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Essentially all marine mining along the East and Gulf coasts of the U.S. is for sand used in beach nourishment projects. The current minimal commercial production of sand and aggregate may increase as conventional, on-shore sources become exhausted or are lost to competing land use. Studies published in the late 1990s document a history of nearly 900 individual episodes of beach nourishment having a total cost in excess of $2 × 109 with several hundred million cubic meters of sand placed along over 645 km (400 mi) of shoreline. As exemplified by studies in Florida, prospecting for sand for use in beach nourishment can begin before site specific needs are identified. A full prospecting starts with assimilation of pertinent literature, local knowledge, and an understanding of the geologic and geomorphic settings in which suitable deposits of sand or aggregate occur. High-resolution seismic profiling follows to outline the three dimensional extent of the sand bodies. Finally, vibratory cores are collected to verify the interpretation of the seismic data and to provide samples for geotechnical, especially granulometric, analyses. The actual method of production often is determined by the local availability of different dredge types. Because the mining of marine sands disturbs meaningful areas of the sea floor, environmental concerns must be considered. While it generally is assumed that dredged areas will be left barren, it is possible to assess the likely rate of recolonization. The disruption of bottom habitat also can affect feeding and spawning areas for fishes and other organisms. Alteration in local currents and wave transformation processes need to be modeled and their consequences assessed. 相似文献
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Izvestiya, Atmospheric and Oceanic Physics - 相似文献
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Seventeen piston cores were collected at 25-km intervals following the 3500-m isobath along a 400-km portion of the continental rise off the southeastern United States. The area extends between the Hatteras Canyon System and the tip of the Blake Outer Ridge. This study evaluates the mechanisms of rise formation over a large continental-rise area.From north to south, the calcium-carbonate content increases, minerals indicative of a northerly source are partially replaced by minerals more representative of the southern U.S. and Caribbean, and the sedimentation rate decreases. No identifiable turbidites were noted in any of the cores. Coarse-grained layers are infrequent; most are less than 2 cm in thickness and none showed grading. Radiography of several cores revealed mottling throughout. Bottom photographs show that present bottom-current movement closely parallels contours and flow is in a general southerly direction.The results indicate that contour-following bottom currents are primarily responsible for shaping this part of the U.S. Atlantic rise. Turbidity currents may be important only as a source of sediment, via overflows, to be transported south by bottom currents. 相似文献
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Janet M. Bradford‐Grieve 《新西兰海洋与淡水研究杂志》2013,47(4):781-793
Two species of benthopelagic calanoid Copepoda, Neoscolecithrix cf. magna (Grice, 1972) and N. ornata n. sp., are described from the upper slope off North Cape, New Zealand. Neoscolecithrix ornata is distinguished from other species of Neoscolecithrix Canu, 1896 s.s. that have a female leg 5 terminal segment with 4 spines (2 terminal and 1 on each border) principally by the transverse row of long, fine spines on the female genital double somite; and by the more squat terminal segment of leg 5 (length/width ratio about 3.7). This is the second time Neoscolecithrix has been recorded from New Zealand. A new genus, Cenognatha n. gen., is distinguished from Neoscolecithrix principally because: rostrum short (bearing 2 filaments); mandibu‐lar gnathobase masticatory margin with slender dorsal spinulose seta; maxilla endite 1 with 5 well‐developed setae, endite 3 without brush‐like sensory seta, endopod usually with 3 long worm‐like sensory setae and 5 brush‐like setae; posterodistal border of basis of legs 1–3 without spines; distal segment of female leg 5 and its basis subequal in length; male leg 5 of similar lengths on both sides (styliform on right), endopod present at least on 1 side, 1‐segmented and spine‐like on right. 相似文献
