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1.
我国渤海湾是地震多发地区 ,该地区的海底输油管线随时都面临地震的威胁。地震成为渤海输油管线必要的设计条件 ,地震载荷是在役管线安全风险评估必须包括的环境载荷。本文综述了国内外在管线抗震设计及相关研究、双层油气管线的工作理论、强度标准与损伤评判等方面的研究工作 ,对我国制定地震条件下海底管线的评估计算方法、管线的抗震设计准则以及地震灾害的防治与风险分析具有一定的参考价值  相似文献   

2.
The magnetic properties from 200 trigger core-top and Van Veen grab sediment samples recovered from throughout the Gulf of Mexico have been analyzed and used to characterize sediment source and flow pattern distributions. Magnetic parameters included are anhysteretic remanent magnetism (ARM) and magnetic susceptibility (MS) measurements. Results from these measurements are compared to previously determined calcium carbonate percentages, and clay and hematite influx trajectories into the Gulf of Mexico for the same samples reported by Balsam and Beeson [Balsam, W.L. and Beeson, J.P., 2003. Sea-floor sediment distribution in the Gulf of Mexico, Deep-Sea Res. I, 50, 1421–1444.]. The ARM results give an estimate of magnetic grain size distributions, and by analogy, grain size distributions in general, whereas MS patterns show high detrital sediment accumulation zones within the Gulf. The dominant influx of modern high susceptibility sediment into the Gulf of Mexico appears to originate from the Red River, flow into Atchafalaya River Basin and out into the Gulf from Atchafalaya Bay, with significant additional contributions from the Mississippi River through the Southwest Pass of the Mississippi River Delta. This material then moves across the continental shelf and down through the Mississippi Canyon into the deep Gulf where it is redistributed at depths > 3600 m. The eastern shelf margins in the Gulf, offshore from Alabama and Florida, are accumulating calcite- or quartz-rich medium to fine-grained sediment that has a very low or diamagnetic MS signature. From the Louisiana to Texas Gulf coast margins, MS is moderate to high, suggesting a river influx of magnetic constituents from the volcanic fields in New Mexico, and from igneous and metamorphic sources in the Mississippi Basin. Offshore from western Mexico, the MS is high to moderate, but the Yucatan Shelf margin is characterized by low to diamagnetic MS values due to sediment dominated by calcite sands and oozes, a trend that continues to the east onto the West Florida Shelf. Additional measurements of samples collected in association with sites characterized by hydrocarbon seepage exhibit anomalously low MS values. The samples from the lower shelf and slope areas are typified by iron reduction by bacterial organisms in these samples. These results produce anomalous localized lows in the MS trends observed.  相似文献   

3.
Submarine canyons and associated submarine fans are in some cases located at the end of a littoral cell where they act as conduits for the transfer of eroded terrigenous sediments to the marine environment. Such fans are generally found in deep-water settings at >500 m water depth. Offshore the Moisie River Delta (NW Gulf of St. Lawrence, Eastern Canada), high-resolution multibeam bathymetry and seismic data led to the discovery of an unusually shallow submarine fan (≤60 m) located at the end of a littoral cell. Sediment is transported westward on the shallow coastal shelf, as demonstrated by the downcurrent displacement of oblique nearshore sandbars where the shelf narrows to less than 1 km. The steep slope near the end of the littoral cell is incised by a channel that feeds a submarine fan composed of smaller channels and depositional lobes. According to existing Holocene evolution models for the region, the fan formed within the last 5,000 years. Its evolution is largely due to the transport of sediment by longshore drift. Multibeam echosounder and seismic data also reveal that the gravity-driven accretion of the submarine fan is characterized mainly by two processes, i.e., frequent small-scale, downslope migration of sandwaves on the slope, and more episodic slumping/turbidity-current activity in the deeper part of the fan. This study documents that, besides their common deep-water location, smaller-scale submarine fans can occur also in very shallow water, implying that they could be more frequent than previously thought both in modern environments and in the rock record.  相似文献   

