首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 78 毫秒
1.
Current meter data from various depths near the sea bottom collected for 31 days at time intervals of 10 minutes using a subsurface buoy system at a depth at 38 m on the continental shelf off Akita, Japan have been analyzed. The results show the existence of a stationary Ekman layer. The typical range of the characteristic parameters are estimated as follows; friction velocity: 0.38 cm s–1; Ekman layer thickness: 16 m; logarithmic layer thickness: 4 m–6 m; constant flux layer thickness: 0.4–0.6 m; Ekman veering: 28.7°; drag coefficient: 0.24×10–2–0.53×10–2. Veering was also observed in the logarithmic layer.  相似文献   

2.
The path of the Kuroshio in Sagami Bay was surveyed through drifter tracking from Oshima-West Channel to Oshima-East Channel. A subsurface drifter with a drogue at 300 m depth flowed around Oshima from Oshima-West Channel to Oshima-East Channel. A difference in flow directions between the upper and lower layers was apparent in the northwest of Oshima. Flow directions there were shown to change from north in the surface layer to east in the bottom layer, and this was confirmed with moored currentmeters.A profile of northward current velocity was estimated from measurements in six layers with currentmeters deployed in the Oshima-West Channel. The profile shows a core of northward flow along the eastern bottom slope and a weak southward flow along the western bottom slope. Volume transport of the Kuroshio into Sagami Bay was estimated to be 1.8×106m3sec–1 from the profile.Long-term current measurement showed that southward flows were observed in Oshima-West Channel in July 1977, May 1978 and April 1979. Cold or warm water masses appearing south of the Izu Peninsula are suggested to have caused the changes.Displacement of the cold water mass in July 1977 is discussed on the basis of current measurements and offshore oceanographic conditions.  相似文献   

3.
Cylindrical sediment traps were deployed at various depths in the anoxic water of Framvaren for two periods of one year (1981–1982 and 1983–1984). The traps were emptied three times during 1981–1982 and five times during 1983–1984. The vertical fluxes of total suspended material, organic carbon and nitrogen were calculated on a daily and annual basis. The average annual sediment flux 20 m above the bottom was approximately 60 g m−2 y−1 and the flux of organic carbon was 20 g m−2 y−1. On the basis of an average C/N ratio of 8 and a constant carbon flux below a depth of 20 m, it is concluded that little mineralization of the organic matter takes place in the anoxic water column. Assuming a primary production of the order to 50–100 g m−2 y−1, 22–24% of that reaches the anoxic water masses. Further breakdown of organic matter takes place in the surface sediments.  相似文献   

4.
Since 1985, a number of measurements have been made in deep water to determine the water-following characteristics of mixed layer drifters with both holey-sock and TRISTAR drogues at 15 m depth. The measurements were done by attaching two neutrally buoyant vector measuring current meters (VMCMs) to the top and the bottom of the drogues and deploying the drifters in different wind and upper ocean shear conditions for periods of 2–4 h. The average velocity of the VMCM records was taken to be a quantitative measure of the slip of the drogue through the water, observed to be 0.5-3.5 cm s−1. The most important hydrodynamic design parameter which influenced the slip of the drogue was the ratio of the drag area of the drogue to the sum of the drag areas of the tether and surface floats: the drag area ratio R. The most important environmental parameters which affected the slip were the wind and the measured velocity difference across the vertical extent of the drogue. A model of the vector slip as a function of R, vector wind and velocity difference across the drogue was developed and a least squares fit accounts for 85% of the variance of the slip measurements. These measurements indicated that to reduce the wind produced slip below 1 cm s−1 in 10 m s−1 wind speed, R > 40. Conversely, if the daily average wind is known to 5 m s−1 accuracy, the displacement of the R = 40 drifter can be corrected to an accuracy of 0.5 km day−1.  相似文献   

5.
Concentrations of total carbonate, alkalinity and dissolved oxygen were obtained near the 1973 GEOSECS stations in the North Pacific subpolar region north of 40°N along 175°E between 1993 and 1994. A difference of excess CO2 content between the GEOSECS and our expeditions was estimated. The maximum difference in water column inventory of excess CO2 has increased by about 280 gC m–2 above 2000 m depth which apparently means an uptake of excess CO2 taken from air to sea during the last two decades. An averaged value of the annual flux of excess CO2 at 75–1000 m depth was 8.63±2.01 gC m–2yr–1 in the North Pacific subpolar region. By introducing the annual flux of excess CO2 into a two-box model for the North Pacific subpolar region, a penetration factor of excess CO2 from air to sea was obtained to be 1.08×10–2 gC m–3ppm–1 in the North Pacific subpolar region. Based on this factor, the surface concentration of excess CO2 in the North Pacific subpolar region was estimated to be 68 mole I–1, suggesting that the North Pacific subpolar region absorbed atmospheric excess CO2 more than the saturated concentration of excess CO2. Total amount of excess CO2 taken from the North Pacific subpolar region by 1993 was estimated to be 36.2×1015 gC, which was equal to about one tenth of that released by human activities after the preindustrial era.  相似文献   

