共查询到20条相似文献，搜索用时 31 毫秒
1.
《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(3):343-366
Deep slope currents and particulate matter concentrations were studied on the Barcelona continental margin in and around the Foix submarine canyon from May 1993 to April 1994. This year-long moored experiment revealed that near-bottom slope currents are strongly influenced by the bottom topography, being oriented along isobaths and along the canyon axis. The deep slope current fluctuations are controlled by the local inertial motion (18.3 h) and also by low-frequency oscillations at periods of 6–10 days, related to the passage of atmospheric pressure cells. Particulate matter concentrations recorded during the experiment do not show a clear seasonal variability, except outside the canyon, where significant peaks of particulate matter concentrations were recorded only during the winter-fall deployment. In addition, the temporal evolution of suspended particulate matter concentration is not linked to changes in the cross-slope or along-slope current components and did not show a clear relationship with river avenues or wave storm events. This suggests that suspended particulate matter exported from the shelf is dispersed on the slope by advective processes, which attenuate the signal of the shelf-slope sediment transfer. Mean particulate matter concentrations differed among sampling sites, but the magnitude of the mean horizontal suspended particle flux reflects a quite similar value in the whole study area, ranging from 2.53 to 4.05 mg m−2 s−1. These horizontal suspended particle fluxes are 27 (canyon head) to 360 (open slope) times higher than the settling particle fluxes measured at the same sampling sites, indicating that the suspended particulate transport on the Barcelona continental slope dominates over the settling particle fluxes, even inside the Foix submarine canyon. 相似文献
2.
The investigation of abyssal bedforms and sediment drifts as a tool for understanding the deep flow characteristics allows us to interprete that a benthic storm is primarily related to sediment distribution, development of longitudinal ripple marks, and concentration of suspended particulate matter. There explicitly exists a strong and periodical bottom flow which is called the benthic storm having a current speed of over 15 cm sec?1 and duration of more than two days. Hydrodynamic regime has been thought to affect underlying sediment textural natures which can be used to distinguish between bottom currents with different velocities. Therefore, concentration of medium silt mode (0.010–0.017 mm in size) delineates a high-velocity core of the benthic storm in the deep sea bottom. Bottom current measurements in most of the North Pacific Ocean indicate that present bottom current speeds are generally less than 10 cm sec?1. It appears likely, therefore, that significant erosion is not taking place today. However, at current passages, bases of sea mounts, and other topographic obstructions locally accelerated current flows are recognized to affect bottom configuration. While, it is concluded from bottom echo-characteristics and bottom current measurements that widespread occurrences of echo type 3 (sediment-drift deposit facies) recognized at 22°N and 42°N in the Northwest Pacific are associated with the North Equatorial current and the North Pacific current respectively, and can best be interpreted to be originated from benthic storms, the source of which were come from those surface currents. 相似文献
3.
Tripod measured residual currents and sediment flux: Impacts on the silting of the Deepwater Navigation Channel in the Changjiang Estuary 总被引：3，自引：0，他引：3
Four bottom-mounted instrument-equipped tripods were deployed at two sections spanning the region characterized by severe sedimentation rates in the Deepwater Navigation Channel (DNC) along the North Passage of Changjiang Estuary in order to observe currents, near-bed suspended sediment, and salinity. Seaward residual currents predominated in the up-estuary section. In contrast, a classical two-layered estuarine circulation pattern occurred in the down-estuary section. Flow moved seaward in the upper layer and a heavier inflow, driven by the salinity gradient, moved landward in the lower layer. The near-bed residual currents in the up-estuary section and the down-estuary section acted in opposing directions, which implies that the region is a convergence zone of near-bed residual currents that trap sediment at the bottom. The maximum salinity gradient at the maximum flood current indicates the presence of a strong front that induces sediment trapping and associated near-bottom convergence of sediment, which explains the high sedimentation rates in this section of the estuary. 相似文献
4.
