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1.
An acoustic doppler current profiler (ADCP) is used to measure the currents and estimate the transports over the Camarinal Sill at the Strait of Gibraltar. The deepest measurements of the ADCP compare well with an underlying conventional current meter. The exchange interface between the Atlantic and the Mediterranean water is defined as the depth of the maximum vertical shear. The mean depth of the shear interface is 147 m. The time series of the depth of the interface and the currents are used to estimate the transports across the Strait. The resulting values are 0.78 Sv for the Atlantic inflow and −0.67 Sv for the Mediterranean outflow. The time series of the shear interface include fortnightly oscillations of 19 m. The time series of the transports are compared with the pressure and sea level difference records across the Strait. Linear multiple regression is used to estimate the (statistical) contribution of each parameter on the variation of transports. The cross strait sea level difference is well correlated with the Atlantic inflow and accounts for 57% of the variability of the transport records which improves to 78% when the fortnightly and monthly cycles are included in the linear regression. The Mediterranean outflow is best correlated with the along strait sea level difference which accounts for only 10% of the variability of the transport record. Again the addition of the Msf and the MM cycles improves the percentage of the variance accounted for to 37%. The local, along strait wind component is significantly correlated with, both the Atlantic inflow and the across strait sea level difference. 相似文献
2.
The effects of tidal forcing on the biogeochemical patterns of surface water masses flowing through the Strait of Gibraltar are studied by monitoring the Atlantic Inflow (AI) during both spring and neap tides. Three main phenomena are defined depending on the strength of the outflowing phase predicted over the Camarinal Sill: non-wave events (a very frequent phenomenon during the whole year); type I Internal wave events (a very energetic event, occurring during spring tides); and type II Internal wave events (less intense, occurring during neap tides).During neap tides, a non-wave event comprising oligotrophic open-ocean water from the Gulf of Cádiz is the most frequent and clearly dominant flow through the Strait. In this tidal condition, the inflow of North Atlantic Central Water (NACW) provides the main nutrient input to the surface layer of the Alboran Sea, supplying almost 70% of total annual nitrate transport to the Mediterranean basin. A low percentage of active and large phytoplankton cells and low average concentrations of chlorophyll (0.3–0.4 mg m−3) are found in this tidal phase. Around 50% of total annual phytoplankton biomass transport into the Mediterranean Sea through the Strait presents these oligotrophic characteristics.In contrast, during spring tides, patches of water with high chlorophyll levels (0.7–1 mg m−3) arrive intermittently, and these are recorded concurrently with the passage of internal waves coming from the Camarinal Sill (type I internal wave events). When large internal waves are arrested over the Camarinal Sill this implies strong interfacial mixing and the probable concurrent injection of coastal waters into the main channel of the Strait. These processes result in a mixed water column in the AI and can account for around 30% of total annual nitrate transport into the Mediterranean basin. Associated with type I internal wave events there is a regular inflow of large and active phytoplankton cells, transported in waters with relatively high nutrient concentrations, which constitutes a significant supply of planktonic resources to the pelagic ecosystem of the Alboran Sea (almost 30% of total annual phytoplankton biomass transport). 相似文献
3.
《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(8):1005-1021
The main sill of the Strait of Gibraltar (Camarinal Sill) is an area of very energetic internal wave activity. The highest amplitude internal wave is the well-known internal bore, generated at critical conditions over Camarinal Sill. A very energetic lee wave has recently been found and reported. This occurs in neap tides when favorable combination of the stratification, vertical profile of horizontal background velocity, and bottom topography determines its generation. When the lee wave is developed the manifestation of high-amplitude internal waves is observed at the sea surface as high-frequency chaotic oscillations, named boiling waters. We analyze the generation of the lee wave over the main sill of Gibraltar Strait on the basis of the data from a ship mounted ADCP, multi-probe CTD data taken during a survey carried out in November 1998, and the numerical solution of the Taylor–Goldstein equation for the prevailing hydraulic conditions previous to its generation. Stratification is computed from CTD data, and the tidal current prediction is made from the 2 years of ADCP hourly data at Camarinal Sill gathered during the Gibraltar Experiment 94-96. The main characteristic is that they happen during neap tides, and their magnitude is comparable to the internal bore generated during spring tides. The classical internal bore and the lee waves are different phenomena, and the presence of the latter is an indicator of minimum flow over Camarinal Sill. A prediction model for lee waves based on the tidal hydrodynamic conditions is also developed. 相似文献
4.
