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821.
The use of explosives to catch fish has caused extensive damage to coral reefs throughout Southeast Asia, but the frequency with which they are used is largely unknown. The aim of this work is to develop a detection system capable of distinguishing underwater explosions from background noise, and locating their origin by triangulation. Blast signals have been recorded over a range of distances and the key features that differentiate them from background noise have been determined. For small charges the effective range of such a detector is more than 12 km and may extend up to 50 km depending on the mass of the charges being used. Such a system would help to determine the scale of the problem, identify areas at greatest risk and quantify the effectiveness of management intervention designed to control destructive fishing practices. It may assist with fisheries enforcement in some areas. 相似文献
822.
823.
Pascal Podwojewski Jean Louis Janeau Séraphine Grellier Christian Valentin Simon Lorentz Vincent Chaplot 《地球表面变化过程与地形》2011,36(7):911-922
In most regions of the world overgrazing plays a major role in land degradation and thus creates a major threat to natural ecosystems. Several feedbacks exist between overgrazing, vegetation, soil infiltration by water and soil erosion that need to be better understood. In this study of a sub‐humid overgrazed rangeland in South Africa, the main objective was to evaluate the impact of grass cover on soil infiltration by water and soil detachment. Artificial rains of 30 and 60 mm h?1 were applied for 30 min on 1 m2 micro‐plots showing similar sandy‐loam Acrisols with different proportions of soil surface coverage by grass (Class A: 75–100%; B: 75–50%; C: 50–25%; D: 25–5%; E: 5–0% with an outcropping A horizon; F: 0% with an outcropping B horizon) to evaluate pre‐runoff rainfall (Pr), steady state water infiltration (I), sediment concentration (SC) and soil losses (SL). Whatever the class of vegetal cover and the rainfall intensity, with the exception of two plots probably affected by biological activity, I decreased regularly to a steady rate <2 mm h?1 after 15 min rain. There was no significant correlation between I and Pr with vegetal cover. The average SC computed from the two rains increased from 0·16 g L?1 (class A) to 48·5 g L?1 (class F) while SL was varied between 4 g m?2 h?1 for A and 1883 g m?2 h?1 for F. SL increased significantly with decreasing vegetal cover with an exponential increase while the removal of the A horizon increased SC and SL by a factor of 4. The results support the belief that soil vegetation cover and overgrazing plays a major role in soil infiltration by water but also suggest that the interrill erosion process is self‐increasing. Abandoned cultivated lands and animal preferred pathways are more vulnerable to erosive processes than simply overgrazed rangelands. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
824.
Vincent Le Fouest Clare PostlethwaiteMiguel Angel Morales Maqueda Simon BélangerMarcel Babin 《Continental Shelf Research》2011,31(17):1869-1879
Tides and wind-driven mixing play a major role in promoting post-bloom productivity in subarctic shelf seas. Whether this is also true in the high Arctic remains unknown. This question is particularly relevant in a context of increasing Arctic Ocean stratification in response to global climatic change. We have used a three-dimensional ocean-sea ice-plankton ecosystem model to assess the contribution of tides and strong wind events to summer (June-August 2001) primary production in the Barents Sea. Tides are responsible for 20% (60% locally) of the post-bloom primary production above Svalbard Bank and east of the Kola Peninsula. By contrast, more than 9% of the primary production is due to winds faster than 8 m s−1 in the central Barents Sea. Locally, this contribution reaches 25%. In the marginal ice zone, both tides and wind events have only a limited effect on primary production (<2%). Removing tides or winds faster than 8 m s−1 promotes a regime more sustained by regenerated production with a f-ratio (i.e. the proportion of nitrate-based “new” primary production in the total primary production) that decreases by up to 26% (east of the Kola Peninsula) or 35% (central Barents Sea), respectively. When integrated over all Barents Sea sub-regions, tides and strong wind events account, respectively, for 6.8% (1.55 Tg C; 1 Tg C=1012 g C) and 4.1% (0.93 Tg C) of the post-bloom primary production (22.6 Tg C). To put this in context, this contribution to summer primary production is equivalent to the spring bloom integrated over the Svalbard area. Tides and winds are significant drivers of summer plankton productivity in the Barents Sea. 相似文献
825.
