Distribution, texture and composition of modern phosphate pellets in Peru shelf muds

Textural analysis, including estimates of concentrations of authigenic phosphate pellets, were made for eight sediment cores from the Peru continental margin. Phosphatic pellets separated from these modern organic-rich sediments are black, spherical-ovoidal in shape, and in thin section often display a concentric structure around a nucleus consisting of inorganic mineral grains. Some pellets have a gray-white exterior coating which appears to be secondary diagenetic calcite. Phosphatic pellets account for upwards of 80% of the sediment mass in some cores. Pellets concentrate in specific size classes, generally between 125 and 500 μm in diameter, and occur within a poorly sorted sediment.     

Design of a caisson plate under wave impact

From the laboratory experiments and field studies it has been shown that when a wave breaks directly on a vertical wall, impact pressures of high magnitude and short duration, are produced. Despite the recent advances made in collecting data on impact pressure histories and their spatial distributions, analyses on the structural behaviour of the walls loaded by the impact forces do not seem adequate. In the present study the theoretical analysis of the response characteristics of a caisson plate, having different aspect ratios, under the wave impact loading is investigated. Numerical results for the dynamic values of moments and transverse displacements are obtained by the method of finite elements. Some prerequisite experimental data for wave breaking and resulting impact pressures are provided. The static results for moments and deflections are also computed for comparing them with the dynamic values. The dynamic results are found significantly greater than the static values. The ratio between the dynamic and static values is called “Dynamic magnification factor” that varies with plate aspect ratio. Based on this factor a procedure is proposed which may have practical consequences in the design of caisson plates.     

The effect of currents on the generation of internal waves by a barotropic tide near an underwater ridge

In the frame of the linear theory for long waves, the paper studies long waves generated by a barotropic tide running at an arbitrary angle over a bottom ridge. The ocean is assumed to be two-layered. In the area of a ridge with a rectangular cross section, geostrophic flows are considered, coupled with the inclinations of the free surface and interface. Wave amplitudes are shown to depend on the angle of an onrunning tide and this allows us to reach a conclusion about the influence of a geostrophic current on the generation of internal waves. Translated by Vladimir A. Puchkin.     

The Amphipod Community as a Bioindicator in Algeciras Bay (Southern Iberian Peninsula) Based on a Spatio-Temporal Distribution

Abstract. The amphipod population associated with Bugula neritina (L.), a verycommon bryozoan species in Algeciras Bay (Strait of Gibraltar), was studied on a spatio-temporal scale, in order to define its role as a bioindicator. Samples were collected in December, March, June and September along a transect running from the external to the internal sampling stations.
Fifty-three species belonging to 22 families were identified; the most abundant species were Jassa marmorata H olmes , Ischyrocerus inexpectatus (R uffo ) and Phtisica marina S labber .
The spatial evolution of the amphipod community reflected the physico-chemical conditions of Algeciras Bay, yielding a clear gradient from the outer to the inner stations. The stations located at the mouth of the bay, characterised by high hydrodynamism and low sedimentation, had a higher diversity and species richness than the inner stations with low water movement and higher sedimentation. Eight species preferred for the outer stations, while another nine species were typical of the inner harbours.
The most notable aspect of the seasonal evolution was the increased dominance of the tube-builder and deposit-suspension feeder Jassa marmorota .
Structural and ordination analyses corroborate the outer-inner gradient in the bay and illustrate the importance of hydrodynamic forces and sedimentation in the amphipod community.     

Effects of spectrum band width on the distribution of wave heights and periods

The statistical distribution of the crest-to-trough heights of narrowband nonlinear sea waves is derived in a semi-closed form. A quantitative comparison of the resulting density and exceedance probability distributions with those of the linear theory is given. It is shown that the nonlinearity of waves, even with steepnesses typical of extreme sea states, has an insignificant influence on the distribution of crest-to-trough heights.     

Photoadaptation of carboxylating enzymes and photosynthesis during a spring bloom

