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1.
《Ocean Modelling》2002,4(3-4):221-248
Three-dimensional numerical simulations of the generation and propagation of the semidiurnal internal tide in a submarine canyon with dimensions similar to those of the Monterey Canyon are carried out using a primitive equation model. Forcing with just sea level at the offshore boundary in an initially horizontally homogeneous ocean with realistic vertical stratification, internal tides are generated at the canyon foot and rim, and along portions of the canyon floor. The results compare favorably with observations, both indicating enhancement of energy along the canyon floor propagating at an angle consistent with linear internal wave theory. Due to the earth's rotation, internal tide energy is distributed asymmetrically in the cross-canyon direction, favoring the southern side. The effect of canyon floor slope is explored, with the finding that small changes in the slope result in large changes in the amount and distribution of the internal tide energy. Canyons whose floors are subcritical with respect to the semidiurnal frequency along their entire length have very little baroclinic energy, whereas canyons that are near-critical along much of their length, such as the Monterey Canyon, develop strong internal tides that propagate shoreward. Canyons that are near-critical at their mouths but supercritical further inshore generate the most internal tidal energy overall, although little of it makes it onto the continental shelf shoreward of the canyon head. The effects of internal tides within the canyons can be seen outside the canyons as well. Water is transported from depth onto the adjacent continental shelf along the canyon rims. This tidal pumping can be responsible for alongshore internal tide propagation and tidal-period surface currents with relatively small horizontal scales of variability.  相似文献   

2.
Internal tidal currents and associated water-mass displacements were investigated during multiple cruises in the Kaoping Submarine Canyon off southwestern Taiwan. Observations from both moored and shipboard Acoustic Doppler Current Profilers and hydrographic casts were conducted along the canyon. The velocity data showed that in the lower layer the major axis of the tidal currents aligned with the orientation of the canyon, and currents moved up-canyon during flood and down-canyon during ebb. The vertical-phase shift and amplitude of the currents indicated that the semidiurnal internal tide dominated with intensity increasing with depth toward the canyon head. Tidal energy was channeled from the shelf landward with a beamlike internal wave, guided by bottom topography. The estimated phase velocity was 1.4–1.7 m s−1, based on normal mode analysis and the phase lag between sampling stations. Empirical orthogonal function analysis of hydrographic profiles confirmed that the first mode (M2 internal tide) explained 70% of the total variance. The strong convergence of internal tidal currents near the canyon head during flood may play an important role in the daily migration of cherry shrimps, which burrow along the canyon wall.  相似文献   

3.
Drainage-extraction algorithms traditionally used for extracting river networks and watersheds from gridded land topography are applied to gridded multibeam bathymetry of the mid-California margin. The algorithms are used to automatically map two regional tributary networks of submarine canyons and deepsea channels draining Monterey Bay, the principal conduits of which are Acension and Monterey Canyons. The algorithms reliably map subaqueous drainage areas, but are prone to error in mapping the extent of submarine canyon and channel thalwegs due to operator subjectivity and algorithm limitations. A geomorphic comparison of the Acension and Monterey Canyon networks, with 12 river networks in the continental U.S., illustrates both the potential and weaknesses of using drainage extraction algorithms to analyze sediment pathways in gridded bathymetry.  相似文献   

4.
Numerical experiments were performed to explain the observed results of the internal tides in Uchiura Bay. The experiments for the generation of the internal tides in Suruga Bay indicate that the internal tides, generated at the slopes in the bay, are not as large an amplitude as those observed in Uchiura Bay. However, when the semidiurnal internal tides incident through the mouth of Suruga Bay are considered, they are amplified. The amplitude at the head of Uchiura Bay is 6–12 times larger than that at the mouth of Suruga Bay under the summer density structure. Under the fall density structure, the amplitude ratio is approximately 4–6. The amplification of the semidiurnal internal tides in Uchiura Bay is considered to be due to resonance of the longitudinal internal seiche of Uchiura Bay. On the other hand, the calculated diurnal internal tides are not as large as those observed. Therefore, the diurnal internal tides are thought to already have these large amplitudes at the mouth of Suruga Bay. Therefore, from the observations and numerical experiments, it is concluded that the internal tides observed in Uchiura Bay are mostly the internal tides originating from the outer region of Suruga Bay, and the semidiurnal tides are the internal seiche which is resonantly amplified.  相似文献   