基于ROMS三维模型, 模拟了珠江口洪季最大浑浊带的轴、侧向分布和大、小潮变化。模拟结果表明, 珠江口伶仃洋最大浑浊带的轴向位置在22.3°—22.45°N之间, 并随着潮流变化而周期性上下游迁移。控制最大浑浊带形成的主要因素是余流作用下的底层泥沙辐聚, 决定最大浑浊带位置的主要因素是水平对流输沙, 泥沙来源主要是上游浅滩沉积物的再悬浮。小潮期间堆积在浅滩的细颗粒沉积物在大潮期间被悬浮, 搬运到下游的滞流点位置, 在中滩南部和西滩外缘落淤。“潮泵”作用在大潮期间将泥沙向下游输运, 在小潮期间向上游输运; 垂向剪切作用则有利于悬浮泥沙的陆向输运; 二者共同作用产生泥沙辐聚, 形成最大浑浊带。大、小潮期间余流结构差异不大, 主要由密度差和潮汐混合不对称共同导致, 其中前者贡献更大。 相似文献
5.
The offshore tide becomes strongly distorted as it propagates into shallow estuarine systems. Observations of sea surface elevation and horizontal currents over periods ranging from three days to one year, at nine stations within Nauset inlet/estuary, document the non-linear interaction of the off-shore equilibrium tidal constituents. Despite strong frictional attenuation within the estuary, the overtides and compound tides of M2, S2 and N2, in particular, reach significant amplitude, resulting in strong tidal distortion. High frequency forced constituents in sea surface are phase-locked, consistently leading the forcing tides by 60–70°, resulting in a persistent distortion where falling tide is longer than rising tide. Forced constituents in currents are more nearly in phase with equilibrium constituents, producing flood currents which are shorter but more intense than ebb currents. A compound fortnightly tide, MSf, modulates the mean water level such that lowest tides occur during neap phase instead of spring phase. This fortnightly tide can be contaminated by storm surge, changing the phase characteristics of this constituent. Implications of the overtides, compound tides, and lower frequency tides on near-bed, suspended and dissolved material transport are profound. 相似文献
6.
《Estuarine, Coastal and Shelf Science》2003,56(3-4):629-639
Residual circulation patterns in a channel network that is tidally driven from entrances on opposite sides are controlled by the temporal phasing and spatial asymmetry of the two forcing tides. The Napa/Sonoma Marsh Complex in San Francisco Bay, CA, is such a system. A sill on the west entrance to the system prevents a complete tidal range at spring tides that results in tidal truncation of water levels. Tidal truncation does not occur on the east side but asymmetries develop due to friction and off-channel wetland storage. The east and west asymmetric tides meet in the middle to produce a barotropic convergence zone that controls the transport of water and sediment. During spring tides, tidally averaged water-surface elevations are higher on the truncated west side. This creates tidally averaged fluxes of water and sediment to the east. During neap tides, the water levels are not truncated and the propagation speed of the tides controls residual circulation, creating a tidally averaged flux in the opposite direction. 相似文献
7.
