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1.
Large oscillations of water level in Nagasaki Bay are calledAbiki and are most frequently observed in winter. The largestAbiki recorded in the past 20 years at the tide station at Nagasaki occurred on March 31, 1979. Simultaneously, a distinct atmospheric pressure disturbance of solitary type with an amplitude of about 3 mb was recorded at several neighbouring stations in Kyûshû, which indicated the pressure disturbance probably travelled eastward with an average speed of about 110 km h–1.The quantitative relation between this pressure disturbance and notable seiches observed in Nagasaki Bay is examined by means of numerical simulation, and it is confirmed that the exceptionally large range of oscillations in the bay, which reached 278 cm at the tide station, was indeed produced by this travelling pressure disturbance.The leading part of shallow water waves induced by the atmospheric pressure disturbance was amplified up to about 10 cm in amplitude, over the broad continental shelf region off China, because of near resonant coupling to the pressure disturbance. After leaving this continental shelf region, the amplified water wave converged into the shelf region (Gotô Nada) surrounded by the north-western coast of Kyûshû and the Gotô Islands and excited eigenoscillations on the shelf. A train of waves thus formed with a period of about 35 min entered Nagasaki Bay and was resonantly amplified at periods of 36 min and 23 min which are the eigen periods of the bay. Besides resonance, the combined effects of shoaling and reflection inside Nagasaki Bay also enhanced the amplification.  相似文献   

2.
Characteristics of seiches in Onagawa Bay are investigated on the basis of observations at the bay head, Konorihama, from May 1972 to May 1973 and at the outside of the bay, Enoshima during the same period. At Konorihama seiches with the double amplitude of 7 to 11 cm occurred most frequently (63 percent of the total samples) and the maximum reached 31 cm. Short-time spectral analyses indicate that the periods of the spectral peaks shift considerably with the lapse of time, and that the location of the nodal line near the bay mouth moves offshore and inshore of Enoshima. The cause of these phenomena seems to be attributed to the change of incident angle of waves coming from the open sea to excite seiches. Amplitudes of the fundamental and of the lateral modes of seiches increase or decrease alternately with time, suggesting the energy transfer between these modes. Bay oscillations induced by remarkable atmospheric pressure-waves were observed. However, the amplitudes of the oscillations were within a few centimeters and dissipated in a few hours.  相似文献   

3.
A field measurement was made at three stations near the head of Onagawa Bay to investigate the two-dimensional pattern of bay oscillations. Characteristics of the eigen oscillations are numerically calculated by finding the eigenvalues and eigenvectors of a matrix derived from a two-dimensional model. The observed oscillations can be explained, to a reasonable degree, by the calculated modes at the periods of 36, 18, 14, 12 and 10 min, where the modes at 18 and 12 min are of longitudinal oscillations and the ones at 14 and 10 min are of lateral oscillations.  相似文献   

4.
Estimation of the offshore form of tsunami waves based on an observed tidegage record at a bay head is attempted by means of an impulse response method and a characteristics method. For several tsunamis in Onagawa Bay, the results estimated by both methods are compared with the observed data at an offshore station. The correlation coefficient between the estimated and the observed values is 0.9 to 0.95, and the present methods are proved to be practical. The validity of the characteristics method is further confirmed in the case of Ofunato Bay.  相似文献   

5.
Natural and wave-induced oscillations in Nagasaki Bay, a coupled bay—river system, are numerically studied. Formulation of the problem is based on the mild slope wave equation with modeled dissipation. Computations are performed by the finite element method originated from the classical variational principle. The numerical results show that the bay at the mean tidal level has natural modes of periods of 30.60 minutes, 17.28 minutes, 10.08 minutes, 7.67 minutes, etc. The 30.60-minute mode of the bay is characterized by a monotonic increase of the amplitude of oscillation from the bay entrance to the Urakami River mouth, whereas the 17.28-minute mode and the 10.08-minute mode attain maximum near Fukahori. It is also demonstrated that the 30.60-minute mode, the 17.28-minute mode and the 10.08-minute mode can be most severely resonated when the bay is subjected to oscillations in the open sea with periods of about 33.2 minutes, 17.9 minutes, and 10.1 minutes, respectively. The existence of the Urakami River seems to have an effect on mitigating the resonant bay oscillations, particularly if the relevant mode is of relatively low frequency and maximizes near the river mouth.  相似文献   