5.
Current measurements in the surface layer in Sagami and Suruga Bays showed existence of significant tidal currents which are considered to be mainly due to internal tides (Inaba, 1982; Ohwaki,ea al., 1991). In addition, the prevailing period of the tidal currents is semidiurnal in Sagami Bay, but diurnal in Suruga Bay. To explain this difference in the prevailing, periods, numerical experiments were carried out using a two layer model. The internal tides are generated on the Izu Ridge outside the two bays. The semidiurnal internal tide propagates into Sagami Bay having characteristics of an internal inertia-gravity wave, while it propagates into Suruga Bay having characteristics of either an internal inertia-gravity wave or an internal Kelvin wave. The diurnal internal tide behaves only as an internal Kelvin wave, because the diurnal period is longer than the inertia period. Thus, the diurnal internal tide generated on the Izu Ridge can be propagated into Suruga Bay, while it cannot propagate into the inner region of Sagami Bay, though it is trapped around Oshima Island, which is located at the mouth of Sagami Bay. The difference in the propagation characteristics between the semidiurnal and diurnal internal tides can give a mechanism to explain the difference in the prevailing periods of the internal tides between Sagami and Suruga Bays.  相似文献   

6.
Monterey Fan is the largest modern fan off the California shore. Two main submarine canyon systems feed it via a complex pattern of fan valleys and channels. The northern Ascension Canyon system is relatively inactive during high sea-level periods. In contrast, Monterey Canyon and its tributaries to the south cut across the shelf and remain active during high sea level. Deposition on the upper fan is controlled primarily by the relative activity within these two canyon systems. Deposition over the rest of the fan is controlled by the oceanic crust topography, resulting in an irregular fan shape and periodic major shifts in the locus of deposition. Margin setting represents fan and/or source area  相似文献   

7.
This study examines the influence of a submarine canyon on the dispersal of sediments discharged by a nearby river and on the sediment movement on the inner shelf. The study area includes the head region of the Kao-ping Submarine Canyon whose landward terminus is located approximately 1 km seaward from the mouth of the Kao-ping River in southern Taiwan. Within the study area 143 surficial sediment samples were taken from the seafloor. Six hydrographic surveys along the axis of the submarine canyon were also conducted over the span of 1 yr. Three different approaches were used in the analysis of grain-size distribution pattern. They include (1) a combination of ‘filtering’ and the empirical orthogonal (eigen) function (EOF) analysis technique, (2) the McLaren Model, and (3) the ‘transport vector’ technique. The results of the three methods not only agree with one another, they also complement one another. This study reveals that the Kao-ping Submarine Canyon is relatively a stratified and statically stable environment. The hydrographic characteristics of the canyon display seasonal variability controlled primarily by the temperature field and the effluent of the Kao-ping River. The hydrographic condition and the bottom topography in the canyon suggest the propagation of internal tides during the flood season (summer) of the Kao-ping River. The submarine canyon acts as a trap and conduit for mud exchange between the Kao-ping River and offshore. Near the head of the canyon there is a region of sediment transport convergence. This region is also characterized by high mud abundance on the seafloor that coincides with the presence of high suspended sediment concentration (SSC) spots in the bottom nepheloid layer. Outside the submarine canyon on the shelf where the evidence of wave reworking is strong, the northwestward alongshore transport dominates over the southeastward transport, which is a common theme on the west coast in southern Taiwan.  相似文献   

8.
High-resolution multichannel seismic data enables the discovery of a previous, undocumented submarine canyon(Huaguang Canyon) in the Qiongdongnan Basin, northwest South China Sea. The Huaguang Canyon with a NW orientation is 140 km in length, and 2.5 km to 5 km in width in its upper reach and 4.6 km to 9.5 km in width in its lower reach. The head of the Huaguang Canyon is close to the Xisha carbonate platform and its tail is adjacent to the central canyon. This buried submarine canyon is formed by gravity flows from the Xisha carbonate platform when the sea level dropped in the early stage of the late Miocene(～10.5 Ma). The internal architecture of the Huaguang Canyon is mainly characterized by high amplitude reflections, indicating that this ancient submarine canyon was filled with coarse-grained sediments. The sediment was principally scourced from the Xisha carbonate platform. In contrast to other buried large-scale submarine canyons(central canyon and Zhongjian Canyon) in the Qiongdongnan Basin, the Huaguang Canyon displays later formation time, smaller width and length, and single sediment supply. The coarse-grained deposits within Huaguang Canyon provide a good environment for reserving oil and gas, and the muddy fillings in Huaguang Canyon have been identified as regional caps. Therefore, Huaguang Canyon is potential area for future hydrocarbon exploration in the northwest South China Sea. Our results may contribute to a better understanding of the evolution of submarine canyons formed in carbonate environment.  相似文献   