4.
The use of artificial reefs in the Arabian Gulf have a history extending back over a century, when date palm trunks, stones, pottery and other materials were sunk in coastal areas to enhance fish catch. Historically, such artificial reefs formed an important component of the socio-economic development of coastal fisheries. In comparison, modern artificial reefs have taken on a variety of forms. The most widely recognized are purpose-build modular artificial reefs designed for the enhancement of fisheries yield, diving, and various other benefits. However, far more common within the Gulf are the large-scale unplanned artificial reefs that have been formed as a result of human activities in the marine system, such as large-scale coastal breakwaters, seawalls, jetties, pipelines, and oil and gas infrastructure. Although there is limited information on the role of these constructions in structuring Gulf marine communities, increasing evidence suggests that abundant and diverse communities of reef fish, coral and other benthos can develop on these structures, with important ecological implications in urbanized coastal areas in the Gulf. However, due to a variety of unintended consequences of artificial reef development such structures may also pose challenges to coastal marine management. We review the current published literature on artificial reefs in the Gulf in order to improve our understanding of the role that these structures play in Gulf coastal ecosystems, and to further develop regional management of artificial reefs. We explore the various types of artificial reef that exist in the Gulf and examine the benefits and challenges that these structures represent for coastal ecology and economics. Such information is essential for our improved understanding and management of these increasingly important ecosystems in the Gulf.  相似文献   

5.
In certain regions,submarine groundwater discharge(SGD) into the ocean plays a significant role in coastal material fluxes and their biogeochemical cycle;therefore,the impact of SGD on the ecosystem cannot be ignored.In this study,SGD was estimated using naturally occurring radium isotopes(~(223)Ra and ~(224)Ra) in a subtropical estuary along the Beibu Gulf,China.The results showed that the Ra activities of submarine groundwater were approximately 10 times higher than those of surface water.By assuming a steady state and using an Ra mass balance model,the SGD flux in May 2018 was estimated to be 5.98×10~6 m~3/d and 3.60×10~6 m~3/d based on ~(224)Ra and ~(223)Ra,respectively.At the same time,the activities of Ra isotopes fluctuated within a tidal cycle;that is,a lower activity was observed at high tide and a higher activity was seen at low tide.Based on these variations,the average tidal pumping fluxes of SGD were 1.15×10~6 m~3/d and 2.44×10~6 m~3/d with ~(224)Ra and ~(223)Ra,respectively.Tidaldriven SGD accounts for 24%-51% of the total SGD.Therefore,tidal pumping is an important driving force of the SGD in the Dafengjiang River(DFJR) Estuary.Furthermore,the SGD of the DFJR Estuary in the coastal zone contributes significantly to the seawater composition of the Beibu Gulf and the material exchange between land and sea.  相似文献   

6.
Surveys were conducted in four seasons in the eastern Beibu Gulf from July 2006 to November 2007,to determine the ichthyoplankton composition,abundance,as well as environmental factors impacted on their spatiotemporal distributions.The fish eggs and larvae were sorted from 303 zooplankton quantitative samples,in which at least 1 order,60 families,31 genera and 61 species of fish eggs and larvae were identified.The species number was highest in summer whereas lowest in winter.With the most abundant fish egg (the average density was 2.41 ind./m 3),spring was the main spawning season,while the greatest mean density of fish larva was 1.35 ind./m 3 in summer.In the whole year around,fish eggs had the trends to aggregate in the nearshore of Guangxi coast,fish larvae were more abundant in the northern water.Relationships between fish eggs and larvae abundance and environmental factors were analyzed by using the Yield-Density model.The spatiotemporal distribution of ichthyoplankton in eastern Beibu Gulf was closely related to the Chl a concentration,and the optimal temperature,salinity and Chl a were 19.4-21.7 C,31.8-33.1 and 1.5-4.8 mg/m 3,respectively.Additionally,the distribution of fish larvae could be effected by ocean currents in summer and autumn.  相似文献   

7.
珠江口盆地陆架坡折带海底滑坡及其影响因素   总被引：3，自引：1，他引：2  
为了解海底滑坡在陆架坡折演化过程中所起的作用并分析影响海底滑坡发育的因素,以最新采集的二维和三维地震资料为基础,综合运用了地貌分析和地震解释技术,通过对滑坡的地貌形态特征及地震响应特征进行详细刻画,在珠江口盆地陆架坡折带新近纪地层中识别出多处海底滑坡,明确了其分布范围并建立了滑坡发育的地质模式。分析认为,珠江口盆地相对海平面变化和流体活动的综合作用是导致研究区海底不稳定的主要因素。海底滑坡发源于海底峡谷的朔源侵蚀,向上陆坡扩展并终止于陆架坡折带。  相似文献   

