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1.
Internal tidal currents are the likely cause of erosional features such as current ripples, sand waves, and truncated bedding horizons on the sediment cap of Horizon Guyot. Current meter data obtained over a 9 month period in 1983–1984 at about 213 m above the guyot show that the tidal currents are anomalously strong for mid-oceanic depths, probably the result of topographically induced generation of internal tidal waves. An analysis of the initiation of motion of the foraminiferal sand by the internal tidal currents indicates that these currents, particularly during the months of March–May, are likely to transport the surficial sediment and generate the observed bedforms. 相似文献
2.
Bin Zhao Yong Yang Gaowen He Heng Zhang Weilin Ma 《Marine Georesources & Geotechnology》2020,38(9):1037-1045
AbstractCobalt-rich crust has attracted increased attention due to their economic value. Studies have indicated that seamounts in the Western Pacific Ocean are rich in cobalt-rich crust resources. The Caiwei Guyot in Western Pacific Ocean is one of the cobalt-rich crust exploration areas contracted between China and the International Seabed Authority. A large volume of research has been conducted to elucidate the tectonic evolution, basement type, sediment type, gravity and magnetic anomaly characteristics, and geochemical characteristics of shallow surface sediments at Caiwei Guyot. However, a research gap exists on the sedimentary strata below the pelagic deposits and above the volcanic basement of the Caiwei Guyot. This paper summarizes that two main types of sediments existing on the top of Caiwei Guyot. The deposition thickness on the top of Caiwei Guyot is characterized by three sedimentary centers and exposed periphery. Pelagic sediments are difficult to form at the northeastern portion and edge area of Caiwei Guyot due to the strong bottom current environment, which makes these areas suitable for crust growth. This paper delineated three cobalt-rich crust prospective areas at the Caiwei Guyot with of significant implications for exploration and mining-lease-block selections at Caiwei Guyot. 相似文献
3.
Sio Guyot, in the westernmost edge of the Mid-Pacific Mountains, is a large, complex volcanic edifice rising to more than 1200 m below sea level. The summit is divided into two flat-topped areas by a WNW-trending sediment-filled trough. Seismic reflection profiles reveal three acoustic units: an upper transparent layer (pelagic cap), a lower opaque layer (reef- and lagoon-derived sediments), and an acoustic (volcanic) basement. Free-air gravity anomalies indicate three eruptive centers or conduits within the main edifice, which apparently was constructed during late Cretaceous time on a broad basement swell or plateau that today is more than 3400 m below sea level (1500 m above regional abyssal depths). 相似文献
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A novel variation of the geophysical technique known as MOSES, for Magnetometric Off-Shore Electrical Sounding, has been developed to map the electrical properties of the sea floor in Aretic regions. The particular target is the permafrost layer under the Beaufort Sea, a layer containing frozen or partially frozen sediment from 100 to 600 m thick underlying shallow sea water, typically 10 to 100 m deep, and several tens of metres of soft sediment. A detailed knowledge of the location and physical properties of the permafrost layer is essential for accurate interpretation of reflection seismic data. The permafrost can contain pockets, regions or layers of gas hydrate. The latter is both a possible resource and a hazard to drilling operations or hydrocarbon production. A local map of the permafrost zone is essential geotechnical information required prior to the construction of an offshore structure or pipeline.The MOSES method is particularly suitable for offshore electrical mapping as it can be made relatively insensitive to the shielding effects of the highly conductive sea water, in sharp contrast to many other electrical techniques. The transmitter is a vertical, long-wire bipole, extending from the sea surface to the sea floor. A commutated current is fed to two large electrodes: one near the sea surface and the other on the sea floor. The return current is through the sea water and the subjacent sediment. The receiver consists of two horizontal orthogonal coils located on the sea floor, and the data are measurements of two components of the magnetic field as a function of frequency and transmitter-receiver horizontal separation.The electrical conductivity of a sample of frozen material is much smaller than that of unfrozen or partially frozen sediment of the same type. Frozen and unfrozen thin layers are often observed sequentially throughout the geological section. The resistivity measured as a function of depth by an electrical logging tool is consequently highly variable. The resulting depth-averaged resistivity, the resistivity resolved by a surface electrical method, is macro-an-isotropic. An experimental design study reveals that both the vertical and horizontal averaged resistivities could be determined in a MOSES sounding without vertical scale distortion.A test of the methodology in very shallow water was conducted in the spring of 1986 at a site, approximate coordinates (70° N, 134.5° W), 85 km north-west of the town of Tuktoyaktuk. The instrumentation was lowered and subsequently recovered through holes in the ice which covers the Beaufort Sea at that time of the year. The transmitter power was obtained from a single lead-acid battery. Transmitter-receiver separations ranged from 10 to 300 m. A rapid increase in sediment resistivity with depth was observed. The higher resistivity values are consistent with those expected for a partially frozen zone. 相似文献
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Side-scan sonar records collected over an area of the North Aleutian Shelf, approximately 250 km west of the head of Bristol Bay, Alaska, identified widespread evidence of active sea floor erosion processes, including sediment transport. Thousands of sea floor depressions, many linear and some containing rippled floors, were identified in water depths of 30 to 90 m. The depressions cover approximately 40 percent of the area surveyed. The sea floor depressions are interpreted to be erosional features, and in conjunction with a field of sand waves, exemplify the dynamic nature of the ocenographic processes active on this area of the sea floor. 相似文献
8.
