Analysis of photographic images of the structure of the surface of the sea near a speck of light

Values of root mean square slope ₀ and its variations -₀ are estimated using the brightness field of an image of the surface of the sea near a speck of light. When ₀ and -₀ are defined it is highly important to take into account direct as well as dissipated solar radiation.The space-time analysis of the structure of the image brightness field is performed. This gives an opportunity to estimate dispersion relationship and the running effect of a brightness contrast packet. Comparison of the parameters obtained with the theoretical dispersion ratio of internal waves (IW) allows one to make a conclusion that IW surface manifestations are recorded in a frame.UDK 551.463.5     

Radiation balance and heat budget at the ocean/atmosphere interface in the western North Pacific

The downward short- and long-wave radiation fluxes at the sea surface (S, L) were measured aboard the R/VHakuho Maru, University of Tokyo, for the period of 117 days on six cruises from 1981 to 1985 in the western North Pacific near Japan. The upward fluxes of short- and long-wave radiation (S, L) were calculated by Payne's (1972) table and the Stefan-Boltzmann's law, respectively. The sensible and laten heat fluxes (Q _h ,Q _e ) were also estimated from an aerodynamic bulk method.From April to August, the daily mean value ofS varied with the amplitude of 100200 Wm^–2. The value ofS was estimated approximately 6% ofS in all seasons. The difference betweenL andL was so small that the net radiation flux (Q _n ) was dominated byS. In addition, the net heat flux at the sea surface was also dominated byS due to small values ofQ _h andQ _e , and then the ocean was warmed at the rate of 111 Wm^–2 in April and 63 Wm^–2 in August in the Oyashio Area, and 132 Wm^–2 in May and 164 Wm^–2 in June in the Kuroshio Area, respectively.From September to March, a remarkable negative correlation between the day to day variation ofS and that ofL was observed except when an intense cold air outbreak occurred. It was found that the correlation was caused by the cloud climatological feature of the western North Pacific in this period.S was not a dominant factor in the net heat flux. The value ofQ _h +Q _e in the Kuroshio Area ranged from 260 Wm^–2 to 630 Wm^–2, much larger thanQ _n which ranged from –8 Wm^–2 to 92 Wm^–2 in the leg mean values (each leg period was about 10 days). Then the ocean was cooled at the rate of –160–620 Wm^–2 during this period. The net heat flux in the Kuroshio Area averaged over five legs from late November to February was –473 Wm^–2. This value is 50100% larger than the climatological values reported so far.The temporal and spatial variability of radiation fluxes and heat fluxes during each leg was also discussed.     

Video observations of marine gravel transport

In an analysis of video observations of gravel transport in the West Slent, UK, collective and individual characteristics of 458 bursts of bedload have been examined and the transport velocity and distance of 1680 individual particles in a consecutive succession of burst events determined. Infrequent, long duration, high stress events account for 60% of total transport in only 24% of the total time with the mean free path and transport velocity for particles being 0.16 m and 0.22 m/s, respectively. Clear links between intense intermittent turbulence and bedload transport revealed in this study, suggest progress in modelling requires a clearer understanding of near bed flow structure.     

Magnetic anomalies associated with the southeastern continental margin of South Africa

A total magnetic intensity, iso-magnetic map is presented and discussed. Between East London and Durban large east-west trending anomalies are known on land and can be traced onto the continental shelf but not beyond the slope. Elsewhere the continental shelf is characterized by a remarkably quiet magnetic field. A feature of the map is the linear anomaly, named the Cape Slope Anomaly, which is parallel to the continental margin and coincides approximately with the 68° small circle about the early pole of opening for the South Atlantic as given by Le Pichon and Hayes (1971). The anomaly is traced between 30°54S, 30°48E and 37°45S, 20°31E and is interpreted as occurring over the truncated edge of a semi-infinite, sub-horizontal, remanently magnetized plate in oceanic crust beyond the continental margin.Between 37°03S, 21°49E and 37°41S, 21°12E the Slope Anomaly occurs over a ridge named the Agulhas Ridge. A continuous seismic reflection profile over the ridge shows acoustic basement occurring under a cover of sediments. A two dimensional model study indicates that the basement materials may belong to the body causing the anomaly with the exception of the basement material that forms the landward peak of the ridge, which is non-magnetic.     

