The impact of scour processes on a smothered reef system in the Irish Sea     

Alexander Callaway  Jennifer Smyth  Craig J. Brown  Rory Quinn  Matthew Service  David Long 《Estuarine, Coastal and Shelf Science》2009,84(3):409-422

The Irish Sea, like many marine areas, is threatened by anthropogenic activities. In particular the Pisces Reef system, a series of smothered rocky reefs are subject to fishing pressures as a result of their position within a Nephrops norvegicus fishery. In an area of sediment deposition and retention the reefs modify the environment by increasing the energy of near-bottom currents which results in localised scouring. This is the first study to attempt to characterise and investigate the ecological functioning of the Pisces Reef system. A multidisciplinary approach was essential for accurate investigation of the area. To facilitate more effective management of the benthic habitats of the Reef system, this study integrates acoustic, seismic, grab sampling and video ground-truthing methods for benthic habitat discrimination. Orientation of the scour hollows also suggest that seabed features could be used to infer dominant flow regimes such as the Irish Sea Gyre. The data revealed significant geology–benthos relationships. A unique biotope was described for the reef habitat and it was demonstrated that scouring may influence community composition through disturbance mechanisms. This study provides preliminary information required for management of a unique habitat within a uniform region.  相似文献   

Resource partitioning by two large planktivorous fishes Micromesistius australis and Macruronus magellanicus in the Southwest Atlantic     

Paul Brickle  Alexander I. ArkhipkinVladimir Laptikhovsky  Andrew StocksAlison Taylor 《Estuarine, Coastal and Shelf Science》2009

The ontogenetic, seasonal, bathymetric and regional variations in the feeding spectrum of 922 specimens of southern blue whiting Micromesistius australis and 512 specimens of hoki Macruronus magellanicus were studied on the Falkland Islands’ shelf (Southwest Atlantic) between November 1999 and April 2003. A total of 49 different prey items were found in the stomach contents of the two species, with the hyperiid Themisto gaudichaudii and Euphausiacea being amongst the most important prey. Although the species composition did not change over fish size, the proportions of individual prey items in their diets did, with an increase in T. gaudichaudii and Euphausiacea with increasing fish size in southern blue whiting. The opposite occurred in hoki. Seasonal variations in the diet were found to mirror the seasonal abundance of prey around the Falkland Islands for the two species. Intra-specific differences in the diet of both predators reflected the distribution of prey, which in turn was determined by the water structure in the two regions sampled, leading to very different diets. In the limited time that the two species occupied the same space there was little or no competition resulting in almost total segregation of their trophic niches in space and time.  相似文献   

New UV-source catalogs,UV spectral database,UV variables and science tools from the GALEX surveys     

Luciana Bianchi  Alexander de la Vega  Bernard Shiao  Ralph Bohlin 《Astrophysics and Space Science》2018,363(3):56

We present a new, expanded and improved catalog of Ultraviolet (UV) sources from the GALEX All-Sky Imaging survey: GUVcat_AIS (Bianchi et al. in Astrophys. J. Suppl. Ser. 230:24, 2017). The catalog includes 83 million unique sources (duplicate measurements and rim artifacts are removed) measured in far-UV and near-UV. With respect to previous versions (Bianchi et al. in Mon. Not. R. Astron. Soc. 411:2770 2011a, Adv. Space Res. 53:900–991, 2014), GUVcat_AIS covers a slightly larger area, 24,790 square degrees, and includes critical corrections and improvements, as well as new tags, in particular to identify sources in the footprint of extended objects, where pipeline source detection may fail and custom-photometry may be necessary. The UV unique-source catalog facilitates studies of density of sources, and matching of the UV samples with databases at other wavelengths.We also present first results from two ongoing projects, addressing respectively UV variability searches on time scales from seconds to years by mining the GALEX photon archive, and the construction of a database of ～120,000 GALEX UV spectra (range ～1300–3000 Å), including quality and calibration assessment and classification of the grism, hence serendipitous, spectral sources.  相似文献   

An Anisotropic Cosmic-Ray Enhancement Event on 07-June-2015: A Possible Origin     

Agnieszka Gil  Gennady A. Kovaltsov  Vladimir V. Mikhailov  Alexander Mishev  Stepan Poluianov  Ilya G. Usoskin 《Solar physics》2018,293(11):154

