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1.
Measurement of the vertical distribution of total suspended matter (TSM) was carried out during summer throughout the Seto Inland Sea. TSM concentration near the bottom is influenced significantly by water movement and turbid bottom water is observed in all areas where median grain size (Md) of the bottom sediment is more than 47gf. The high concentration of TSM near the bottom may be due to resuspension of the surface layer of bottom sediments. Comparison of the organic content of the resuspended matter with that of the bottom sediment shows that the resuspended matter contains more organic matter with a lower C : N ratio than the bottom sediment. The C : N ratio of the resuspended matter is similar to that of TSM in the surface layer of the water column. It is thought that TSM in surface waters sinks and settles on the surface of the bottom sediment. This deposited material is then easily resuspended in the water column by tidal currents before becoming permanently incorporated into the bottom sediment. 相似文献
2.
Shipley Thomas H. Bangs Nathan L. Henning Alison T. 《Marine Geophysical Researches》1998,20(6):479-494
In deep ocean settings where water depth greatly exceeds the source-to-receiver length, the geometry is insufficient for accurate determinations of velocity from reflection-moveout. However, velocities are crucial for estimates of physical properties and image processing. Focusing analyses with conventional post-stack two-dimensional migration improves images, but does not produce geologically meaningful velocities except in the special case of a two-dimensional earth. For the more general case of the three-dimensional earth there is no a priori method to determine the degree of geometrical complexity. We present a technique using a short-offset three-dimensional (3-D) data set over the 5 km deep trench west of the Lesser Antilles. These data illustrate highly sensitive post-stack 3-D focusing analyses (± 20 m s–1 interval velocities), and the relationship of these seismically derived velocities to rock velocities. In our Barbados example we were able to establish the presence of a widespread 80-160 m thick low-velocity zone at and above the main low-angle fault. This observation suggests the water-rich décollement leaks water into the overlying sections. Also evident is a low-velocity section associated with turbidite sands. These results are confirmed with sparse logging data and well samples. Deep-water short offset 3-D experiments provide a potentially effective approach for velocity estimation, replacing the operational complexity of long-offsets with simpler short-offset techniques. In areas of structural complications and abundant diffracted energy, it is a surprisingly accurate method, utilizing the high fidelity 3-D wavefield and the information carried in zero-offset diffraction ellipsoids. The velocity used to properly collapse a diffraction ellipsoid is explicitly the velocity of propagation in the media since the travel path is known exactly. Thus, the derived velocities should closely represent rock velocities, unlike the 2-D case where the propagation geometry is not known. 相似文献
3.
东海不同底质类型海域春季悬浮体通量及影响因素 总被引：7，自引：2，他引：7
利用1994年4月在东海陆架不同底质类型海域即泥质和砂质区的水文和泥沙观测资料，分析和计算了两个站的悬浮体含量的分布、余流分布和悬浮体通量，以代表两个局部海域悬浮体含量分布和输送的特征。结果表明，在底质类型、生物活动、水动力环境和悬浮体物源各因素的影响下，两个海域的悬浮体通量和悬浮体含量垂直分布各有其特征，是东海悬浮体输送和垂直分布的两种典型类型。111站周围海域的悬浮体通量较大，上、中层水体（0－40m)中的悬浮体向东南方向输送，下层和底层的悬浮体向东北方向输送，且下层和底层的通量大于中上层；砂质区的悬浮体通量相对较小，且从表层到底层均向东北方向运移。 相似文献
4.
5.