根据浙江中部近海2018年4月—2018年10月的近岸锚系流速观测数据和同步的风速风向数据,结合锚系点周边水域全潮大、中、小潮水文观测资料,进而分析了该海域水流的变化特征。锚系点余流主要沿着与等深线平行的方向(东北-西南向),余流散点图的主轴方向为25.5°(东北偏北向),沿着主轴方向的余流与垂直于主轴方向的余流标准差分别为0.12m/s和0.02m/s。余流北分量和风速北分量具有良好的相关性,两者月平均时间序列的相关系数达到了0.96,逐时整点时间序列的相关系数为0.69。锚系点余流具有13.37 d和28.49 d的周期性变化特征,该周期与大、小潮的更替周期非常接近。小潮期间,潮流的强度相对较弱,余流对风的响应较为显著,余流和风的相关性较好,两者相关系数为0.72;而在大潮期间,潮差较大且潮流流速较强,余流和风的相关性相对较差,两者相关系数为0.30。本研究,得到了锚系点及其周边水域的流速分布特征,初步获悉天文潮和风场等的非线性作用对研究区域潮流和余流的影响,可以为浙江中部沿岸海洋开发和环境保护提供动力学方面的依据。 相似文献
8.
To clarify the time change in water exchanges between Ise Bay and the adjacent ocean, repeated hydrographic observations were
conducted along the longitudinal section in Ise Bay. The results show that the mixing condition at the bay mouth (Irago Strait)
changed fortnightly in summer. During the spring tides, the strait water below the pycnocline was well-mixed and nearly homogeneous.
By contrast, it was weakly stratified during the neap tide. There is a strong negative correlation between the tidal range
and the density difference between the upper and lower layers at the strait. In summer, the intrusion depth of oceanic water
into the bay and consequent hydrographic conditions inside the bay changed frequently according to the tidal strength. During
the spring tides a prominent bottom front was created at the bay mouth, indicating that the strait water, which is a mixture
of oceanic and bay waters, intruded through the middle layer. On the other hand, during the neaps, cold and saline oceanic
water intruded through the bottom layer into the bay. The intrusion depth is significantly correlated with the tidal range.
It is considered that the wellmixed strait water, which has a density equivalent to the middle layer inside the bay, is lighter
than the bottom bay water and thus intrudes through the middle layer during the spring tides, while insufficient mixing makes
the bottom water at the strait heavier than the bay water, leading to the bottom intrusion during the neap tides. 相似文献
9.
Observations of the velocity and salinity structure of the Tees estuary were made at eight stations along the estuary axis between Victoria Bridge and the sea during the summer of 1975. The measurements were made on ten separate tidal periods covering neap and spring tides.The data were collected over a period of relatively low freshwater flows and the residual current was found to have a strong dependence on the Stokes drift. At the upstream stations, the residuals were more than an order of magnitude greater than the currents anticipated from the freshwater discharge. Although the mean stratification decreased as the tidal range increased, the vertical circulation was stronger on spring tides than on neaps. Vertical variations in the amplitude and phase of the tidal current results in a current which strengthens the vertical circulation. However, this effect only made a relatively small contribution to the observed vertical circulation.The relative contribution of the individual salt flux terms to the net upstream transport of salt varies along the estuary. As the estuary narrows, the contribution by the oscillatory terms dominates that from the shear in the steady state flow. Of these oscillatory terms, the correlation of velocity and salinity fluctuations plays a key rôle in the salt transport. The depth mean values make a greater contribution than deviations from the depth mean and the flux due to phase variations over depth is smaller than either of these. Since the Stokes drift is compensated by a down-stream steady state flow, it does not contribute to the tidal mean transport of salt.At the seaward end of the estuary, the salt fluxes due to the steady state vertical shear and the convariance of the tidal fluctuations act in a complementary way to counter the seaward transport of salt by the freshwater flow. With the possible exceptions of the wide or narrow reaches of the Tees, the longitudinal fluxes of salt due to transverse variations in velocity, salinity and depth and turbulent fluctuations are of secondary importance as contributors to the estuary salt budget.On both neap and spring tides, the computed total salt transports at the Newport and Victoria bridges did not match the values required for a salt balance with the corresponding freshwater flows. These fluxes were probably the cause of the observed downstream displacement of the tidal mean salinity distribution between neap and spring tides. 相似文献
10.
