Letter to the editor Are the North Atlantic Oscillation and the Southern Oscillation related in any time-scale?     

R. García  P. Ribera  L. Gimenoo  E. Hernández 《Annales Geophysicae》2000,18(2):247-251

The North Atlantic Oscillation (NAO) and the Southern Oscillation (SO) are compared from the standpoint of a possible common temporal scale of oscillation. To do this a cross-spectrum of the temporal series of NAO and SO indices was determined, finding a significant common oscillation of 6/8 years. To assure this finding, both series were decomposed in their main oscillations using singular spectrum analysis (SSA). Resulting reconstructed series of 6/8 years oscillation were then cross-correlated without and with pre-whitened, the latter being significant. The main conclusion is a possible relationship between a common oscillation of 6/8 years that represents about 20% of the SO variance and about 25% of the NAO variance.  相似文献   

Geology and rural landscapes in central Spain (Guadalajara, Castilla—La Mancha)     

A. García-Quintana  J. F. Martín-Duque  J. A. González-Martín  J. F. García-Hidalgo  J. Pedraza  P. Herranz  R. Rincón  H. Estévez 《Environmental Geology》2005,47(6):782-794

Methods commonly used in regional geological analysis were employed to study the visual landscapes of the Sigüenza–Molina de Aragón area (Spain). Landscape data were compiled to produce a landscape map and a photograph catalogue. Lithological composition, tectonic structure and recent erosive processes are the main factors controlling the visual landscapes. Territorial properties, such as colours and agricultural capacities, are controlled by these geological characteristics. The landscape map and the photographic catalogue is the main contribution of this paper. The first level of landscape classification distinguishes zones with dominance of either flat, concave or convex areas. Other parts of the territory are, however, composed of concave and convex combinations that originate hybrid orographic structures. In a second level of classification, several subdivisions for each of these types are established.  相似文献   

Deriving Wind Force Terms from Nautical Reports Through Content Analysis. The Spanish and French Cases     

M. R. Prieto  D. Gallego  R. García-Herrera  N. Calvo 《Climatic change》2005,73(1-2):37-55

Records of wind strength taken onboard Spanish and French ships during the 1750–1850 period have been digitized and examined using content analysis techniques to derive the equivalent wind strength in terms of the current Beaufort scale, this conversion being a key step in any attempt to compare ancient records with modern climatologies. During the analysis it was evident that Spanish and French officers used a great number of different terms to describe the wind force. However, when the records are analyzed and homogenized, a broadly common and essentially narrow vocabulary was identified, indicating that, at this period, a great effort had been made to regulate the maritime language. Using contemporary dictionaries and navigation manuals, an equivalence was established between the original wind force terms and the Beaufort scale.  相似文献   

Petrogenesis and tectonomagmatic significance of volcanic and subvolcanic rocks in the Albanide–Hellenide ophiolitic mélanges     

Emilio  Saccani  Adonis  Photiades 《Island Arc》2005,14(4):494-516

Abstract Ophiolitic mélanges associated with ophiolitic sequences are wide spread in the Mirdita–Subpelagonian zone (Albanide–Hellenide Orogenic Belt) and consist of tectonosedimentary ‘block‐in‐matrix‐type’ mélanges. Volcanic and subvolcanic basaltic rocks included in the main mélange units are studied in this paper with the aim of assessing their chemistry and petrogenesis, as well as their original tectonic setting of formation. Basaltic rocks incorporated in these mélanges include (i) Triassic transitional to alkaline within‐plate basalts (WPB); (ii) Triassic normal (N‐MORB) and enriched (E‐MORB) mid‐oceanic ridge basalts; (iii) Jurassic N‐MORB; (iv) Jurassic basalts with geochemical characteristics intermediate between MORB and island arc tholeiites (MORB/IAT); and (v) Jurassic boninitic rocks. These rocks record different igneous activities, which are related to the geodynamic and mantle evolution through time in the Mirdita–Subpelagonian sector of the Tethys. Mélange units formed mainly through sedimentary processes are characterized by the prevalence of materials derived from the supra‐subduction zone (SSZ) environments, whereas in mélange units where tectonic processes prevail, oceanic materials predominate. In contrast, no compositional distinction between structurally similar mélange units is observed, suggesting that they may be regarded as a unique mélange belt extending from the Hellenides to the Albanides, whose formation was largely dominated by the mechanisms of incorporation of the different materials. Most of the basaltic rocks surfacing in the MOR and SSZ Albanide–Hellenide ophiolites are incorporated in mélanges. However, basalts with island arc tholeiitic affinity, although they are volumetrically the most abundant ophiolitic rock types, have not been found in mélanges so far. This implies that the rocks forming the main part of the intraoceanic arc do not seem to have contributed to the mélange formation, whereas rocks presumably formed in the forearc region are largely represented in sedimentary‐dominated mélanges. In addition, Triassic E‐MORB, N‐MORB and WPB included in many mélanges are not presently found in the ophiolitic sequences. Nonetheless, they testify to the existence throughout the Albanide–Hellenide Belt of an oceanic basin since the Middle Triassic.  相似文献   

