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1.
This work presents the first detailed facies analysis of the upper Nyalau Formation exposed around Bintulu, Sarawak, Malaysia. The Lower Miocene Nyalau Formation exposures in NW Sarawak represent one of the closest sedimentological outcrop analogues to the age equivalent, hydrocarbon-bearing, offshore deposits of the Balingian Province. Nine types of facies associations are recognised in the Nyalau Formation, which form elements of larger-scale facies successions. Wave-dominated shoreface facies successions display coarsening upward trends from Offshore, into Lower Shoreface and Upper Shoreface Facies Associations. Fluvio-tidal channel facies successions consist of multi-storey stacks of Fluvial-Dominated, Tide-Influenced and Tide-Dominated Channel Facies Associations interbedded with minor Bay and Mangrove Facies Associations. Estuarine bay facies successions are composed of Tidal Bar and Bay Facies Associations with minor Mangrove Facies Associations. Tide-dominated delta facies successions coarsen upward from an Offshore into the Tidal Bar Facies Association. The Nyalau Formation is interpreted as a mixed wave- and tide-influenced coastal depositional system, with an offshore wave-dominated barrier shoreface being incised by laterally migrating tidal channels and offshore migrating tidal bars. Stratigraphic successions in the Nyalau Formation form repetitive high frequency, regressive–transgressive cycles bounded by flooding surfaces, consisting of a basal coarsening upward, wave-dominated shoreface facies succession (representing a prograding barrier shoreface and/or beach-strandplain) which is sharply overlain by fluvio-tidal channel, estuarine bay or tide-dominated delta facies successions (representing more inshore, tide-influenced coastal depositional environments). An erosion surface separates the underlying wave-dominated facies succession from overlying tidal facies successions in each regressive–transgressive cycle. These erosion surfaces are interpreted as unconformities formed when base level fall resulted in deep incision of barrier shorefaces. Inshore, fluvio-tidal successions above the unconformity display upward increase in marine influence and are interpreted as transgressive incised valley fills. 相似文献
2.
High frequency sea level oscillations at Wells Harbor (Maine, Northeastern US), with periods in the range of several tens of minutes, display a tidally modulated response. During low tides, these sea level oscillations reach amplitudes of 10–20 cm, while during high tides they are significantly smaller. Wells Harbor is located in a low lying area with a tidal range of about 2 m and is connected to the open ocean through a narrow channel. Thus, the extent and depth of the bay significantly vary over a tidal cycle. This changing geometry determines both the resonant periods and the amplification factor of the bay. Numerical results confirm the link between observed variability and these specific topographic features. Results imply that when exceptionally energetic long waves reach the Wells Harbor entrance (as in the case of a tsunami or meteotsunami) the expected response will be significantly stronger during low tide than during high tide. Although mean sea level would be lower in the former case, the currents inside the bay would be stronger and potentially more dangerous. This tidally modulated response could be extrapolated to other sites with similar topographic characteristics. 相似文献
3.
The Middle Devonian Gauja Formation in the Devonian Baltic Basin preserves tide‐influenced delta plain and delta front deposits associated with a large southward prograding delta complex. The outcrops extend over 250 km from southern Estonia to southern Lithuania. The succession can be divided into 10 facies associations recording distributary channel belts that became progressively more tide influenced when traced southwards towards the palaeo‐shoreline, separated by muddy intra‐channel areas where deposition was characterized by crevasse splays, delta plain lakes, abandoned channel deposits and tidal gullies. Tidal currents influenced deposition over the entire delta plain, extending up to 250 km from the contemporary shoreline. Tidal facies on the upper delta plain differ from those on the lower delta plain and delta front. In the former case, deposition from river currents was only occasionally interrupted by tidal currents, e.g. during spring tides, resulting in mica and mudstone drapes, and distinctive graded cross‐stratification. The lower delta plain was dominated by tidal facies and tidal currents regularly influenced deposition. There was a change from progradation to aggradation from the lower to the upper part of the Gauja Formation coupled with a vertical decrease in tidal influence and a decrease in coarse‐grained sediment input. The Gauja Formation contrasts with established models for tide‐influenced deltas as the active delta plain was not restricted by topography. The shape of the delta plain, the predominant southward (basinward)‐directed palaeocurrents, and the thick sandstone succession, show that although tidal currents strongly influenced deposition at bed scale, rivers still controlled the overall morphology of the delta and the larger‐scale bedforms. In addition, there are no signs of wave influence, indicating very low wave energy in the basin. The widespread tidal influence in the Devonian Baltic Basin is explained by changes in the wider basin geometry and by local bathymetrical differences in the basin during progradation and aggradation of the delta plain, with changes in tidal efficiency accompanying the change in basin geometry produced by shoreline progradation. 相似文献
4.
