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1.
Long-range sidescan sonar (GLORIA) data over Porto and Vigo Seamounts collected in 1978 has been re-interpreted in the light of SEABEAM bathymetric surveys conducted in 1982. The application of quantitative bathymetric information enables the interpreter to allow for artefacts inherent in the GLORIA data and to separate topography-related primary backscattering variations on the sonographs from more subtle changes that result from textural, slope and outcrop effects. The distinctions are made easier when slant-range corrected GLORIA data are available.Use of the combined survey data to precisely locate seismic profiling tracks and to identify likely areas of outcrop has allowed refined geological maps of the seamounts to be drawn and regional fault trends detected. The overall outline of the seamounts appears strongly fault-controlled.Porto and Vigo Seamounts are made up of the same geological formations and have had a similar structural history since their uplift as continental fault blocks in the Late Cretaceous to Middle Eocene period. Ravines that dissect the presumably lithified scarps bounding the seamounts may be relict features but still appear to control sediment input to gulley and channel systems in the surrounding topography. Sedimentary ridges associated with the seamounts represent anomalously thick sequences of post-Eocene material and probably result from interaction of downslope sedimentary processes and contour-following boundary currents.Contribution No. 274 from the Groupe d'Etude de la Marge Continentale (ERA 605).  相似文献   

2.
The reflection and breaking of internal waves on a sloping beach were studied in a small wavetank filled with water and petroleum. The dependence of the reflection coefficient of the internal waves on wave steepness and on beach slope is found to be very similar to that of surface waves. The reflection coefficient is small for the very gentle slope, increases rapidly as the slope increases, and becomes almost constant for the steep slope. The reflection coefficient decreases with increase of the wave steepness. Also, the transition slope at which the coefficient curve has the maximum gradient increases with increase of the wave steepness. Breaking pattern of the internal waves is classified into four types; breaking, semi-breaking, wrinkle-generating, and non-breaking. Their dependence on beach slope and wave steepness is examined. The regular sequence of the four breaking types from breaking to non-breaking is observed with decrease of wave steepness or with increase of beach slope.  相似文献   

3.
On the basis of the generalization of the concept of standard ocean to the Black Sea, we deduce practical formulas for the conversion of pressure into depth and vice versa depending on the latitude of the place with regard for the equation of state for 1980. The error of these relations for the standard Black Sea (whose salinity is equal to 22.2 at a temperature of +9°C from the surface to the bottom) does not exceed ±0.2m and ±0.2dbar. The difference between the practical and actual depths in winter and summer periods does not exceed ±0.35m for depths varying within range 0–2000m. The proposed practical formulas enable one to simplify the procedure of rapid evaluation of depth (or pressure) in real time by excluding the procedure of integration over a specific volume.  相似文献   

4.
High-resolution, side-looking sonar data collected near the seafloor (100 m altitude) provide important structural and topographic information for defining the geological history and current tectonic framework of seafloor terrains. DSL-120 kHz sonar data collected in the rift valley of the Lucky Strike segment of the Mid-Atlantic Ridge near 37° N provide the ability to quantitatively assess the effective resolution limits of both the sidescan imagery and the computed phase-bathymetry of this sonar system. While the theoretical, vertical and horizontal pixel resolutions of the DSL-120 system are <1 m, statistical analysis of DSL-120 sonar data collected from the Lucky Strike segment indicates that the effective spatial resolution of features is 1–2 m for sidescan imagery and 4 m for phase-bathymetry in the seafloor terrain of the Mid-Atlantic Ridge rift valley. Comparison of multibeam bathymetry data collected at the sea-surface with deep-tow DSL-120 bathymetry indicates that depth differences are on the order of the resolution of the multibeam system (10–30 m). Much of this residual can be accounted for by navigational mismatches and the higher resolving ability of the DSL-120 data, which has a bathymetric footprint on the seafloor that is 20 times smaller than that of hull-mounted multibeam at these seafloor depths (2000 m). Comparison of DSL-120 bathymetry with itself on crossing lines indicates that residual depth values are ±20 m, with much of that variation being accounted for by navigational errors. A DSL-120 survey conducted in 1998 on the Juan de Fuca Ridge with better navigation and less complex seafloor terrain had residual depth values half those of the Lucky Strike survey. The quality of the bathymetry data varies as a function of position within the swath, with poorer data directly beneath the tow vehicle and also towards the swath edges.Variations in sidescan amplitude observed across the rift valley and on Lucky Strike Seamount correlate well with changes in seafloor roughness caused by transitions from sedimented seafloor to bare rock outcrops. Distinct changes in sonar backscatter amplitude were also observed between areas covered with hydrothermal pavement that grade into lava flows and the collapsed surface of the lava lake in the summit depression of Lucky Strike Seamount. Small features on the seafloor, including volcanic constructional features (e.g., small cones, haystacks, fissures and collapse features) and hydrothermal vent chimneys or mounds taller than 2 m and greater than 9 m2 in surface area, can easily be resolved and mapped using this system. These features at Lucky Strike have been confirmed visually using the submersible Alvin, the remotely operated vehicle Jason, and the towed optical/acoustic mapping system Argo II.  相似文献   

