A note on the joint distribution of wave height and period during the growth phase of a storm

In this note the effect of changes in sea-state, as measured by the significant wave heigh H_s, on the joint distribution of individual wave height and period are considered. Wave data, obtained from a Waverider buoy during the growth phase of a storm, are used in the analysis. It is found that, by correctly scaling the individual heights and periods, the form of the joint distribution does not depend on H_s, but is dependent on the bandwidth of the spectrum. The results obtained also give some indication of the period of individual, high zero-upcrossing waves.     

Study of fluoride in polluted and unpolluted estuarine environments

Mindhola River estuary, which receives industrial waste containing high concentrations of fluoride, and Purna River estuary, which is free from fluoride contamination, have been investigated. While fluoride behaved conservatively in Purna River estuary, significant deviation from the theoretical dilution line (TDL) in the chlorinity range 0·5–8‰ was observed in Mindhola River estuary due to the externally added fluoride which largely remained in solution. The excess of fluroide over the theoretically calculated value was at a maximum around a chlorinity of 3‰. High natural fluoride content of the river waters resulted in F/Cl ratios exceeding 300 × 10⁻⁵ at low chlorinities. The ratio decreased rapidly with increasing chlorinity and the value near to that of seawater was observed at chlorinities above 14‰.     

Trace element distributions in coastal waters along the US-Mexican boundary: relative contributions of natural processes vs. anthropogenic inputs

Trace element concentrations (Pb, Cd, Mn, Fe, and Zn) were measured along four surface water transects across the continental shelf off Baja California, to evaluate the magnitude of heavy metal contamination in the coastal waters along the US-Mexican boundary. These initial measurements of trace elements in Mexican neritic waters revealed offshore concentration gradients, with the highest levels in coastal waters with high salinities and nutrient concentrations. There were also longshore gradients, with lower concentrations in the southern locations. Although the relative enrichment of metals detected at nearshore stations along the US-Mexican border appeared to correspond to wastewater discharges in that area, these trace metal enhancements were found to be primarily associated with physical oceanographic processes (upwelling and advection), rather than anthropogenic inputs. This was demonstrated both by metal-nutrient correlations and multivariate statistical analyses. Mass balance calculations also indicated that about 1% of Cd, 9% of Zn, and 29% of Pb were from urban discharges within the area.     

A detailed survey near Mount Eratosthenes Eastern Mediterranean

A detailed marine survey made to the South West of Mount Eratosthenes is described. The results show the existence of a narrow zone of WNW trending deformed sediment west of the mount surrounded by an evaporite sequence in different stages of deformation.This work was intended to settle the conflict between the results of three previous interpretations of the tectonic structure of this area. We see the area being characterised by five areas with different degrees of tectonic deformation yet showing little causal relationship to overburden of Nile Cone sediments. A fault controlled cliff coincides with the previously described salt wall and strike slip fault yet we see no evidence for its diapiric origin nor positive evidence for strike slip motion along it. We concur with the previously observed area of higher free-air gravity anomalies termed the Eratosthenes tectonic zone, although it is traversed by several boundaries between areas of different deformation. Our results thus show some agreements and some re-interpretations of the observations. This complicated region is not yet fully understood however.     

Tectonics at the intersection of the East Pacific Rise with Tamayo Transform fault

During the Fall of 1979, a manned submersible program, utilizing DSRV ALVIN, was carried out at the intersection of the East Pacific Rise (EPR) with the Tamayo Transform boundary. A total of seven dives were completed in the vicinity of the EPR/Tamayo intersection depression and documented the geologic relationships that characterize the juxtaposition of these types of plate boundaries. The young volcanic terrain of the EPR axis can be traced into and across the Tamayo Transform valley but becomes buried by sedimentary talus that is being shed from sediment scarps along the unstable sediment slope that defines the north side of the intersection depression. Within 4 km of the transform boundary, the dominant trend (000°) of the fissures and faults that disrupt the rise-generated volcanics is markedly oblique to the regional direction of sea floor spreading (120°). Since no evidence was found to suggest that these structures accommodate significant amounts of strike-slip displacement, they are taken to reflect a distortion of the EPR extensional tectonic regime by a transform generated shear couple. The floor of the Tamayo Transform valley in this area is inundated by mass-wasted sediment, and the principal transform displacement zone is characterized at the surface by a narrow (<1.5 km) interval of fault scarps in sediment that trends parallel with the transform valley. Extrapolated to the west, this zone links with zones of transform deformation investigated during earlier submersible studies (CYAMEX and Pastouret, 1981). Evidence of low-level hydrothermal discharge was seen at one locality on the EPR axis and at another 8 km west of the axis at the edge of the zone of transform deformation.     

Lower Eocene red-clay sedimentation on the George Bligh/Rockall Channel

Core 7710, recovered on the George Bligh/Rockall Channel, is composed of fine grained ocher-colored sediments rich in ferriferous smectite (montmorillonite, beidellite). These sediments were deposited during early Eocene in a shallow marine environment. Their mineralogic, chemical and isotopic constituents indicate subaerial weathering of lower Eocene intermediate igneous rocks (ferrodiorite, marscoiite) eroded from the still-emergent George Bligh and Rockall Banks. Lack of any post Eocene Sediments may be due to major morphologic and hydrologic changes forming sedimentation gaps.     

Optimum design of a servo-controlled breathing regulator for underwater divers

This article deals with the analysis, synthesis and performance evaluation of the flow and dynamic characteristics of the new class of servo-controlled breathing regulators for underwater divers.Emphasis on such a class of regulators has been stimulated by their tremendous potential in extending the dive depth and duration because they reduce the diver breathing effort to a great extent. This would eliminate the unnecessary exhaustion of the diver under such extreme diving conditions and accordingly improve his work efficiency underwater.The study aims at developing rational design procedures and guides that would enable the regulator designers to select the optimal design parameters of this class of regulators. Such design guides are based on the analysis of the flow and dynamic characteristics of the servo-controlled regulator as well as the basic principle of the theory of optimum control.The study presents also experimental evaluation techniques of the dynamic characteristics of this class of regulators in order to provide common quantitative means for comparison with the conventional regulator designs.The presented results emphasize the merits and the potential of the servo-controlled regulators as essential tools of supporting the life of divers underwater.     

Semisubmersible response to transient ice forces

The paper presents an analytical and experimental study on the transient response of semisubmersibles to bergybit impact and the strength of bergybit ice to high strain-rate loadings. Two approaches have been proposed for the solution of the semisubmersible-bergybit interaction problem, one using the energy approach and the other using the conventional structural dynamics approach with initial velocity conditions. In addition the local behaviour of the impacted regions have been analysed for deformation and failure. Numerical results have been given for local behaviour of an impacted column and global behaviour of semisubmersible-bergybit system. Experimental study has been reported on the impact strength of iceberg ice at strain rates of 10⁻³, 10⁻² and 10⁻¹; the indentation impact strength of ice is found to be 3–4 times the unaixial compressive strength, at the same strain rate.