基于2018年8月福建三沙湾湾内外共两个定点站位的船基和座底三脚架观测数据,研究了三沙湾底边界动力过程及悬沙输运特征。结果表明,三沙湾湾内湾外两个站位均表现出涨落潮历时相近但涨落潮流速明显不对称的现象,即湾内涨潮流速大于落潮流速,湾外则相反。湾内水体受淡水输入影响较大,表现出落潮期间显著的温盐层化,而涨潮期间水体混合良好;湾外水体受淡水影响不明显,表现为水体温度主导的层化。通过对底边界层动力过程的分析表明,湾内（距底0.75 m）、湾外（距底0.50 m）站位底边界层的平均摩阻流速分别是0.016 m/s、0.013 m/s,且两个站位拖曳系数基本相等（2.03×10-3）,表明在相同流速下湾内站位的底部切应力更大,近底沉积物再悬浮和搬运相对湾外站位更为显著。因此观测期间悬沙浓度最大值出现在湾内站位,为109 mg/L,且悬沙在垂向上的分布可达上层水体;湾外站位悬沙浓度更低,并且底部悬浮泥沙仅能影响至距底5 m的水体。悬沙通量机制分解结果表明,三沙湾夏季的潮周期单宽悬沙从湾外向湾内方向净输运,湾内站位向湾内方向净输运74.88 g/(m·s),平流输沙占主导作用,贡献率41.7%;湾外站位向湾内方向净输运10.57 g/(m·s),主要受平流输沙和垂向净环流的控制,贡献率94.9% 相似文献
6.
Ikuo Yoshikawa Hiroshi Kawamura Kuniaki Okuda Yoshiaki Toba 《Journal of Oceanography》1988,44(3):143-156
The structure of the turbulent boundary layer underneath laboratory wind waves was studied by using a combination of a high-sensitivity thermometer array with a two-component sonic flowmeter. The temperature fluctuations are used to detect movements of water parcels, with temperature as a passive quantity. The turbulence energy was dominant in the frequency range (0.01 0.1 Hz), which was much smaller than the wind-wave frequency (2 5 Hz), and in which the turbulence was anisotropic. There was a frequency range (0.2 2 Hz for velocity, 0.2 5 Hz for temperature fluctuation) where the turbulence was isotropic and had a –5/3 slope in the energy spectrum. These points are the same as those in previous works. However, by analyses of the time series by using a variable-interval time-averaging technique (VITA), it has been found that conspicuous events in this main turbulence energy band are the downward bursting from the vicinity of the water surface. Thus the structure of the water layer underneath the wind waves has characters which are similar to the familiar turbulent boundary layer over a rough solid wall, as already conceived. It has been found that, at the same time, the turbulence energy can be related to quantities of the wind waves (the root mean squared water level fluctuation and the wave peak frequency), for different wind and wave conditions. That is, the turbulence underneath the wind waves develops under a close coupling with the wind waves. 相似文献
7.
Field measurements of cross-shore currents 0.25 m from the bed were made on two natural beaches under a range of incident wave conditions. The results indicated the presence of a relatively strong, offshore-directed mean current, both within and seaward of the surf zone. Typical velocities within the surf zone were of the order of 0.2–0.3 m/s. This bed return flow, or “undertow”, represents a mass conservation response, returning water seaward that was initially transported onshore in the upper water column, primarily above the trough of the incident waves. The measurements demonstrated that the bed return flow velocity increases with the incident wave height. In addition, the crossshore distribution of the bed return flow is characterised by a mid-surf zone maximum, which exhibits a strong decrease in velocity towards the shoreline and a more gradual decay in the offshore direction. Several bed return flow models based on mass continuity were formulated to predict the cross-shore distribution of the bed return flow under an irregular wave field and were compared with the field data. Best agreement was obtained using shallow water linear wave theory, after including the mass transport associated with unbroken waves. The contribution of the unbroken waves enables net offshore-directed bottom currents to persist outside the region of breaking waves, providing a mechanism, other than rip currents, to transport sediment offshore beyond the surf zone. 相似文献
8.