Cyclical variability of suspended sediment concentration over a low-energy tidal flat in Jiaozhou Bay,China: effect of shoaling on wave impact 总被引：1，自引：0，他引：1
During the spring-neap period of 17–24 August 2004, turbidity, horizontal and vertical current velocities and echo intensity
were measured using OBS-3A and ADP-XR instruments over an intertidal flat within the semi-enclosed Jiaozhou Bay, China, to
examine patterns in suspended sediment concentration (SSC) and possible control factors. SSC was found to be lower than 30 mg
l−1 in most of the water column and for most of the tidal cycle. This is attributed mainly to the low hydrodynamic energy, in
particular weak currents (near-bottom maximum 1- and 8-min-interval velocities were only 26.1 and 14.2 cm s−1, respectively), and limited fine-grained sediment supply by rivers. However, high SSC values ranging from 100 to >1,000 mg
l−1 occurred over short periods at the beginning and the end of inundation. This phenomenon is attributed to the shoaling effect
of frequent wind-generated waves, as a result of which near-bottom SSC fluctuations display a U-shaped trend during each tidal
cycle. 相似文献
5.
The Meriadzek Terrace (a 2100m deep plateau on the North-East Atlantic continental slope) was chosen as the experimental site for a multidisciplinary programme to observe the parameters needed for a better understanding of biological processes in the benthic environment.Two approaches were used to study the input of particulate matter to the bathyal seabed: sediment traps and indirect particle concentration measurements with nephelometry. These two technologies do not measure particles of the same size range, but as we are interested in the fluctuations of the particle supply, their results are complementary.Vertical profiles of nephelometry show that over the Meriadzek Terrace there is 125m thick nepheloid layer immediately above the bottom.The dynamics in the deep layer has been determined by measurements made with a Module Autonome Pluridisciplinaire (MAP), an in situ monitoring device developed at IFREMER which measures currents, nephelometry, temperature vertical profile near the bottom.Throughout six months of measurements in 1984, the currents at 0.5m and 120m above the bottom were subject to semi-diurnal tidal oscillations. The intensity of light scattering recorded with the nephelometer on the MAP was highly correlated with current velocities especially with semidiurnal tidal oscillations which seem to induce local resuspension. There are also longer term fluctuations, notably a very strong event which lasted several days during August. This event lagged behind a period of high intensity of internal waves correlated with a reversal in current direction. The sediment trap (Pièges à Particules “PAP”) observations showed that the particle fluxes on the Meriadzek Terrace have a cycle of variation similar to primary production which is characterized by a maximum in May during the phytoplankton bloom and a minimum during January. There was also interannual fluctuation.These two kinds of results point out the different time scales (from some hours to several months) of the large temporal fluctuations which affect the near-bottom particle behaviour. 相似文献
6.
《Journal of Sea Research》1999,41(1-2):19-33
Electron microprobe analysis of suspended-matter samples collected at different water depths at ten stations in the Angola Basin indicated that at each station, from top to bottom, the elementary composition of the suspended matter was very similar and differed from the composition of the suspended matter at the adjacent stations. This indicates that the downward settling of the suspended matter is much faster than the horizontal transport and mixing by the currents. Assuming that the suspended matter settles in the form of flocs, or is scavenged by settling flocs, the suspended matter can indeed reach the bottom in a shorter period than needed for the currents to cover the distance between adjacent stations. Comparison with sediment trap data from the literature shows that also lateral transports and/or deep water gyres have to be invoked to further increase residence times of suspended matter in the water column. 相似文献
7.
The CTD and nephelometric sounding data are considered along with the parameters of the nearbottom currents and particulate fluxes measured by a subsurface mooring station in the northern part of the Bear Island Trough. It is shown that the near-bottom current is characterized by highly variable parameters, while the distribution of suspended particulate matter demonstrates surface and bottom maximums. The horizontal and vertical fluxes of sedimentary matter in the nepheloid layer are studied. 相似文献
8.
