Formation and distribution of manganese nodule deposit in the northwestern margin of Clarion-Clipperton fracture zones,northeast equatorial Pacific

In the northwestern margin of the Clarion and Clipperton fracture zones, manganese nodules are latitudinally variable in character, resulting from the progressive (re)generation of nodules since the Oligocene as the Pacific Plate migrates northwestward beneath the equatorial production zone. Complemented by the surface water productivity, bottom current activities have concentrated nodules in the Oligocene to Miocene siliceous clay. Resedimentation processes on nodules form three types of nodules with concentric structures and 10 Å-manganaterich bottoms, by periodically causing the diagenetic growth of nodules within the topmost sediment layer.     

A formal derivation and numerical modelling of the improved Boussinesq equations for varying depth

A formal derivation of the improved Boussinesq equations of Madsen and Sørens (1992) is presented to provide the correct forms of the depth-gradient related terms. Linear shoaling characteristics of the new equations are investigated by the method of Madsen and Sørensen (1992) and by the energy flux concept separately and found to agree perfectly, whereas these approaches give conflicting results for the equations derived by Madsen and Sørensen (1992). Furthermore, Nwogu's (1993) modified Boussinesq model is found to produce a linear shoaling-gradient identical with the present work. Numerical modelling of the derived equations for directional waves is carried out by three-time-level finite-difference approximations. A higher-order radiation condition is implemented for effective absorption of the outgoing waves. Several test cases are included to demonstrate the performance of the model.     

Some statistical methods of the objective classification of oceanographic data

Algorithms for the compression and objective classification of low-volume samplings according to the test of their belonging to different statistical populations are given. Samplings are discriminated by thex ² test. The distributions of the temperature patch horizontal scales in the upper ocean are analysed. It is shown that optimum empirical thresholds exist when the abstract classification mechanism goes over to the objective natural classification.Translated by Mikhail M. Trufanov.     

Wave climate in a groin field

Wave records at seven different locations within a groin field have been analysed by both statistical and spectral approaches to study the general wave climate. The wave heights and periods from the wave records were obtained by both upcross and downcross methods for the statistical approach. The variation of different wave height and wave period parameters with respect to the time of measurement at a particular location and its variation at different locations within the groin field at a particular instant of time are presented and discussed in detail in this paper. It is generally found that the wave heights follow the Weibull distribution.     

Sea-floor observations in the tongue of the ocean,Bahamas: An Argo/SeaMARC survey

SeaMARC side-scan sonographs and Argo video and photographic data suggest that the recent sedimentary environment of the floor of the Tongue of the Ocean is controlled by an interplay of turbidity current flow from the south, sediment spill-over from the carbonate platform to the east (windward side), and rock falls from the west carbonate escarpment (lee side). The spill-over forms a sandy sedimentary deposit that acts as a topographic obstruction to the turbidity current flow from the south. This obstruction is expressed by the westward migration of a northwest-southeast oriented turbidity-current-cut channel.     

Oceanic thermohaline intrusions: observations

Intrusions are commonly observed in the upper, deep and coastal oceans, and are closely linked to lateral fluxes of heat, salt and momentum. This is a review of observations of intrusions and the results of comparisons of properties such as scale, slopes, microstructure activity, and fluxes with theoretical models. A summary of estimates of lateral heat fluxes indicates a wide range of lateral diffusivities. We conclude by noting that our present knowledge is insufficient to predict the structure, length-scales and lateral fluxes of thermohaline intrusions with confidence, and list a number of unresolved questions. Suggestions are made for compilation of existing data into a database for exploratory analysis and testing of theoretical hypotheses. An outline is given of a potential collaborative field experiment using CTD, fluorescent dye, and microstructure observations.     

Use of Continuous Plankton Recorder information in support of marine management: applications in fisheries, environmental protection, and in the study of ecosystem response to environmental change

The Continuous Plankton Recorder (CPR) survey was conceived from the outset as a programme of applied research designed to assist the fishing industry. Its survival and continuing vigour after 70 years is a testament to its utility, which has been achieved in spite of great changes in our understanding of the marine environment and in our concerns over how to manage it. The CPR has been superseded in several respects by other technologies, such as acoustics and remote sensing, but it continues to provide unrivalled seasonal and geographic information about a wide range of zooplankton and phytoplankton taxa. The value of this coverage increases with time and provides the basis for placing recent observations into the context of long-term, large-scale variability and thus suggesting what the causes are likely to be. Information from the CPR is used extensively in judging environmental impacts and producing quality status reports (QSR); it has shown the distributions of fish stocks, which had not previously been exploited; it has pointed to the extent of ungrazed phytoplankton production in the North Atlantic, which was a vital element in establishing the importance of carbon sequestration by phytoplankton.The CPR continues to be the principal source of large-scale, long-term information about the plankton ecosystem of the North Atlantic. It has recently provided extensive information about the biodiversity of the plankton and about the distribution of introduced species. It serves as a valuable example for the design of future monitoring of the marine environment and it has been essential to the design and implementation of most North Atlantic plankton research.     

Metal accumulation in mussels of the Kuril Islands, north-west Pacific Ocean

Concentrations of cadmium, copper, iron, lead, manganese, nickel and zinc were investigated in two species of mussel from the Kuril Islands in the north-western Pacific Ocean: the short-lived mussel Mytilus trossulus and the much larger and longer-lived Crenomytilus grayanus. The concentrations of most elements were low, and these reported levels are believed to reflect background values for pristine locations. However, both iron and zinc concentrations were elevated in some samples taken from areas of hydrothermal vent activity, and these are believed to reflect the enrichment of the two metals in solution at such sites. Furthermore, the concentrations of cadmium were unusually elevated in both species of mussel, especially in the longer-lived C. grayanus. The high accumulation of cadmium in mussels from the Kuril Islands is believed to reflect regional upwelling, but it is also postulated that filtration rates of the mussels are high due to low levels of suspended matter, and this leads to a high assimilation efficiency for cadmium. The distribution of cadmium amongst the tissues of C. grayanus is also reported, and the need for further ecotoxicological studies in the area is proposed.     

Detection of buried targets using a synthetic aperture sonar

This paper presents observations of buried target detections made using a 20-kHz synthetic aperture sonar. At grazing angles below the critical angle, surprisingly high signal-to-noise detections were made of cylindrical targets buried at depths of 15 and 50 cm. During a separate set of measurements, buried spheres were clearly seen at steep grazing angles, but were generally not seen below the critical angle. Since scattering from wave-generated sand ripples may contribute to detections at grazing angles below critical angle, the information available on the ripple fields is discussed and used in acoustic backscatter simulations for the buried spheres. Lack of information on the ripple height precludes a definitive explanation for the absence of buried sphere detections at subcritical grazing angles.