A time-series sediment trap was deployed from December 1994 to February 2002 at the mouth of Tokyo Bay (35°03′ N, 139°40′
E; water depth, 850 m). Sinking particles were obtained with a time interval of one week at a depth of approximately 100 m
above the sea floor. Observed total mass fluxes varied from 3.3 to 226.7 g/m2/day with an average of 28.0 g/m2/day. Concentrations of rare earth elements, Al, Ca and Si in particulate materials were measured. The combustible fraction
at 450°C is assumed to be equivalent to the organic matter content. Contents of biogenic materials, namely organic matter,
opal and calcium carbonate, were about 30% and the content of lithogenic material was about 70%. Using La/Yb ratios of particles
from the sediment trap and Tama-gawa River and surface sediment of Tokyo Bay, it was estimated that about 50% of the lithogenic
particles collected in the sediment trap at the mouth of Tokyo Bay originated from resuspended surface sediment in Tokyo Bay.
An increasing trend of Opal/CaCO3 ratio in the sinking particles was found in the spring season. It is suggested that the relative increase of diatoms is due
to the decreasing dissolved inorganic nitrogen input into Tokyo Bay. 相似文献
9.
J. Kirk Cochran Juan Carlos Miquel Robert Armstrong Scott W. Fowler Pere Masqu Beat Gasser David Hirschberg Jennifer Szlosek Alessia M. Rodriguez y Baena Elisabet Verdeny Gillian M. Stewart 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1487-1501
Disequilibrium between 234Th and 238U in water column profiles has been used to estimate the settling flux of Th (and, by proxy, of particulate organic carbon); yet potentially major non-steady-state influences on 234Th profiles are often not able to be considered in estimations of flux. We have compared temporal series of 234Th distributions in the upper water column at both coastal and deep-water sites in the northwestern Mediterranean Sea to coeval sediment trap records at the same sites. We have used sediment trap records of 234Th fluxes to predict temporal changes in water column 234Th deficits and have compared the predicted deficits to those measured to determine whether the time-evolution of the two coincide. At the coastal site (327 m water depth), trends in the two estimates of water column 234Th deficits are in fairly close agreement over the 1-month deployment during the spring bloom in 1999. In contrast, the pattern of water column 234Th deficits is poorly predicted by sediment trap records at the deep-water site (DYFAMED, 2300 m water depth) in both 2003 and 2005. In particular, the transition from a mesotrophic to an oligotrophic system, clearly seen in trap fluxes, is not evident in water column 234Th profiles, which show high-frequency variability. Allowing trapping efficiencies to vary from 100% does not reconcile the differences between trap and water column deficit observations; we conclude that substantial lateral and vertical advective influences must be invoked to account for the differences.Advective influences are potentially greater on 234Th fluxes derived from water column deficits relative to those obtained from traps because the calculation of deficits in open-ocean settings is dominated by the magnitude of the “dissolved” 234Th fraction. For observed current velocities of 5–20 cm s−1, in one radioactive mean-life of 234Th, the water column at the DYFAMED site can reflect 234Th scavenging produced tens to hundreds of kilometers away. In contrast, most of the 234Th flux collected in shallow sediment traps at the DFYFAMED site was in the fraction settling >200 m d−1; in effect the sediment trap can integrate the 234Th flux over distances 40-fold less than water column 234Th distributions. In some sense, sediment trap and water column sampling for 234Th provide complementary pictures of 234Th export. However, because the two methods can be dominated by different processes and are subject to different biases, their comparison must be treated with caution. 相似文献
10.
江苏如东西太阳沙及烂沙洋海域潮流泥沙数值模拟 总被引：10，自引：0，他引：10
基于不规则三角形网格有限差分法并考虑波浪及其破碎作用,建立了平面二维潮流场和泥沙场数学模型.该模型对有望建设成深水码头和深水航道的江苏如东西太阳沙和烂沙洋海域的潮流场和泥沙场进行了细化数值模拟.数值模拟结果表明：（1）本海区潮流基本上是顺深槽流动的往复流,潮流流速大,烂沙洋北水道和西太阳沙附近大潮涨落潮最大流速分别在2 m/s和1 m/s以上;（2）本海区的潮平均水体含沙量在0.5 kg/m^3以下,落潮含沙量大于涨潮含沙量;（3）小浪对水体含沙量影响很小,大浪作用下水体含沙量明显增加. 相似文献
11.