8.
Abstract

Submarine trenching for pipeline installation in potentially unstable sediments has recently been of increasing concern. Although typical pipeline depths are less than 3 or 4 m, trenching operations generally cause local stress concentrations within the sediments and induce excess pore pressures. The result of these stress concentrations and pore pressure increases may be spreading of submarine slumps that can endanger pipelines or other nearby installations. A simplified analytical approach is described to estimate the extent of slump spreading caused by trenching. It is shown that the spreading potential is affected by many geotechnical characteristics of the sediments in addition to geomorphic processes and the oceanographic regimes governing the area. The primary geotechnical factors that influence spreading include the porepressure parameter Af , the degree of consolidation, the coefficient of earth pressure at rest, and the strength characteristics of the soil. Dimensionless parameters are developed to illustrate graphically the functional relationships among these parameters. A Gulf of Mexico soil profile is used to quantify the spreading phenomenon.  相似文献   

9.
琼东南盆地深水区新近系海底扇沉积特征与资源潜力   总被引：1，自引：1，他引：0  
综合利用钻井、岩心、薄片及分析化验资料研究了琼东南盆地深水区新近系海底扇沉积特征,并利用最新的三维地震资料,通过井震精细标定、多属性融合技术、方差体切片、三维地貌砂体镂空等综合技术手段,精细刻画了海底扇砂体的空间分布特征。研究结果表明,深水区新近系海底扇是由陆架区的砂体滑塌并二次搬运形成,形成过程具有多期次性。受不同物源的影响,海底扇岩性和物性存在较大的差异。海底扇岩性及沉积构造具有砂质滑塌、碎屑流、浊流和深水底流改造的特征。海底扇的沉积微相、厚度、砂泥比和砂泥岩空间配置关系直接控制了地震振幅反射强度和频率的变化。砂体纵向叠置,横向连片,并被后期泥质水道切割分块形成多个岩性圈闭。综合分析认为,深水区海底扇砂体发育区烃源条件优越,储盖配置关系和圈闭条件良好,具备形成大中型岩性油气藏的有利条件,具有较大的油气勘探潜力。  相似文献   

10.
Recently acquired (2005) multi-beam bathymetric and high-resolution seismic reflection data from the E–W-oriented Gulf of Gökova off SW Anatolia were evaluated in order to assess the uneven seafloor morphology and its evolution in terms of present-day active regional tectonics. Stratigraphically, the three identified seismic units, i.e., the basement, deltaic sediments deposited during Quaternary glacial periods, and modern gulf deposits, are consistent with those observed in previous studies. Structurally, the folds and faults with strike-slip and reverse components have been regionally mapped for the first time. Of these, NE–SW-oriented left-lateral strike-slip faults with compressional components forming the so-called Gökova Fault Zone intersect and displace two WNW–ESE-oriented submarine ridges and deep submarine plains. Thus, strike-slip faults are the youngest major structures in the gulf, and control present-day active tectonism. E–W-oriented folds on the inner and outer shelf, which are generally accompanied by reverse faults, delimit the margins of these submarine ridges, and deform the young basin deposits. These features also reveal the concomitant existence of a compressional tectonic regime. The compressional structures probably represent pressure ridges along left-lateral strike-slip fault segments. However, some E–W-oriented normal faults occur on the northwestern and partly also southern shelf, and along the borders of the adjacent deep submarine plains. They are intersected and displaced by the strike-slip faults. The lower seismicity along the normal faults relative to the NE–SW-oriented strike-slip faults suggests that the former are at present inactive or at least less active.  相似文献   

11.
墨西哥湾波候统计特性分析   总被引：2，自引：0，他引：2  
简要介绍了波候的概念,简述Ｗｅｉｂｕｌｌ分布及对数一正态分布的拟合方法,提出最大熵分布拟合有效波高、峰周期分布的新方法;选取半封闭海湾墨西哥湾内水深不同、地理位置不同的六个观测站一年的连续资料,以上述三种拟合方法对其有效波高,峰周期概率分布进行拟合,并与观测直方图进行比较检验,结果表明,在墨西哥海湾内,最大熵分布优于对数－正态分布,对数－正态分布优于Ｗｅｉｂｕｌｌ分布。  相似文献   