Dilution of North Pacific Intermediate Water studied with chlorofluorocarbons

Assessment was made of residual ratio of North Pacific Intermediate Water (NPIW) produced in subpolar region of the North Pacific using chlorofluorocarbons, CFC-11 and CFC-12 (CCl₃F and CCl₂F₂), along 175°E. NPIW on density horizons less than 26.80 remained more than 80% north of 30°N. It was suggested that new NPIW laterally spreads over the northern North Pacific without hardly being diluted by the surroundings. For density horizons greater than 26.80 north of 30°N, NPIW remained less than 60%. The difference in the residual ratio between <26.80 and >26.80 north of 30°N suggests that NPIW is produced on density horizons less than 26.80, which contacts the atmosphere in the subpolar region, and that NPIW is diluted by upwelling deep water on density horizons greater than 26.80 in high latitude of the North Pacific. NPIW on a density horizon of 26.80 remained about 50% south of 30°N. The decrease in the horizontal distribution of the residual ratio of NPIW suggests that half the new NPIW produced in the subpolar region is laterally spread over the North Pacific with the southward movement of NPIW.     

Variability of temperature and currents measured near Pipe Organ hydrothermal vent site

Temperature and currents were measured 100 m south of the Pipe Organ vent site on the Juan de Fuca Ridge during a 5-day interval in September 1997 to examine the temporal variability of hydrothermal heat signals close to a source. Temperatures were sampled at three depths every 15 s while current speed and direction were sampled at a single depth hourly. Results show that rapid potential temperature () changes of as much as 0.02°C occurred at all three depths, partly caused by changes in current speed and direction. Spectra of showed no prominent spectral peaks, however. An analytic model of heat transport under variable currents was used to help put observed temporal variability into context and to point out problems with estimating hydrothermal heat fluxes from mooring data. Model distributions, when contoured on a horizontal plane and animated, demonstrate the pooling of effluent over vents at various times, the streaming of effluent as a very narrow plume away from vents at times of large current speed, and the spawning of boluses of heated fluid and their transport away from venting regions when a pooling period is followed by a streaming period. Model results also show that estimated heat flux based on mooring data is strongly dependent on analysis assumptions and suggest that vents are capable of causing measurable anomalies as far as several kilometers downstream.     

Glacial to Holoceneδ 13C variations in intermediate depth water masses of North Indian Ocean

The ¹⁸O and ¹³C compositions of glacial- to Holocene-aged benthic foraminifera in a core collected from the eastern Arabian sea (water depth 1230 m) were determined to investigate glacial—interglacial variations in the intermediate depth water chemistry of the North Indian Ocean. In addition, we determined the ¹³C composition of Holocene benthic foraminifera from seven cores for which the ¹⁸O and ¹³C of benthic foraminifera from last glacial maximum (LGM) were reported by Kallel et al. (1988). The ¹³C_DIC in the intermediate waters was generally depleted by 0.3–0.4 during the last glacial maximum compared to Holocene.     

Seasonal variability and the types of currents in the upper layer of the Black Sea

Spectral analysis of the climatic circulation in the upper 10 m layer of the Black Sea has been carried out. The current field was calculated from a three-dimensional baroclinic non-linear model. The mode composition of the circulation was derived. It is shown that the surface climatic circulation can be represented as the superposition of a finite number of elementary currents of two types:n- andm-modes. Only 4n-modes are shown to be energy-dominant throughout the year. A relation is established between the different sources of energy supply of currents and the modes which assimilate this energy. Problems concerning the nature of the classical Black Sea currents such as the main Black Sea current (MBSC) and the Knipovich spectacles are discussed. A scenario of the field large-scale experiment is suggested which allows the reconstruction of the amplitudes of the first 10n- and the first 10m-modes from mooring data.Translated by Mikhail M. Trufanov.     