悬沙组分对再悬浮过程响应的初步研究——以长江口南槽口门为例 总被引：2，自引：1，他引：1
根据2011年5月31日至6月3日在长江口南槽口门附近海域投放三角架观测系统获取的沉积动力观测数据以及现场采集的水样和底质样品,进行底部边界层参数、悬沙粒度及悬沙组分分析,以探讨研究区近底部边界层特征和沉积物再悬浮过程。结果表明,研究区海域的悬沙以粉砂组分为主,潮周期内近底部流速与相应层位的悬沙浓度变化呈正相关,存在显著的再悬浮作用。分析发现,随着水体中悬沙砂组分的增加,再悬浮通量随之显著增加;砂组分减小,则再悬浮通量亦减小。因此,悬沙砂组分是对再悬浮过程响应的敏感组分,在一定程度上可指示和"示踪"再悬浮效应。 相似文献
9.
Richard A. Feely 《Marine Chemistry》1975,3(2):121-156
During cruises 71-A-12 and 73-A-3 of the R/V “Alaminos” eighty-six samples of suspended matter at eleven near-bottom stations in the Gulf of Mexico and northwestern Caribbean Sea were collected, and simultaneously, values for light scattering were measured. Selected samples of the suspended matter were analyzed for particulate aluminum, silicon, iron, calcium, magnesium, organic carbon and inorganic carbon. The results indicate that a permanent but highly variable near-bottom nepheloid layer exists in the Gulf of Mexico but not in the northwestern Caribbean Sea. Average total-suspended loads in the Gulf of Mexico nepheloid layer are two times higher than in the clear water above the nepheloid layer.Since there is a significant increase in the alumino-silicate fraction and a corresponding decrease in the organic fraction of the suspended matter in the nepheloid layer relative to the overlying water, it appears that sediments are the most probable source of the increased concentrations of suspended matter in the nepheloid layer. This hypothesis is supported by X-ray diffraction analyses on the nepheloid material collected at one station which show the same mineral assemblages as the underlying sediments.Time studies over periods of one week and one and one-half years showed large total-suspended-matter variations which indicate that non steady-state processes, primarily vertical eddy diffusion and possibly advection, are controlling the distribution of suspended matter in the nepheloid layer. 相似文献
10.
In order to study particle behaviour and its time-variability in the near-bottom layer on the Porcupine Abyssal Plain (48°50′N, 16°30′W, 4850 m), long-term measurements were made of currents, and nephelometry and particle samples were collected using an autonomous lander between mid-1996 and mid-1998. Water samples, collected in the Bottom Nepheloid Layer within 1000 m of the bottom, were filtered for suspended particles whose contents of organic carbon, nitrogen and pigments were determined. This study was co-ordinated with a water column flux study and a detailed programme of benthic studies to understand how the abyssal boundary layer responds to and modifies inputs of organic matter from the water column (MAST3/BENGAL programme).There were strong seasonal fluctuations in the near-bottom (2 m above the bottom, mab) particle flux, whose variation were correlated in time with the water column fluxes. During the periods of peak flux, the near-bottom flux was sometimes higher than that recorded higher up in the water column, but not always at other times. These excesses were attributed to the resuspension events, since we observed a correlation between current speed and nephelometry. However, in summer the peak in the particle resuspension flux could not be explained by the variations in the tidal amplitude. Instead we attribute it to the large quantities of fresh large particles (aggregations) that had just arrived on the bottom; it was probably linked to the feeding activity and sediment reworking by the rich and varied benthic and benthopelagic megafauna.In both 1997 and 1998, the nephelometry signal (directly related to fine particle concentration) and its variability increased after the peaks in large particle flux with a time-lag of 2–3 months. We assume that this time lag corresponds to the time it takes for the large fresh particles, once they have settled on the bottom, to be disaggregated into smaller particles, and hence become subject to resuspension in the quiet current conditions then prevailing in the BENGAL area. The suspended particle analyses confirm the vertical structure of the Bottom Nepheloid Layer, the lower part of which corresponds to the Bottom Mixed Layer (BML) where resuspension and mixing are higher. 相似文献
11.
