Editorial to the second PECS 2008 special issue of Ocean Dynamics     

Alejandro J. Souza  Roger Proctor 《Ocean Dynamics》2010,60(2):181-182

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Lower Carboniferous post-orogenic granites in central-eastern Sierra de Velasco,Sierras Pampeanas,Argentina: U–Pb monazite geochronology,geochemistry and Sr–Nd isotopes     

Pablo Grosse  Frank Söllner  Miguel A. Báez  Alejandro J. Toselli  Juana N. Rossi  Jesus D. de la Rosa 《International Journal of Earth Sciences》2009,98(5):1001-1025

The central-eastern part of the Sierra de Velasco (Sierras Pampeanas, NW Argentina) is formed by the large Huaco (40 × 30 km) and Sanagasta (25 × 15 km) granite massifs and the small La Chinchilla stock (2 × 2 km). The larger granites intrude into Ordovician metagranitoids and crosscut Devonian (?) mylonitic shear zones, whereas the small stock sharply intrudes into the Huaco granite. The two voluminous granites are biotitic-muscovitic and biotitic porphyritic syeno- to monzogranites. They contain small and rounded tonalitic and quartz-dioritic mafic microgranular enclaves. The small stock is an equigranular, zinnwaldite- and fluorite-bearing monzogranite. The studied granites are silica-rich (SiO₂ >70%), potassium-rich (K₂O >4%), ferroan, alkali-calcic to slightly calk-alkalic, and moderately to weakly peraluminous (A/CNK: 1.06–1.18 Huaco granite, 1.01–1.09 Sanagasta granite, 1.05–1.06 La Chinchilla stock). They have moderate to strong enrichments in several LIL (Li, Rb, Cs) and HFS (Nb, Ta, Y, Th, U) elements, and low Sr, Ba and Eu contents. U–Pb monazite age determinations indicate Lower Carboniferous crystallization ages: 350–358 Ma for the Huaco granite, 352.7 ± 1.4 Ma for the Sanagasta granite and 344.5 ± 1.4 Ma for the La Chinchilla stock. The larger granites have similar ?Nd values between ?2.1 and ?4.3, whereas the younger stock has higher ?Nd of ?0.6 to ?1.4, roughly comparable to the values obtained for the Carboniferous San Blas granite (?1.4 to ?1.7), located in the north of the sierra. The Huaco and Sanagasta granites have a mainly crustal source, but with some participation of a more primitive, possibly mantle-derived, component. The main crustal component can be attributed to Ordovician peraluminous metagranitoids. The La Chinchilla stock derives from a more primitive source, suggesting an increase with time in the participation of the primitive component during magma genesis. The studied granites were generated during a post-orogenic period in a within-plate setting, possibly as a response to the collapse of the previous Famatinian orogen, extension of the crust and mantle upwelling. They are part of the group of Middle Devonian–Lower Carboniferous granites of the Sierras Pampeanas. The distribution and U–Pb ages of these granites suggests a northward arc-parallel migration of this mainly post-orogenic magmatism with time.  相似文献   

Determination of heterogeneities in the hydraulic properties of a phreatic aquifer from tidal level fluctuations: a case in Argentina     

Eleonora S. Carol  Eduardo E. Kruse  Jorge L. Pousa  Alejandro R. Roig 《Hydrogeology Journal》2009,17(7):1727-1732

A well-known analytical solution of Jacob (1950) for groundwater flow due to tidal-wave propagation, together with field measurements along a complete tidal cycle and geological data, were used to evaluate the heterogeneities in the hydraulic properties of a phreatic aquifer located next to the River Ajo in the coastal plain environment of the southern sector of the Samborombon Bay wetland, Argentina. From the analysis of water-table fluctuations in a set of monitoring wells located along a riverbank-normal transect, it was possible to quantify the piecewise spatial variations of the hydraulic diffusivity of the phreatic aquifer. The results show the strong lateral variations of the sedimentary environment due to the influence of the different transport and deposition agents that characterize the coastal plain. The known thickness of the phreatic aquifer and the estimated range of the specific yield allowed the hydraulic conductivity to be identified as the most influential factor. [Jacob CE (1950) Flow of ground water. In: Rouse H (ed) Engineering Hydraulics. Wiley, New York]  相似文献   

A rootless suture and the loss of the roots of a mountain chain: The Variscan belt of NW Iberia     