Field data support of three-seconds power law andgu *σ−4-spectral form for growing wind waves

Observational data on air-sea boundary processes at the Shirahama Oceanographic Tower Station, Kyoto University, obtained in November, 1969, was analyzed and presented as an example representing the structure of growing wind-wave field. The condition was an ideal onshore wind, and the data contained continuous records of the wind speed at four heights, the wind direction, the air and water temperatures, the tides, and the growing wind waves, for more than six hours. The main results are as follows. Firstly, in both of the wind speed and the sea surface wind stress, rather conspicuous variations of about six-minute period were appreciable. Secondly, the three-seconds power law and its lemma expressed byH ^*=BT ^*3/2 and=2BT ^*–1/2, respectively, are very well supported by the data, whereH ^*(gH/u _* ²) andT ^*(gT/u _*) are the dimensionless significant wave height and period, respectively, the wave steepness,u _* the friction velocity of air,g the acceleration of gravity, andB=0.062 is a universal constant. Thirdly, the spectral form for the high-frequency side of the spectral maximum is well expressed by the form of()= _sgu_*^–4, where is the angular frequency and() the spectral density. The value of _s is determined as 0.062±0.010 from the observational data. There is a conspicuous discrepancy between the spectral shape of wind waves obtained in wind-wave tunnels and those in the sea, the former containing well-defined higher harmonics of the spectral peak, and consequently there is an apparent difference in the values of _s also. However, it is shown that the discrepancy of _s may be eliminated by evaluating properly the energy level of the spectral form containing higher harmonics.     

Numerical modelling of the Sea of Azov's dynamics resulting from narrowing of the mouth of Taganrog Bay

The currents and surface level oscillations in the Sea of Azov ensuing from contraction of the mouth of Taganrog Bay are computed using the grid technique on the basis of a numerical solution to the system of quasi-linear, degenerate, parabolic, partial derivative equations (shallow-water equations). It is demonstrated what changes are to be expected in the dynamics of the Sea of Azov should this project be realized. The computations were carried out for typical wind directions.Translated by Vladimir A. Puchkin.     

Laxmi Ridge – A continental sliver in the Arabian Sea

Identification by Bhattacharya et al. (1994) of seafloor spreading type magnetic anomalies in the basin lying between Laxmi Ridge in the Arabian Sea and the Indian continent necessitates a change in plate tectonic reconstruction. Naini and Talwani (1982) named this basin the Eastern Basin and we will continue to use this term in this paper. Others, in the literature, have called this the Laxmi Basin. Previous reconstructions had assumed that the Eastern Basin is underlain by continental crust. The new reconstruction moves Seychelles' original location closer to India and ameliorates a space problem in the Mascarene Basin. A new rotation pole between anomaly 28 and 34 times avoids skipping of fracture zones resulting from rotation poles described earlier. The negative gravity anomaly over the Eastern Basin is a necessary consequence of a continental sliver lying between oceanic crust on either side. Seismic velocities that are slightly greater than 7 km s^–1 under the Eastern need not be necessarily interpreted as material that underplates continental crust.     

The distribution of geothermal fields along the East Pacific Rise from 13°10′ N to 8°20′ N: Implications for deep seated origins

In 1983 a combined SeaMARC I, Sea Beam swath mapping expedition traversed the East Pacific Rise from 13°20 N to 9°50 N, including most of the Clipperton Transform Fault at 10°15 N, and a chain of seamounts at 9°50 N which runs obliquely to both the ridge axis and transform fault trends. We collected temperature, salinity and magnetic data along the same track. These data, combined with Deep-Tow data and French hydrocasts, are used to construct a thermal section of the rise axis from 13°10 N to 8°20 N.Thermal data collected out to 25 km from the rise axis and along the Clipperton Transform Fault indicate that temperatures above the rise axis are uniformly warmer by 0.065°C than bottom water temperatures at equal depths off the axis. The rise axis thermal structure is punctuated by four distinct thermal fields with an average spacing of 155 km. All four of these fields are located on morphologic highs. Three fields are characterized by lenses of warmed water 20 km in length and 300 m thick. Additional clues to hydrothermal activity are provided in two cases by high concentrations of CH₄, dissolved Mn and ³He in the water column and in another case by concentrations of benthic animals commonly associated with hydrothermal regions.We use three methods to estimate large-scale heat loss. Heat flow estimates range from 1250 MW to 5600 MW for one thermal field 25 km in length. Total convective heat loss for the four major fields is estimated to lie between 2100 MW and 9450 MW. If we add the amount of heat it takes to warm the rest of the rise axis (489 km in length) by 0.065.°C, then the calculated axial heat loss is from 12,275 to 38,525 MW (19–61% of the total heat theoretically emitted from crust between 0 and 1 m.y. in age).     