基于2020年7月特大洪水期间长江口浑浊带南槽、北槽和北港多站位同步实测水沙动力数据,研究了河口浑浊带分粒级输沙时空特征及其对泥沙来源响应的指示意义,结果表明：1）北港和北槽是流域泥沙净向口外输移的主要输沙通道,南槽是海域泥沙净向口内输移的主要输沙通道,主槽内粉砂是主要输沙组分,占比63.2%,口外粉砂和黏土是主要输沙组分,分别占43.2%、40.9%;2）大潮粉砂输运占比高于小潮,黏土输运占比低于小潮,口外测站砂组分在大小潮期间在横沙浅滩和九段沙间沿岸输移,横沙浅滩附近大、小潮离岸输沙分别是北港口外的1.7倍和8倍,不利于横沙浅滩淤涨;3）当前流域减沙高达70%,此次特大洪水期间黏土、粉砂和砂三组分近底净向口内输移为减沙背景下的口外供沙提供了有力的佐证。 相似文献
11.
基于非结构有限体积法海洋模型FVCOM(Finite-Volume Community Ocean Model), 建立了马六甲海峡及其毗邻海域高分辨率水动力数值模型, 研究了风和潮流作用下的余环流结构以及水体输运特征。结果表明, 马六甲海峡航道中央潮流运动以往复流为主, 边缘存在旋转流; 主要研究区域内落潮流速略大于涨潮流速, 东南窄道处流速最大; 因峡道束窄变浅, 在涨落潮过程中潮流发生汇聚与分离; 主要研究区域东南段存在3个显著的潮致余环流; 东北季风驱动时模型响应为海峡海流整体向西北方向流动, 西南季风时反之; 季风期间潮致表层余环流结构被破坏, 但底层余流仍存在水平环流结构, 且随着风速增加, 底层余环流的数目、大小、形状、位置均会产生变化; 季风过渡期余环流结构也会发生部分改变, 尤其是小潮期间风场影响效果显著。 相似文献
12.
Observations of the residual fluxes of water, salt and suspended sediment are presented for seven stations along the Tamar Estuary. The data include measurements over single spring and neap tidal cycles, and are generally applicable to medium or high run-off conditions.Surface to bed differences in salinity are typically of the order of several parts per thousand. Gravitational circulation is an important component of residual flow in the deep, lower reaches of the estuary. Here, Stokes drift is insignificant. In the shallow upper reaches, the major residual currents are generated by Stokes drift and freshwater inputs. Data are compared with predictions from Hansen and Rattray's (1966) model of estuarine circulation.Salt fluxes due to tidal pumping and vertical shear are directed up-estuary at spring tides, tidal pumping being dominant. Tidal pumping of salt is also directed up-estuary at neap tides, although it is insignificant in the lower reaches, where vertical shear dominates.Tidal pumping of suspended sediment is directed up-estuary near the head at spring tides, and probably contributes to the formation of the turbidity maximum. The existence of the turbidity maximum is predicted using a simplified model of the transport of water and sediment. The model shows that an additional mechanism for the existence of the turbidity maximum is an up-estuary maximum in the tidal current speeds (and thus resuspension). In the lower reaches, transport of suspended sediment is directed down-estuary at both spring and neap tides, and sediment is essentially flushed to sea with the fresh water. 相似文献
13.