6.
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7.
Sea-bottom pressure gauges were used to measure sea levels at two points on the shelf off the southern coast of Satsuma Peninsula, Kyushu, Japan. Spectral analysis of the observed records and the tide-gauge record of Makurazaki Harbor revealed several predominant common peaks. At the same time, the eigenmodes for the trapped waves on the shelf and inside Makurazaki Bay were obtained numerically using a two-dimensional model, and the periods and the spatial distribution of amplitudes of the proper modes were obtained. A comparison of the calculated modes with the periods and phase patterns of the observed peaks clarified that peaks with periods of 19.5, 16, 13.3, and 12.2 minutes in the shelf region were the modes of standing-edge waves, and the peak with the period of 16 minutes in Makurazaki Harbor was the fundamental mode of the harbor. Among the modes of standing-edge waves, the mode of the period 16 minutes on the shelf had nearly the same period as that of the fundamental mode of Makurazaki Harbor. An analysis of changes of spectral densities of these two modes confirmed that the fundamental mode of the Makurazaki Harbor was induced by this standing-wave mode.  相似文献   

8.
The study synthesises current understanding of the predominant physical processes responsible for the seasonality of harmful algal blooms, notably Alexandrium catenella and Dinophysis spp., in the nearshore environment of Saldanha Bay on the west coast of South Africa. Saldanha Bay is one of the few naturally sheltered areas on the South African coastline suitable for in situ shellfish farming and is the major site for the production of black mussel Mytilus galloprovincialis in South Africa. Mussel farming started there in 1985 and the present level of production is some 2 700 tons per annum. Since 1994, disruption of harvesting as a result of the presence of harmful algal species has been a regular late-summer phenomenon. Toxic blooms that are ultimately advected into the bay develop on the continental shelf to the north between 32°S and St Helena Bay, a region characterized by favourable conditions for dinoflagellate growth and circulation patterns that facilitate build-up of intense blooms during late summer. Offshore dinoflagellate populations are advected shorewards and polewards in response to relaxation of upwelling at the Namaqua cell to the north. Dinoflagellate blooms are advected south from the southern Namaqua shelf during upwelling relaxation. Under such conditions, the gyre south of Elands Bay moves offshore and a barotropic flow past Cape Columbine is established. Evidence suggests that the near surface component of the flow occurs as a sudden "flood" event. These dinoflagellate-containing shelf waters are in turn advected into Saldanha Bay when upwelling relaxes, when the density gradient between the bay and the shelf drives surface inflow and bottom water outflow. These flows are reversed with the resumption of upwelling over the shelf, resulting in intrusion and entrainment of bottom water and surface outflow. Entrainment dictates that the bay acts as a net importer of bottom water and net exporter of surface waters over a synoptic cycle. This system of exchange between Saldanha Bay and the shelf curtails the duration and severity of toxic episodes in the bay relative to the shelf.  相似文献   

9.
Measurements of NH4, NO3, urea and HCO3 uptake using 15N and 13C stable isotope tracers were undertaken in Saldanha Bay, South Africa, between January 2012 and January 2013. These studies provide the first direct measurements of N utilisation by the plankton in the bay. Primary production in the bay is driven predominantly by the advection of nutrients from the neighbouring shelf environment during upwelling events, with terrestrial and other sources providing minor inputs. New production (NO3-based) was calculated from the f-ratio and total primary production and was used to provide estimates of potential carrying capacity for bivalve culture. Despite the apparent light limitation of NO3 uptake in the winter, the availability of NO3 appeared to exert the major influence on new production throughout the year. In addition, new production was modulated by NH4 availability as shown by the suppression of NO3 uptake by concentrations higher than 1?1.5?mmol m?3. The estimated areal new production of 0.60?g C m?2 d?1 yielded a bay-wide annual estimate of 9 811 t C ha?1 y?1, slightly higher than previous calculations based on physical models. It is estimated that the total annual production of mussels and oysters, respectively, for a 1 000-ha cultivation area is approximately 40 000–53 000 t y?1 (mainly Mytilus galloprovincialis) and 4 600–6 000 t y?1 (Crassotrea gigas). The combined total production figures constitute only 24–31% of the surplus new production. A combined harvestable carrying capacity of 74 000–82 000 t y?1 can be calculated from this surplus. However, from a management and ecological perspective, bivalve culture should be limited to well below this theoretical maximum. Even with this constraint, there appears to be considerable scope for expansion of bivalve farming over the modest, present levels with little jeopardy to ecological integrity.  相似文献   