Hee Jun Lee 《Ocean Science Journal》2010,45(3):187-195
This study briefly investigated sediment transport by tidal currents in Gomso Bay, on the mid-west coast of Korea during the summer season. Hydrodynamic measurements with benthic tripods (TISDOSs) show that near-bed suspended sediments are transported toward the bay mouth along the low-water line of tidal flats in the southern part of the bay, while they are directed offshore in front of the major tidal channel at the bay mouth according to tidal asymmetry. However, suspended sediments in the main body of sea water, observed from transect and anchor-site measurements, indicate a consistent incoming toward the uppermost tidal flats. A brief episode of relatively strong winds from the west and southeast displays that wind waves can yield the near-bed suspended sediment concentrations (SSC) overwhelming the SSC by tidal currents alone in the remaining duration. 相似文献
12.
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
13.
基于ADP-XR和OBS-3A的潮滩水文泥沙过程研究以胶州湾北部红岛潮滩为例 总被引：2，自引：1，他引：2
于2004年8月17~24日在胶州湾北部红岛潮滩上用OBS-3A和ADP-XR观测了水深、浊度、水平和垂直流速、回声强度、波浪、盐度、水温等水文泥沙要素,同时采集了悬沙和底沙样品作粒度分析.结果和结论为:(1)潮流动力较弱,表层和近底层最大流速分别只有31和26cm/s;(2)弱潮流动力导致潮周期大部分时间的悬沙浓度小于30mg/dm3,但浅水阶段近底悬沙浓度为100~1000mg/dm3;浅水阶段的短暂高悬浮泥沙浓度和其余长淹没时段的低悬沙浓度共同构成悬沙浓度的“U”形潮周期过程线;(3)悬沙浓度的垂直成层分布主要发生在潮周期的深水阶段和平静天气;(4)由于潮流弱和风浪的干扰,悬沙浓度未呈现大小潮周期的变化规律;(5)水体盐度为23.6~29.5;(6)淹没期的温度(21.4~28.6℃)比出露期的(19.3~30.9℃)稳定,温度极高值出现在午后出露期,而极低值出现在凌晨出露期;(7)“浅水效应”是弱动力潮滩泥沙运动的重要特点. 相似文献
14.
A simple technique for studying near-bed hydrodynamics and sediment dynamics is presented. The method combines the use of (1) a benthic tripod hosting a series of electromagnetic current meters, and (2) a newly developed near-bed multi-level water-sediment mixture sampler. The instrument package was deployed successfully at a shallow water station in the eastern English Channel. The currents at elevation 0.9 m above the bottom were asymmetrical, the flood current peak being slightly stronger than the ebb current peak. At elevation 0.3 m above the bottom, the ebb/flood current peak asymmetry vanished. The observed SSCs (suspended sediment concentrations) were tidally modulated, with a contrasting vertical distribution over the ebb and flood phases of the tidal current: the profile was uniform in the ebb phase whereas a stratification appeared in the flood phase. The depth dependence and time evolution of the SSCs are attributable to a combination of local resuspension and advection-dispersion of remotely suspended fine sediment by ebb currents. Suspended sediment fluxes were uniform during the ebb phase and increased with elevation above the bottom during the flood phase. 相似文献
15.
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
16.
17.
Nikolay G. Granin Natalia A. Radziminovich Liba Z. Granina Vadim V. Blinov Ruslan Y. Gnatovskiy 《Geo-Marine Letters》2012,32(5-6):453-464
In September 2008, freshening of near-bottom water and an increase in concentration of suspended particles were observed in the western part of southern Lake Baikal. The reduction in the content of total dissolved solids was about 0.4–0.7?mg/kg (0.7?%), and average suspended particle concentration increased strongly to 6–9?mg/l, the background value being 0.2?mg/l. The spatial distribution of these waters was virtually identical to the focal area of the Mw6.2 Kultuk earthquake that occurred on 27 August 2008. It is suggested that there was a causal relationship between these two phenomena. Freshening of a significant amount (about 20?km3) of near-bottom waters was plausibly caused by an input of poorly mineralized pore waters from bottom sediments as a result of dissociation of methane gas hydrates suspected to occur in the area. The energy radiated by the earthquake source was four orders of magnitude smaller than that needed to explain the observed freshening of near-bottom waters. This points to other mechanisms leading to seismic-induced sediment failure and possible subsequent hydrate dissociation in the case of the Kultuk earthquake. 相似文献
18.