9.
Monterey Fan is the largest modern fan off the California shore. Two main submarine canyon systems feed it via a complex pattern of fan valleys and channels. The northern Ascension Canyon system is relatively inactive during high sea-level periods. In contrast, Monterey Canyon and its tributaries to the south cut across the shelf and remain active during high sea level. Deposition on the upper fan is controlled primarily by the relative activity within these two canyon systems. Deposition over the rest of the fan is controlled by the oceanic crust topography, resulting in an irregular fan shape and periodic major shifts in the locus of deposition.  相似文献   

10.
High-resolution multichannel seismic data enables the discovery of a previous, undocumented submarine canyon(Huaguang Canyon) in the Qiongdongnan Basin, northwestern South China Sea. The Huaguang Canyon with a NW orientation is 140 km in length, and 2.5 km to 5 km in width in its upper reach and 4.6 km to 9.5 km in width in its lower reach. The head of the Huaguang Canyon is close to the Xisha carbonate platform and its tail is adjacent to the Central Canyon. This buried submarine canyon is formed by gravity flows from the Xisha carbonate platform when the sea level dropped in the early stage of the late Miocene(around 10.5 Ma). The internal architecture of the Huaguang Canyon is mainly characterized by high amplitude reflections, indicating that this ancient submarine canyon was filled with coarse-grained sediments. The sediment was principally scourced from the Xisha carbonate platform. In contrast to other buried large-scale submarine canyons(Central Canyon and Zhongjian Canyon) in the Qiongdongnan Basin, the Huaguang Canyon displays later formation time,smaller width and length, and single sediment supply. The coarse-grained deposits within the Huaguang Canyon provide a good environment for reserving oil and gas, and the muddy fillings in the Huaguang Canyon have been identified as regional caps. Therefore, the Huaguang Canyon is a potential area for future hydrocarbon exploration in the northwestern South China Sea. The result of this paper may contribute to a better understanding of the evolution of submarine canyons formed in carbonate environment.  相似文献   

11.
Alternating up- and downcanyon currents with velocities up to 50 cm/sec are found in submarine canyons. These alternations have patterns that usually can be matched between adjacent stations in the same canyon, even where separated by as much as 16 km. The matching of curves from adjacent stations is obtained by time shifts. In 20 out of 23 comparisons, the patterns were best fitted by shifting so that a later time of arrival is indicated for the upcanyon station. This indicates that internal waves (mostly tidal in period) are advancing up the submarine canyons or rarely downcanyon. Because the data come from canyons off California, the East Coast of the United States, and the Hawaiian Islands and include depths to as much as 3,500 m, it is suggested that these canyon internal waves may be worldwide. The exceptional downcanyon advances appear to be the result of unusual canyon bathymetry, perhaps combined with unusual tides.  相似文献   

12.
Tidal currents observed in a surface layer overlying deep water in Sagami and Suruga Bays frequently have large amplitude in summer and fall. Numerical experiments show that the current amplitude due to the surface tides is below 1.0 cm sec–1 for the semidiurnal and diurnal constituents in the inner region of the two bays. The observed current amplitudes are larger than the calculated ones due to the surface tides. Therefore, the observed tidal currents are indicated to be due mainly to the internal tides. In addition, the semidiurnal currents dominate the diurnal currents in Sagami Bay, while the opposite occurs in Suruga Bay. These results suggest that the prevailing periods of the internal tides differ between the two bays,i.e., the internal tide has a semidiurnal period in Sagami Bay and a diurnal period in Suruga Bay.  相似文献   

