision to the east of Tamiahua. Between the cyclonic and anticyclonic domains, the maximum pressure differential of these water masses' core occurrences was 150 to 280 dbar. The topographic transition zone defined by these strata occurred between the cyclonic and anticyclonic domains and coincided unambiguously with the anticyclone's collision zone. Within the continental shelf, we identified low temperature (12°C) and low salinity (31) coastal waters contributed by river runoff. Driven by the northerly wind stress, these coastal waters were advected toward the south hugging the coastline. The coastal and continental shelf waters demarcated a sea surface temperature, salinity, and dissolved oxygen discontinuity region that coincided with the horizontal baroclinic flow transition zone associated to the anticyclone's collision.  相似文献   

Effect of crude petroleum on water repellency in a clayey alluvial soil     

D. C. Marín-García  R. H. Adams  R. Hernández-Barajas 《International Journal of Environmental Science and Technology》2016,13(1):55-64

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Further evidence for magnetic susceptibility as a proxy for the evaluation of heavy metals in mining wastes: case study of Tlalpujahua and El Oro Mining Districts     

Juan Morales  María del Sol Hernández-Bernal  Pedro Corona-Chávez  Avto Gogichaishvili  Francisco Bautista 《Environmental Earth Sciences》2016,75(4):309

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SHIA_Landslide: a distributed conceptual and physically based model to forecast the temporal and spatial occurrence of shallow landslides triggered by rainfall in tropical and mountainous basins     

Edier Aristizábal  Jaime Ignacio Vélez  Hernán Eduardo Martínez  Michel Jaboyedoff 《Landslides》2016,13(3):497-517

Landslides are a main cause of human and economic losses worldwide. For this reason, landslide hazard assessment and the capacity to predict this phenomenon have been topics of great interest within the scientific community for the implementation of early warning systems. Although several models have been proposed to forecast shallow landslides triggered by rainfall, few models have incorporated geotechnical factors into a complete hydrological model of a basin that can simulate the storage and movement of rainwater through the soil profile. These basin and full hydrological models have adopted a physically based approach. This paper develops a conceptual and physically based model called open and distributed hydrological simulation and landslides—SHIA_Landslide (Simulación HIdrológica Abierta, or SHIA, in Spanish)—that is supported by geotechnical and hydrological features occurring on a basin-wide scale in tropical and mountainous terrains. SHIA_Landslide is an original and significant contribution that offers a new perspective with which to analyse shallow landslide processes by incorporating a comprehensive distributed hydrological tank model that includes water storage in the soil coupled with a classical analysis of infinite slope stability under saturated conditions. SHIA_Landslide can be distinguished by the following: (i) its capacity to capture surface topography and effects concerning the subsurface flow; (ii) its use of digital terrain model (DTM) to establish the relationships among cells, geomorphological parameters, slope angle, direction, etc.; (iii) its continuous simulation of rainfall data over long periods and event simulations of specific storms; (iv) its consideration of the effects of horizontal and vertical flow; and (vi) its inclusion of a hydrologically complete water process that allows for hydrological calibration. SHIA_Landslide can be combined with real-time rainfall data and implemented in early warning systems.  相似文献