12.
The distributions of iodide, iodate and total iodine were determined along a transect from the Sargasso Sea and across the Gulf Stream to the continental shelf of the South Atlantic Bight during November 1990. The western boundary of the Gulf Stream at the outer shelf-upper slope was characterized by steeply sloping isotherms and isopleths of iodide and iodate, resulting from a dome of cold water that was rich in iodate and nearly devoid of iodide at the slope. Both the mid and the inner shelf were relatively well mixed vertically. The concentration of iodate in the surface waters decreased shoreward from >0.3 μM in the Sargasso Sea/Gulf Stream/outer shelf, to 0.29 μM in the midshelf, 0.19 μM in the outer-inner shelf and 0.11 /IM in the inner-inner shelf. Concomitantly, the concentration of iodide increased from <161 nM to 175 nM, 257 nM and 300 nM. The concentration changes were more abrupt in the inner-inner shelf within about 30 km from the shore. There was no evidence of significant concentrations of organic iodine. These distributions of iodide and iodate suggest that the South Atlantic Bight may act as a geochemical processor of dissolved iodine. Iodate is added to the shelf during topographically induced upwelling and frontal exchange with the Gulf Stream. In the shelf waters, iodate is reduced to iodide in situ. Iodide is exported from the shelf to the Gulf Stream which may eventually further transport it to the ocean interior. A ☐ model calculation suggests that 28% and 43% of the iodate added to the Bight and the inner shelf, respectively, are converted to another form in these waters, almost all of which is iodide. About a third of the reduction of iodate to iodide in the Bight occurs in the inner shelf. Thus, the inner shelf may be the most geochemically active zone within the Bight. The residence times of iodide relative to its production and that of iodate relative to its removal are 3.1 and 3.6 months in the Bight and 0.9 and 1.8 months in the inner shelf.  相似文献   

13.
The potential threat of plastic pollution to seabirds within the Hauraki Gulf was assessed by determining its abundance and distribution at two different spatial scales and assessing the community of resident seabirds during July to September 2008. Samples of floating plastics within the gulf were taken during 66 trawls from the surface of the water in three regions within the inner gulf and Waitamata harbour. Within each of these regions, samples were taken in and outside of visually identified natural slick lines that are surface manifestations of small-scale convergence zones. During each trawl, the identity and abundance of seabirds were assessed. Plastic debris was recorded in all three regions sampled with the greatest abundance being recorded in the harbour. Plastics and debris were also significantly more concentrated within natural slick lines. Both user and industrial plastics were identified and consisted of colours and lengths likely to be mistaken as food items for small to medium seabirds. Surface or near-surface feeding seabirds in the gulf most likely mistakenly to consume plastics were fluttering shearwaters, Cape pigeons and Buller's shearwaters. However, these birds were most abundant in the area of the gulf where abundance of plastic pollution was lowest. The Hauraki Gulf is considered significantly less polluted by plastic debris than other severely polluted areas cited in literature.  相似文献   

14.
Deep sea drilling in the Central Gulf of California, a young and active spreading centre, shows that the high heat flow typical of these regions causes extensive alteration of sediment organic matter, especially near sills and above magma chambers where hydrothermal activity is concentrated. Even on the nearby passive margin, where there are no sills, heat flow is moderately high and hydrocarbon generation has begun in immature sequences. Migrating light hydrocarbons are detected especially where hydrothermal activity is concentrated. Thermogenic methane is more widespread, though not in the passive margin bordering the spreading centre. Despite the incidence of hydrocarbon generation and migration, the amounts of hydrocarbons involved are relatively small and apparently do not lead to commercially significant accumulations of petroleum.The organic matter in these sediments is mostly marine because the Gulf of California generally has low runoff from land and highly productive surface waters. Turbidites rich in terrigenous organic material are locally abundant in the mainly pelagic section in the Guaymas Basin. The highest concentrations of organic matter are found in laminated diatomites deposited on the Guaymas passive margin within the oxygen minimum zone.  相似文献   