10.
The outer shelf of Funka Bay, located at the bay head of Hidaka Bay, is a recognised main winter spawning ground for walleye pollock (Theragra chalcogramma), whose newly hatched juveniles migrate eastward along the Hidaka shelf to the nursery ground located in the Doto area. To examine the seasonal change of the coastal current along this migration route, four current moorings were deployed along the shelf in Hidaka Bay from April, 2004 to June, 2006. Since these mooring sites were close to the coast, the circulation was estimated after removal of the wind-driven component. It was found that the winter coastal flow, forced by a north-westerly monsoon wind, is clockwise along the Hidaka shelf. However, this flow is weak due to the superimposition of the opposite Coastal Oyashio flow trapped on the shelf. In summer, a bifurcation of the coastal current occurs along the north-eastern Hidaka shelf with a south-eastward flow, associated with the Tsugaru Gyre, and a north-westward flow, consisting of a branch from this gyre. Our results provide a new understanding of the migration of juvenile walleye pollock: (1) very slow transport of juveniles along the Hidaka shelf from winter to spring, and (2) selection of earlier spawning survivors due to the bifurcated flow in early summer.  相似文献   

11.
Trapping of fine sediment in a semi-enclosed bay, Palau, Micronesia   总被引：1，自引：0，他引：1  
Airai Bay, Palau, is a small (3 km2), semi-enclosed, mangrove-fringed, meso-tidal, coral lagoon on the southeast coast of Palau. It drains a small catchment area (26 km2) of highly erodible soils in an area with high annual rainfall (3.7 m). River floods are short-lived and the sediment load is very large, with suspended fine sediment concentration exceeding 1500 mg l−1. The resulting river plume is about 2 m thick. The brackish water residence time is about 7 days; during this period the plume remains a distinct surface feature even after river runoff has ceased. About 98% of the riverine fine sediment settles in Airai Bay, of which about 15–30% is deposited in the mangroves during river floods. This mud remains trapped in Airai Bay because the bay is protected from ocean swells and the tidal currents and locally generated wind waves are too small to resuspend the mud in quantity. The mud is smothering coral reefs, creating a phase shift from coral to fleshy algae dominance, and is even changing habitats by creating mud banks. The persistence of Airai Bay marine resources may not be possible without improved soil erosion control in the river catchment.  相似文献   

12.
This two-year study investigates the possible factors that determine spatial and temporal dynamics of picoplankton (heterotrophic bacteria, autotrophic picoplankton—Synechococcus spp., Prochlorococcus, and picoeukaryotes) and nanoflagellate abundance in the subtropical Ilan Bay, Taiwan, where the inner bay is affected by freshwater run-off from the Lanyang River and the eastern outer bay by the Kuroshio Current. In the inner bay, there was more rain and freshwater discharge in 2005 than in 2004 during the warm season (>24° C, June–September). The abundance of bacteria, Synechococcus spp., Prochlorococcus, and picoeukaryotes and the percentage contributions of pigmented nanoflagellate (PNF %) were two- to eight-fold greater during this period (July in 2005) than for other sampling periods. Relatively low abundance of heterotrophic nanoflagellates (HNF) in the presence of abundant picoplankton prey suggests that top-down control determined HNF abundance in the Ilan Bay, Taiwan.  相似文献   