5.
GLORIA side-scan sonographs from the Bering Sea Basin show a complex pattern of interference fringes sub-parallel to the ship's track. Surveys along the same trackline made in 1986 and 1987 show nearly identical patterns. It is concluded from this that the interference patterns are caused by features in the shallow subsurface rather than in the water column. The fringes are interpreted as a thin-layer interference effect that occurs when some of the sound reaching the seafloor passes through it and is reflected off a subsurface layer. The backscattered sound interferes (constructively or desctructively) with the reflected sound. Constructive/destructive interference occurs when the difference in the length of the two soundpaths is a whole/half multiple of GLORIA's 25 cm wavelength. Thus as range from the ship increases, sound moves in and out of phase causing bands of greater and lesser intensity on the GLORIA sonograph. Fluctuations (or wiggles) of the fringes on the GLORIA sonographs relate to changes in layer thickness. In principle, a simple three dimensional image of the subsurface layer may be obtained using GLORIA and bathymetric data from adjacent (parallel) ship's tracks. These patterns have also been identified in images from two other systems; SeaMARC II (12 kHz) long-range sonar, and TOBI (30 kHz) deep-towed sonar. In these, and other cases world-wide, the fringes do not appear with the same persistence as those seen in the Bering Sea.  相似文献   

6.
Dependences have been determined which connect the parameters of the dispersion relation of the lowest mode of internal waves with the integral characteristics of the seasonal thermocline when 10 min30 min, 20 mh150 m, and 0·4 m2/s2 Q5·2 m2/s2.Translated by Mikhail M. Trufanov.  相似文献   

7.
The heat lability of succinic dehydrogenase, malic dehydrogenase and lactate dehydrogenase in cell-free extracts ofVibrio marinus MP-1 grown at 15C was compared for the tris buffer suspended enzymes and the NaCl suspended enzymes. The tris buffer suspended enzymes lost 50 percent activity at low thermal exposure between 5C and 27C. No activity was evident on thermal exposure between 32C and 39C. The enzyme extracts suspended in NaCl at 36 % were more heat stable, losing 50 percent activity after exposure between 16C and 40C. The enzymes lost all activity on thermal exposure between 33C and 42C in the presence of NaCl.  相似文献   

8.
We compare the results obtained by using theoretical and semiempirical models developed for the evaluation of the dissipation rate of turbulent energy in a stratified ocean with independent distribution of this quantity established by the authors for the active layer of the Black Sea (50–300 m) by using a one-dimensional model taking into account the balance of heat, salt, and fluid inside the layer. It is shown that, in a layer with gradual variation of the Väisälä–Brunt frequency N as a function of depth, the predominant sink of the energy of motion into dissipation N 2 is ensured by the flow of energy through the spectrum of internal waves toward low frequencies and small vertical scales. On the contrary, in layers with abrupt drops of density as a function of depth (layers with jumps of density), an important role is played by the interface-type waves and the dependence of on N transforms into N .  相似文献   