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Takashi Ichiye 《Journal of Oceanography》1980,36(2):105-120
Non-dimensional equations of motion are derived for the A.C.C. of the barotropic mode, including the bottom friction and the horizontal eddy viscosity. Integration of the vorticity equation along a streamline leads to the zeroth order stream function which is dependent only on depth divided by Coriolis parameter. Integration of the momentum equation along a streamline yields the relation between the momentum input by wind stress and its dissipation by the bottom friction and by the horizontal eddy viscosity. This relation determines the magnitude of the stream function. It explains differences in the total transport of the A.C.C. obtained byBryan andCox (1972), though it gives only one third of the total transport obtained byKamenkovich (1972) with his vertical eddy viscosity of 102cm2 s?1. With 1 cm2 s?1 of this viscosity,Bryan andCox obtained the transport of about 650 or less than 32×106m3s?1 for constant or variable depth models, respectively. The higher transport is mainly due to broadening of the width of the A.C.C., whereas the lower value is due to its narrowing and meandering which in turn make the horizontal eddy viscosity more effective (by exercising friction on both sides of the A.C.C.) and the wind stress input smaller than the almost zonal streamlines for constant depth. In the Appendix dynamics of the bottom boundary layer is treated to give rational estimates of the bottom stress in terms of the geostrophic flow and is compared to the recent observations of the benthic boundary current in the Straits of Florida and off San Diego. 相似文献
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Francisco Benítez-Villalobos Julia P. Díaz-Martínez 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(1):157-161
We analysed the reproductive biology of the asteroid species Styracaster elongatus based on time-series samples from a 5000-m-deep site on the Porcupine Abyssal Plain (N.E. Atlantic). The ratio of males to females, the gonadosomatic index (GI), and pyloric caecum index (PCI) were determined and the results were corroborated by histological examination of the gonads. Fecundity and oocyte-size distribution were determined by histological and image analyses. Styracaster elongatus is a gonochoric asteroid and the ratio of males to females was not significantly different throughout the year. Oogenesis was asynchronous. The previtellogenic oocytes grew to a size of ～230 μm before undergoing vitellogenesis. Maximum oocyte size was ～620 μm. The ovary volume was mainly occupied by small previtellogenic oocytes (100–150 μm) at any one time. Mean GI was 6.38±3.30 for females and 9.04±4.1 for males. Mean PCI was 7.44±1.66 for females and 7.66±1.46 for males. Mean fecundity was 16,373±5988 oocites per female. There were no seasonal variations in GI and fecundity. There was evidence of a pyiloric caecum seasonal development for females and males. For S. elongatus there is no direct relationship among seasonal primary production at the surface and production of vitellogenic oocytes. Nevertheless, this species takes advantage of the pulse of phytodetritus to the seabed by increasing the storage of nutrients in the pyloric caecum in order to maintain a constant production of eggs and sperm. 相似文献
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《Marine Policy》2015
Feedbacks occur when advocates engage to clarify the implementation of a policy innovation such as the requirement that federal activities be consistent with objectives of state coastal management plans. Discrete policy feedbacks include advocacy, litigation, appeals of decisions as well as other activities inserted into policy implementation by interests or government agencies acting in their behalf. Feedback analysis is applied to the time after the passage of the 1972 U.S. Coastal Zone Management Act. Conflicts after passage of the law resulted in a negative feedback in the form of a Supreme Court decision in 1984 and a subsequent positive feedback through the 1990 revision of the law effectively reversing the Court decision. New insights documented here suggest that feedback switching, wherein old disputes are moved to new arenas, provides the greatest opportunity for overcoming negative feedbacks that could diminish or eliminate the policy innovation. Furthermore observing feedbacks through time and across multiple policy spaces as demonstrated here provides a robust interpretation of policy evolution from a new perspective. This analysis demonstrates how feedbacks convert a voluntary state program into one with authority over certain federal actions. These findings will be important for other areas of coastal policy and, more broadly, policy evolution in general. 相似文献