13.
The relation between the intensity of breaking of individual wind-wave crests and parameters of wave size and wave form (e. g., height, period, steepness and skewness) is examined, and the process of change of these parameters is studied in a wind-wave tank (reference wind speed 15 m sec−1, fetch 16 m). Distributions of the wave form parameters are different for breaking and nonbreaking waves. Fully breaking waves seem to hold the relationH ∞T 2, whereH is the individual wave height andT is the period. The condition of breaking is not simply determined by the simple criterion of Stokes' limit. Wave height and steepness of a breaking wave are not always larger than those of a nonbreaking wave. This suggests the existence of an overshooting phenomenon in the breaking wave. The wave form parameters are found to change cyclically in a statistical sense during the wave propagation. The period of the cycle in the present case is estimated to be longer than four wave periods. An intermittency of wave breaking is associated with this cyclic process. Roughly speaking, two or three succeeding breaking-waves sporadically exist among a series of nonbreaking waves along the fetch.  相似文献   

14.
全新世胶州湾海侵及大沽河古河口湾的形成和演变   总被引：4，自引：0，他引：4  
晚更新世盛冰期低海面时,胶州湾为陆地,大沽河流于其上,河口在黄海陆架边缘。全新世海侵时,海水沿古河道侵入,约在9．6kaB．P．左右,胶州湾地区被海水淹没,并于湾顶西北侧形成196km^2的大沽河溺谷型河口湾,当时大沽河河口退缩至今谈家庄一沽河镇(李哥庄)一带。随后,河流泥沙在该河口湾快速淤积,形成十余米厚的水下冲积扇和1～2m厚的冲积层,将溺谷湾充填。约在4kaB．P．左右大沽河河口外延至现今营海码头村、三角底一带。  相似文献   

15.
In this paper, the main results of field research into the seawater dynamics on the shelf of the Crimea in the summer of 1991 are reported. It is shown that in the weather frequency band, the oscillations with periods of 11–12 days have the greatest amplitude. These represent coastal-trapped waves with a spatial scale of the order of the length of the Black Sea coastline. These waves are generated by distant winds and significantly disturb the response of the Crimea shelf waters to local wind forcing. A transient upwelling-downwelling circulation having a period of 5–7 days is induced by local winds and is not accompanied by the generation of trapped waves at the frequency of forcing. Since the average circulation on the shelf of the Crimea is of cyclonic character, downwelling events are found more frequently and have longer time periods than the upwelling events. The wind-generated trapped waves on the shelves of the Crimea and Kerch Peninsula have an average period of 27 h. The inertial oscillations were well expressed during an experiment resembling long-wave motions.Translated by Mikhail M. Trufanov.  相似文献   

16.
It is indeed my great honor to receive the Okada Prize (1983) for my studies on the population dynamics and production of inshore marine copepods. This article summarizes the lecture I gave under the above title. It has long been postulated that there is some mechanism whereby a species can repopulate after its disappearance from the plankton, since the appearance of many temperature marine copepods clearly occurs on a seasonal basis. During the last decade, evidence of resting egg production has been found for more than 20 species belonging to Temoridae, Centropagidae, Pontellidae, Acartiidae and Tortanidae. In the Inland Sea of Japan, a summer-fall copepodTortanus forcipatus lays diapause (obligatory resting) eggs in the fall, which overwinter in the sediment on the sea floor until the following summer when water temperature reachesca. 15°C. On the other hand, in Onagawa Bay,Acartia clausi is perennial and produces only subitaneous eggs, many of which, however, sink to the bottom and undergo quiescence (facultative resting eggs) due to adverse environmental conditions (e.g. low temperature, deoxygenation, darkness). There are a large quantity (0.5–2.0×106 eggs m−2) ofA. clausi resting eggs in the sediments of Onagawa Bay, which may play an important role in maintaining a more constant planktonic population. The parameters of population dynamics,i.e. the rates of egg production, recruitment and mortality, have been analyzed forA. clausi in Onagawa Bay, by an integration of field and laboratory studies. Recruitment into the planktonic population older than NIII only accounts for 10–20% of egg production. This apparent loss of eggs, which coincides with the benthic resting phase, may be a characteristic feature of the population dynamics of this species. Stage-specific mortality is generally similar in most of the stages, although CI and CVI suffer more severe mortality, possibly as a result of great morphological change in the former stage and heavy predations in the latter. The seasonal change in daily production byA. clausi has also been investigated, its annual production being 2.45 gC m−2. Daily production and biomass (P:B) ratios increase linearly with temperature. Estimated values of production for other inshore marine copepods are reviewed in relation to P:B ratios and the ratio between secondary and primary production.  相似文献   