The Neogene and Quaternary sediments of the Faeroe-Shetland Channel and West Shetland shelf and slope rest upon a major regional unconformity, the Latest Oligocene Unconformity (LOU), and have been deposited through the interaction of downslope and parallel-to-slope depositional processes. The upper to middle continental slope is dominated by mass-transport deposits (debris flows), which progressively diminish downslope, and were largely generated and deposited during glacial cycles when ice sheets supplied large quantities of terrigeneous sediment to the upper slope and icebergs scoured sea-floor sediments on the outer shelf and uppermost slope. Large-scale sediment failures have also occurred on the upper slope and resulted in deposition of thick, regionally extensive mass-transport deposits on portions of the lower slope and channel floor. In contrast, large fields of migrating sediment waves and drift deposits dominate most of the middle to lower slope below 700 m water depth and represent deposition by strong contour currents of the various water masses moving northeastward and southwestward through the channel. These migrating sediment waves indicate strong northeastward current flow at water depths shallower than 700 m and strong southwestward current flow at water depths from 700 to >1,400 m. These flow directions are consistent with present-day water-mass flow through the Faeroe-Shetland Channel. The Faeroe-Shetland Channel floor is underlain by thin conformable sediments that appear to be predominantly glacial marine and hemipelagic with less common turbidites and debris flows. No evidence is observed in seismic or core data that indicates strong contour-current erosion or redistribution of sediments along the channel floor. 相似文献
12.
The activity of234Th (t
1/2=24.1 days) in dissolved, particulate and sediment trap samples was determined in the water column off southwestern Taiwan during 2–4 October, 1993. Vertical234Th fluxes measured by the free-floating sediment traps ranged from 363 to 2290 dpm m–2 d–1 in the upper 450 m. Th-234 fluxes predicted from the irreversible scavenging model concur with those measured by the sediment traps. Comparison of the residence times of particulate234Th and particulate organic carbon showed that their respective values differ by a factor of approximately 23, which suggests organic carbon is preferentially recycled relative to234Th in the euphotic zone. 相似文献
13.
—A comprehensive analysis is conducted based on observations on topography.tidal current.salinity.suspended sediment and bed load during the years of 1982.1983.1988.1989.1996 and 1997 in theYangtze Estuary.Results show that the deformation of tidal waves is distinct and the sand carrying capaci-ty is large within the mouth bar due to strong tidal currents and large volume of incoming water and sedi-ments.Owing to both temporal and spatial variation of tidal current.deposition and erosion are extremelyactive.In general a change of up to 0.1 m of bottom sediments takes place during a tidal period.The maxi-mum siltation and erosion are around 0.2 m in a spring to neap tides cycle.The riverbed is silted duringflood when there is heavy sediment load.eroded during dry season when sediment load is low.The annualaverage depth of crosion and siltation on the riverbed is around 0.6 m.In particular cases.it may increaseto 1.4 m to 2.4 m at some locations. 相似文献
14.
Dong Lixian 《海洋学报(英文版)》1998,17(4):469-482
ThisstudywassupportedbytheNationalNaturalScienceFoundationofChinaundercontractNo.49276274,theZhejiangProvinceNaturalScienceFoundationundercontractNo.490013,theChina-Australiabilateralscienceandtechnologyprogram,theAustralianInstituteofMarineScience,theModellingLaboratoryoftheMarineScienceintheSecondInstituteofOceanographyoftheStateOceanicAdministration.INTRODUCTIONTheJiaojiangEstuaryis1ocatedintheeasterncoastofChina,2OokmfromthesouthoftheChangjiangRiver(YangtzeRiver),linkedin… 相似文献
15.