9.
Possibilities of using the GLORIA system for manganese nodule assessment   总被引：1，自引：0，他引：1  
The I.O.S. long range side-scan sonar GLORIA has been widely used over a variety of seabed types, but until recently had not been used over an independently authenticated field of manganese nodules. In the Eastern Atlantic Ocean at approximately 31°25 N 25°15 W, a field of nodules approximately 3–6 cm in diameter covering up to 18% of the seafloor was observed using an underwater camera. The nodule field occurred over approximately 2.8 km of the 8.3 km camera run. The corresponding GLORIA image shows an area of medium intensity backscattering, approximately 3.7 km in diameter. Considering the likely contrast in acoustic reflectivity between manganese nodules and deep sea sediments, we propose a correlation between the nodules observed in the photographs and the medium intensity echo target revealed by the GLORIA system.  相似文献   

10.
We analyze the data of investigation of the intrusive structure of the Gulf-Stream frontal zone obtained in making frequent drift sections with the help of an MGI-8102 probing complex, study the regularities of variation of temperature, salinity, and density along separate intrusions, and present a series of results connected with the specific features of initiation and development of intrusions and the types of exchange processes determining their transformations. It is shown that the T-diagrams of all intrusions are well separated into segments with different slopes. Moreover, by comparing the slopes and locations of these segments with each other and with the T-diagrams of the Gulf Stream and slope waters, we can fairly reliably attribute the corresponding segments of intrusions to one of the following four types: initial dynamic folds of the frontal zone, layers of domestic water separating the intrusive segments of foreign water from each other, intrusive segments characterized by the penetration of ambient water, and segments not intrusive initially but getting the required slope as a result of interaction with upper and lower intrusive segments. For segments of the last two types, it is possible to specify the predominant type of exchange.  相似文献   

11.
The maximum uptake rate (max) and affinity constant (K s) for nitrate and ammonium were estimated in the surface water of offshore Oyashio in May (spring) and September (summer), 1990. The average max/Chl.a for ammonium was 2.1 times larger than that of nitrate in both seasons. The average max/Chl.a for both nitrogens were 3.5 times larger in summer than in spring. Water temperature and size composition of phytoplankton population were related to the seasonal difference in the max/Chl.a. Phytoplankton population showed high affinity for both nitrogens in the spring and summer. In addition, the contribution of new production to total production was estimated by max[max–No3/(max–NO3+max–NH4)]. The spring value was in the range of 0.26 to 0.45 (mean±SD=0.35±0.092), and the values in spring bloom were especially a little over 0.4. The summer value was in the range of 0.30 to 0.37 (0.34±0.04).  相似文献   

12.
Independent evidence of changes in sea level and tidal range in the Bay of Fundy during the last 9000 years is used to evaluate the lithologies in 17 cores from the sublittoral part of Chignecto Bay. The composite tidal sequence identified is complex because of changes from microtidal through mesotidal to macrotidal conditions associated with changing water depths. Despite the complex stratigraphy, lithology correlates well with the depositional environment on a bed-by-bed basis. We postulate that such variations in tidal range are important to the interpretation of tidalite deposits from the geologic record.  相似文献   

13.
Scientific sea-floor dredging is currently used in marine geology primarily by the hard-rock community interested in the recovery of basement rock samples from the unsedimented deep ocean floor. The technique has generally been eclipsed by ocean drilling for recovery of sedimentary rocks, because of perceived uncertainties in the location of sampling and in the representativeness of recovered material. This contribution reviews dredging equipment currently in use by marine geological institutions and refers to pinger attachments that allow precise information on the behaviour of the dredge to be telemetered back to the ship. We argue that improvements in ship navigation and transponder navigation at the seafloor, when used in conjunction with surface and/or deeply towed sidescan and swathemapping surveys, now allow for considerably less uncertainty on the location of dredge sampling. Refined sorting criteria for dredge hauls are now also available. Recent comparisons of regional sample recovery by ocean drilling and by dredge sampling indicate that the dredge hauls can usefully supplement the drilling data in the construction of sedimentary and tectonic histories of seafloor areas.  相似文献   