17.
Dynamical properties of short-period temperature fluctuations are studied. Water temperature was measured continuously at several depths at the following stations: at 38°29.5′N, 141°35.8′E (100 m depth) on the continental shelf off Miyagi Prefecture in the summer of 1967, at 35°01.8′N, 139°0.8.5′E (100 m depth) in Sagami Bay in the summer of 1968, and at 32°32.2′N, 129°53.7′E (74 m depth) in Tachibana Bay in the summer of 1970. These measurements were made with a thermistor array laid down from the R. V.Tanseimaru (Ocean Research Institute, University of Tokyo) which was fixed with bow and stern anchors. Significant temperature fluctuations found at the first and the third stations are thought to be due to first mode internal waves having amplitude 3 to 5 m and period 5 to 20 minutes. The wave length of the waves is estimated to be 25 m to 400 m from the observed density structure. At the second station, we found second-mode internal waves. The period, amplitude and wave length of the waves are about 30 minutes, 1.3 m and 600 m, respectively. In all cases, the spectral density of the temperature fluctuations decreases with increase in frequency. However, the decrease obey neither the ?3 power law nor the ?5/3 power law. Coherences in the temperature fluctuations between two depths of measurement in the seasonal thermocline are significantly high in the range of frequencies lower than the local Brunt-Väisälä frequency, but are low in the higher frequency range. At the first and the third stations, the difference in the level of coherences between the lower frequencies and the higher frequencies are large. Phase differences between two depths in the thermocline are small in the lower frequency range. This suggests that the first-mode internal waves are predominant over higher-mode internal waves and over other disturbances.  相似文献   

18.
The community composition,abundance and culturablity of heterotrophic bacterioplankton in the Dapeng Bay of the South China Sea were investigated by morphological method,bacterial cultivation and biochemical methods over an annual cycle.Aeromonas and Pseudomonas were the predominant genera among the Gram-negative bacteria.The bacterioplankton abundance fluctuated from 2.07×10 8 to 2.44×10 9 cells/dm 3 ,and culturable bacteria abundance ranged between 0.1×10 6 and 16.07×10 6 CFU/dm 3 .The Culturablity of heterotrophic bacteria ranged between 0.01% and 1.31%.The relationship between bacterial culturablity and the environmental factors was also studied in different sites of the Dapeng Bay.Throughout the bay,a significantly positive relationship was evidenced between bacterial culturability and temperature,meanswhile bacterial culturability was significantly inversely related with salinity.The positive relationship was shown at the central bay while a negative relationship was observed at the bay mouth and there was no significant correlation at top bay between bacterial culturablity and chlorophyll a of sea water.A positive relationship was found between culturability and DIN all the bay,but DIP showed a significantly negative relationship with bacterial culturability only at the mouth of the bay.  相似文献   

19.
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   

20.
Hourly fluctuations of vertical velocity in relation to components of flow and wind and temperature oscillations at a morring site in the shelf waters off the west coast of India are discussed. The vertical velocities were computed from a time series of vertical temperature profiles assuming that horizontal advection of temperature is negligible. The computed values at a depth of 40 m during the 72-h period of observation were of the order of 10−1 to 10−2cm s−1, with a mean value of −2·77 × 10−2 cm s−1 indicating a net upward movement of water. The computed vertical velocity showed fluctuations of about 2–3 h, in addition to weaker signals of about 12 h. Based on the spectral estimates, we speculate that these fluctuations of 2–3 h in the vertical velocity may be caused by the fluctuations in the along-shore wind. The oscillations of isotherms found in the temperaturedepth time series and the spectral estimates of temperature and cross-shore flow component showed a periodicity of about 12 h, which indicated the presence of semi-diurnal internal waves. The fact that these internal wave troughs were associated with the measured onshore flow suggested that the waves were propagating offshore. The computed stability parameters showed little evidence of instability or mixing. It was found that the isotherm troughs in the temperaturedepth time series at about 12-h period coincided with high vertical shear in the cross-shore direction and low values of Brunt Vaisälä frequency.  相似文献   

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