6.
A simple advection-diffusion model is applied to the deep water of the North Pacific Ocean. The physical mixing parameter, i.e., the ratio of vertical advection velocity (W) to vertical eddy diffusivity (D), is obtained from the vertical distribution of a conservative property such as salinity. The rate of decomposition of organic matter is estimated from the oxygen consumption rate which is obtained from dissolved oxygen content. The calcium carbonate flux in the deep water is obtained from alkalinity. Using these values and the vertical distribution of a radioisotope,14C or226Ra, the vertical eddy diffusivity and the upwelling velocity are found to be 1.2 cm2/sec and 1.4 ×10–5 cm/sec, respectively, at the Geosecs 1969 station. The oxygen consumption rate at 3 km depth of the station is found to be 1.4×10–3ml/l/yr.  相似文献   

7.
Some observations were carried out to understand the structure of the vertical residual flow in Kasado Bay. The results of current measurements at three points in the lower layer indicated that a horizontal counterclockwise tidal residual circulation converges in the lower layer. The velocity of upward residual flow was estimated to be about 4.5×10–3 cm s–1. The distributions of water temperature, salinity and grain size in the sediment support the existence of this upward motion.  相似文献   

8.
Measurements of plankton respiration and heterotrophic bacterial abundance and production were made at seven deep water stations within the upper 500 m of the Gulf of Mexico during the summer of 1995. Bacterial abundance [(1.1–4.6)×108 1−1] and rates of bacterial production (2–19 nM C h−1) and plankton respiration (50–245 nM O2 h−1) decreased with depth by four- to nine-fold, and were similar to those reported for oligotrophic waters. Bacterial turnover times increased with depth from approximately 1 to 5 days. Bacterial growth efficiencies decreased from 15% at the surface to 8% at 500 m. Depth-integrated plankton respiration exceeded known estimates of primary production for the region, suggesting that heterotrophic utilization of previously and concurrently produced organic matter (e.g. spring phytoplankton growth, and summer blooms of Trichodesmium sp.) was occurring during the summer. Estimates for the upper 500 m showed that roughly half of the bacterial biomass (56%), bacterial production (49%), and plankton respiration (60%) occurred below the euphotic zone. Routine oceanographic studies have focused exclusively on the metabolic activity occurring within the euphotic zone. Our measurements, however, indicate that mesopelagic plankton also contribute substantially to heterotrophic metabolism and nutrient cycling in the ocean.  相似文献   

9.
An array of sediment traps was deployed for the analysis of the pattern of particulate organic carbon (POC) supply to the sea bottom in April, May and July 1988 at the mouth of Otsuchi Bay (about 80 m depth), Northeastern Japan.On the basis of a simple two-component mixing model using stable carbon isotope ratios, the POC flux was separated into marine planktonic and terrestrial components. Both the planktonic and terrestrial POC fluxes had maximum values at 30 m above the sea bottom throughout the three experiments. The planktonic POC flux showed a significant decrease with depth between 30 m and 10 m or 5 m above the bottom. Vertical supply of the planktonic POC and supply of the resuspended planktonic POC were estimated on the basis of regression lines between water depth and the planktonic POC flux in the depth range where the flux decreases with depth.Vertical supply of the planktonic POC and supply of the resuspended planktonic POC to the sea bottom were largest in May (52.1 mgC m–2 d–1 and 19.5 mgC m–2 d–1 at 5 m above the sea bottom), and horizontal supplies of the terrestrial POC were almost constant (31.9±3.5 mgC m–2 d–1 at 5 m above the bottom) throughout the three experiments.  相似文献   