Ewa Słaby Michał Śmigielski Tomasz Śmigielski Andrzej Domonik Klaus Simon Andreas Kronz 《Contributions to Mineralogy and Petrology》2011,162(5):909-927
As has been demonstrated in recent years, the heterogeneities of coeval magmas can be more successfully revealed by zoned
megacrysts rather than by analysis of the whole rocks hosting them. Here, the geochemical heterogeneities of feldspar megacrysts
from the Karkonosze granite, Poland, are investigated by LA-ICP-MS. The crystals are the product of migration and growth in
regions of poorly mixed magmas. 3D-modeling of the Ba, Sr, and Rb distributions emphasizes the importance of micro-domain
growth morphologies. Two models of element behavior—a relative concentration model and a composition gradient model—provide
a potentially effective tool for tracking the mixing process on a microscale. Measured concentrations of elements of different
mobilities do not agree with what might be expected from the mixing of two end-member magmas. If mixing was the only process
occurring, linear correlations between the concentrations of any two elements should be observed; this, however, is not the
case. For combinations of any two of the three elements, modeling reveals differing non-linear correlations between concentrations.
The megacryst heterogeneities provide an insight into how mixing magmas are chaotically advected to growing crystals and the
degree of inter-magma element exchange between the magmas. 相似文献
826.
The subsurface temperature field of a rock slope is a key variable influencing both bedrock fracturing and slope stability. However, significant unknowns remain relating to the effect of air and water fracture flow, which can rapidly transmit temperature changes to appreciable depths. In this work, we analyze a unique set of temperature measurements from an alpine rock slope at ~2400 m a.s.l. in southern Switzerland. The monitored area encompasses part of an active slope instability above the village of Randa (VS) and is traversed by a network of open cracks, some of which have been traced to >80 m depth. We first describe distributed temperature measurements and borehole profiles, highlighting deep steady temperatures and different transient effects, and then use these data to approximate the conductive temperature field at the site. In a second step, we analyze the impact of air and water circulation in deep open fractures on the subsurface thermal field. On multiple visits to the study site in winter, we consistently noted the presence of warm air vents in the snowpack following the trace of deep tension cracks. Measurements showed that venting air changed temperature gradually from ~3 to 2 °C between December and May, which is similar to the rock temperature at around 50 m depth. Comparison with ambient air temperature suggests that winter conditions favor buoyancy‐driven convective air flow in these fractures, which acts to cool the deep subsurface as the rock gives up heat to incoming air. The potential impact of this process on the local thermal field is revealed by a disturbed temperature profile in one borehole and transient signals observed at depths well below the thermal active layer. Seasonal water infiltration during snowmelt appears to have little impact on the temperature field in the monitored area. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
827.
The Kimberlites and related rocks of the Kuruman Kimberlite Province,Kaapvaal Craton,South Africa 总被引:2,自引:0,他引:2
Cara L. Donnelly William L. Griffin Suzanne Y. O’Reilly Norman J. Pearson Simon R. Shee 《Contributions to Mineralogy and Petrology》2011,161(3):351-371
The Kuruman Kimberlite Province is comprised of 16 small pipes and dikes and contains some of the oldest known kimberlites
(>1.6 Ga). In this study, 12 intrusions are subdivided into three groups with distinct petrology, age, and geochemical and
isotopic compositions: (1) kimberlites with groundmass perovskites defining a Pb–Pb isochron age of 1787 ± 69 Ma, (2) orangeite
with a U–Pb perovskite age of 124 ± 16 Ma, and (3) ultramafic lamprophyres (aillikite and mela-aillikite) with a zircon U–Pb
age of 1642 ± 46 Ma. The magma type varies across the Province, with kimberlites in the east, lamprophyres in the west and
orangeite and ultramafic lamprophyres to the south. Differences in the age and petrogenesis of the X007 orangeite and Clarksdale
and Aalwynkop aillikites suggest that these intrusions are probably unrelated to the Kuruman Province. Kimberlite and orangeite
whole-rock major and trace element compositions are similar to other South African localities. Compositionally, the aillikites
typically lie off kimberlite and orangeite trends. Groundmass mineral chemistry of the kimberlites has some features more
typical of orangeites. Kimberlite whole-rock Sr and Nd isotopes show zoning across the Province. When the kimberlites erupted
at ~1.8 Ga, they sampled a core volume (ca 50 km across) of relatively depleted SCLM that was partially surrounded by a rim
of more metasomatized mantle. This zonation may have been related to the development of the adjacent Kheis Belt (oldest rocks
~2.0 Ga), as weaker zones surrounding the more resistant core section of SCLM were more extensively metasomatized. 相似文献
828.