The Frewens sandstone is composed of two elongate tide-influenced sandstone bodies that are positioned directly above and slightly landward of a more wave-influenced lobate sandstone. The 20-km-long, 3-km-wide Frewens sandstone bodies coarsen upwards and fine away from their axes, have gradational bases and margins and have eroded tops abruptly overlain by marine shales. These sandstones are superbly exposed in large cliffs on the banks of the South Fork of the Powder River in central Wyoming, USA. The deposits change upwards from thinly interbedded sandstones and mudstones to metre-thick heterolithic cross-strata and, finally, to metres-thick sandstone-dominated cross-strata. There is abundant evidence for tidal modulation of depositional flows; however, palaeocurrents were strongly ebb-dominated and nearly parallel the trend of sandstone-body elongation. Detailed mapping of stratal geometry and facies across these exposures shows a complex internal architecture. Large-scale bedding units within sandstone bodies are defined by alternations in facies, bed thickness and the abundance of shales. Such bedsets are inclined (5°–15°) in walls oriented parallel to palaeoflow and gradually decrease in dip over hundreds of metres as they extend from the sandstone-dominated deposits higher in a sandstone body to muddier deposits lower in the body. Where viewed perpendicular to palaeoflow, bedsets are 100-metre-wide lenses that shingle off the sandstone-body axis towards its margins. The sandstone bodies are interpreted as sand ridge deposits formed on the shoreface of a tide-influenced river delta. Metres-thick cross-strata in the upper parts of sandstone bodies resemble deposits of bars (sandwaves) formed where tidal currents moved across shallows and the tops of tidal ridges. Heterolithic deposits lower in sandstone bodies record fluctuating currents caused by ebb and flood tides and varying river discharge. Erosion surfaces capping sandstone bodies record tidal ravinement. The tidal ridges were abandoned following transgression and covered with marine mud as waters deepened. 相似文献
5.
An experiment was conducted to study megaripple morpho dynamics on a sandy intertidal shoal in a mesotidal mangrove creek (Gordon Creek, Townsville, Australia). Tidal current velocity and depth were recorded with S4 current meters over a period of 35 tides. The tidal megaripples were 0.06–0.2 m in height and 1–2 m in wavelength, and their movement was monitored by (1) electromagnetic bed-elevation probes (which automatically recorded bed level every 2 min at three positions along the survey transect) and (2) daily surveying for 8 days around spring tidals. The tidal currents in Gordon Creek are ebb-dominated, with maximum depth-mean current velocities for the flood and ebb tides of 0.62 and 0.98 m s?1 respectively. Significant bedload transport occurs only during spring tides, and only on the larger of the unequal semi-diurnal tides. Bedload transport is overwhelmingly in the ebb direction. Megaripple migration rates reach 5.6 m per tide in the ebb direction and up to 0.1 m min?1 within individual tides. Within-tide ‘bedform transport rates’are up to 0.29 kg m?1 s?1. The results suggest that for reconstruction of palaeoflows from deposits of preserved fine- to medium-grained sandy tidal megaripples, it is valid to use a depth-averaged velocity of 0.5–0.6 m s?1 as the migration threshold. Velocity thresholds associated with partial or complete reversal of megaripple asymmetry are invalid. 相似文献
6.
为揭示河口湾水动力环境对滩涂利用的累积响应过程,以珠江口伶仃洋河口湾为例,基于潮波数学模型和潮流数学模型,研究了1981年以来湾内进出潮量、分潮振幅和潮流流速的累积变化。结果表明:相对于1981年,2018年岸线条件下伶仃洋湾口断面涨落潮量累积减少4.9%~6.0%、内伶仃断面涨落潮量累积减少9.0%~12.8%、深圳湾断面涨落潮量累积减少17.8%、南沙断面涨落潮量累积减少5.0%~6.3%;伶仃洋M2分潮振幅呈增加趋势,振幅增幅由南向北增加,潮波由南向北变形进一步加剧;伶仃洋最大可能潮差变化与M2分潮振幅变化趋势一致,潮汐性质没有发生变化;伶仃洋潮流流速总体减小,西岸流速减幅高于东岸,湾顶附近流速略有增加。 相似文献
7.