10.
Direct current measurements of the branch current of the Kuroshio intruding into Sagani Bay were carried out during 1989–1990 in order to clarify the frequency characteristics of the eddies in the lee of Izu-Oshima Island, which are well recognized as cold water mass produced by upwelling. Satellite and ADCP (Acoustic Doppler Current Profiler) data indicated that current velocity in the eddy fluctuates with periods of 2–4 days and 6–8 days.When the Kuroshio branch current intruding into Sagami Bay from the western channel is weak and its velocity at the depth of 400 m is approximately 10 cm s–1, the 6–8 day period fluctuation is dominant. On the other hand, when the branch current strongly intrudes from the western channel with a velocity of approximately 20 cm s–1, the 2–4 day period fluctuation dominates. The relationship between the periods and velocities agrees well with theory based on laboratory experiments for a flow of a homogeneous fluid past a circular obstacle. These periods correspond to the time scale of appearance of the eddy caused by the intrusion of the Kuroshio branch current into Sagami Bay and Izu-Oshima Island.  相似文献   

11.
The concentration of methane in seawater was determined approximately once a month for one year from August 1990 to July 1991 at a station close to the center of Funka bay (92 m depth) and some supplementary observations were also carried out. The concentration of methane was usually increased with increasing depth, suggesting that methane was emitted from the bottom of the bay. While highly variable both spatially and temporally, the emission was intense in March and April, a period immediately after the spring bloom of phytoplankton. The maximum of methane found in the intermediate water suggests its source from the slope of the bay. The concentration of methane in the surface water changed seasonally and also interannually. The annually averaged flux of methane transferred to the atmosphere in the bay was estimated to be 6×10–3 gCH4m2/day. The coastal zone in the world may be a significant source of the atmospheric methane, although its source strength has yet to be accurately estimated from more data in different coastal seas.  相似文献   

12.
The concentrations of228Ra in surface waters of the Seto Inland Sea were determined. Surface waters from the central region of the Seto Inland Sea, Hiuchi Nada and Bingo Nada, contained concentrations of228Ra of 655–811 dpm/1000 l which were 100 times higher than those obtained in the Pacific Ocean. These high concentrations of228Ra must be supported by a228Ra flux from the bottom sediment. The lower limit of this flux was estimated to be more than 0.16 dpm cm–2 y–1. The228Ra concentrations decreased markedly from central regions of the Seto Inland Sea to about 18 dpm/1000 l in the Kii and the Bungo Channels as salinity increased. Using a box model and the228Ra data, the mean residence time of sea water in the Seto Inland Sea with respect to the exchange with the open ocean water was estimated to be less than 10 y, and the most probable value is the order of several years.  相似文献   

13.
The detailed flow structure around a tical front in Hiuchi-Nada, Japan was observed with the use of ADCP (Acoustic Doppler Current Profiler). The surface convergence region is observed at the transition zone between vertically well mixed area and the stratified area. The surface divergence regions exist next to the surface convergence region. The strong downward current is estimated in the middle layer just below the surface convergence region. The maximum surface convergence and the maximum downward velocity in the middle layer are 1.0×10–4 s–1 and 0.12 cm s–1, respectively.  相似文献   

14.
Underwater observations of infaunal amphiurid ophiuroids were made at a depth of about 480 m in Suruga Bay, central Japan, using a free-fall system which consists of time-lapse stereo-photography units and current meters. The megabenthos fauna was characterized by the dominance of infaunal echinoderms; in particular, amphiurid ophiuroids were numerically dominant. The density and biomass of the amphiurids were 170 m–2 and 37 g m–2, respectively. They buried their discs in the sediment and extended their arm tips out of the sediment surface. They protruded 2.2 arms per individual on the average. Strong bottom currents were observed, and the average velocity was 12 cm sec–1 at 4 m above the sea floor. No arm tip was observed to be raised vertically into the water column for suspension feeding utilizing the bottom current, and amphiurids were considered to be primarily a surface deposit feeder at the present site.  相似文献   

