Deep Sea Research and Oceanographic Abstracts最新文献

Large-scale variations of temperature/salinity finestructure have been observed in the main thermocline of the northwest Atlantic Ocean on an oceanographic section along 70°W from the Sargasso Sea to the continental slope. Results suggest that temperature/salinity variability associated with vertical oceanic mixing increases linearly northward as the continental slope and the Gulf Stream are approached from the Sargasso Sea in the south.

Analytical design considerations and the measured behavior of a freely-falling, self-rotating oceanographic instrument using hydrodynamic airfoil wings to control vertical fall rate and enhance stability are presented.

Oceanic measurements of a vehicle of payload 30 kg, wing length 2 m, wing chord 0.16 m, and overmass of 5 kg (in seawater) show tilts from the vertical of order 2 × 10⁻³ radians and a fall velocity of 0.114 m s⁻¹ ±0.5%. The rotation rate is 21.8 s and perceptibly constant. Vertical velocity gradients measured on one drop are compared with vertical and horizontal accelerometer records, documenting the tilt and fall rate constancy. The fall rate and rotation rate compare well with the analytically derived formula.

Six species of abyssal ascidians of the family Styelidae (class Ascidiacea) which have similar external features are described. Three of the species are new: Styela tenuibranchia, S. polypes and S. calva.

A discontinuity in the slope of the property-property relationships for the deep water in the central Atlantic is clearly confirmed by the Geochemical Ocean Sections (GEOSECS) data. The potential temperature and salinity of the discontinuity water lie within the limits $\text{2.08 ± 0.15°}\text{C}\text{and}\text{34.90 ± 0.01‰}$ from 40°N to 30°S. The horizon slopes up from a depth of 4.0 km (σ_θ = 27.92) at the northern to 3.2 km (σ_θ = 27.90) at the southern end of this region. The discontinuity water consists of 89% water of northern and 11% water of southern origin. It is proposed that this water represents the outflow from the topographically confined abyssal Atlantic. If so, the ratio of the input rate to the northern end member to that of the southern end member is about 8. The changes in abundance of the nutrient elements along the discontinuity horizon are best explained if respiration and opal dissolution take place primarily in the eastern basin. An alternate hypothesis for the origin of the discontinuity involves the active erosion of a previously more extensive mixing zone between North Atlantic Deep Water and Antarctic Bottom Water.

Estimates of low-frequency horizontal advection of temperature are made with small errors by using a representation of horizontal advection of temperature as a function of the speed and turning about the vertical of the horizontal current. Within these errors the horizontal advection of temperature accounts for the observed local time changes of temperature during the 40-day Internal Wave Experiment (IWEX) period. The importance of horizontal advection indicates the dominant heat balance is not that of local time change of temperature balanced by vertical advection of temperature as assumed in wave models linearized about a mean stratification. These estimates suggest that a more appropriate linear model should be based on a mean state including mean horizontal gradients of temperature and hence a mean vertical shear of horizontal velocity. The mean state is not that of the long-term mean, however, but one associated with motions of time-scale longer than the measurement period of 40 days. Using this linearization, comparisons are made with a baroclinic instability model to investigate energy transfer between motions of different time-scales. In the context of this model, the direction of potential energy transfer between the mean and perturbation fields can be determined from the sign of the temporal phase lag between negative horizontal advection and local change of temperature. For these estimates negative horizontal advection leads local change suggesting that mean potential energy is increasing at the expense of perturbation potential energy. This phase lag, however, is not significantly different from zero so that a longer record is needed to establish the direction of potential energy transfer.

The submarine ridge between the eastern tip of Cuba and the northwestern tip of Haiti forms the sill of the Windward Passage and is the topographic barrier between the deep water of the Atlantic Ocean and that of the Cayman Basin in the northwestern Caribbean Sea. The controlling depth of this ridge was shown to be 1560 m by a bathymetric survey using a precision radar ranging system.The results agree with previous estimates based on temperature distribution and bathymetric surveys.

An empirical relationship between an apparent diffusivity and the scale of diffusion can be used in numerical modeling for oceanic dispersion. Some care must be exercised primarily because the diffusivity and the diffusion scale are usually defined somewhat arbitrarily. On the basis of the diffusion equation with a scale-dependent diffusivity, it is shown that the proper formula may differ numerically by an order of magnitude from the empirical relation.