R. Verney J.-C. Brun-Cottan R. Lafite J. Deloffre J. A. Taylor 《Estuaries and Coasts》2006,29(4):653-664
Tidal currents and the spatial variability of tidally-induced shear stress were studied during a tidal cycle on four intertidal
mudflats from the fluvial to the marine part of the Seine estuary. Measurements were carried out during low water discharge
(<400 m3 s−1) in neap and spring tide conditions. Turbulent kinetic energy, covariance, and logarithmic profile methods were used and
compared for the determination of shear stress. The cTKE coefficient value of 0.19 cited in the literature was confirmed. Shear stress values were shown to decrease above mudflats
from the mouth to the fluvial part of the estuary due to dissipation of the tidal energy, from 1 to 0.2 N m−2 for spring tides and 0.8 to 0.05 N m−2 for neap tides. Flood currents dominate tidally-induced shear stress in the marine and lower fluvial estuary during neap
and spring tides and in the upper fluvial part during spring tides. Ebb currents control tidally-induced shear stress in the
upper fluvial part of the estuary during neap tides. These results revealed a linear relationship between friction velocities
and current velocities. Bed roughness length values were calculated from the empirical relationship given by Mitchener and
Torfs (1996) for each site; these values are in agreement with the modes of the sediment particle-size distribution. The influence
of tidal currents on the mudflat dynamics of the Seine estuary was examined by comparing the tidally-induced bed shear stress
and the critical erosion shear stress estimated from bed sediment properties. Bed sediment resuspension induced by tidal currents
was shown to occur only in the lower part of the estuary. 相似文献
8.
Kuo-Chuin Wong 《Estuaries and Coasts》1993,16(2):335-345
Great South Bay is the largest of a series of interconnected bar-built estuaries on the south shore of Long Island, New York. The depth-averaged barotropic motions in the bay were simulated by using a finite element two-dimensional numerical model. The barotropic motions were driven with astronomical tides, subtidal coastal sea level fluctuations induced by longshore wind stress over the adjacent continental shelf, and local wind stress over the surface of the bay. There was vigorous exchange at tidal frequencies between the western part of Great South Bay and the surrounding waters, but the tidal exchange was heavily damped in the eastern part of the bay. At subtidal frequencies the volume exchange did not exhibit significant attenuation in the interior of the bay. In the eastern part of Great South Bay, the magnitude of the subtidal volume exchange could exceed that of the tidal exchange. The principal mode of subtidal volume exchange was found to be associated with subtidal sea level fluctuations along the coast, which characteristically caused a filling or emptying of the system from all open boundaries of Great South Bay. 相似文献
9.
古河口湾沉积环境的恢复主要根据下列证据进行:1.淡化水证据:小个体薄壳生物组合和沉积物中低的硼含量;2.古地理位置处于古河流入海部位;3.潮汐能量大于河流能量,潮汐作用控制了主要沉积过程;4.沉积层序与现代河口湾层序可以类比。虽然河口湾生命短暂,沉积物常被改造,但一个时期的古代河口湾沉积物仍是可以被识别的。 相似文献
10.
On the linkages among density, flow, and bathymetry gradients at the entrance to the Chesapeake Bay 总被引：1，自引：0，他引：1
Arnoldo Valle-Levinson William C. Boicourt Michael R. Roman 《Estuaries and Coasts》2003,26(6):1437-1449
Linkages among density, flow, and bathymetry gradients were explored at the entrance to the Chesapeake Bay with underway measurements of density and flow profiles. Four tidal cycles were sampled along a transect that crossed the bay entrance during cruises in April–May of 1997 and in July of 1997. The April–May cruise coincided with neap tides, while the July cruise occurred during spring tides. The bathymetry of the bay entrance transect featured a broad Chesapeake Channel, 8 km wide and 17 m deep, and a narrow North Channel, 2 km wide and 14 m deep. The two channels were separated by an area with typical depths of 7 m. Linkages among flows, bathymetry, and water density were best established over the North Channel during both cruises. Over this channel, greatest convergence rates alternated from the left (looking into the estuary) slope of the channel during ebb to the right slope during flood as a result of the coupling between bathymetry and tidal flow through bottom friction. These convergences were linked to the strongest transverse shears in the along-estuary tidal flow and to the appearance of salinity fronts, most markedly during ebb periods. In the wide channel, the Chesapeake Channel, frontogenesis mechanisms over the northern slope of the channel were similar to those in the North Channel only in July, when buoyancy was relatively weak and tidal forcing was relatively strong. In April–May, when buoyancy was relatively large and tidal forcing was relatively weak, the recurrence of fronts over the same northern slope of the Chesapeake Channel was independent of the tidal phase. The distinct frontogenesis in the Chesapeake Channel during the increased buoyancy period was attributed to a strong pycnocline that insulated the surface tidal flow from the effects of bottom friction, which tends to decrease the strength of the tidal flow over relatively shallow areas. 相似文献
11.