Alteration induced changes of magnetic fabric as exemplified by dykes of the Koolau volcanic range     

David Krása  Emilio Herrero-Bervera 《Earth and Planetary Science Letters》2005,240(2):445-453

We studied 93 samples from 8 basaltic dykes of the Koolau volcanic range on the island of Oahu,Hawaii,USA,to determine the influence of hydrothermal alteration on the magnetic fabric as determined by anisotropy of magnetic susceptibility (AMS) measurements. Rock magnetic as well as microscopic investigations show that only ≈25% of the samples have retained their original magnetomineralogical composition of unaltered Ti-poor titanomagnetite. The remaining samples have undergone hydrothermal alteration which transformed the primary magnetic phase into a granular intergrowth of titanomagnetite, titanomaghemite and hematite. In both sample groups,this magnetic phase occurs in coarse (tens of microns),irregularly shaped particles as well as interstitial clusters of smaller (< 5 μm) grains. Our investigations show that hydrothermal alteration does change the bulk susceptibility and the degree of anisotropy but not the directions of principal axes of the AMS ellipsoid which are predominantly corresponding to normal magnetic fabric. The stability of AMS directions, regardless of the degree of alteration, points towards the model of distribution anisotropy as the controlling factor for the observed magnetic fabric.  相似文献   

Interannual Variability of the Annual Cycle of Temperature over Northern Africa   总被引：1，自引：0，他引：1  

M. Tesouro  L. Gimeno  R. Nieto  L. de la Torre  P. Ribera  D. Gallego  R. García-Herrera  E. Hernández 《Studia Geophysica et Geodaetica》2005,49(1):141-151

In this study, the imprints of two major atmospheric variability modes - ENSO and NAO - on the annual cycle of temperature over Northern Africa, a region sensitive to both modes, are investigated. Results from adjusting the annual cycle from daily data on a high resolution grid, indicate that both NAO and ENSO are able to influence significantly the amplitude and phase of the seasonal cycle and, consequently, that interannual trends found in amplitude and phase can be not exclusively due to greenhouse gases effects.  相似文献   

Sulphide-mining impacts in the physical environment: Sierra de Cartagena–La Unión (SE Spain) case study     

V. M. Robles-Arenas  R. Rodríguez  C. García  J. I. Manteca  L. Candela 《Environmental Geology》2006,51(1):47-64

The environmental impact and potential-risk assessment of an abandoned sulphide-mining site in a semiarid climate is presented here, by the study case of Sierra de Cartagena–La Unión (SE Spain), a 2,500-year-old mining district extending over an area of 100 km². The regional map illustrates the existence of 12 open-pits, 1,902 mining wells, 2,351 waste deposits, including 89 tailing dams and waste rock derived from mining processes. Mine wastes occupy an area of 9 km² and have an approximate volume of 200 Mm³. Mineralogical, physical and chemical data distinguish nine different types of mine and metallurgical waste. According to the concentration of sulphate and heavy metals in sediment, soil, rainwater, surface water and groundwater samples, it is possible to conclude that the impact of mine activities occurs not only in the immediate mining area (100 km²), but also in the surrounding areas (an affected area of 1,000 km² approximately). The hydrochemical data show that groundwater, runoff water and some rainwater samples exceed Spanish and European water quality guideline values for water supply. The main geochemical process recognised is sulphide-mineral oxidation and later-generated sulphate dissolution by groundwater and runoff. Runoff and wind are the major mechanisms of metals and sulphate transport in the study area and adjacent zones.  相似文献   

The Pulpí gigantic geode (Almería, Spain): geology, metal pollution, microclimatology, and conservation     

Ángel Fernández-Cortés  José María Calaforra  Javier García-Guinea 《Environmental Geology》2006,50(5):707-716

The discovery of the giant Geode of Pulpí (Almería, Spain) was considered as an important highlight in the geological heritage of Spain. Projects developed for their conservation were immediately initiated with legal figures of protection and tourist projects. The Geode has a tourist interest, which must be tempered by environmental restrictions limiting the public visits. First results demonstrate that a continuous visit of two or three people for more than 10 min provokes the appearance of condensation and risks corrosion of the gypsum crystals. In addition, the electron microprobe analyses confirms (1) the hydrothermal phases of iron–manganese in carbonated host rock; (2) the presence of sulphides with Fe–Zn–Pb–Ag–Sb–Cu–Hg–As–Te–Se; and (3) Ba, Ca, and Sr sulphates with mercury traces. The present proposal to label the geode and the mining environment as geological-natural heritage is feasible, although any tourist adaptation must not permit visits to the geode indoor and Hg levels must be controlled.  相似文献   