José R. Martínez Catalán  Ricardo Arenas  Jacobo Abati  Sonia Sánchez Martínez  Florentino Díaz García  Javier Fernández Suárez  Pablo González Cuadra  Pedro Castiñeiras  Juan Gómez Barreiro  Alejandro Díez Montes  Emilio González Clavijo  Francisco J. Rubio Pascual  Pilar Andonaegui  Teresa E. Jeffries  James E. Alcock  Rubén Díez Fernández  Alicia López Carmona 《Comptes Rendus Geoscience》2009,341(2-3):114-126

Ophiolites of different Paleozoic ages occur in North-West (NW) Iberia in a rootless suture representing the remnants of the Rheic Ocean. Associated allochthonous terranes in the hanging- and foot-walls of the suture derive from the former margins, whereas the relative autochthon corresponds to the Paleozoic passive margin of northern Gondwana. The Paleozoic tectonic evolution of this part of the circum-Atlantic region is deduced from the stratigraphical, petrological, structural and metamorphic evolution of the different units and their ages. The tectonic reconstruction covers from Cambro-Ordovician continental rifting and the opening of the Rheic Ocean to its Middle to Upper Devonian closure. Then, the Variscan Laurussia–Gondwana convergence and collision is briefly described, from its onset to the late stages of collapse associated with the demise of the orogenic roots.  相似文献   

Global velocity field and bubbles in the blue compact dwarf galaxy Mrk 86     

A. Gil de Paz  J. Zamorano  J. Gallego 《Monthly notices of the Royal Astronomical Society》1999,306(4):975-987

We have studied the velocity field of the blue compact dwarf galaxy Mrk 86 (NGC 2537) using data provided by 14 long-slit optical spectra obtained in 10 different orientations and positions. This kinematical information is complemented with narrow-band ([O  iii ]5007 Å and H α ) and broad-band ( B , V , Gunn r and K ) imaging. The analysis of the galaxy global velocity field suggests that the ionized gas could be distributed in a rotating inclined disc, with projected central angular velocity of Ω=34 km s⁻¹ kpc⁻¹. The comparison between the stellar, H  i and modelled dark matter density profile indicates that the total mass within its optical radius is dominated by the stellar component. Peculiarities observed in its velocity field can be explained by irregularities in the ionized gas distribution or local motions induced by star formation.
Kinematical evidences for two expanding bubbles, Mrk 86–B and Mrk 86–C, are given. They show expanding velocities of 34 and 17 km s⁻¹, H α luminosities of 3×10³⁸ and 1.7×10³⁹ erg s⁻¹, and physical radii of 374 and 120 pc, respectively. The change in the [S  ii ]/H α , [N  ii ]/H α , [O  ii ]/[O  iii ] and [O  iii ]/H β line ratios with the distance to the bubble precursor suggests a diminution in the ionization parameter and, in the case of Mrk 86–B, an enhancement of the shock-excited gas emission. The optical–near-infrared colours of the bubble precursors are characteristic of low‐metallicity star‐forming regions (∼0.2 Z_⊙) with burst strengths of about 1 per cent in mass.  相似文献   

Thank you to 2022 Ocean Dynamics reviewers     

Ezer  Tal  Carniel  Sandro  Amin  Chabchoub  de Camargo  Ricardo  Estrada-Allis  Sheila N.  Gao  Guoping  Greatbatch  Richard J.  Lermusiaux  Pierre F. J.  Liu  Zhiyu  Miyazawa  Yasumasa  Forster  Alejandro Orfila  Panickal  Swapna  Phillips  Helen  Pinones  Andrea  Stanev  Emil  Volker  Christoph  Xu  Fanghua  Young  Emma 《Ocean Dynamics》2023,73(1):35-38

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High Arctic sea ice conditions influence marine birds wintering in Low Arctic regions     

Laura McFarlane Tranquilla  April Hedd  Chantelle Burke  William A. Montevecchi  Paul M. Regular  Gregory J. Robertson  Leslie Ann Stapleton  Sabina I. Wilhelm  David A. Fifield  Alejandro D. Buren 《Estuarine, Coastal and Shelf Science》2010

