Deep Sea Research and Oceanographic Abstracts最新文献

The high pressure specific volumes of seawater (relative to pure water and 1 atm) have been measured from 0 to 40°C, 0 to 1000 bars and 5 to 40 ‰ salinity with a high pressure magnetic float densimeter (Millero, Knox andEmmet, Journal of Solution Chemistry,1, 173–186, 1972). The results of the measurements have been fitted to a secant bulk modulus (K) equation of state K = V⁰P/(V⁰ − V^P) = K⁰ + AP + BP², where V⁰ and V^P are the measured specific volumes of seawater at applied pressure zero and P, respectively, K⁰ = 1/β^o, the reciprocal of the isothermal compressibility at atmospheric pressure, A and B are all salinity- and temperature-dependent parameters. The specific volumes have been fitted to this equation with a standard deviation of 7 ppm (on the measurement residuals) over the entire salinity, temperature and pressure range. The fitted relative specific volumes (V^P − V⁰) are in excellent agreement (within ±5ppm) with the sound-derived data ofWang andMillero (Journal of Geophysical Research,78, 7122–7128, 1973) over the oceanographic range of salinity, temperature and pressure. The derived P-V-T properties have been compared with the experimental work of Ekman (Publications de circonstance. Conseil permanent international pour l'exploration de la mer,43, 1–47, 1908);Wilson andBradley (Deep-Sea Research,15, 355–363, 1968);Bradshaw andSchleicher (Deep-Sea Research,17, 691–706, 1970; personal communication 1974);Duedall andPaulowich (Review of Scientific Instruments,44, 120–127, 1973);Emmet andMillero (Journal of Geophysical Research,79, 3463–3472, 1974) and the sound-derived data ofWang andMillero (1973);Fine, Wang andMillero (Journal of Marine Research,32, 433–456, 1974).

A complete set of linearly independent relationships among the different cross spectral components obtained from pairs of moored instruments is derived which can be utilized to test whether or not the observed fluctuations within the internal wave frequency band represent a field of propagating internal waves. A further complete set of relationships is derived which enables to test whether or not the internal wave field is horizontally isotropic and (or) vertically symmetric. These relations are compared with corresponding relations for alternative models (standing internal wave modes, three-dimensional isotropic turbulence) and their capability to discriminate between the various models is investigated. The tests are applied to a set of data for which it is found that the observed fluctuations are consistent with both propagating and standing internal waves whereas isotropic turbulence must be rejected for the most part of the internal wave frequency band.

A sampler using manganese impregnated acrylic fibers inside a 30-1. Niskin bottle is used to concentrate radium isotopes from 500 to 1500 1. of seawater near the sea floor. Seawater contact is minimized during descent by expendable closures held in place with a soluble link and during ascent by the regular Niskin bottle closures. A single sampler will concentrate radium equivalent to 1000 to 2000 1. of seawater during a 2-h soak.

A technique for the objective analysis of oceanic data has been developed and used on simulated data. The technique is based on a standard statistical result—the Gauss-Markov Theorem-which gives an expression for the least square error linear estimate of some physical variable (velocity, stream function, temperature, etc.) given measurements at a limited number of data points, the statistics of the field being estimated in the form of space-time spectra, and the measurement errors. An expression for the r.m.s. error expected in this estimate is also derived and illustrated in the form of ‘error maps’.

Efficient sampling arrays can be designed through trial-and-error adjustment of array configurations until a suitable balance of mapping coverage and accuracy, as measured by the error maps, is achieved. Examples of the mapping ability of some simple arrays are given.

Using statistics inferred from the preliminary Mid Ocean Dynamics Experiments various realizations of likely flow fields were simulated. The 16 element MODE-I array was tested by comparison of the simulated fields and the objective maps based on inferred ‘measurements’ at the array points. The reliability of statistics inferred from observations was estimated by comparing correlations derived from limited observations of the simulated fields with the known statistics. Correlations derived from two realizations differed significantly but most calculations reproduced the known statistics moderately well.

An intercomparison of Eulerian measurements (current meters) and Lagrangian measurements (neutrally buoyant drifters) was also carried out using the objective interpolation method.

It is shown that both bubble effects and small temperature differences between the conductivity cell and the temperature sensing elements are important considerations when using conventional S.T.D. systems for monitoring sea surface salinity whilst steaming. By carefully attending to these details, merely placing an S.T.D. in a bucket flushed with a hose will provide a system capable of absolute accuracy of 0·01% and resolution 0·001%.

Over 250 samples of Atlantic seawater have been analyzed for the dissolved helium isotopes, and distinctive pattern has emerged. Two components of excess ³He are seen: a component due to in situ decay of nuclear-era tritium, and a primordial component evolved from the solid Earth. A prominent feature at about 3-km depth can be traced from 5°N along the western boundary to the equator. The source of this feature is most probably in the Gibbs fracture zone, where we suppose that primordial ³He is released into westward-flowing bottom water. The South Atlantic profiles clearly show the effect of ³He-rich CCircumpolar Water, entrained by Antarctic Intermediate Water flowing northward. The excess ³He in the upper 1 km, when combined with tritum concentrations measured byO¨stlund, Dorsey and Rooth (1974, Earth and Planetary Science Letters, 23, 69–86) at the same locations and depths, yields ‘tritium-helium ages’, which in some cases represent the time interval between equilibration wwith the atmosphere and sampling.

A few coastal upwelling events occur during summer off the Oregon coast. During one such event in July 1973 the southward wind stress (maximum t′'_o ≈ 5dynes cm⁻² occured between periods of northward stress. Vertical velocities from hydrographic observations decreased exponentially with distance offshore, producing a zonal scale about 15 km. The time scale for the onset of the mesoscale waas 1 to 3 days. At the surface the wind-generated surface drift was about 50 cm⁻¹, 45°cum sole to the direction of the wind stress. The wind-drift layer was about 15 m thick and the eddyviscosity coefficient of the turbulent motions within it was about 55 cm²s⁻¹. During the event the Ekman transport computed from wind observations was nearly equal to the measured offshore transport. Several of the observations were compared with recent hypothesis of the dominant processes controlling the dynamics of coastal upwelling.

Sonobuoy modified to receive low (< 100 Hz) frequency sounds in the deep ocean were deployed from the R.V. Yaquina on the Rivera fracture zone and 4·3 kmoff San Benedicto Island. An array of at least two operating sonobuoys was maintained for 24 h at each station. Calculated earthquake magnitudes were 2·2 to 3·7 on the Richter scale. Most of the acoustic energy in the signals was below 40 Hz and recorded well on the modified sonobuoys but poorly on simultaneously monitored unmodified buoys. A swarm of microearthquakes following a magnitude 4·3 earthquake was recorded on the Rivera fracture zone site while seismic activity at the San Benedicto Island was more sporadic. Epicentral distance from the sonobuoys, calculated from the T-P interval (when present), ranged from 10 to 120 km, most less than 20 km. The earthquake magnitude versus occurrence rate curve for the Rivera fracture zone events has b value of 0·6, indicating that the earthquakes were associated with the fracture zone rather than the median rift of the East Pacific Rise.