长江口深水航道以悬沙落淤为主,回淤泥沙较为松散、上覆有流动性较强的高密度浮泥层,航槽需进行常年维护。为提高疏浚效率、降低疏浚成本,基于耙头动力改进的思路,提出适用于长江口沉积物特性的掺气扰动耙具,并通过室内试验,探讨耙具推荐型式,推荐空压机流量及压力指标,估算掺气耙具扰动效果。结果表明,2 mm气嘴耙具掺气扰动后水体含沙量增幅高于其他孔径;相同孔径、相同气流量下,气嘴间距越大、扰动效果越明显,因此推荐耙具气嘴孔径2 mm、20 cm间距交错布置型式。对于推荐耙型,当气体压力低于4.8×105Pa、气流量小于1.1 m3/min时,扰动后水体含沙量基本呈线性增长;当气体压力超过4.8×105Pa,扰动后水体含沙量无明显变化。以室内试验推荐压力4.5×105Pa为基础,估算施工作业水深15 m,结合实际作业水深及气力损耗,现场空压机选型参考值为气流量61.7 m3/min、工作压力为0.7 MPa。据此推算设计航速1.286 m/s时,中上层(0～4 m)水体掺气扰动疏浚耙具悬扬原状土方量约800 m3/h。 相似文献
16.
Sediment trap experiments were carried out 39 times during the years from 1977 to 1981 in Funka Bay, Hokkaido, Japan. The observed total particulate flux varies seasonally, that is, the particulate fluxes in winter and spring are larger than those in summer. The fluxes in all seasons increased with depth. Major components of settling particles are aluminosilicate in winter, biogenic silicate in spring and organic matter and terrestrial material in summer, respectively. The fluxes of each chemical component observed with sediment traps are normalized to that of Al by assuming that the actual flux of Al is equal to the accumulation rate onto the sediment surface. Vertical changes of the normalized flux of each chemical component indicate the following: Fe was not regenerated from the settling particles in the water column. Mn was regenerated from the settling particles in the lower layer exclusively between 80 m depth and the sediment surface. Cd was actively regenerated in the upper layer above 80 m depth. Phosphate was regenerated in the upper layer, while biogenic silicate was in the lower layer. The silicate regeneration, therefore, occurs after phosphate regeneration. The material decomposing in the water column below 40 m has an atomic ratio of P ∶ Si ∶ C = 1 ∶ 52 ∶ 128. 相似文献
17.
Assessment was made of residual ratio of North Pacific Intermediate Water (NPIW) produced in subpolar region of the North Pacific using chlorofluorocarbons, CFC-11 and CFC-12 (CCl3F and CCl2F2), along 175°E. NPIW on density horizons less than 26.80 remained more than 80% north of 30°N. It was suggested that new NPIW laterally spreads over the northern North Pacific without hardly being diluted by the surroundings. For density horizons greater than 26.80 north of 30°N, NPIW remained less than 60%. The difference in the residual ratio between <26.80 and >26.80 north of 30°N suggests that NPIW is produced on density horizons less than 26.80, which contacts the atmosphere in the subpolar region, and that NPIW is diluted by upwelling deep water on density horizons greater than 26.80 in high latitude of the North Pacific. NPIW on a density horizon of 26.80 remained about 50% south of 30°N. The decrease in the horizontal distribution of the residual ratio of NPIW suggests that half the new NPIW produced in the subpolar region is laterally spread over the North Pacific with the southward movement of NPIW. 相似文献
18.