Variability of the axial morphology and of the gravity structure along the Central Spreading Ridge (North Fiji Basin): evidence for contrasting thermal regimes

The Central Spreading Ridge (CSR) is located in the central part of the North Fiji Basin, a complex back-arc basin created 12 Ma ago between the Pacific and Indo-Australian plates. The 3.5 Ma old CSR is the best developed, for both structure and magmatism, of all the spreading centers identified in the basin, and may be one of the largest spreading systems of the west Pacific back-arc basins. It is more than 800 km long and 50–60 km wide, and has been intensively explored during the French-Japanese STARMER project (1987–1991).The CSR is segmented into three first order segments named, from north to south, N160°, N15° and N-S according to their orientation. This segmentation pattern is similar to that found at mid-ocean ridges. The calculated spreading rate is intermediate and ranges from 83 mm/yr at 20°30 S to 50 mm/yr at 17°S. In addition, there is a change in the axial ridge morphology and gravity structure between the northern and southern sections of the CSR. The axial morphology changes from a deep rift valley (N160° segment), to a dome split by an axial graben (N15° segment) and to a rectangular flat top high (N-S segment). The Mantle Bouguer Anomalies obtained on the northern part of the CSR (N160°/N15° segments) show bull's eye structures associated with mantle upwelling at the 16°50S triple junction and also in the middle of the segments. The Mantle Bouguer Anomalies of the southern part of the ridge (N-S segment) are more homogeneous and consistent with the observed smooth topography associated with axial isostatic compensation.At these intermediate spreading rates the contrast in bathymetry and gravity structure between the segments may reflect differences in heat supply. We suggest that the N160° and N15° segments are cold with respect to the hot N-S segment. We use a non-steady-state thermal model to test this hypothesis. In this model, the accretion is simulated as a nearly steady-state seafloor spreading upon which are superimposed periodic thermal inputs. With the measured spreading rate of 50 mm/yr, a cooling cycle of 200,000 yr develops a thermal state that permits to explain the axial morphology and gravity structure observed on the N160° segment. A spreading rate of 83 mm/yr and a cooling cycle of 120,000 yr would generate the optimal thermal structure to explain the characteristics of the N-S segment. The boundaries between the hot N-S segment and its cold bounding segments are the 18°10 S and 20°30 S propagating rifts. A heat propagation event along the N-S segment at the expense of the adjacent colder failing segments, can explain the sharp changes in the observed morphology and structure between the segments.     

Some remarks on the spectrum of rapid-changing random data in the ocean

Spectral characteristics of rapid-changing random data in the ocean are discussed. Analysis shows that, if records are approximated by saw-toothed random series ₁ and step series ₂, ₁ and ₂ generally have spectral ranges of the –4th power and –2nd power, respectively, with respect to frequency (or wave number).     

Chlorinated hydrocarbons in the North Pacific and Indian Oceans

PCBs, DDT compounds and HCH isomers were detected in the air and surface waters of the North Pacific and Indian Oceans, including the Bering Sea, East China Sea, South China Sea, Bay of Bengal and the Arabian Sea. The general concentrations of each chlorinated hydrocarbon were as follows: water PCBs 0.1 to 1.0, DDT 0.01 to 1.0, HCH 1.0 to 10 ngl ^–1; air DDT 0.01 to 1.0, HCH 0.1 to 10 ng m^–3. PCB concentrations in surface waters were slightly lower than those of the North Atlantic and North Sea previously reported, while DDT concentrations in the air and water were higher. Remarkably high concentrations of DDT and HCH were found in the air off the western coast of India. Also in the Pacific site off Central America, a fairly high concentration of DDT was observed in an air sample. These data suggest that large amounts of DDT and HCH are being used in the tropical zone, especially in southern Asia. Furthermore, high concentrations were observed both in the air and water of the Northwest Pacific between 30°N and 40°N latitude. There is a possibility that both pesticides are not only still being used in lower latitude countries but also in the mid-latitude ones of the Asian continent excluding Japan. In addition to this atmospheric circulation may also contribute to the concentration of these pesticides in the mid-latitudinal zone.     