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《中国海洋大学学报(自然科学版)》2015,(12)
本文在前人对黄土高原灵台剖面的研究基础上,以磁化率、平均粒径分别作东亚夏、冬季风替代指标,采用经验模态分解(Empirical Mode Decomposition,EMD)方法对其粒径、磁化率时序进行不同时间尺度周期的分离,以探讨7百万年来东亚冬、夏季风演化时频特征及其主要天文控制因子。结果表明,EMD方法可以灵敏地捕捉到东亚冬、夏季风"Milankovitch天文周期"(如~2万年、~4万年、~10万年等典型轨道周期),特别是~40万年、~100万年等偏心率长周期,且与传统的Blackman-Tukey功率谱分析的结果基本吻合;天文长周期对东亚冬、夏季风的影响不可忽视。 相似文献
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海带和长海带配子体无性繁殖系微卫星DNA多态性比较分析 总被引：1，自引：0，他引：1
探讨促进海带配子体克隆资源的有效保存和合理利用途径,进行海带良种和杂交海带培育,开发了18个海带微卫星DNA标记,并用这些标记分析了海带和长海带配子体克隆的遗传多样性.这些标记相互独立,至少在1个物种中呈多态性.在36份海带配子体中,这些标记检测到的等位基因数量从2～7个不等,揭示的基因多样性在0.21(H144)和0.75(H120)之间,揭示的香农氏信息指数在0.37(H144)和1.55(H120)之间.长海带和海带的平均等位基因数(1.5/3.3),平均基因多样性(0.12/0.45)和平均香农氏信息指数(0.20/0.81)显著不同.根据总样本确定的前2个最丰富等位基因中,绝大多数的频率在长海带和海带之间存在显著差异.长海带和海带之间在基因多样性和香农氏信息指数反映的遗传多样性上的平均遗传分化分别达35.6%和36.9%. 相似文献
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Brenninkmeijer K. A. M. Ginzburg A. S. Elansky N. F. Mokhov I. I. 《Izvestiya Atmospheric and Oceanic Physics》2021,57(1):1-17
Izvestiya, Atmospheric and Oceanic Physics - This is the introductory article for the special issue of Izvestia, Atmospheric and Oceanic Physics dedicated to the 2019 Lomonosov Gold Medal of the... 相似文献
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The U.S. government requires renewable energy facilities installed in federal waters provide financial security to help ensure decommissioning obligations are carried out in the event the operator is unable to meet its obligations or goes bankrupt. The size of the bond is determined by the estimated decommissioning cost and is required prior to the approval of construction activities. The purpose of this paper is to develop decommissioning cost estimates for proposed U.S. offshore wind farms. Removal and site clearance cost are estimated across each stage of activity using empirical and hypothetical relations under current technology and market conditions without inflationary adjustment. Preliminary development plans characterize and define the system and serve as model input. A bottom-up approach based on operational stages is developed across removal, transport, processing and disposal activities. Disposal cost is calculated on a per ton basis and is estimated separately for each wind farm component. The model is parameterized with data from four proposed U.S. offshore wind farms and decommissioning costs are found to range from 115,000 to 135,000 $/MW, approximately 3-4% of estimated capital costs. 相似文献
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《Marine Policy》2013
Bycatch presents a challenge to optimizing yield in commercial fisheries, where bycatch can total more than 1 million mt per year in the United States. Yet the economic impacts of bycatch have rarely been evaluated in the scientific literature. These economic impacts largely occur from the loss of landings through (1) early closure of fisheries when catch limits of bycatch species are reached; and (2) discards of marketable catch due to regulatory requirements in the fishery. This paper illustrates the economic impacts of early closures due to bycatch in U.S. fisheries by describing past case studies, as well as evaluating the economic impacts of discarding fish in U.S. commercial fisheries. Premature closures in the fisheries reviewed resulted in potential losses ranging from $34.4 million to $453.0 million annually. Nationally, bycatch estimates in the form of regulatory discards are annually reducing the potential yield of fisheries by $427.0 million in ex-vessel revenues, and as much as $4.2 billion in seafood-related sales, $1.5 billion in income, and 64,000 jobs. Our review also shows that some of the most promising work to reduce bycatch over the last decade has been the development of gears or gear modifications, termed “conservation engineering.” 相似文献