2013年5月、8月和11月调查了象山港大黄鱼网箱养殖区及附近沉积物中总有机氮(TON)、总有机碳(TOC)和总磷(TP)含量,并采用实验室模拟法研究了底泥耗氧率(SOCs)和沉积物-水界面营养盐(NH+4、NO-2+NO-3和PO3-4)通量。结果表明:养殖区(YZ)沉积物中的TON和TP含量显著高于距离养殖区50 m(F1)和100 m(F2)的区域(P<0.05)。底泥释放NH+4到上覆水中,但是从上覆水中吸收NO-2+NO-3和PO3-4。沉积物-水界面营养盐通量表现出明显的季节性变化,在8月,NH+4及PO3-4的释放量达到最大值。上覆水中NH+4、NO-2+NO-3和PO3-4的质量浓度随着沉积物-水界面营养盐通量的变化而变化。研究表明,象山港大黄鱼养殖活动对养殖区底泥造成了一定污染,且通过影响沉积物-水界面营养盐通量影响上覆水中营养盐分布,最终给整个养殖系统造成生态负担。 相似文献
19.
The DYFAMED sediment trap station in the Ligurian Sea (NW Mediterranean) has been active since 1986 and today comprises the longest time‐series of downward particle flux in the Mediterranean Sea. As such, it provides valuable information on the interannual variability of the particle flux, and also documents possible recent changes in the NW Mediterranean pelagic ecosystems. We report an unprecedented episode of downward flux of mucilaginous material at the DYFAMED station during summer 2002 in association with singular hydrometeorological conditions. The rain of mucilaginous aggregates clogged a PPS5 sediment trap at 260 m depth and was also clearly detected at 1080 m depth. The possible factors governing the development and sinking of the mucilaginous material are discussed. A very sharp increase of sea surface temperature during June and the presence of freshened waters in the surface the following month resulted in a stronger than usual stratification of the upper water column throughout the summer season. We suggest that the steepness of the vertical density gradient was responsible for the unusual accumulation of mucous aggregates. Additionally, a diatom bloom took place during the nutrient‐depleted conditions typical of summer, a factor which may have contributed to feed the pycnocline with transparent exopolymer substances. A storm occurring in the beginning of August relaxed the stratification and promoted the deposition of the mucilaginous aggregates accumulated in the upper water column during the preceding months. Important similarities of ambient conditions preceding the apparition of mucilaginous material in our open‐sea site and those reported in the Adriatic Sea during major mucilage events, suggest that general climatic conditions, rather than local factors, drive the occurrence of major accumulations of mucilaginous material in the water column at both sub‐basins of the Mediterranean Sea. In this regard, the strength of the air temperature increase during the onset of the stratified season is proposed as a major controlling factor. 相似文献
20.
1950～2000年黄河入海水沙的逐日变化及其影响因素 总被引：1，自引：0，他引：1
对 195 0～ 2 0 0 0年的 5 1年黄河经利津水文站入海的逐日水沙实测资料进行统计分析 ,展示了黄河入海水沙的极端情况 ,如洪峰和沙峰等逐渐变少到消失的过程及逐日入海水沙量的变化规律 ,并对其影响因素进行了初步分析。结果显示 :在黄河年均入海水沙锐减的背景下 ,2 0世纪 90年代日均流量 <5 0 0m3 /s的天数增加到了是 2 0世纪 5 0年代的 3倍多 ;>2 0 0 0m3 /s的洪季流量由初期频发至 1997年消失 ;>40 0 0m3 /s的洪峰流量自 1989年以后消失 ;>60 0 0m3 /s的洪峰流量从 1986年就不再发生。 >5 0 0t/s的日均输沙率 (4 3 .2× 10 6t/d的沙峰 )都出现在 1989年以前 ;>70 0t/s的日均输沙率 (60 .5× 10 6t/d的沙峰 )出现在 1977年以前 ;含沙量 >80kg/m3 的历时和可能产生异重流的含沙量天数都逐步减少。进入 2 0世纪 90年代以来基本不存在大洪灾及由沙峰造成的河口河道快速堆积而使河流改道现象 ,引起这些变化的因素除降雨外主要为流域耗水量不断增加及大中型水库的建成运用等 ,黄河入海水沙的这种锐减及水沙峰的极端情况都会对河口演变和河口区的生态环境产生重要的影响。 相似文献