A usual event, called anisotropic cosmic-ray enhancement (ACRE), was observed as a small increase (\({\leq}\,5\%\)) in the count rates of polar neutron monitors during 12?–?19 UT on 07 June 2015. The enhancement was highly anisotropic, as detected only by neutron monitors with asymptotic directions in the southwest quadrant in geocentric solar ecliptic (GSE) coordinates. The estimated rigidity of the corresponding particles is \({\leq}\,1\) GV. No associated detectable increase was found in the space-borne data from the Geostationary Operational Environmental Satellite (GOES), the Energetic and Relativistic Nuclei and Electron (ERNE) on board the Solar and Heliospheric Observatory (SOHO), or the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instruments, whose sensitivity was not sufficient to detect the event. No solar energetic particles were present during that time interval. The heliospheric conditions were slightly disturbed, so that the interplanetary magnetic field strength gradually increased during the event, followed by an increase of the solar wind speed after the event. It is proposed that the event was related to a crossing of the boundary layer between two regions with different heliospheric parameters, with a strong gradient of low-rigidity (\({<}\,1\) GV) particles. It was apparently similar to another cosmic-ray enhancement (e.g., on 22 June 2015) that is thought to have been caused by the local anisotropy of Forbush decreases, with the difference that in our case, the interplanetary disturbance was not observed at Earth, but passed by southward for this event.  相似文献   

Comment on “Chelyabinsk,Zond IV,and a possible first-century fireball of historical importance”     

William K. Hartmann  Alexander Forte  Alina SABYR 《Meteoritics & planetary science》2018,53(10):2243-2246

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Origin and transportation history of lunar breccia 14311          下载免费PDF全文

Renaud E. Merle  Alexander A. Nemchin  Martin J. Whitehouse  Robert T. Pidgeon  Marion L. Grange  Joshua F. Snape  Fiona Thiessen 《Meteoritics & planetary science》2017,52(5):842-858

In this paper, we compare the U‐Pb zircon age distribution pattern of sample 14311 from the Apollo 14 landing site with those from other breccias collected at the same landing site. Zircons in breccia 14311 show major age peaks at 4340 and 4240 Ma and small peaks at 4110, 4030, and 3960 Ma. The zircon age patterns of breccia 14311 and other Apollo 14 breccias are statistically different suggesting a separate provenance and transportation history for these breccias. This interpretation is supported by different U‐Pb Ca‐phosphate and exposure ages for breccia 14311 (Ca‐phosphate age: 3938 ± 4 Ma, exposure age: ~550–660 Ma) from the other Apollo 14 breccias (Ca‐phosphate age: 3927 ± 2 Ma, compatible with the Imbrium impact, exposure age: ~25–30 Ma). Based on these observations, we consider two hypotheses for the origin and transportation history of sample 14311. (1) Breccia 14311 was formed in the Procellarum KREEP terrane by a 3938 Ma‐old impact and deposited near the future site of the Imbrium basin. The breccia was integrated into the Fra Mauro Formation during the deposition of the Imbrium impact ejecta at 3927 Ma. The zircons were annealed by mare basalt flooding at 3400 Ma at Apollo 14 landing site. Eventually, at approximately 660 Ma, a small and local impact event excavated this sample and it has been at the surface of the Moon since this time. (2) Breccia 14311 was formed by a 3938 Ma‐old impact. The location of the sample is not known at that time but at 3400 Ma, it was located nearby or buried by hot basaltic flows. It was transported from where it was deposited to the Apollo 14 landing site by an impact at approximately 660 Ma, possibly related to the formation of the Copernicus crater and has remained at the surface of the Moon since this event. This latter hypothesis is the simplest scenario for the formation and transportation history of the 14311 breccia.  相似文献   

青藏高原东缘活动构造   总被引：74，自引：0，他引：74  

周荣军  李勇  Michael A.Ellis  何玉林  王凤林  黎小刚 《矿物岩石》2006,26(2):40-51

青藏高原东缘由岷山断块和龙门山构造带构成。以活动构造地貌学为主线,在解析该地区主干断裂晚第四纪以来活动的地质地貌表现的基础上,对一批断裂运动学和史前强震活动的定量数据进行分析研究,结果表明:在岷山断块中,虎牙断裂的平均左旋滑动速率为1.4 mm/a,垂直滑动速率为0.3 mm/a。岷江断裂的平均垂直滑动速率介于0.37 mm/a~0.53 mm/a之间,左旋位错量与垂直位错量大致相当;在龙门山构造带中,茂汶-汶川断裂、北川-映秀断裂和彭县-灌县断裂的平均垂直滑动速率均在1 mm/a左右,且几条主干断裂的右旋位错量与垂直位错量相当。结合震源机制解结果和GPS测量资料,建立晚新生代以来青藏高原东缘向南东方向逸出的构造变形模式。  相似文献   

