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951.
Current palaeoclimatic reconstructions for the Río de la Plata region during the latest Pleistocene (30,000 e10,000 yr BP) propose dry conditions, with rainfall at the Last Glacial Maximum amounting to one-third of today's precipitation. Despite the consequential low primary productivity inferred, an impressive megafauna existed in the area at that time. Here we explore the influence of the flooding from a huge extinct system of water bodies in the Andean Altiplano as a likely source for wet regimes that might have increased the primary productivity and, hence, the vast number of megaherbivores. The system was reconstructed using specifically combined software resources, including Insola, Global Mapper v13, Surfer and Matlab. Changes in water volume and area covered were related to climatic change, assessed through a model of astronomical forcing that describes the changes in insolation at the top of the at-mosphere in the last 50,000 yr BP. The model was validated by comparing its results with several proxies (CH4, CO2, D, 18O) from dated cores taken from the ice covering Antarctic lakes Vostok and EPICA Dome C. It is concluded that the Altiplano Lake system drained towards the southeast in the rainy seasons and that it must have been a major source of water for the Paraná-Plata Basin, consequently enhancing primary productivity within it. 相似文献
952.
Andrea Dini Gianfranco Di Vincenzo Giovanni Ruggieri Jeffrey Rayner Pierfranco Lattanzi 《Mineralium Deposita》2005,40(3):337-346
The Monte Ollasteddu deposit represents a major gold discovery in the Variscan basement of southeastern Sardinia. Gold occurs
in late-Variscan extensional brittle structures hosted by meta-volcanic, and subordinately meta-sedimentary, rocks. The vein
mineralogy is dominated by quartz; arsenopyrite is the main sulphide. Reconnaissance 40Ar–39Ar dating gives ages around ∼260 Ma on K-feldspar from mineralized veins, whereas metamorphic white mica from the host rock
gives ages clustering at ∼307 Ma. The best age estimate for biotite from a nearby leucogranite body is 286.3±2.2 Ma. The Pb
isotope signature of ore and gangue minerals is entirely consistent with literature data for Variscan deposits of Sardinia,
and for European Variscan gold deposits. Fluid inclusion data point to the presence of both CO2-bearing and CO2-free fluids, with homogenization temperatures ranging from 220 to 415°C, with low-to-moderate salinities (0.4–6.2 wt% NaCl
equivalent). Monte Ollasteddu shows several features similar to European Variscan gold deposits; however, the age of mineralization
might post-date granitoid intrusion by as much as 30 Ma, being instead coeval with very late calc-alkaline basaltic dykes,
marking the transition to a post-orogenic, pre-Tethyan geodynamic setting.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
953.
Harold Wolman George Galster Royce Hanson Michael Ratcliffe Kimberly Furdell Andrea Sarzynski 《The Professional geographer》2005,57(1):94-105
Lack of agreement on how to define and measure sprawl has hampered development of policy related to its causes and consequences. We question previous work for two reasons: the use of study areas that overbound or underbound sprawl landscapes, and the failure to account for land unavailable for development. We formulate “extended urban areas,” based on housing density and commuting patterns and argue that they represent a preferable geographic basis for measuring sprawl. We operationalize with satellite imagery a way for measuring land unavailable for development in these areas. We then compute five measures of urban development using the National Land Cover Data Base and decennial census data to assess the extent of sprawl in the extended urban areas of Atlanta, Baltimore, Boston, Los Angeles, and Washington. Our sensitivity analyses reveal that the measurement of sprawl critically depends on which land area forms the basis of the analysis, and, to a lesser degree, how one accounts for land unavailable for development. 相似文献
954.
García-Borboroglu P Boersma PD Ruoppolo V Reyes L Rebstock GA Griot K Rodrigues Heredia S Adornes AC da Silva RP 《Marine pollution bulletin》2006,52(2):193-198
Petroleum pollution is a problem for seabirds along the Southwest Atlantic coast. Twenty-five groups from Salvador, Brazil (12 degrees 58'S) to San Antonio Oeste, Argentina (40 degrees 43'S) survey or rehabilitate sick or oiled seabirds. Four groups, one each in Brazil and Uruguay, and two in Argentina, kept counts of birds found alive and in need of rehabilitation. An average of 63.7% of the seabirds found were Magellanic penguins (Spheniscus magellanicus), with 3869 reported since 1987. Mainly adult penguins were found in Argentina (1605 of 2102 penguins of known age class) and Uruguay (158 of 197). Juveniles were most common in Brazil (234 of 325). Oil fouling was the most frequent cause of injury or sickness. The number of oiled penguins reported in their wintering range has greatly increased since the early 1990s and is strongly correlated with petroleum exports from Argentina. Our results show that chronic petroleum pollution is a problem for wildlife from Southern Brazil through Northern Argentina, and regulations and enforcement are failing to protect living resources. 相似文献
955.
Jochen Woessner Danciu Laurentiu Domenico Giardini Helen Crowley Fabrice Cotton Gottfried Grünthal Gianluca Valensise Ronald Arvidsson Roberto Basili Mine Betül Demircioglu Stefan Hiemer Carlo Meletti Roger W. Musson Andrea N. Rovida Karin Sesetyan Massimiliano Stucchi The SHARE Consortium 《Bulletin of Earthquake Engineering》2015,13(12):3553-3596
956.
957.
Natural Hazards - Earthquakes can generate large volumes of debris which may threaten public health, hinder reconstruction and impact the environment. The present paper aims at investigating how... 相似文献
958.
Andrea Stolte Andrea Ghez Mark Morris Jessica Lu Wolfgang Brandner Keith Matthews 《Astrophysics and Space Science》2009,324(2-4):137-140
We have measured the proper motion of the Arches cluster near the Galactic Center (GC) with respect to the ambient field, using Keck/NIRC2 LGS-AO and VLT/NAOS-CONICA NGS-AO observations spanning a baseline of 4.3 yr. Combined with the radial velocity, we derive a 3D space motion of 232±30 km?s?1 for the Arches cluster. This motion is exceptionally large compared to molecular cloud orbits at the GC, and places stringent constraints on the formation scenarios for starburst clusters in dense, nuclear environments. 相似文献
959.
We interpret the rapid correlated UV/optical/X-ray variability of XTE J1118+480 as a signature of the coupling between the
X-ray corona and a jet emitting synchrotron radiation in the optical band. We propose a scenario in which the jet and the
X-ray corona are fed by the same energy reservoir where large amounts of accretion power are stored before being channelled
into either the jet or the high energy radiation. This time-dependent model reproduces the main features of the rapid multi-wavelength
variability of XTE J1118+480. A strong requirement of the model is that the total jet power should be at least a few times
larger than the observed X-ray luminosity, implying a radiative efficiency for the jet ∊j3 × 10−3. This would be consistent with the overall low radiative efficiency of the source. We present independent arguments showing
that the jet probably dominates the energetic output of all accreting black holes in the low-hard state.
Partially supported by PPARC 相似文献