在进行庵东潮坪水文要素定点测量的基础上,对地貌特征,沉积粒度,沉积构造及重向剖面作了全面分析与研究。结果表明,滩地位于杭州湾进、退潮流的交会点,控制其发育的主动力为潮汐作用,具明显的不规则半日潮特性,涨潮流强度远大于落潮流,造就了宽达十余公里的潮滩地貌。滩地水动力深受湾内水流影响,高潮期服从其总体潮流流向,导致潮坪上发育众多与杭州湾深槽系统相连的潮沟,破坏了沉积物正常分布规律,高潮坪存在一定向平行岸线的大型潮沟,受强劲水流影响,沉积粒度粗化,并因快冲快淤而产生变形构造;中潮坪接受退潮期潮沟漫岸物质,粒度相对较小,分选性变差,沉积构造以直脊流水波痕及板状交错层理为主;低潮坪潮流作用大、沉积粒度粗,分选性最佳,发育小型流水波痕,内部构造以槽状交错层理,“青鱼刺”层理及再作用构造为特征。潮坪近岸处潮沟迁移层序及浪成波痕层理的发现反映水动力异常强大,威胁人工海塘的安全,建议停止进一步围垦滩涂,采取促淤方法,抑制潮沟的发育,以维持滩地稳定。 相似文献
12.
海南岛洋浦湾沉积作用研究 总被引：9，自引：0，他引：9
本文对海南岛洋浦湾海域的洋浦湾、新英湾、洋浦深槽及拦门沙浅滩的沉积环境和沉积特征做了描述、讨论，对河流、海岸侵蚀和珊瑚礁生物的３种沉积物来源及数量做了分析计算，得出其总量为９×１０4ｍ３／ａ。根据钻孔柱状样的14Ｃ及210Ｐｂ分析，得出８０００ａＢ．Ｐ．以来沉积速率为０．１～０．２ｃｍ／ａ，近百年来沉积速率为１～２ｃｍ／ａ。 相似文献
13.
Analysis of heavy-mineral distribution in modern sediments of Willapa Bay, Washington, indicates a dominance of two mineralogic assemblages, one with approximately equivalent amounts of hornblende, orthopyroxene and clinopyroxene, the other dominated by clinopyroxene. The hornblende-orthopyroxene-clinopyroxene suite is derived from the Columbia River, which discharges into the ocean a short distance south of the bay. The clinopyroxene suite is restricted in modern sediments to sands in rivers flowing into the bay from the east. The heavy-mineral distributions suggest that sand discharged from the Columbia River, borne north by longshore transport, and carried into the bay by tidal currents accounts for most of the sand within the interior of Willapa Bay.Three heavy-mineral assemblages are present in the surrounding Pleistocene deposits; two of these are identical to the modern assemblages described above. These heavy-mineral assemblages reflect the relative influence of tidal and fluvial processes on the Late Pleistocene deposits; their relative influences are consistent with those inferred on the basis of sedimentary structures and stratigraphic relations in about two-thirds of the samples examined. The anomalies can be explained by recycling of sand from older deposits. The persistence of the two heavy-mineral assemblages suggests that the pattern of estuarine sedimentation in Late Pleistocene deposits closely resembled that of the modern bay.The third heavy-mineral suite, dominated by epidote, occurs in a few older Pleistocene units. On the north side of the bay, the association of this suite with southwest-directed foresets in crossbedded gravel indicates derivation from the northeast, perhaps from an area of glacial outwash. The presence of this suite in ancient estuarine sands exposed on the east side of the bay suggests that input from this northerly source may have intermittently dominated bay deposition in the past. 相似文献
14.