15.
Environmental parameters that affect the growth ofChattonella antiqua were monitored throughout the outbreak period of this species around the Ie-shima Islands, the Seto Inland Sea, in the summer of 1987 (20 July–13 August). Averaged cell concentration ofC. antiqua over the water column (21 m) was below 10 cells· ml–1 on 20 July, gradually increased to reach the maximum of 250 cells·ml–1 on 7 August, and then rapidly decreased to the value of 30 cells·ml–1 on 13 August.Thermal stratifications were prominent from 20 July to 3 August and were destroyed after 4 August. Temperature and salinity were optimum for the growth ofC. antiqua throughout the survey period.At the bloom initiation period (20–21 July), concentrations of N- and P-nutrients (S N andS P ) were high throughout the water column. From 22 July to 3 August, whenC. antiqua increased its populations,S N andS P at the depth of 0–5m were low but those at the depth of 10–20m kept a high value. After 4 August,S n andS P at the depth of 10–20m decreased rapidly due to wind mixing coupled with the nutrient uptake byC. antiqua. When the populations ofC. antiqua reached the maximum (7–9 August), N-nutrients were depleted throughout the water column but P-nutrients were not. Concentrations of vitamin B12 were almost in the same range as those of the previous years and were optimum for the growth ofC. antiqua.GP- value (growth potential of the seawater with respect to nitrogen and phos-phorus) was higher than 0.6 even at the surface layer (0–5 m) at the bloom-initiation period. During the bloom development period (22 July–3 August), GP at the surface layer (0–5m) was low (<0.2), but GP at the depth of 10–20m kept a rather high value (>0.4).In situ growth rates ofC. antiqua at the depth of 0 and 5m estimated from bottle experiments coincided well with the values expected from GP. A high value of GP at the surface layer in the initiation period and a shallow GP-cline in the development period, combined with the ability of diurnal vertical migration seemed to be at least one reason that natural populations ofC. antiqua grew at a rather high rate and formed red tides in the summer of 1987.  相似文献   

16.
Time-series measurements of temperature, salinity, suspended matter and beam attenuation coefficient () were measured at four hour intervals for about two days in June/ July 1982 in the middle shelf region and the coastal region of the southeastern Bering Sea. Current meters were also moored at the same locations.Depth-time distributions of indicated that profiles of suspended matter resulted from a combined process of resuspension of underlying sediments and sinking of suspended particles. Average-values for all measurements for particles revealed that the upward transport of particles due to resuspension formed a boundary layer, with a thickness apparently related to scalar speed. The average-profiles of the particle volume concentration were assumed to result from a balance between the sinking and diffusive flux of particles under a steady state, and the upward fluxes were calculated. Within the boundary layer, values of the upward fluxes of particulate organic matter linearly decreased with the logarithm of distance from the bottom. Fluxes of organic carbon at the upper edge of the boundary layer were 0.375 gC·m–2·day–1 in the middle shelf region (18 m above the bottom, bottom depth=78m) and 0.484gC·m–2·day–1 in the coastal region (25 m above the bottom, bottom depth=33m), and fluxes of nitrogen in both regions were 0.067 gN·m–2·day–1. The flux of organic carbon obtained in the middle shelf region (18 m above the bottom) agreed approximately with the flux (0.416 gC·m–2·day–1) calculated by substituting primary production data into the empirical equation of Suess (1980).  相似文献   

17.
Repeated measurements of depth profiles of 234Th (dissolved, 1–70 and >70 μm particulate) at three stations (Orca, Minke, Sei) in the Ross Sea have been used to estimate the export of Th and particulate organic carbon (POC) from the euphotic zone. Sampling was carried out on three JGOFS cruises covering the period from October 1996 (austral early spring) to April 1997 (austral fall). Deficiencies of 234Th relative to its parent 238U in the upper 100 m are small during the early spring cruise, increase to maximum values during the summer, and decrease over the course of the fall. Application of a non-steady-state model to the 234Th data shows that the flux of Th from the euphotic zone occurs principally during the summer cruise and in the interval between summer and fall. Station Minke in the southwestern Ross Sea appears to sustain significant 234Th removal for a longer period than is evident at Orca or Sei. Particulate 234Th activities and POC are greater in the 1–70 μm size fraction, except late in the summer cruise, when the >70 μm POC fraction exceeds that of the 1–70 μm fraction. The POC/234Th ratio in the >70 μm fraction exceeds that in the 1–70 μm fraction, likely due in part to the greater availability of surface sites for Th adsorption in the latter. Particulate 234Th fluxes are converted to POC fluxes by multiplying by the POC/234Th ratio of the >70 μm fraction (assumed to be representative of sinking particles). POC fluxes calculated from a steady-state Th scavenging model range from 7 to 91 mmol C m−2 d−1 during late January–early February, with the greatest flux observed at station Minke late in the cruise. Fluxes estimated with a non-steady-state Th model are 85 mmol C m−2 d−1 at Minke (1/13–2/1/97) and 50 mmol C m−2 d−1 at Orca (1/19–2/1/97). The decline in POC inventories (0–100 m) is most rapid in the southern Ross Sea during the austral summer cruise (Smith et al., 2000. The seasonal cycle of phytoplankton biomass and primary productivity in the Ross Sea, Antarctica. Deep-Sea Research II 47, 3119–3140. Gardner et al., 2000. Seasonal patterns of water column particulate organic carbon and fluxes in the Ross Sea, Antarctica. Deep-Sea Research II 47, 3423–3449), and the 234Th-derived POC fluxes indicate that the sinking flux of POC is 30–50% of the POC decrease, depending on whether steady-state or non-steady-state Th fluxes are used. Rate constants for particle POC aggregation and disaggregation rates are calculated at station Orca by coupling particulate 234Th data with 228Th data on the same samples. Late in the early spring cruise, as well as during the summer cruise, POC aggregation rates are highest in near-surface waters and decrease with depth. POC disaggregation rates during the same time generally increase to a maximum and are low at depth (>200 m). Subsurface aggregation rates increase to high values late in the summer, while disaggregation rates decrease. This trend helps explain higher values of POC in the >70 m fraction relative to the 1–70 m fraction late in the summer cruise. Increases in disaggregation rate below 100 m transfer POC from the large to small size fraction and may attenuate the flux of POC sinking out of the euphotic zone.  相似文献   