Properties of the light saturation curve of photosynthesis and ribulose-1,5-bisphosphate carboxylase (RuBPC) activity are shown to change qualitatively in a natural population of marine phytoplankton during a spring bloom. Evidence is presented to show that these changes constitute photoadapative responses to increasing irradiance. As irradiance increased during the bloom, both the level of light-saturated photosynthesis (P_m) and the initial slope of the light saturation curve (α = photosynthetic efficiency) increased whether those parameters were normalized to chlorophyll a concentration (P_m^b, α^b) or to cell numbers (P_m^c, α^c). The magnitudes of these changes were such that I_k (= P_m/α, the photoadaptation parameter) did not change, but I_m, the light intensity at which photosynthesis becomes saturated, increased. RuBPC activity, both chlorophyll a (RuBPC^b) and cell number normalized (RuBPC^c), also increased during the bloom. We suggest that these adaptations were achieved by simultaneously increasing the number of photosynthetic units, proportionately decreasing the photosynthetic unit size, and increasing both the concentrations of the enzymes of the dark reactions and possibly also of photosynthetic electron transport components.We also observed diminished levels of photoinhibition in the high light adapted cells late in the bloom and have suggested that this was a consequence of the same suite of physiological changes.In situ carbon fixation per cell increased during the bloom whereas no change occurred in this parameter when normalized to chlorophyll a concentration. Although these photoadaptive responses thus permitted carbon to be fixed in situ more rapidly per cell, at a constant efficiency with respect to investment of energy in the photosynthetic apparatus, they did not result in a change in growth rate. Based on consideratios of the role of time scale in physiological adaptation, however, it is suggested that the observed alterations in photosynthesis with increasing irradiance might permit a cell to more rapidly fill an energy quota for division, possibly an advantage in a mixing environment in which energy is patchily distributed, both spatially and temporalyy.Phosphoenolpyruvate carboxylase activity when normalized to chlorophyll a (PEPC^b) did not change during the bloom while chlorophyll a normalized dark carbon fixation decreased sharply and was quantitatively small compared to PEPC^b. On this basis and considering that RuBPC^b increased during the bloom, it is suggested that, although PEPC may be involved in dark carbon fixation, its most important quantitative role is probably an indirect one in light dependent photosynthesis.We have also considered the relevance of laboratory results on photoadaptation to interpretations of field studies and have suggested that batch culture studies must be treated with caution but that turbidistat and semi-continuous methods provide reasonable simulations of natural conditions.     

Sound velocity,density, and related properties along a transect across the Bay of Bengal

Physical properties, sound velocity and density of 95 core samples from ten locations along a transect (parallel to 15°N latitude) across the Bay of Bengal were measured. Results indicate that sound velocities range from 1,482 to 1,679 m/s (av: 1,583 m/s) and densities from 1,338 to 1,757 kg/m³ (av: 1,527 kg/m³). It has been observed that dark colored clays and sandy clays show higher values of sound velocity and density than the average values. A comparative study of the same with that of the sediment cores collected from the Norwegian basin, Mediterranean Sea, and Hatteras, Nares Abyssal plains, western North Atlantic Ocean was done.     

A fish hepatocyte model for the investigation of the effects of environmental contaminants

An isolated fish hepatocyte culture system was developed as a models ystem to investigate the mechanisms of action of environmental contaminants. Hepatocytes were isolated from striped bass (Morone saxatilis) by an adaptation of the two stage perfusion technique of Seglen.¹ The system was used to evaluate metal binding protein (MBP) induction in response to cadmium, a primary inducer of metallothionein (MT) in rat hepatocytes. Striped bass hepatocytes appeared to be refractory to the induction of MBP by cadmium, since there was no significant increase in the synthesis of MBP for any of the doses at any of the time points investigated. However, when a similar experiment was performed using rat hepatocytes there was induction of MBP that was related to both dose and time. These comparative experiments indicate that although there are similarities between the hepatocytes of the two species in regard to ³⁵S incorporation into low molecular weight metal-binding proteins, there appear to be significant quantitative differences as well in regard to MBP kinetics. This in vitro model system could potentially be utilized to investigate the toxicological properties of other environmental contaminants.     

Wave transmission and reflection characteristics of a rigid surface and submerged horizontal plate

The wave transmission and reflection characteristics of a rigidly fixed surface and submerged horizontal plate were investigated experimentally in detail for a wide range of incident wave steepnesses and for different depths of submerge of the plate in deep water conditions in regular water wave fields. The experiments were conducted at the Ocean Engineering Centre, Indian Institute of Technology, Madras, India, in a wave flume 10 m long, 0.3 m wide and in a constant water depth of 0.8 m. The horizontal plate is 0.22 m thick and 1.2 m in length, covering the enrire width of the flume. From the present investigation, it is found that for a rigid surface plate, the coefficient of transmission is a minimum and the coefficient of reflection is a maximum, but the maximum value of the coefficient of energy loss occurs for plates submerged closer to the still-water level (SWL) and not for the surface plate. It is also found that the value of the coefficient of reflection increases with the increase in the value of the Reddy-Neelamani (RN) number, the ratio of horizontal water particle excursion at the bottom of the plate in its absence to the length of the plate. The coefficient of transmission is found to decrease rapidly with increase in the value of RN number up to 0.1. The wave transmission is only 5% for RN from 0.1 to 0.2. It is also found that for RN number greater than 0.04, the minimum energy dissipation is consistently about 60% of the incident wave energy.