Suguru Ohta 《Journal of Oceanography》1985,41(2):121-133
A peculiar swimming holothurian referable toEnypniastes eximia Theel, of the family Pelagothuriidae was photographed frequently on the continental slopes within Suruga Bay and Sagami Bay. The holothurians of this family are gelatinous, medusa-like creatures with a specific gravity nearly equal to that of seawater, and they have been thought to live a pelagic life. Of the 35 individuals in the bottom photographs taken near the bottom, 26 individuals (74.3 %) were swimming, 1 (2.9 %) was just landing on the bottom and 8 (22.8 %) were walking on the sea floor. Correction for the pyramidal shape of the camera's field of view suggests that 90 % of the population was swimming within several meters of the bottom, and 10 % was on the sea floor. When swimming, 12 antero-dorsal appendages, inter-connected by webe to form a velum as in the elpidiid holothurianPeniagone, are either folded anteriorly in a circle or opened posteriorly like an umbrella. Propulsion seems to be accomplished by metachronal fanning of the posterior webbed podia and by undulatory movement of the antero-dorsal veil-like structure. The latter might also function as a parachute or stabilizer in descending. When on the sea floor, the holothurian always faces downstream with the velum stretched forward, while the aspidochirote tentacles, which are folded in swimming, are pressed on the sediment surface. In addition, this organism leaves trails and constricted fecal strings on the sediment. These observations suggest thatE. eximia does not ingest food in midwater, but, rather feeds selectively on the surface deposits of the sea floor. Although the holothurian has lost the ability to walk effectively on the sea floor by podia, it may utilize the swifter bottom current above the turbulent Ekman layer for locomotion and dispersal. 相似文献
9.
使用重力取样器、渔网、深潜器等手段,已经在海底及以下浅表层的区域采获天然气水合物样品,但关于浅表层水合物的发育机制、分布规律、与海底地形的关系等问题还缺乏基本认识。根据2006年鄂霍次克海天然气水合物调查航次的调查数据,发现萨哈林东北陆坡区,特别是中、下陆坡区发育大量海底凸起。这些凸起一般呈不对称的丘形,宽几百米,高几十米。与海底沙波、沙脊不同,海底凸起为孤立海底地形,在南北方向上并不连续。海底剖面仪结果清楚地显示古陆坡凸起的发育。现今海底陆坡凸起的幅度普遍地要小于古陆坡凸起的幅度,个别地方古今陆坡凸起的形态有所变化,但大部分古、今陆坡凸起是一一对应的,基本形态没有根本变化。在萨哈林陆坡地区存在两个方向的挤压应力场,分别是由德鲁根盆地向萨哈林陆坡方向的挤压应力场和萨哈林陆坡沿萨哈林走滑断裂向南的挤压应力场,海底陆坡凸起是这两大应力场复合作用的结果。浊反射区中的游离气是底辟构造中的超高压多相物质向上迁移形成的,浊反射区上方对应的海底凸起应该是宏观构造挤压和局部底辟发育叠合的结果,浊反射区上方的海底凸起,在形态等方面应该和其他仅由挤压构造原因形成的凸起有所区别,比如顶部发育裂口等。在底辟构造中,由于游离气体的向上迁移,在整个水合物稳定域中从下到上,直至海底都可能形成水合物。 相似文献
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为对辽东湾觉华岛附近海域海底工程地质环境进行系统评估,利用高分辨海底声学探测设备获取调查海区的精密水深地形数据,利用筛析法、激光粒度仪实验法确定沉积物类型及粒度参数特征,最终综合分析得到研究区海底地形地貌及沉积物分布特征。研究发现,目标海域测量水深介于4~22m之间,平均水深15m左右,海底地形平坦,整体表现为平缓的近岸缓坡,地貌以近岸粉砂淤泥质浅滩地貌为主,局部发育微型海底沙波;海底浅地层第一声学反射界面清楚连续,可全区追踪,穿透深度0.5~5m不等,沉积物厚度相对稳定;表层沉积物中值粒径普遍较小,沉积物类型东区以粉砂和砂质粉砂为主,西区以砂质粉砂为主;表层沉积物组分和粒度参数的空间变化规律较为复杂,分析认为其主要受到沉积物物源以及辽东湾内往复流、沿岸流的影响。。 相似文献
11.