14.
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.  相似文献   

15.
The heat balance of the upper ocean under a land and sea breeze was investigated based on observations of sea water temperature in the upper 300 m layer and heat flux across the sea surface at a fixed station in Sagami Bay (3510N, 13925E) during two periods of two days in August 1980 and three days in August 1981. During both periods, a typical land and sea breeze of 4–6 m sec–1 at maximum prevailed in the observation area. Large diurnal variation of sea surface temperature with a maximum peak around noon LST was observed during both periods (the daily value of the range was 0.9C and 2.5C in 1980, and 1.2C, 1.5C and 1.7C in 1981). It was found that these large temperature variations were caused by diurnal variation of the wind speed which dropped to 0–3 m sec–1 at noon when the strongest insolation (–270 Wm–2) penetrated the sea and at midnight in association with alternations of the land breeze and the sea breeze. On the other hand, vertical mixing of the sea water caused by the wind stress and/or convection due to cooling at night extended down only to the surface 10 m layer. Horizontal heat advection was negligibly small. Therefore the local time change of the heat content in the upper 10 m water column was affected mainly by the heat flux across the air-sea interface which was estimated from data on radiation fluxes measured directly on board and latent and sensible heat fluxes calculated by the aerodynamic bulk method. The water temperature below the 10 m layer also varied with time and the temperature variation in the thermocline (20–50 m depth) was frequently larger than that of the sea surface temperature. However, the variation in the upper 10 m layer was little influenced by that below the layer.  相似文献   

16.
The storm surges which occurred in Tosa Bay in August 21, 1970 were numerically simulated. First of all NOAA's model SPLASH (Special Program to List Amplitudes of Surges from Hurricanes) was used and the effects of the typhoon's parameters, the bottom topography, the coastal configuration and the coordinate systems of storm surges were examined. SPLASH was then modified to suit computations of storm surges in the open sea and open boundary conditions were studied. Finally a two layer model was developed and the effects of the two layer system on surges were investigated.  相似文献   

17.
Inversion modelling of marine gravity anomalies to derive predicted seafloor topography has provided significant advance in delineating deep-ocean bathymetry where the seafloor both conforms to the half-space cooling model of seafloor spreading, and largely sediment-free. Similar modelling for elevated ridges and seamounts, that are formed by processes other than seafloor spreading and/or have proximal sediment sources (e.g., continental margins and volcanic arcs), have significantly higher errors when validated against modern shipborne echo-sounding data. A three-dimensional, five-layer gravity model is emulated for the cases of both synthetic and real seamounts, with varying degrees of sediment burial, to establish the sensitivity of variable sediment cover as a source of error. A simple `Gaussian' seamount with base radius of 30 km, 2000 m of relief, has a maximum 140–160 mGal anomaly, that decreases to 50 mGal with the addition of 1 km of sediment cover with simple `flood' geometry. Complete burial, with a typical sediment density of 2300 kg m–3, results in a 120 mGal difference from a sediment-free seamount model. Increasing sediment density results in an exponential decay of the seamount anomaly. More complex synthetic geometries of varying basement relief and sediment thickness show that the anomaly amplitude remains significant, especially where the latter is >700–800 m thick. For the real case, seamounts of the Three Kings Ridge (northern New Zealand) imaged with seismic reflection data, with varying degrees of sediment cover of up to 1 km, when modelled both with and with-out the inclusion of a sediment layer, typically have rms differences of 30 mGal between observed and modelled gravity anomalies. Significantly, the rms errors are reduced by 50% with the inclusion of a sediment layer that corresponds to a reduction of predicted seafloor topography rms errors of 192–684 m to 78–360 m.  相似文献   