Strong Tidal Mixing and Ventilation of Cold Intermediate Water at Kashevarov Bank, Sea of Okhotsk 总被引：1，自引：0，他引：1
Konstantin A. Rogachev Eddy C. Carmack Alexandr S. Salomatin 《Journal of Oceanography》2000,56(4):439-447
Tidal mixing at the Kashevarov Bank, Sea of Okhotsk, has been investigated using observations of bottom pressure and currents. The tides are dominated by the diurnal constituents. The water motion over the Bank is predominantly controlled by strong diurnal tidal currents, which bring cold water on the bank from its source, a cold intermediate layer. The temperature fluctuations are about 1.2°C at the southern edge of the bank. The maximum observed velocity is about 164 cm/s at the top of the bank. A superposition of the original diurnal constituents K1 and O1 reveals a strong fortnightly (Mf) variability of the current speed. Tidal-induced mixing is responsible for ventilation of the cold intermediate layer of the Sea of Okhotsk. Strong tidal mixing creates a well-defined tidally mixed front around the bank. This front acts like a barrier separating well-mixed water on the bank from stratified water on its flanks. There is a residual current of the order of 10 cm/s. 相似文献
14.
长江河口悬沙与盐分输运机制分析 总被引：2，自引：0，他引：2
2004年9月15~22日在长江口南支口门区域进行了水位、流速、悬沙浓度、盐度的全潮观测,基于这些现场数据,分析河口区域流速结构、悬沙浓度与盐度的时空分布特征;利用机制分解法研究河口悬沙、盐分的通量和输运机制,并探讨它们与水体垂向结构之间的关系。主要结论如下:长江河口区的悬沙浓度存在显著的时空变化特征,从口内向口外,悬沙浓度呈显著减小趋势,大潮期间的悬沙浓度较大,是小潮期间的数倍。通量机制分析结果表明,长江河口区以欧拉余流为主,向海输运,并有向海方向逐渐减小的趋势,斯托克斯余流向陆输运,在大、小潮期间有显著差异。盐分输运机制中,以欧拉余流占主导地位,潮泵效应、垂向重力环流、垂向剪切扩散作用的贡献次之。长江河口悬沙净输运率在向海方向逐渐减小,大潮期间的悬沙净输运率比小潮期间的大1~2个数量级,水动力条件是造成长江河口悬沙净输运时空差异的主要因素。悬沙输运机制小潮期间以欧拉余流占主导地位,在大潮期间则以与紊流相关的垂向剪切扩散作用取代欧拉余流占据主导地位。悬沙瞬时输运机制中的剪切扩散项在中下层水体的理查德森数(Ri)小于0.25时才有较大的量值,在南槽内,当底层水体的理查德森数(Ri)处于-0.1相似文献
15.
C.M. Davies 《Marine Geology》1974,16(2):M31-M38
Two separate current systems have been identified in Swansea Bay — a rotatory current system, located in the northern part of the embayment, and a rectilinear current system, offshore. The amount of fine-grained sediment suspended in the rotatory currents varies with both direction during a tide cycle and tidal range. Measurements of suspended sediment indicate that the suspended load is higher on neap tides than spring tides. This is due to a change in axial orientation of the rectilinear system, which directs ebb-tide currents towards the northern part of the embayment on neap tides, but “deflects” ebb-tide currents from the northern area on spring tides. 相似文献
16.
The 25-h measurements of current speed, flow direction, water depth, suspended sediment concentration and salinity were carried out at six anchored stations in the study area during spring and neap tides in winter of 1987 and summer of 1989. Caculations and analyses of the data obtained show that large amounts of suspended sediments are moved back and forth under the action of tidal current, and the net transport of sediment is small, with its predominance upstream in winter and downstream in summer. These calculations and analyses also suggest that the advective transport of sediment is dominant, while the vertical gravitational circulation of the suspended sediment comes next. Meantime, it is indicated that tidal currents play a major role in the suspended sediment transport, and residual flows have effect on the net transport of the suspended sediment, which is more remarkable during neap tide than during spring tide. 相似文献
17.