Escanaba Trough, the median valley of Gorda Ridge, is partly filled with terrigenous sediment which was eroded mostly from rocks in the Klamath and Columbia River drainage basins and transported across the sea floor to the trough by turbidity currents. Basal or lower cores contain sand derived from the south-central metamorphic belt of the Klamath Mountains, whereas the upper cores have sand derived from the Columbia River drainage basin. Columbia River sediment reached Escanaba Trough either after a barrier at Blanco Valley had been destroyed by tectonic movement or after a gradient, sufficient to maintain turbidity current momentum, had developed between the Astoria Fan apex and the trough. Sediment in Escanaba Trough is young and most probably was deposited when sea level was lower than at present, perhaps during the Wisconsin Glacial Age. 相似文献
12.
Coherent reflection of an acoustic plane wave from a random sediment layer over an elastic sea floor
The problem of coherent reflection of an acoustic plane wave from a seabed consisting of a randomly inhomogeneous sediment layer overlying a uniform elastic sea floor is considered in this analysis. The random perturbation in the sediment layer is attributable to the sound-speed variations, resulting in volume scattering due to medium inhomogeneities. An approach based upon perturbation theory, combining with a derived Green's function for a slab bounded above and below, respectively, by a fluid and an elastic half-space, is employed to obtain an analytic solution for the coherent field in the sediment layer. A linear system is then constructed to facilitate the computation of the coherent reflection field. The results of the coherent reflection coefficient for various sediment randomness, frequency, sediment thickness, and sea floor elasticity have been numerically generated and analyzed. It is found that the higher/larger the randomness, frequency, thickness, and shear-wave speed, the lower is the coherent reflection. Physical interpretations for the characteristics of the various results are provided. 相似文献
13.
钱塘江河口细颗粒泥沙絮凝沉降特性研究 总被引：3，自引：0，他引：3
钱塘江口河口上游河流和海域来沙多为细颗粒泥沙,粘性细颗粒泥沙由于其特殊的表面电化学性质遇到强电解质海水而产生絮凝沉降,是形成河口淤积的原因之一。影响絮凝的因素很多,除了电解质,还有泥沙粒径的大小、盐度、含沙量、PH值、温度、有机质含量、矿物成分、水流速度及紊动情况等。本文通过粒度分析、静水沉降、动水沉降等各种实验手段分析钱塘江口泥沙的基本特性,找出最佳絮凝盐度以及泥沙不淤流速等值,初步探讨了细颗粒泥沙的絮凝机理,为治理钱塘江口提供科学依据。 相似文献
14.
A newly developed towed transient electromagnetic (TEM) system is capable of measuring the electrical conductivity of the
uppermost 5–10 m of sediments on the sea floor. The profiles of conductivity may be interpreted to give the porosity and likely
texture of the bottom sediments. Recent tests of the system have demonstrated that data may be collected continuously in a
surveying mode. Results from Knight Inlet, British Columbia, are in good agreement with sea floor samples from the area.
Applications for the system include the rapid identification of sediment types for dredging operations, geotechnical surveys,
or reconnaissance mapping of Quaternary geology. 相似文献
15.