15.
The studies carried out by the Karpinskii All-Russia Research Institute of Geology using side-scan profiling, echo sounding, and surface sediment sampling allowed revealing the detailed structure of the underwater coastal slope in the eastern Gulf of Finland. In particular, a submarine sand terrace was found at depths of 4–5 m. An attempt at the reconstruction of the coastal evolution over the period of the Late Holocene was made using mathematical modeling in order to explain the observed morphology of the submarine coastal slope. The key assumption of the concept suggested is that, at the earlier stage, the tectonic processes played the main role, while, at the later stage, the sea-level changes were of greater importance. The tectonic block comprising the investigated area of the Gulf of Finland at first rapidly increased and then it stabilized and was influenced by the sea level’s rise. These processes resulted in the formation of a series of terraces. The earlier of those are now located on dry land, while the later terraces are observed on the submarine slope. Within the concept proposed, the coastal evolution in the Late Holocene appears as a process of the gradual erosion of the above-water terraces and the formation of new underwater terraces. During the transgressive phases, the rate of the coast’s recession reached 0.5 m year−1, while decreasing by a factor of two during the intermediate stages. The submarine terrace developed over the period of 3.2–1.2 thousand years ago, and it extended in equal measure due to the coast’s recession and the material’s accumulation near its external edge. During that period, the coast retreated by approximately 500 m, while the average accumulation rate could have been as high as 0.7 m3 m−1 year−1.  相似文献   

16.
《Progress in Oceanography》2007,72(2-3):214-232
Centropages typicus is one of the most common, abundant and best studied calanoid copepods in neritic waters of the Mediterranean Sea, which means it can provide useful information about the long-term dynamics of the Mediterranean epipelagic ecosystem. This paper presents the first comparative overview of the seasonal and long-term variability of C. typicus in different Mediterranean regions. This review is based on quantitative information from the published literature and novel data from five ongoing zooplankton time-series carried out in the Mallorca Island (Balearic Sea), the Bay of Villefranche (Ligurian Sea), the Gulf of Naples (Tyrrhenian Sea), the Gulf of Trieste (North Adriatic Sea), and the Saronikos Gulf (Aegean Sea). In most Mediterranean regions, C. typicus has a perennial occurrence, with peaks of abundance that reflect the succession of different generations. Throughout the Mediterranean, the annual cycle of C. typicus is characterized by minima in winter and major peaks in April–June, which is earlier than those observed in European Atlantic waters, where the peaks are more frequently recorded in summer and fall. In the regions investigated, the annual cycle shows remarkable similarities in terms of timing, but notable differences in the peak height; populations are far more abundant in coastal north-western regions and less abundant in the eastern basin. In the long-term, changes in C. typicus phenology observed in the Bay of Villefranche and in the Gulf of Naples are related to the North Atlantic Oscillation (NAO) index. In these two regions, the species responds to climate forcing similarly in terms of average seasonal patterns (bi-modal patterns in years of positive NAO, unimodal patterns in years of negative NAO) but oppositely in terms of quantity, indicating different influence of the NAO on the two regions. At decadal scales, C. typicus populations show high interannual variability with marked geographical differences. In some areas, the patterns are clearly characterized by alternate phases of higher and lower annual abundances, at higher frequency (mainly 1–2 years) in the Gulf of Naples, and lower frequency in the Saronikos Gulf (mainly 4–5 years) and in the Gulf of Trieste (mainly 5–6 years). Synchronous phases of increasing or decreasing abundance are discernable only for a few sites and short periods, for example from 1998 to 2000 in the Gulf of Naples, Gulf of Trieste and Saronikos Gulf. The regional differences observed in the long-term patterns of C. typicus populations suggest that the temporal dynamics of this species are significantly more affected by local conditions than by any possible common driving force acting at basin scale through teleconnections.  相似文献   