18.
The mechanism of the development of wind-waves will be proposed on the basis of the observed wave spectra in the wind tunnels and at Lake Biwa (Imasato, 1976). It consists of two aspects: One is that the air flow over the wind-waves transfers momentum concentratively to the steepest component waves and the other is that the upper limit of the growth of a wave spectral density is given by the ultimate value in the slope spectral density. The first aspect means that the wave field has the momentum transfer filter on receiving the momentum from the air flow. Wind-waves in the stage of sea-waves receive the necessary amount of momentum by the form drag,e.g. according to the Miles' (1960) inviscid mechanism, through a very narrow frequency region around a dominant spectral peak. On the other hand, wind-waves in the stage of initial-wavelets receive it according to the Miles' (1962a) viscous model through a fairly broad frequency region around the peak. The upper limit ofS max developing according to viscous mechanism is given byS max =6.40×10–4 k max –2cm2s andS max =2.03C(f max )–2cm2s(S max is the power density of the wave spectral peak with the frequencyf max ,k max is the wave number corresponding to the frequencyf max andC is the phase velocity).From the second aspect, the upper limit of the growth of wave spectral density is given by 33.3f –4cm2s in the frequency region of late stage of sea-waves. Therefore, the spectral peak, which has the largest value in the slope spectral density in the component waves of the wave spectrum, rises high over the line 4.15f –5cm2s. The energy is transported from the spectral peak to the high frequency part and to the forward face of a wave spectrum by nonlinear wave-wave interaction. This nonlinearity is confirmed by the bispectra calculated from the observed wind-wave data. In the stage of sea-waves, nonlinear rearrangement of the wave energy comes from a narrow momentum transfer filter, and, in the stage of initial-wavelets, it comes mainly from small corrugations and small steepness of the wave field.  相似文献   

19.
A study of Sea Beam bathymetry and SeaMARC II side-scan sonar allows us to make quantitative measures of the contribution of faulting to the creation of abyssal hill topography on the East Pacific Rise (EPR) 9°15 N–9°50 N. We conclude that fault locations and throws can be confidently determined with just Sea Beam and SeaMARC II based on a number of in situ observations made from the ALVIN submersible. A compilation of 1026 fault scarp locations and scarp height measurements shows systematic variations both parallel and perpendicular to the ridge axis. Outward-facing fault scarps (facing away from the ridge axis), begin to develop within 2 km of the ridge and reach their final average height of 60 m at 5–7 km. Beyond these distances, outward-dipping faults appear to be locked, although there is some indication of continued lengthening of outward-facing fault scarps out to the edge of the survey area. Inward-facing fault scarps (facing toward the ridge axis), initiate 2 km off axis and increase in height and length out to the edge of our data at 30 km, where the average height of inward fault scarps is 60–70 m and the length is 30 km. Continued slip on inward faults at a greater distance off axis is probable, but based on fault lengths, 80% of the lengthening of inward fault scarps occurs within 30 km of the axis (>95% for outward faults). Along-strike propagation and linkage of these faults are common. Outward-dipping faults accommodate more apparent horizontal strain than inward ones within 10 km of the ridge. The net horizontal extension due to faulting at greater distances is estimated as 4.2–4.3%, and inward and outward faults contribute comparably. Both inward- and outward-facing fault scarps increase in height from north to south in our study area in the direction of decreasing inferred magma supply. Average fault spacing is 2 km for both inward-dipping and outward-dipping faults. The azimuths of fault scarps document the direction of ridge spreading, but they are sensitive to local changes in least compressive stress direction near discontinuities. Both the ridge trend and fault scarp azimuths show a clockwise change in trend of 3–5° from 9°50 N to 9°15 N approaching the 9° N overlapping spreading center.  相似文献   

20.
The Apennine Chain provides the first example of stratigraphic (time) and synsedimentary tectonic (space) distribution of the calcari aLucina Miocene equivalents of modern cold-vent carbonates. Chemosynthetic faunal assemblages and related carbonate deposits are found at different stratigraphic levels, with peaks during Langhian-Serravallian and late Tortonian-early Messinian times. A general increase in frequency and volume occurs with time. A genetic link between venting and the Messinian Evaporite event is difficult to demonstrate. However,Lucina limestones are limited to preevaporitic times, and their maximum abundance is reached just before the onset of the Messinian Evaporite accumulation.Lucina limestones occur in almost all tectofacies of the orogen, from backland to foreland.  相似文献   

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