GIORGIO BASILICI PEDRO HENRIQUE VIEIRA DE LUCA ELSON PAIVA OLIVEIRA 《Sedimentology》2012,59(5):1613-1639
Open‐coast tidal flats are hybrid depositional systems resulting from the interaction of waves and tides. Modern examples have been recognized, but few cases have been described in ancient rock successions. An example of an ancient open‐coast tidal flat, the depositional architecture of the Lagarto and Palmares formations (Cambrian–Ordovician of the Sergipano Belt, north‐eastern Brazil) is presented here. Detailed field analyses of outcrops allowed the development of a conceptual architectural model for a coastal depositional environment that is substantially different from classical wave‐dominated or tide‐dominated coastal models. This architectural model is dominated by storm wave, low orbital velocity wave and tidal current beds, which vary in their characteristics and distribution. In a landward direction, the storm deposits decrease in abundance, dimension (thickness and spacing) and grain size, and vary from accretionary through scour and drape to anisotropic hummocky cross‐stratification beds. Low orbital wave deposits are more common in the medium and upper portion of the tidal flat. Tidal deposits, which are characterized by mudstone interbedded with sandstone strata, are dominant in the landward portion of the tidal flat. Hummocky cross‐stratification beds in the rock record are believed, in general, to represent storm deposits in palaeoenvironments below the fair‐weather wave base. However, in this model of an open‐coast tidal flat, hummocky cross‐stratification beds were found in very shallow waters above the fair‐weather wave base. Indeed, this depositional environment was characterized by: (i) fair‐weather waves and tides that lacked sufficient energy to rework the storm deposits; (ii) an absence of biological communities that could disrupt the storm deposits; and (iii) high aggradation rates linked to an active foreland basin, which contributed definitively to the rapid burial and preservation of these hummocky cross‐stratification deposits. 相似文献
15.
In this study, we apply the traditional hydraulic engineering approach to model an inter-connected multiple-bay-inlet system that can represent the Great South Bay-Moriches Bay system on Long Island, New York. We show that the hydraulic model captures the essential physics of the system, despite its apparent simplicity in mathematical expressions. The model gives good estimates of bay tidal transmissions, including the tidal ranges, phase lags, and the flood-ebb asymmetry behavior in Moriches Bay. The hydraulic modeling results compare well with the simulations from a 3D coastal ocean circulation model, in particular the changes in bay tides due to the breach of Old Inlet by Hurricane Sandy. The modeled inlet discharge rates are in good agreement with the observations. 相似文献
16.
In October of 2004, a 3-d observational program to measure flow and sediment resuspension within a coastal intertidal salt
marsh was conducted in the North Inlet/Winyah Bay National Estuarine Research Reserve located near Georgetown, South Carolina.
Current and acoustic backscatter profiles were obtained from a moored acoustic Doppler current profiler (ADCP) deployed in
a shallow tidal channel during the spring phase of the tidal cycle under high discharge conditions. The channel serves as
a conduit between Winyah Bay, a large brackish estuary, and North Inlet, a saline intertidal coastal salt marsh with little
freshwater input. Salinity measurements indicate that the water column is vertically well mixed during flood, but becomes
vertically stratified during early ebb. The stratification results from brackish (15 psu) Winyah Bay water entering North
Inlet via the tidal channel, suggesting an exchange mechanism that permits North Inlet to receive a fraction of the poor water
quality and high discharge flow from upland rivers. Although maximum flood currents exceed maximum ebb currents by 0.2 m s−1, suspended sediment concentrations are highest during the latter ebb phase and persist for a longer fraction of the ebb cycle.
Even though the channel is flood-dominated, the higher concentrations occurring over a longer fraction of the ebb phase indicate
net particulate transport from Winyah Bay to North Inlet during spring tide accompanied by high discharge. Our evidence suggests
that the higher concentrations during ebb result from increased bed friction caused by flow asymmetries and variations in
water depth in which the highest stresses occur near the end of ebb near low water despite stronger maximum currents during
flood. 相似文献
17.
MARTIN R. WELLS PETER A. ALLISON GARY J. HAMPSON MATTHEW D. PIGGOTT CHRISTOPHER C. PAIN 《Sedimentology》2005,52(4):715-735
Due to a lack of modern analogues, debate surrounds the importance of tides in ancient epi-continental seas. However, numerical modelling can provide a quantitative means of investigating palaeo-tidality without recourse to analogues. Finite element modelling of the European Upper Carboniferous epi-continental seaway predicts an exceedingly low Lunar tidal range (ca 5 cm in the open water regions of the UK and Southern North Sea). The Imperial College Ocean Model (ICOM) uses finite element methods and an unstructured tetrahedral mesh that is computationally very efficient. The accuracy and sensitivity of ICOM tidal range predictions were tested using bathymetric data from the present-day Mediterranean Sea. The Mediterranean Sea is micro-tidal and varies in depth up to 5·4 km with an average depth of 1–2 km. ICOM accurately predicts the tidal range given both a realistic, but smoothed, bathymetry and a straight sided basin with a uniform depth of 1 km. Variation in uniform depth from 100 to 3000 m with and without islands consistently predicts micro-tidality, demonstrating that the model is robust and the effect of bathymetric uncertainty on model output is relatively small. The extremely low tidal range predicted for the European Upper Carboniferous is thus deemed robust. Putative Upper Carboniferous tidal deposits have been described in the UK and southern North Sea, but are represented by cyclic rhythmites and are limited to palaeo-estuaries. Calculations based on an embayed coast model show that the tidal range could have been amplified to ca 1 m in estuaries and that this is sufficient to form cyclic rhythmites. Without tidal mixing, the tropical equatorial heat and salinity enhancement would promote stratification in the open water body. The introduction of organic matter probably caused anoxia, biotic mortality and carbon accumulation, as evidenced by numerous black ‘marine-band’ shales. 相似文献
18.