13.
Located in the south-eastern part of the Bay of Biscay, the Capbreton Canyon incises the continental shelf up to the 30 m isobath contour, and acts as a natural conduit for continental and shelf-derived sediments. EM1000 multibeam bathymetry shows two main features characterising the canyon — a deeply entrenched meandering channel, bordered by fluvial-like terraces constituting large sediment traps. A dataset of cores and seismic profiles together with a multibeam bathymetry map has enabled the characterisation of recent sedimentary activity in the axial channel and on the terraces. Data analysis evidenced the major role of the canyon head in recent sediment dynamics. This part of the canyon is a temporary reservoir for sediments, accumulated by coastal hydrodynamic processes. Exceptional climatic, tectonic or hydrodynamic events can mobilise the sediments and generate gravity-driven flows. Under the present-day sea-level highstand conditions, these flows are not powerful enough to bring their bedload to the deep sea, and are confined mainly to the upper part of the canyon. Turbidity currents model the axial channel pathway and are at the origin of terrace formation. Terraces in the Capbreton Canyon are not typical but rather are reduced to confined levees. Three factors control the vertical growth of a terrace: (1) the amount of overspilled sediments brought by turbidity currents, (2) hemipelagic sedimentation and (3) terrace height. The amount of sediment spilling over a terrace decreases with increased terrace elevation. Concurrently, the proportion of hemipelagic fallout depositing on a terrace increases. Terraces are considered to be fossil when the height of the terrace prevents further deposition by overspilling. The terraces studied in this paper are interpreted as having formed during the Holocene, implying that the sediment dynamics of the Capbreton Canyon is continuous through time. Highstand periods differ from lowstand periods because they show a decrease in the energy of erosive processes. Temporal variations in erosive and depositional processes in the canyon are controlled by the Adour River, which delivers large amounts of sediment to the system.  相似文献   

14.
The autonomous underwater glider "Spray"   总被引：4，自引：0，他引：4  
A small (50-kg, 2-m long) underwater vehicle with operating speeds of 20-30 cm/s and ranges up to 6000 km has been developed and field tested. The vehicle is essentially an autonomous profiling float that uses a buoyancy engine to cycle vertically and wings to glide horizontally while moving up and down. Operational control and data relay is provided by GPS navigation and two-way communication through ORBCOMM low-Earth-orbit satellites. Missions are envisioned with profile measurements repeated at a station or spaced along a transect. The initial instrument complement of temperature, conductivity, and pressure sensors was used to observe internal waves and tides in the Monterey underwater canyon  相似文献   

15.
胶州湾潮汐潮流动边界数值模拟   总被引：11，自引：4，他引：7  
基于普林斯顿海洋模式,通过干湿网格判别法引入潮汐潮流的漫滩过程,考虑M2,S2,K1,O1,M4和MS4六个主要分潮,建立了胶州湾潮汐潮流数值模拟和预报模型,研究了该海域潮汐潮流特征,并讨论了漫滩对潮流模拟的影响。与实测资料的对比验证表明,该模式能够对胶州湾的潮汐和潮流做出较为合理的预测。给出了胶州湾潮汐、潮流、余流等分布特征,模拟的潮流场以及余流场涡旋等现象与观测符合良好;计算了潮波能通量,从能量角度探讨了潮波的传播特性;对潮位与潮流场演变规律,以及潮能通量的分析表明,胶州湾内的潮波以驻波为主。通过数值试验发现,漫滩过程的引入对胶州湾潮流速度的模拟至关重要,不考虑漫滩过程的模式会夸大或者低估潮流流速。对于滩涂面积广阔的海域来说,潮流数值模式中考虑漫滩的影响是必要的。  相似文献   

16.
Long-term temperature measurements of the subsurface layer near Uchiura-Bay head were made in summer 1978 and 1979 to further investigate the characteristics of the internal tides in more detail. The temperature measurements indicate that the internal tides were present at all times during the observational period. The semidiurnal internal tides are usually dominant over the diurnal, but at times the diurnal internal tides have comparable amplitudes with the semidiurnal. When the semidiurnal internal tides are predominant, the fundamental period of the longitudinal internal seiche in Uchiura Bay estimated from the observed density structure is close to the semidiurnal period. However, the reason for the occasional amplification of the diurnal internal tides is not clear.  相似文献   