Campanian Climatic Change: Isotopic Evidence from Far East, North America, North Atlantic and Western Europe     

Yuri D. Zakharov  Yasunari Shiget  Kazushige Tanabe  Yasuhiro I  Olga P. Smyshlyaev  Ekaterina A. Sokolov  Alexer M. Popov  Tatiana A. Velivetskay  Tamara B. Afanasyeva 《《地质学报》英文版》2007,81(6):1049-1069

Paleoclimatic settings have been reconstructed for the Campanian using original oxygen-isotopic analyses of well-preserved molluskan and foraminifera shells from Russian Far East, Hokkaido, USA, Belgium and some DSDP holes (95, 98, 102, 390A, and 392A) in North Atlantic. Early Early Campanian climatic optimum has been recognized from data on high bottom shelf water paleotemperatures in middle latitudes of both the western circum-Pacific (to 24.2°C) and the eastern circum-Pacific (to 26.4°C) areas and high bottom shallow water paleotemperatures in high latitudes of the Koryak Upland (22.4–25.5°C), which agrees with the data on the Campanian Barykovskaya flora in high latitudes (Golovneva and Herman, 1998) and Jonker flora and its equivalents in middle latitudes. Judging from the data on comparatively high bottom shallow water paleotemperature values in high latitudes, South Alaska (19.4°C) and the Koryak Upland (22.4–25.5°C), we also expect Latest Campanian temperature maximum, which has not been confirmed, however, for low and middle latitudes by neither of isotopic nor paleobotanic data now. Main climatic tendency during the Campanian (with the exception of Latest Campanian) has been learned from isotopic composition of Campanian aragonitic ammonoid shells from the Hokkaido-South Sakhalin (Krilyon) marine basin. In contrary to Huber’s et al. (2002) assumption, we expect warm greenhouse conditions during the most part of the Campanian.  相似文献   

Dynamic propagation criteria for catastrophic failure in planar landslides          下载免费PDF全文

Wangcheng Zhang  Dong Wang  Mark F. Randolph  Alexander M. Puzrin 《国际地质力学数值与分析法杂志》2016,40(17):2312-2338

Quantitative assessment of the risk of submarine landslides is an essential part of the design process for offshore oil and gas developments in deep water, beyond the continental shelf. Landslides may be triggered by a reduction in shear strength of subsea sediments over a given zone, caused for example by seismic activity. Simple criteria are then needed to identify critical conditions whereby the zone of weakness could grow catastrophically to cause a landslide. A number of such criteria have been developed over the last decade, based either on ideas drawn from fracture mechanics, or considering the equilibrium of the initial weakened zone and adjacent process zones of gradually softening material. Accounting for the history of the weak zone initiation is critical for derivation of reliable propagation criteria, in particular considering dynamic effects arising from accumulating kinetic energy of the failing material, which will allow the failure to propagate from a smaller initial zone of weakened sediments. Criteria are developed here for planar conditions, taking full account of such dynamic effects, which are shown to be capable of reducing the critical length of the softened zone by 20% or more compared with criteria based on static conditions. A numerical approach is used to solve the governing dynamic equations for the sliding material, the results from which justify assumptions that allow analytical criteria to be developed for the case where the initial softening occurs instantaneously. The effect of more gradual softening is also explored. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Magma chambers and localization of deformation during thrusting     

Domenico Montanari  Giacomo Corti  Alexander Simakin 《地学学报》2010,22(5):390-395

Terra Nova, 22, 390–395, 2010 Abstract We present the results of coupled analogue and numerical models that provide new insights into the relationships between volcanoes and thrusts. The effects of both upper‐crustal magma chambers and the load of volcanoes on the geometry of thrust systems were investigated. Analogue modelling points to a strong influence exerted by a magma chamber on thrust geometry, which, as suggested by the numerical models used to rationalize these results, is related to the stress redistribution around the weak heterogeneity. The low‐viscosity body below a volcanic edifice localizes compressional deformation and causes a curvature of the thrusts towards the magma chamber, opposite to the direction of tectonic transport. In these conditions, the volcanic load has a negligible effect on the structural geometry. These results are in contrast with those of previous studies, where intrusions or the load of major volcanoes generated a curvature of the thrusts away from volcanic edifices in the direction of tectonic transport.  相似文献