基于椒江河口大、小潮期间水位、流速、盐度和悬沙浓度观测数据,研究了椒江河口主潮汐通道的水动力、盐度和悬沙浓度的时空变化特征,解释了高浊度强潮作用下的层化物理机制。椒江河口大潮期悬沙浓度和盐度均大于小潮期,主潮汐通道区域落潮期悬沙浓度大于涨潮期;盐度随潮变化,盐水锋面出现在S2测站,锋面附近出现最大浑浊带;自陆向海,悬沙浓度递减,盐度递增;随水深增加,悬沙浓度与盐度递增。Richardson数与混合参数显示,盐度和悬沙引起的层化现象,是随着潮汐的变化而变化,涨潮时的层化均强于落潮,小潮时的层化持续时间最长,区域更广。混合参数随潮周期变化,大潮期高于临界值1.0,小潮期低于临界值1.0。小潮期水体层化强于大潮期;潮汐应变项是影响势能差异变化率的重要因素;落潮期间层化向混合状态转化,涨潮相反。 相似文献
18.
横向流 (垂直于海湾主轴方向的流动) 对横向动量以及物质分布具有重要影响。已往研究表明,潮汐应变对横向流的垂向空间结构具有重要的调控作用。但这种认识仅局限于强层化海区,弱层化条件下潮汐应变对于横向流空间结构的影响仍未可知。为此,本文以象山港为例,基于实测数据阐释了弱层化条件下潮汐应变对横向流及其余环流垂向空间结构的调控作用。结果显示,象山港内湾横向流的垂向空间结构随大小潮呈现出明显的变化规律。大潮时,潮汐应变现象明显,涨潮时较强的垂向混合使得横向流在高潮阶段呈现出一层结构;落潮时垂向混合较弱,横向流在低潮时呈现两层结构。小潮时,潮汐应变受到抑制,垂向混合在涨落潮时均较弱,因此横向流在高低潮阶段均呈现出两层结构。经过潮时均进一步得到的横向余环流呈现出上层向南、下层向北的两层结构。由于潮汐应变的大小潮变化,横向余环流的反转深度反转点自大潮到小潮呈现出上升的趋势。 相似文献
19.
河口泥沙运动有其独特的规律,需要采用高分辨率的观测手段进行系统的现场观测,以此发现河口流速和泥沙分布结构,进而探讨其形成机制,应用声学多普勒流速剖面仪和声学悬浮泥沙观测系统,通过定点和走航式观测长江河口不同潮型和流态下流速和悬浮泥沙浓度时空分布发现:(1)不同潮型出现高浓度“事件”的次数和成因存在差异,中潮型出现高浓度“事件”的可能性最大;(2)抛泥泥沙浓度垂向分布至少有3种结构类型,即上小下大的“L”型、指数型和上大下小的“漂浮”型;(3)受抛泥泥沙输移的影响,断面流场形成低流速区,它们的强度随落潮流的扩散逐渐减弱;(4)不同潮型的落潮流表现出不同的输移行为,大、小潮型落潮流偏北,中潮型落潮流偏南;(5)在落潮流和颗粒重力共同作用下抛泥泥沙同时存在输移扩散和沉降过程,小潮型抛泥泥沙主要就近扩散和沉降,中潮和大潮型抛泥泥沙输移扩散范围较远。 相似文献
20.
南海北部东沙岛附近的内潮和余流特征 总被引：4，自引：2，他引：2
采用东沙岛附近的一个长达9个月的锚定潜标的观测资料对南海北部的正压潮、内潮和余流情况进行了分析,得到了当地正压潮和内潮的特征。此处正压潮流以全日潮为主,秋、冬季相对较大,春季相对较小;正压余流受海盆尺度环流和地形的限制,在潜标观测期间的秋、冬、春三季基本以偏西向的正压流为主。内潮同正压潮一样,也以全日分潮为主,潮流椭圆随水深发生旋转,在110—120m附近存在内潮非常弱的一层。斜压余流在2009年2—3月比较异常,这是由于在此其间有一个中尺度涡经过。对此潜标数据采用经验正交函数分解的方法进行分析,发现海流的各个主要EOF模态与内波的垂向模态结构有一定的关联。 相似文献