18.
Suspended particulate matter (SPM) concentration and properties (particle size and settling velocity), water column and boundary layer dynamics were measured during a 60-d period at a site in 110 m water depth in the northern North Sea. The site was in stratified waters and measurements were made during September–November as the seasonal thermocline was progressively weakening. SPM concentration was low, c. 1 mg dm−3 in the surface mixed layer and maximum values of 2 mg dm−3 in the bottom mixed layer. The bottom layer was characterised by larger mean particle size. SPM signals in the two layers were decoupled at the start of the period, when the thermocline was strong, but were increasingly coupled as the thermocline progressively weakened. A spring-neap cycle of resuspension and deposition of SPM was observed in the bottom mixed layer. Bed shear stresses were too small to entrain the bottom sediment (a fine sand) but were competent to resuspend benthic fluff: threshold bed shear stress and threshold current velocity at 10 mab were 0.02–0.03 Pa. and 0.18 m s−1, respectively. Maximum SPM concentration in the bottom layer preceded peak spring tide currents by 3 d. Simulation of fluff resupension by the PROWQM model confirms that this was due to a finite supply of benthic fluff: the fluff layer was stripped from the seabed so that fluff supply was zero by the time of peak spring flow. SPM was redeposited over neap tides. Fluff resuspension must have been enhanced by intermittent inertial currents in the bottom layer but unequivocal evidence for this was not seen. There was some resuspension due to wave activity. Settling velocity spectra were unimodal or bimodal with modal values of 2×10−4–2×10−3 mm s−1 (long-term suspension component) and 0.2–5.7 mm s−1 (resuspension component). The slowest settling particles remained in suspension at peak spring tides after the fluff layer had been exhausted. There was evidence of particle disaggregation during springs and aggregation during neaps.  相似文献   

19.
In order to clarify detailed current structures over the continental shelf margin in the East China Sea, ADCP measurements were carried out in summers in 1991 and 1994 by the quadrireciprocal method (Katoh, 1988) for removing diurnal and semidiurnal tidal flows from observed flows, together with CTD measurements. We discussed the process of the Tsushima Current formation in the East China Sea. The Tsushima Current with a volume transport of 2 Sv (1 Sv=106 m3s–1) was found north of 31°N. A current with a volume transport of 0.4 Sv was clearly found along the 100 m isobath. Between the Kuroshio and the current along the 100 m isobath, southeastward component of velocity was dominant compared to northwestward one. Four eastward to southeastward currents were found over the sea bed shallower than 90 m depth. Total volume transport of these four currents was 1 Sv, and they seemed to be originated from the Taiwan Strait. Intrusion of offshore water into the inner shelf northwest of Amami Oshima was estimated to have a volume transport of 0.6 Sv. It is concluded that the Tsushima Current is the confluence of these currents over the continental shelf margin with the offshore water intruding northwest of Amami Oshima.  相似文献   

20.
An intelligent ADCP (Acoustic Doppler Current Profiler) fish, called DRAKE (Depth and Roll Adjustable Kite for Energy flux measurements) was developed with the controllable wings which can adjust the submerging depth of the fish and stabilize its roll motion. The Kuroshio west of Okinawa was measured in a roundtrip course on the same traverse line by the ADCP fish. The forward survey obtained the maximum submerging depth of 208 m at a fish operation speed of 2.9 ms–1. The maximum fish speed of 5.4 ms–1 was achieved at a submerging depth of 48 m in the return survey. The data in the overlapped area of data acquisition between depths 212 and 276 m were used to examine the accuracy of velocity measurement for the towed ADCP system. The summation of both survey data made it possible to estimate a sectional velocity structure and transport of the upper 600 m corresponding roughly to the whole section of the Kuroshio in this region.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号