A field study of the deep chlorophyll maximum and associated nitrite maximuum of the central North Pacific compared the standing crop, growth rates, and physiological characteristics of phytoplankton from the mixed layer, the chlorophyll maximum, and a depth well below the chlorohyll maximum. (1) The chlorophyll maximum is primarily due to increased cellular chlorophyll rather than an accumulation of cells at depth, and (2) the cells within and below the chlorophyll maximum are liiving but limited by radiant energy.

A simple box model was constructed to cover the depth internal of the primary nitrite maximum. Solution of the model, which assumed constant vertical mixing, indicated sufficient uptake of upwardly diffusing nitrate to account for the appearance of nitrate. It is suggested that nitrous acid diffuses out of phytoplankton, and that there is a steady-state concentration of extracellular nitrite in which the rate of uptake by phytoplankton equals its rate of passive diffusion out of the cells.

Culture studies of the marine diatom,Thalassiosira pseudonana, indicate that the cells produce nitrite at rates sufficient to account for the primary nitrite maximum, and that there is a steady-state concentration of nitrite that does not exceed 4 μM.

A three-dimensional numerical model is used to study and compare two previously proposed theories for the development of the Somali Current. The rapid propagation of internal planetary waves at the equator provides a means whereby a baroclinic western boundary current can be established quickly, even by remote winds. This theory, first developed for the linear case by Lighthill, is studied numerically and extended to the nonlinear case. Local winds, parallel to the western boundary, and the accompanying Ekman suction, also produce a western boundary current, although different in spatial and temporal characteristics from the above. Comparison with observations indicates that local driving is dominant during the establishment of the current. Remote forcing may produce significant alterations in the flow later. In the nonlinear cases, horizontal shearing instability produces eddy-like features in the western boundary current similar to those observed.

The relative densities of Baltic Sea waters have been measured from 3.5 to 20‰ salinity and 0.36 to 20°C with a vibrating densimeter. The directly measured densities were compared with those determined from the seawater equation of state (Millero, Gonzalez and Ward, Journal of Marine Research, 34, 691–693, 1976) at the same true salinity given by $\text{S(‰)}{}_{\mathrm{T}}\text{= a + bS(‰)}$, where a is related to the river water input of dissolved solids, $\text{b = (35.171-a)/35.000}\text{and}\text{S(‰) = 1.00566}\text{Cl}\text{(‰)}$. By adjusting a to 0.123±0.005 g kg⁻¹ the differences between the directly measured and calculated densities had a minimum standard deviation of 8.7 × 1-⁻⁶ g cm⁻³. The value of a determined from the density data is excellent agreement with the value (0.121 ± 0.019 g kg⁻¹) determined from the composition of these same samples (Kremling, 1969, KielerMeeresforschungen, 24, 1–20, 1970; Deep-Sea Research, 19, 377–383, 1972b). the measured densities have been fitted by at least squares method to the equation: $\text{d = d}{}^0\text{+ AS(‰)}{}_{\mathrm{T}}\text{+ BS(‰)}{}_{\mathrm{T}}{}^{\mathrm{<mtext>sol;2</mtext><mtext>3</mtext>}}$, where d⁰ is the density of pure water (Kell, Journal of Chemical and Engineering Data, 12, 66–69, 1976), A and B are temperature dependent parameters. The densities fit this equation to a standard deviation of 7.1 × 10⁻⁶ g cm⁻³. The smoothed densities are in good agreement (± 6ppm) with the results of Knudsenet al. (Kongelige DanskeVidenskabernes Selskabs, 1, 1–151, 1902) providing the comparisons are made at the true salinity. These results demonstrate that the densities of a natural estuary are equal (within experimental error) to those of seawater diluted with pure water when compared at the same total dissolved solid concentration, which is in agreement with theoretical calculations (Millero, Marine chemistry in the coastal environment. A.C.S. Symposium Series Vol. 18, pp. 25–55, 1975) and measurements on an artificial estuary (Millero, Lawson and Gonzalez, Journal of Geophysical Research, 18, 1177–1179). The physical chemical properties of the Baltic or any estuary can thus be determined from those of seawater diluted with pure water by using only the river input of total solids (a).