Bispectra of spike-array type time series and their application to the analysis of oceanic microstructures

Bispectral analysis is applied to records of the vertical profile of the vertical temperature gradient in the oceanic thermocline in the San Diego Trough. The bispectra exhibit three notable features; (1) bispectral peaks at the points (0.2 m^–1, 0.2 m^–1) and (0.2 m^–1, 0.1 m^–1), (2) bispectral ridges along the lines ( ₁= ₀, ₂= ₀ and ₁+ ₂= ₀ corresponding to peak wavenumbers ₀ in power spectra, and (3) array of bispectral peaks of interval of 0.2 m^–1 The results are compared with the bispectra of several modeled time series of spike-array type. The periodicity of 5 m found in the records seems to have two meanings: spacing of predominant spikes and wavelength of predominant sinusoidal wave. If this indicates the existence of internal waves having a vertical wavelength the same as the scale of homogeneous layers, it would suggest the possible importance of internal waves in the formation and maintenance mechanisms of oceanic microstructure.     

Regeneration of silicate in the ocean

Regeneration of silicate in the Japan Sea, an example of semi-closed sea, was studied. In the Japan Sea Proper Water the apparent regenerative ratio of the nutrients was determined to be:O C N P Si=–289 (116)14.3181.It was assumed that the dissolved silicate present in sea water is grouped into three fractions; 1)preformed silicate of conservative nature, 2)oxidative silicate which dissolves in oxidation process of organisms with consumption of oxygen, and 3)non-oxidative silicate which dissolves without oxygen consumption. The dissolution rate ofnon-oxidative silicate in the Japan Sea Proper Water was estimated to be 0.07g-at. Si/l/yr from the data ofAOU values and assumed rates of oxygen consumption. This dissolution rate ofnon-oxidative silicate agreed with that obtained in the deep Pacific by the vertical advection diffusion model byKido andNishimura (1972).     

Water colour index of the Guinean sector of the Atlantic Ocean

The distribution of the colour index is considered in the region bounded by 8–11°N and 13°30–18°30W based on the results of measurements made on board vessels of the Marine Hydrophysical Institute of the Ukrainian SSR Academy of Sciences (MHI) in 1977–1985. Mean values and statistical characteristics are calculated for the colour index variability over one-degree squares. A map of its multi-yearly average distribution is plotted.Translated by M. M. Trufanov.     

The evolution of isolated vortices interacted with steep slope

Numerical solutions are examined for isolated, intense vortices as influenced by western bounding bottom topography through the use of a rigid-lid, two-layer primitive -plane numerical model. Systematic studies are made of the sense of rotation (cyclonic/anticyclonic), the consequence of varying the gradient of bottom slope, and the different vertical shear in a two layer ocean. In the basin with a bottom slope, the nearly barotropic anticyclonic vortex forms a modon-like vortex for S with fixedRo ₂<O(1) (where is the ratio between the variation of the Coriolis parameter across the eddy to the Coriolis parameter in the center, S the topographic effect and,Ro ₂ the Rossby number in the lower layer) and its generation is due to a compound effect of the planetary beta, topographic beta, avvection, and mirror image. The formation of the modon-like vortex and the propagation of the original vortex onto the bottom slope depends on the strength of slope gradient and the baroclinicity of the vortex. The nearly barotropic anticyclonic vortex evolves into the stronger upper ocean one with increasing S: the gradient of the bottom slope becomes steeper. Then the original vortex lives longer because the barotropic component of the energy is converted to the baroclinic one and it moves toward southeast in forming a modon-like vortex in the lower layer. The evolution of a vortex in the model results are compared to observational results of a Kuroshio warm core ring (KWCR) obtained from hydrographic data (June, 1985) and from NOAA satellite infrared images (April, 1985 to July, 1985). It is shown that a KWCR (June, 1985) is influenced by the western continental slope/shelf of the East Japan.     

Calcium-alkalinity relationship in the North Pacific

The dissolution of calcium carbonate in deep ocean water causes variation in calcium concentration (Ca) and alkalinity (TA) in the ratio of one to two. The decomposition of organic matter generates nitric acid, phosphoric acid and sulfuric acid. A proton flux which is derived from this process also changes alkalinity. Using the variation in nitrate concentration (NO₃) as an index of the proton flux, the relationship betweenCa,TA andNO₃ is expressed asCa=0.5TA+0.63NO₃ The values of Ca obtained from direct measurements in the North Pacific are in good agreement with the values estimated from this equation.