A 2,500-km2 area of sea floor on the south-eastern flank of the Greater Antilles Outer Ridge north of the Puerto Rico Trench displays anomalously high acoustic backscattering properties on GLORIA longrange sidescan-sonar data. Previously collected dredges, bottom photographs, and sediment cores indicate the presence of Fe–Mn nodules within the area of high backscatter. We were able to map the extent of the inferred nodule field on the basis of acoustic property contrast between the nodule-covered sediment and the surrounding nodule-free sediment. 相似文献
16.
David Thistle Lisa A. Levin Andrew J Gooday Olaf Pfannkuche P John D. Lambshead 《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(12):185
Although much of the deep sea is physically tranquil, some regions experience near-bottom flows that rework the surficial sediment. During periods of physical reworking, animals in the reworked layer risk being suspended, which can have both positive and negative effects. Reworking can also change the sediment in ecologically important ways, so the fauna of reworked sites should differ from that of quiescent locations. We combined data from two reworked, bathyal sites on the summit of Fieberling Guyot (32°27.631′N, 127°49.489′W; 32°27.581′N, 127°47.839′W) and compared the results with those of more tranquil sites. We tested for differences in the following parameters, which seemed likely to be sensitive to the direct or indirect effects of reworking: (1) the vertical distribution of the meiofauna in the sea bed, (2) the relative abundance of surface-living harpacticoids, (3) the proportion of the fauna consisting of interstitial harpacticoids, (4) the ratio of harpacticoids to nematodes. We found that the vertical distributions of harpacticoid copepods, ostracods, and kinorhynchs were deeper on Fieberling. In addition, the relative abundance of surface-living harpacticoids was less, the proportion of interstitial harpacticoids was greater, and the ratio of harpacticoids to nematodes was greater on Fieberling. These differences between Fieberling and the comparison sites suggest that physical reworking affects deep-sea meiofauna and indicate the nature of some of the effects. 相似文献
17.
Kenneth S. Davis Niall C. Slowey Ingo H. Stender Hannelore Fiedler William R. Bryant Gunther Fechner 《Geo-Marine Letters》1996,16(3):273-278
The relationship between spatial variations of the properties of sea-floor sediments and acoustic backscatter from the surface of the sea floor on the continental shelf off of Panama City, Florida, USA, is investigated using surficial sediment grab samples and digital side-scan sonar data. Acoustic backscatter strength has a high, direct correlation with the mean grain size of the sediments. Acoustic backscatter strength also correlates directly with the carbonate content of the sediments, particularly in medium-and coarse-sand facies, because large, irregularly shaped, carbonate particles affect both the mean grain size of the sediments and the roughness of the surface of the sea floor. 相似文献
18.
Acouso-physical properties of sea floor sediments in the southeast offshore sea area of Hainan Island on the northern continental shelf of the South China Sea are analyzed. In many cruises, conductivity-temperature-depth measurements of seawater, measurements of shallow stratum and side-scan sonar have been made. Acoustic parameters, basic sedimentary parameters, physical-mechanical parameters and 14C age, etc., have been measured. The sediment elastic parameters, including Young's modulus, bulk modulus, constrained modulus, rigidity modulus, Poisson's ratio, Lames constant, etc., have been calculated. Results show that the compression wave velocity of the seafloor sediment in the sea area ranges from 1474–1700 m/s, and there are high and low sound velocity sediment types in the different sea areas; the shear wave velocity is 150–600 m/s; at 100 kHz the sediment sound attenuation is 35–260 dB/m, the sediment density is 1.4–2.0 g/cm3; the sediment porosity is 42–88%. Sound field parameters and describing sound reciprocity between sea and seafloor are described. 相似文献
19.
Large volumes of fine-grained sediment have been transported to the deepbasin floor in the Bering Sea, especially during glacial low stands of sea level. Turbidity currents and several types of mass movement have been the chief transporting agents. 相似文献
20.
In recent years significant interest has emerged regarding bottom currents and sediment dispersal over continental shelves and shallow marine waters. Although many papers have been written on sediment dispersal mechanisms, they include relatively few long-term observations of bottom currents and/or sediment transport. Lack of observational data is related to the hostile nature of the environment, and the difficulty associated with placing and retrieving instruments on the floor of the continental shelf during some seasons and environmental conditions.This paper describes an instrumentation system designed for use on the floor of the continental shelf. It can remain submerged for periods of one month continuously recording water speed and direction 1 m from the sea bed, differential pressure, and bed nature by means of half-hourly photographs. Four of these systems are presently in use in arrays across the continental shelf of Washington. 相似文献