Alan R. Hastie Simon F. Mitchell Matthew J. Minifie 《Geochimica et cosmochimica acta》2011,75(17):5049-5072
Compositionally, high-Nb basalts are similar to HIMU (high U/Pb) ocean island basalts, continental alkaline basalts and alkaline lavas formed above slab windows. Tertiary alkaline basaltic lavas from eastern Jamaica, West Indies, known as the Halberstadt Volcanic Formation have compositions similar to high-Nb basalts (Nb > 20 ppm). The Halberstadt high-Nb basalts are divided into two compositional sub-groups where Group 1 lavas have more enriched incompatible element concentrations relative to Group 2. Both groups are derived from isotopically different spinel peridotite mantle source regions, which both require garnet and amphibole as metasomatic residual phases. The Halberstadt geochemistry demonstrates that the lavas cannot be derived by partial melting of lower crustal ultramafic complexes, metasomatised mantle lithosphere, subducting slabs, continental crust, mantle plume source regions or an upper mantle source region composed of enriched and depleted components. Instead, their composition, particularly the negative Ce anomalies, the high Th/Nb ratios and the similar isotopic ratios to nearby adakite lavas, suggests that the Halberstadt magmas are derived from a compositionally variable spinel peridotite source region(s) metasomatised by slab melts that precipitated garnet, amphibole, apatite and zircon. It is suggested that high-Nb basalts may be classified as a distinct rock type with Nb > 20 ppm, intraplate alkaline basalt compositions, but that are generated in subduction zones by magmatic processes distinct from those that generate other intraplate lavas. 相似文献
829.
Etienne Balan Simon Delattre Damien Roche Loïc Segalen Guillaume Morin Maxime Guillaumet Marc Blanchard Michele Lazzeri Christian Brouder Ekhard K. H. Salje 《Physics and Chemistry of Minerals》2011,38(2):111-122
The crystallinity of natural and synthetic apatite samples is often determined from the broadening of ν
4 PO4 infrared absorption bands. However, various physical mechanisms contribute to the observed linewidth. In the present study,
the factors determining the linewidth in the powder spectrum of synthetic fluorapatite and hydroxyapatite samples are investigated.
The temperature dependence of the infrared spectrum (10–270 K) is used to assess the respective contributions of homogeneous
broadening, related to the decay of phonons through anharmonic coupling, and heterogeneous broadening related to elastic strain
and macroscopic electrostatic effects. This latter contribution is dominant in the investigated samples and depends on the
shape of powder particles. It is discussed under the light of the theoretical modeling of the low-frequency dielectric properties
of apatite based on first-principles density functional theory calculations. The linewidth of the weak ν
1 PO4 absorption band provides a reliable information on microscopic sources of broadening, i.e., apatite crystallinity. In comparison,
the other more intense PO4 bands are more sensitive to long-range electrostatic effects. 相似文献
830.
Isaac G. Roseboom Kevin A. Pimbblet Michael J. Drinkwater Russell D. Cannon Roberto De Propris Alastair C. Edge Daniel J. Eisenstein Robert C. Nichol Ian Smail David A. Wake Joss Bland-Hawthorn Terry J. Bridges Daniel Carson Matthew Colless Warrick J. Couch Scott M. Croom Simon P. Driver Paul C. Hewett Jon Loveday Nic Ross Donald P. Schneider Tom Shanks Robert G. Sharp Peter Weilbacher 《Monthly notices of the Royal Astronomical Society》2006,373(1):349-360
We present a detailed investigation into the recent star formation histories of 5697 luminous red galaxies (LRGs) based on the Hδ (4101 Å), and [O ii ] (3727 Å) lines and the D4000 index. LRGs are luminous ( L > 3 L *) galaxies which have been selected to have photometric properties consistent with an old, passively evolving stellar population. For this study, we utilize LRGs from the recently completed 2dF-SDSS LRG and QSO Survey (2SLAQ). Equivalent widths of the Hδ and [O ii ] lines are measured and used to define three spectral types, those with only strong Hδ absorption (k+a), those with strong [O ii ] in emission (em) and those with both (em+a). All other LRGs are considered to have passive star formation histories. The vast majority of LRGs are found to be passive (∼80 per cent); however, significant numbers of k+a (2.7 per cent), em+a (1.2 per cent) and em LRGs (8.6 per cent) are identified. An investigation into the redshift dependence of the fractions is also performed. A sample of SDSS MAIN galaxies with colours and luminosities consistent with the 2SLAQ LRGs is selected to provide a low-redshift comparison. While the em and em+a fractions are consistent with the low-redshift SDSS sample, the fraction of k+a LRGs is found to increase significantly with redshift. This result is interpreted as an indication of an increasing amount of recent star formation activity in LRGs with redshift. By considering the expected lifetime of the k+a phase, the number of LRGs which will undergo a k+a phase can be estimated. A crude comparison of this estimate with the predictions from semi-analytic models of galaxy formation shows that the predicted level of k+a and em+a activities is not sufficient to reconcile the predicted mass growth for massive early types in a hierarchical merging scenario. 相似文献