Peter J. J. Kamp Fraka J. Harmsen Campbell S. Nelson Susan F. Boyle 《Sedimentary Geology》1988,60(1-4):173-195
Pliocene, non-tropical, widespread and locally thick (up to 100 m) limestones occur in Hawke's Bay, eastern North Island, where they are intimately associated with very thick ( > 5 km), terrigenous-dominated, Neogene sequences that formed in a tectonically active convergent margin setting. The non-tropical character of the limestones is shown unequivocally by (1) the complete dominance of skeletal calcarenites and calcirudites, (2) the occurrence of oyster banks as the only in situ organic structures, (3) the dominance of barnacles, epifaunal molluscs, bryozoans, echinoderms, foraminifers, brachiopods and calcareous red algae as skeletal components, and (4) the preponderance of calcite over aragonite in the mineralogy of the skeletal grains and cements. The abundance of barnacle fragments in the limestones, and the related exclusive occurrence of only one major organic association, a barnacle-(epifaunal) bivalve-bryozoan assemblage, is striking and unusual given the extent of the limestones. Pecten and oyster valves acted as substrates for barnacle attachment, and their growth was promoted by strong tidal paleocurrents that swept the depositional setting: a long (450 km), narrow (30–50 km) forearc basin seaway, which formed between an actively deforming subduction complex to the east and an uplifting structural ridge to the west. Synsedimentary deformation promoted limestone formation on the margins of the seaway by creating current-swept, clastic-free submarine ridges that acted as the sites of carbonate production. Tidal flows dispersed the carbonate constituents and organised them into a wide spectrum of tide-influenced, cross-bedded and horizontal structures. Most spectacular are occurrences of giant tabular cross-beds, with sets 10–40 m thick and foreset dips of 7–36°, some interpreted as the deposits of major sand bars on carbonate deltas marginal to the mouths of saddles traversing the rising antiforms, and others analogous to modern linear sand ridges. The small- to large-scale planar and trough cross-beds, and the horizontal and lenticular beds that are invariably associated with the giant cross-beds and dominate most sections, represent mainly the deposits of sand waves and sand sheets at inner- to mid-shelf depths in the seaway. 相似文献
19.
Observations of current velocity profiles and hydrography over and near a tall sill in a Chilean glacial fjord are used to
illustrate the interactions between barotropic and baroclinic tides. The character of the barotropic tide in the glacial fjord
is mixed with semidiurnal dominance. The ratio of sill height to water column depth at the study site is ca. 0.95. Water column
stratification appeared only in the upper 5 m of the water column. Current velocity variations in the stratified surface layer
were quite different to those underneath. Below the pycnocline, nonlinear interactions between semidiurnal M2 and diurnal K1 oscillations yielded a third-diurnal distortion MK3. Most interesting, surface layer currents were distortedby the superposition of semidiurnal M2 and sixthdiurnal M6 oscillations. The oscillations with M6 variability were identified, through wave superposition approaches, as reflected internal tides linked to M2 tidal variations. This was confirmed by theoretical results of stratified barotropic tidal flows interacting with abrupt
bathymetry. Under the predominantly tidally mixed regime of the study area, the distortion to surface currents caused by the
reflected wave was nearly symmetric during the large tidal ranges of the diurnal cycle. Nearly symmetric distortions resulted
as the phase lag between incident and reflected wave-inducted currents was small (reflected currents developing a few minutes
after maximum tidal flows). During the small ranges of the diurnal cycle, distortions were asymmetrical because of the relatively
larger phase lags of the reflected signal (reflected currents developing tens of minutes after maximum tidal flows). 相似文献