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61.
62.
Abstract. Cymodocea nodosa is a relatively small seagrass species which is common in the Mediterranean. An intensive survey on its growth and production was carried out in a dense, monospecific stand located in a semi-estuarine embayment. Data on leaf appearance and growth, shoot recruitment and death, rhizome growth, above- and belowground biomass, and nutrient content in the different parts of the plant were obtained over 2 years. All these variables showed a clear seasonality. In general, maximum growth and production occurred in early summer (July), and maximum biomass was reached between July and September. Biomass, shoot density, growth and production showed clear minima in winter. 相似文献
63.
Ernesto Medina Marta Francisco Leonel Sternberg William T. Anderson 《Estuarine, Coastal and Shelf Science》2005,63(4):527-536
The 87Sr, 13C, and 15N isotopic signatures of organic matter in sediments from the continental shelf facing the Orinoco Delta were measured to determine the contribution of sediments transported from the Amazon River by the coastal Guayana current and the sediments transported by the Orinoco River. Box core samples between 60 and 300 m water depth collected along 4 transects located eastwards to the Orinoco Delta were analyzed. Carbon and nitrogen concentrations decreased with depth under water on the shelf, and were strongly correlated indicating homogeneity of organic matter composition. Phosphorus content was also associated to organic matter in most samples, but some of them revealed deposition of P-enriched sediments. The 87Sr/86Sr ratios showed a strong continental signature averaging 0.7117, therefore, limiting the possible carbon and nitrogen sources associated with these sediments to C3 trees, C4 grasses, or freshwater phytoplankton. The δ13C values were relatively high averaging −21‰, above values reported for sediments on the Amapá shelf and the Amazon River in Brazil. Average δ13C values did not differ significantly among transects. High δ13C values point to the influence of organic matter transported from the C4-plants dominated savannas in the northern fringe of the Orinoco River. δ15N values were positive and averaged 5‰, being within the range of values measured in the Marajo island (Amazon River) and the estuary of the Pará River. The δ15N values differed significantly among transects (4.9–5.2‰), lowest values corresponding to the northernmost transect near the coast of Trinidad, and the highest values corresponding to the transect located at the southernmost position. 相似文献
64.
We employ numerical and analytical methods to investigate the effect of the presence of rigid porphyroblasts such as garnets on layer strengthening and the folding instability. We use a 50% fraction of non‐overlapping, circular‐shaped inclusions with a wide size distribution. These inclusions cause a fourfold effective viscosity increase and can significantly promote the folding instability. This is not only due to the increased viscosity but also due to the layer interface roughness generation driven by relative movement of inclusions. The increase in layer viscosity promotes strengthening of the whole system. However, with progressive fold development, the system undergoes an effective softening that may counteract the strengthening effect of the porphyroblast growth. 相似文献
65.
We use numerical simulations to investigate the evolution of sheath folds around slip surfaces in simple‐shear‐dominated monoclinic shear zones. A variety of sheath fold shapes develops under general shear, including tubular folds with low aspect ratio eye patterns and tongue‐like structures showing bivergent flanking structures in sections normal to the sheath elongation, which may potentially lead to confusing shear sense interpretations. Not all investigated monoclinic flow end‐members lead to the development of sheath folds sensu stricto (folds with apical angle <90°). The aspect ratio of the eye patterns, Ryz, correlates with the ratio between the principal strain in the Y‐direction and the smaller of the principal strains in the X–Z plane, and thus it could be used in strain analysis. 相似文献
66.
Uranium mines are the often forgotten source of nuclear power. This article studies impacts and social movements at a uranium mining frontier looking at the interaction between the global social metabolism, industrial dynamics and local ecologies of resistance. Namibia, the world's fourth largest producer of uranium, stands at the vanguard of the global uranium rush with 66 granted prospecting licenses and two operating mines. We focus on three generic attributes that help to explain the emergence and intensity of resistance by local communities to uranium mining: the ecology and geography of the resource; the degree and type of political and economic marginalisation of the community; and crucially, the connection and integration of local concerns with broader social movements and political demands. We show with the use of empirical material how these factors play out differently in five Namibian communities that have been, or stand to be, affected by uranium mining, and explain how local ecologies of resistance shape, or fail to shape, the global uranium rush. Our work offers an example of an integrative approach for the analysis of the global–local dynamics of environmental change in relation to the extraction and flow of the essential materials that fuel industrial economies. 相似文献
67.