The September 8–9, 1998 Rain-Triggered Flood Events at Motozintla, Chiapas, Mexico     

L. Caballero  J. L. Macías  A. García-Palomo  G. R. Saucedo  L. Borselli  D. Sarocchi  J. M. Sánchez 《Natural Hazards》2006,39(1):103-126

In September 1998 tropical storm “Earl” swept southern Mexico, producing intense rainfall in the states of Oaxaca and Chiapas. Among the most devastated cities was Motozintla, located in the drainage basin of the Allende, La Mina and Xelajú Grande Rivers. The rainfall from the tropical storm totaled 175 mm on September 8 and 130 mm on September 9, duplicating in two days the average monthly precipitation in the region. Numerous landslides occurred in the vicinity of Motozintla, depositing large volumes of material into the Xelajú Grande stream. Much of this sediment was subsequently remobilized, yielding debris flows, hyperconcentrated flows, and sediment-laden flows that inundated most sections of Motozintla city. The flows covered an approximate area of 3.15 km² with a minimum volume of 4.4 × 10⁶ m³ of sediment. Communication of Motozintla with the rest of the Chiapas State was interrupted for about a month, as was the supply of potable water, food, electricity, and fuel. The geologic record around Motozintla indicates that the Xelajú Grande River has been a pathway for similar large floods during the last 6000 years. The oldest deposit yielded a radiocarbon age of 5320 ± 100 ¹⁴C years. B.P. At least two historic floods have occurred during the last 100 years, a time period defined by a stratigraphically distinct tephra of 1902. Frequency analysis of the historical record of daily rainfall in the Motozintla area suggests that events like that of September, 1998, have a recurrence interval of about 25 years. After the catastrophic flows of 1998, the mitigation measures by Municipal Authorities were made without regard to geological and environmental factors, or to taking into consideration the flow magnitude and appropriate hazard-mitigation techniques, with the result that Motozintla remains at serious risk for future floods. Unfortunately, prior to the publication of this study, in early October 2005, Motozintla was seriously damaged again by intense rain provoked by Hurricane Stan.  相似文献   

Relationships between Trophic State, Paleosalinity and Climatic Changes during the First Holocene Marine Transgression in Rocha Lagoon, Southern Uruguay     

H. Inda  F. García-Rodríguez  L. del Puerto  V. Acevedo  D. Metzeltin  C. Castiñeira  R. Bracco  J. B. Adams 《Journal of Paleolimnology》2006,35(4):699-713

Paleolimnological data are presented on trophic development, climatic change and sea level variations in Rocha Lagoon, a 72 km² coastal lagoon in southern Uruguay. Using a sediment core that extended from 7000 to about 3700 yr BP, analyses of organic matter, carbonate, diatoms and chrysophyte cysts were used to track the early Holocene paleolimnological conditions of Rocha Lagoon. Opal phytoliths were also counted and identified, both temperature and humidity indices were calculated, and Opal Phytolith Association Zones (OPAZ) were identified by performing Principal Coordinates Analysis (PCO). Diatom Association Zones (DAZ) corresponding to marine/brackish and brackish/freshwater episodes were closely related to changes in trophic state. Those DAZ representing marine/brackish stages exhibited a lower trophic state than those DAZ dominated by brackish and freshwater diatoms. This highlights that during the first Holocene marine transgression, Rocha Lagoon did not continuously exhibit marine/brackish conditions as reported in previous papers. Instead, three brackish/freshwater episodes related to sea level variation and changes in humidity were identified. The first episode, by ~6000 yr BP, was related to sea level change as no significant changes in either temperature or humidity indices were observed. The second episode, between 5000 and 4400 yr BP, was related to both a sea level decrease and an increase in humidity, as a transition from humid to very humid climate was inferred. Concomitant decreases in salinity and increases in trophic state were also observed. The third episode, after ~4000 yr BP, was related to the end of the first Holocene regressive phase when sea level was slightly below present levels. Further decreases in salinity and increases in trophic state were detected. The paleoclimatic trends inferred in this study were in close agreement with other regional studies on climatic change, as cool temperatures were inferred. However, major changes in humidity were also detected. A humid to very humid climate was inferred for ~7000–4500 yr BP, but the occurrence of a semiarid/arid climate was inferred for ~4500–3700 yr BP. Our data suggest that during transgressive and regressive events there might be higher frequency and lower amplitude sea level oscillations that might lead to changes in salinity and trophic state of coastal aquatic systems. Such oscillations could only be tracked by high resolution analyses of sedimentary records and could be best interpreted with complementary data on paleoclimate. In addition, microfossils such as diatoms and opal phytoliths were shown to be very sensitive to such paleoenvironmental changes.  相似文献