17.
To date, facies architecture models of submarine channel–levees have largely been derived from seismic data, isolated core data and limited field studies. We report field observations of an Upper Cretaceous submarine channel–levee complex within the Rosario Formation, Baja California, Mexico, which provide high-resolution data of lithofacies and ichnofacies distribution, and levee depositional thickness decay along transects perpendicular to the channel axis. Within the levee, both sandstone thickness and the overall proportion of sandstone decrease according to a power law away from the channel axis. Spatial variation in sedimentary structures away from the channel axis is predictable and provides an important link to the depositional flow regime. In channel-proximal locations, structureless sands, parallel lamination, overturned ripples, and ripple cross-lamination (including climbing ripple cross-lamination) are common; in channel-distal localities starved ripples are abundant. Sandstone bed thickness generally increases up stratigraphy within the levee succession, which is interpreted to indicate increasing turbidity current magnitude and/or contemporaneous channel floor aggradation reducing relative levee relief. However, in the most channel-proximal location sandstone bed thickness decreases with height; combined with evidence from both facies and palaeocurrent analysis this allows the position of the levee crest to be inferred. The thickest beds occur at higher levels with increasing distance from the channel axis, using this evidence we present a model for levee growth and migration of the crest.Quantitative analysis of ichnofacies distribution reveals that traces typical of the Cruziana and Skolithos ichnofacies are superimposed over the ‘normal’ background Nereites ichnofacies, forming a ‘bioturbation front’ which is indicative of proximity to the channel. By analogy with modern canyons and channels, the association of Cruziana and Skolithos ichnofacies with the channel may be attributed to oxygen and nutrient enrichment and possible turbidity current transport of organisms responsible for these ichnofacies.  相似文献   

18.
南海北部湾海洋工程地质特征   总被引：8，自引：0，他引：8  
根据地球物理、声学探测及海底取样等实测资料详细分析,发现北部湾油气勘探开发区具有近岸、水浅等优越自然条件以及复杂的海洋工程地质特征。海底地形地貌较为复杂,存在潮流沙脊与潮沟、海底沙坡、埋藏古河道、浅层气、埋藏古陡坡、滑塌断层及可能的砂土液化层等潜在灾害地质因素,对海上构筑物存在直接或潜在的危险性。尤其在东部,海底坎坷不平,活动性的潮流消脊、侵蚀沟槽、海底沙波及浅层气等很发育,是海底工程建设的危险区,应引起高度重视。  相似文献   

19.
The freshwater discharge from the Gulf of St. Lawrence and Hudson Bay accounts for more than 80% of the total freshwater discharge from eastern Canada and approximately 70% of the total discharge from the eastern seaboard of North America, from Baffin Island to Florida. If the Gulf of Mexico is included, the Gulf of St. Lawrence/Hudson Bay discharge is still more than half of the total.Both the Gulf of St. Lawrence and Hudson Bay have some distinctly estuarine characteristics and discharges of metals can be estimated using estuarine models. For Al, Mn, Fe, Co, Ni, Cu and Zn, the distributions can be described by simple, highly significant relationships with salinity. These regressions can be used in conjunction with knowledge of water discharges to estimate net metal inputs to the North Atlantic from these two systems.Most of the discharge from the Gulf of St. Lawrence flows along the Scotian Shelf to the Gulf of Maine. Metal-salinity relationships can also be used to estimate metal transports through this region for some metals. The applicability of this estuarine model, however, tends to break down as the oceanography becomes more complex and metal distributions are determined more by oceanic rather than estuarine processes.  相似文献   

20.
Chang-Feng  Dai 《Marine Ecology》1993,14(3):185-204
Abstract. The distribution pattern of corals and benthic space partitioning patterns on the fringing reefs of southern Taiwan were studied by the line-transect method. The bathymetric distribution of corals in the study area was basically homogeneous except on the protected reef slopes and the exposed reef fronts and terraces. Corals on protected reef slopes are mainly foliaceous, including Montipora foliosa, Merulina ampliata, Mycedium elephantotus , and Pachyseris speciosa , but the dominant species on a reef slope vary from site to site. The formation of the foliaceous coral community is possibly related to a complex of environmental factors, chance, and biological interactions. The reef fronts and submarine terraces of exposed areas are dominated by alcyonacean corals. The most abundant species are Sarcophyton trocheliophorum, S. crassocaule , and Lobophytum sarcophytoides ; their distributions are relatively homogeneous. The formation of alcyonacean-dominated assemblages can be related to the special adaptive strategies of these corals. In regard to space partitioning patterns, the major space occupiers on those reefs exposed to storm disturbances are alcyonacean soft corals, scleractinian corals, and algae; on reefs protected from storms, scleractinian corals and algae dominate. Two conspicuous features of the study area are the high proportion of space occupied by algae and the abundant unoccupied space. The dense algal cover is possibly caused by sewage pollution and overfishing of the reef area. The unoccupied space is most likely related to the high frequency of typhoon disturbances.  相似文献   

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