17.
Monitoring using a thermistor array and an acoustic Doppler current profiler was carried out in the outer part of Tokyo Bay from May 20 to November 30, 2006. Current fluctuations with tidal periods were amplified during the maximum temperature period in early September. The strong current interfered with fishing operations using set nets. Although the current fluctuation was speculated to be baroclinic motion from a phase relationship among fluctuations of temperature, current and sea level, empirical orthogonal function analysis showed the dominance of a barotropic structure. Such a discrepancy in the current structure was explained by an internal tide propagating along a deep canyon in the outer part of Tokyo Bay. Furthermore, amplification of the semidiurnal internal tide and the warming of the temperature field were found to be induced by the intrusion of Kuroshio warm water. The amplification mechanism was examined using a two-dimensional model with idealized topography. It was concluded that the large amplitude of the semidiurnal internal tide is resonantly generated in the deep canyon in the outer Tokyo Bay when stratification becomes strong and the period of the internal seiche approaches the semidiurnal period.  相似文献   

18.
Remarkable tidal currents associated with temperature fluctuations in the subsurface layer have been observed in Uchiura Bay. In order to study the characteristics of these tidal currents, we carried out current measurements in November 1972 and October 1974. It was confirmed from the first set of observations in 1972 that the tidal currents above and below the seasonal thermocline oscillate out of phase with each other and the tidal currents are associated with internal tides.In the second set of observations in 1974 not only current measurements but also serial BT lowerings were made. The phase of the thermocline displacements lagged behind the tidal currents by 81 for the semidiurnal constituent and by 83 for the diurnal constituent, and it is thus concluded that the internal tides in Uchiura Bay behave as standing waves.  相似文献   

19.
Long-term hourly data from 35 tide gauge stations, including 15 stations in the Gulf of Finland, were used to examine tidal sea level oscillations of the Baltic Sea. High-resolution spectral analysis revealed the well-defined fine structure of tidal peaks with diurnal peaks at most stations being higher than semidiurnal. At some stations (e.g., Narva, Daugava, and Wladyslawowo), high frequency radiational tidal peaks with periods multiple of the solar day (3, 4, 5, 6, and 8 cpd) were detected; the respective oscillations are supposed to be caused by seabreeze winds. Harmonic analysis of tides for individual yearly sea level series followed by vector averaging over the entire observational period was used to estimate the amplitudes and phases of 16 tidal constituents. The maximum tidal oscillations of 17–19 cm were found to be observed in the Gulf of Finland and, first of all, in Neva Bay (in the head of the gulf). Diurnal or mixed diurnal tides are predominant in almost the entire Baltic Sea. The comparison of the observed tides with those theoretically computed showed that the existing numerical models of the main tidal harmonics generally quite accurately reproduce the structure of the tides in the Baltic Sea except for some regions of the Gulf of Bothnia.  相似文献   

20.
Dune erosion is shown to occur at the embayment of beach mega-cusps O(200 m alongshore) that are associated with rip currents. The beach is the narrowest at the embayment of the mega-cusps allowing the swash of large storm waves coincident with high tides to reach the toe of the dune, to undercut the dune and to cause dune erosion. Field measurements of dune, beach, and rip current morphology are acquired along an 18 km shoreline in southern Monterey Bay, California. This section of the bay consists of a sandy shoreline backed by extensive dunes, rising to heights exceeding 40 m. There is a large increase in wave height going from small wave heights in the shadow of a headland, to the center of the bay where convergence of waves owing to refraction over the Monterey Bay submarine canyon results in larger wave heights. The large alongshore gradient in wave height results in a concomitant alongshore gradient in morphodynamic scale. The strongly refracted waves and narrow bay aperture result in near normal wave incidence, resulting in well-developed, persistent rip currents along the entire shoreline.

The alongshore variations of the cuspate shoreline are found significantly correlated with the alongshore variations in rip spacing at 95% confidence. The alongshore variations of the volume of dune erosion are found significantly correlated with alongshore variations of the cuspate shoreline at 95% confidence. Therefore, it is concluded the mega-cusps are associated with rip currents and that the location of dune erosion is associated with the embayment of the mega-cusp.  相似文献   


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