Erwan Messager Vincent Lebreton Laurent Marquer Elda Russo-Ermolli Ronan Orain Josette Renault-Miskovsky David Lordkipanidze Jackie Despriée Carlo Peretto Marta Arzarello 《Quaternary Science Reviews》2011,30(11-12):1439-1447
The present study focuses on new palaeobotanical data (pollen, phytoliths and fruits) from three of the oldest Early Palaeolithic sites in Eurasia (Dmanisi in Georgia, Ca’ Belvedere di Monte Poggiolo in Italy and Pont-de-Lavaud in France). The main aim is to examine the ecological factors associated with the first human dispersals out of Africa into Eurasia. The palaeoecological data are discussed with regards to chronology and geographical location of the settlements. The vegetation pattern of each site consists of temperate Eurasian and Mediterranean taxa, subtropical trees being more or less recorded depending on climatic and geographic features. The new palaeobotanical data show that different vegetation structures occurred between the first human dispersal in Caucasus and the later dispersals in western Eurasia. However, in all cases hominins seemed to be adapted to temperate ecosystems. In Caucasus, human occupation took place at 1.7 Ma in a forest-steppe environment, while at ca 1 Ma human populations occupied various settings such as open landscapes or dense forests. These data suggest that during the Early Pleistocene, human populations evolved and dispersed in western Eurasia, gradually increasing their degree of adaptation to diversified environments. 相似文献
68.
Marta Burgay Nanda Rea GianLuca Israel Andrea Possenti Luciano Burderi Tiziana Di Salvo Nichi D’Amico Luigi Stella Elisa Nichelli 《Astrophysics and Space Science》2007,308(1-4):531-534
We have performed deep searches for radio pulsations from four southern anomalous X-ray pulsars (AXPs) to investigate their
physical nature in comparison with the rotation powered pulsars. The data were acquired using the Parkes radio telescope with
the 1.4 GHz multibeam receiver. No pulsed emission with periodicity matching the X-ray ephemeris have been found in the observed
targets down to a limit of ∼0.1 mJy. A blind search has also been performed on all the 13 beams of the multibeam receiver
(the central beam being pointed on the target AXP), leading to the serendipitous discovery of two new radio pulsars and to
the further detection of 18 pulsars. Also a search for single dispersed pulses has been performed in the aim to detect signals
similar to those of the recently discovered rotating radio transients.
相似文献
69.
Bryan M. Gaensler Maura McLaughlin Stephen Reynolds Kazik Borkowski Nanda Rea Andrea Possenti Gianluca Israel Marta Burgay Fernando Camilo Shami Chatterjee Michael Kramer Andrew Lyne Ingrid Stairs 《Astrophysics and Space Science》2007,308(1-4):95-99
“Rotating RAdio Transients” (RRATs) are a newly discovered astronomical phenomenon, characterised by occasional brief radio
bursts, with average intervals between bursts ranging from minutes to hours. The burst spacings allow identification of periodicities,
which fall in the range 0.4 to 7 seconds. The RRATs thus seem to be rotating neutron stars, albeit with properties very different
from the rest of the population. We here present the serendipitous detection with the Chandra X-ray Observatory of a bright point-like X-ray source coincident with one of the RRATs. We discuss the temporal and spectral properties of
this X-ray emission, consider counterparts in other wavebands, and interpret these results in the context of possible explanations
for the RRAT population.
B.M.G. acknowledges the support of NASA through LTSA grant NAG5-13023 and of an Alfred P. Sloan Fellowship. 相似文献
70.
In this study, a hydrometeorological dataset of unglaciated High Arctic catchment is presented. The time series encompasses air temperature, precipitation, wind speed, relative humidity, and runoff data from 2014 to 2019. Meteorological data come from continuous meteorological monitoring carried out at the Hornsund station located in SW Spitsbergen. Flow in the Fuglebekken stream was measured using a portable flowmeter Nivus PCM-F with Active Doppler sensor. Continuous hydrometeorological monitoring in polar environments is crucial for the understanding processes controlling the water circulation in the catchments. Inter- and intra- annual variability of the provided variables gives an insight into river functioning. The data set is provided in an open-access PANGAEA repository (https://doi.pangaea.de/10.1594/PANGAEA.921921), in three time intervals (6, 12, and 24 hours). It may serve as the input to rainfall-runoff hydrological models, and allows multi-model parameter estimation and validation. It can be used in a variety of research topics, including streamflow projections, and more generally in examining Arctic ecosystems and climate change impact studies. 相似文献