太平洋悬浮体特征及近底雾状层(雾浊层)探讨 总被引：2，自引：0，他引：2
2005年在太平洋12个测站分层采集了悬浮体水样及连续的水体温度、盐度、深度等数据.利用水体悬浮体含量在垂向上的分布特征初步分析了大洋雾状层的特点,并讨论了水体中悬浮体颗粒物质的来源,对不同海洋环境中悬浮体分布进行了对比,发现大洋水体中悬浮体含量总体很小,一般不超过0.30mg/dm3,但在一定水层内悬浮体含量相对较高,形成雾状层.雾状层在大洋内广泛分布,一般以表层雾状层和近底雾状层形式存在.大洋水体中悬浮体颗粒物来源广泛.表层雾状层的形成主要受透光层内生物作用的影响,而底质沉积物的再悬浮是影响底部雾状层形成的重要因素.因受水体物理海洋环境和物质来源的影响,不同区域水体中悬浮体含量不同,雾状层的分布不同.海山顶部受水流及岩石基底影响雾状层分布不明显,海山底部与开辟区洋盆海域雾状层更普遍.开辟区东西区由于物源差异水体中悬浮体含量差别明显,靠近火山喷口的西区水体中悬浮体含量明显高于东区的. 相似文献
19.
P. L. Christoffersen C. Christiansen J. B. Jensen T. Leipe S. Hille 《Geo-Marine Letters》2007,27(5):325-338
Information on grain-size distribution and total organic carbon (TOC) content of surface sediment and cores from the Bornholm
Basin, together with dating of cores using the 210Pb method and shallow seismic chirp profiling, has been analysed to elucidate long-term accumulation patterns. The presence
of non-depositional areas with lag sediments and low TOC content below the wave base indicates that inflows of dense bottom
water originating in the North Sea and associated near-bottom currents have strong influence on the depositional patterns
of bulk sediment and organic matter in this deep basin. The general fining in mean grain size towards the northeast corresponds
to the direction of inflow currents and prevailing winds. Recent and previously found 210Pb-based mean accumulation rates vary greatly within the basin, between 129 and 1,144 g m−2 year−1. The accumulation rate may vary by a factor of three even between stations located only 3–4 km apart. Rates recorded close
to a seismic profile are consistent with the variation in Holocene sediment thickness. This variation reflects a depositional
system controlled by near-bottom inflow currents, consisting of a large-scale channel and a wedge-formed sediment package.
The spatial variation in TOC content depends partly on water depth, presumably due to generally poorer degradation in the
deepest part of the basin because of less frequent oxygen supply by inflow water. Moreover, there is a tendency of higher
TOC contents in the southern part of the basin, which may be due to the input of sediments originating from the Oder River.
Compared to values for the central, deep Baltic Sea, TOC contents show lower values of 4–6% and insignificant temporal variations.
This may be due to the Bornholm Basin being located much closer to the source of the more oxic inflow water, resulting in
more favourable degradation conditions. 相似文献
20.
Theoretical and laboratory results indicate that bottom velocities within shoaling internal gravity waves intensify upslope approximately inversely proportional to the water depth. The elevated velocities (and bottom stresses) caused by shoaling and, possibly, breaking internal waves might explain the generation and maintenance of near-bottom nepheloid zones and attached turbid plumes that have been observed over certain continental shelves and slopes. This process is proposed as an explanation of zones of relatively low transmissibility that emanate from the upper continental slope near Newport submarine canyon off southern California. 相似文献