Ocean climate change is having profound biological effects in polar regions. Such change can also have far-reaching downstream effects in sub-polar regions. This study documents an environmental relationship between High Arctic sea ice changes and mortality events of marine birds in Low Arctic coastal regions. During April 2007 and March 2009, hundreds of beached seabird carcasses and moribund seabirds were found along the east and northeast coasts of Newfoundland, Canada. These seabird “wrecks” (i.e. dead birds on beaches) coincided with a period of strong, persistent onshore winds and heavily-accumulated sea ice that blocked bays and trapped seabirds near beaches. Ninety-two percent of wreck seabirds were Thick-billed Murres (Uria lomvia). Body condition and demographic patterns of wreck murres were compared to Thick-billed Murres shot in the Newfoundland murre hunt. Average body and pectoral masses of wreck carcasses were 34% and 40% lighter (respectively) than shot murres, indicating that wreck birds had starved. The acute nature of each wreck suggested that starvation and associated hypothermia occurred within 2–3 days. In 2007, first-winter murres (77%) dominated the wreck. In 2009, there were more adults (78%), mostly females (66%). These results suggest that spatial and temporal segregation in ages and sexes can play a role in differential survival when stochastic weather conditions affect discrete areas where these groups aggregate. In wreck years, southward movement of Arctic sea ice to Low Arctic latitudes was later and blocked bays longer than in most other years. These inshore conditions corresponded with recent climate-driven changes in High Arctic ice break-up and ice extent; coupled with local weather conditions, these ice conditions appeared to be the key environmental features that precipitated the ice-associated seabird wrecks in the Low Arctic region.  相似文献   

Pressure and density gradients in H II Regions     

José Franco  Stan E. Kurtz  José A. GarcÍa-Barreto  Guillermo GarcÍa-Segura  Eduardo de la Fuente  Peter Hofner  Alejandro Esquivel 《Astrophysics and Space Science》2001,277(1):71-74

Here we discuss the effects of large ambient pressures and decreasing density gradients on the observed properties of dusty UC hii regions. Dust absorption can effectively reduce the size of the photo ionized region, and density gradients can modify the spectral index of the emission. The effects of the density gradients seem to be present in both galactic and extragalactic HII regions.  相似文献   

A New Ionosphere Monitoring Technology Based on GPS   总被引：1，自引：0，他引：1  

Claudio Brunini  Amalia Meza  Francisco Azpilicueta  María Andrea Van Zele  Mauricio Gende  Alejandro Díaz 《Astrophysics and Space Science》2004,290(3-4):415-429

Although global positioning system (GPS) was originally planned as a satellite-based radio-navigation system for military purposes, civilian users have significantly increased their access to the system for both, commercial and scientific applications. Almost 400 permanent GPS tracking stations have been stablished around the globe with the main purpose of supporting scientific research. In addition, several GPS receivers on board of low Earth orbit satellites fitted with special antennas that focus on Earth's horizon, are tracking the radio signals broadcasted by the high-orbiting GPS satellites, as they rise and set on Earth horizon. The data of these ground and space-born GPS receivers, readily accessible through Internet in a ‘virtual observatory’ managed by the International GPS Service, are extensively used for many researches and might possibly ignite a revolution in Earth remote sensing. By measuring the changes in the time it takes for the GPS signals to arrive at the receiver as they travel through Earth's atmosphere, scientists can derive a surprising amount of information about the Earth's ionosphere, a turbulent shroud of charged particles that, when stimulated by solar flares, can disrupt communications around the world. This contribution presents a methodology to obtain high temporal resolution images of the ionospheric electron content that lead to two-dimensional vertical total electron content maps and three-dimensional electron density distribution. Some exemplifying results are shown at the end of the paper.  相似文献   

Changes in solar irradiance and atmospheric turbidity in Costa Rica during the total solar eclipse of July 11, 1991     

Walter Fernández  Vilma Castro  Jaime Wright  Hugo Hidalgo  Alejandro Sáenz 《Earth, Moon, and Planets》1993,63(2):119-132

Solar global radiation was measured in several places in Costa Rica during the total solar eclipse that occurred on July 11, 1991. In two of these places, Puntarenas and Santa Cruz, measurements in the ultraviolet range (295–385 nm) were also taken. In Santa Cruz, a normal incidence pyrheliometer with Schott filters OG530 and RG630 was used to measure direct solar radiation in its whole range, and in the 530–2800 nm and 630–2800 wavebands respectively. Global radiation, and consequently direct, diffuse and irradiance in any of the wavebands considered, decreased gradually as the sun was being eclipsed and reached zero during the totality, then increased to their normal values. Data registered in Santa Cruz were used to determine Ångstrom's atmospheric turbidity parameters and. Computations show that between 13:00 and 14:30 LT (local time), decreased and increased significantly. This indicates that atmospheric turbidity was high and large particles were more abundant than small ones. The size of hygroscopic particles increased during the eclipse when temperature decreased and relative humidity increased in a comparatively short time.  相似文献