Artificial Reefs in the Low Productive Marine Environments of the Southeastern Mediterranean

Abstract. Fishery yields in the oligotrophic waters of the Southeastern Mediterranean arc low due to habitat and food limitations. A four year study of a complex of artificial structures established in the coastal waters of Israel points to several possible solutions to these problems. One approach is the artificial enrichment of the man-made reef with trash fish. This, together with the configuration of the reef, caused a significant increase in the abundance of fish predators such as groupers of the genus Epinephclus. Omnivores and herbivores were attracted only by the presence of artificial structures. Some species, such as the slipper lobster Scyllurides lulus, only use the man-made reef for shelter during part of the day or season; they forage over a much larger area the rest of the time and are important "importers" of food to the artificial habitat. Artificial kelp were effective in recruiting juveniles and small fishes to the site.     

Nankai Trough: A hot trench?

Heat flow estimated from the gas hydrate layers on the landward slope of the Nankai Trough reveals that heat flow increases downslope toward the trench floor. This data plus six new heat flow values obtained by a conventional probe and two values available from DSDP drill holes give a fairly detailed heat flow distribution in the Nankai Trough area, when combined with the already existing data set. There appears to be a zonal pattern parallel to the trough axis, with a high heat flow zone on the floor of the trough that is quite anomalous for a subduction zone. It might be explained as a result of subduction of the hot portion of the Philippine Sea plate, i.e. the Shikoku Basin, and/or of more local effects such as heating due to intrusion of hot water from subducted sediments to shallow depth beneath the trough floor. Surface heat flow patterns landward of the trough were calculated for a simple thermal model of subduction. Perfect reproduction of the observed zonal pattern is difficult to achieve by the simple model, suggesting the necessity for further heat flow and other observations.     

Geoid height anomalies over the Cape Verde Rise

Geoid height anomalies, as determined by satellite altimetry, suggest that the Cape Verde Rise is in local isostatic equilibrium, supported by a low-density root of altered lithosphere. A depth anomaly map shows the Cape Verde Rise to be approximately 1600 km wide and 2km high. Removal of a quadratic surface from the observed geoid heights leaves a residual positive anomaly with the same shape as the rise and an amplitude of about 8 m. The ratio of residual geoid height anomaly to depth anomaly is consistent with an isostatic root only 40 km deep on average.     

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.     

On the use of grate-turbulators for tests of microstructural probes

Highly sensitive microstructural probes subjected to noise disturbances are free of these in laboratory tests. This leads necessarily to the working out of methods for complex testsin situ. The paper reports on the successful use for this purpose of a grate (net) suspended from a free-falling probe. The grate sets up turbulence with reproducible structure in the area of sensor location.UDK 551.46.085     

New sets of wavelet-forming functions

One of the most efficient tools of studying meteorological and climatic time series is wavelet analysis, which allows local properties of a nonstationary time series to be examined. New sets of continuous and discrete wavelet-forming functions are proposed. All proposed wavelets are finite (have a bounded carrier), even, and well localized in the spectral space.     

Hotspots in ambient noise caused by ice-edge eddies in the Greenland and Barents Seas

Mesoscale eddies are frequently observed in the Greenland and Barents Seas' marginal ice zone (MIZ). The objective of this study was to investigate the hypothesis that acoustic hotspots along the ice-edge region are due to mesoscale eddy currents interacting with the broken-up ice floes in the MIZ. To test this hypothesis, ambient-noise case studies were carried out during the MIZEX 85-87 and SIZEX 89 field experiments. In each experiment, ice-edge eddies were localized visually from aircraft and by use of satellite remote-sensing data obtained in near real time. Sonobuoys were, thereafter, deployed by fix-wing aircraft and helicopters in selected eddy areas. Ambient-noise data, recorded over several hours by aircraft, were analyzed estimating averaged ambient-noise levels at four selected frequencies: 40, 100, 315, and 1000 Hz. The analysis showed high mean levels and large gradients in ambient noise near ice-edge eddies and during strong wind and wave forcing against the ice edge. The conclusion of this study is that mapping of the ice edge and localization of mesoscale ocean processes using remote sensing from space will provide important input to ambient-noise prediction in the MIZ.     

Application of wavelet transforms to the decoupling of free-roll decay data

This study presents the results of the decoupling of a free-roll decay test by wavelet transforms. A free-roll decay test was performed to determine the coefficients of damping terms in equations of motion. No motion of the model was restricted during the experiment. A slight yaw motion was found while the model was in the free-roll decay motion. It was necessary to extract a pure roll motion from the experimental data. Wavelet transforms were applied to the signals to extract the pure roll motion. The results were compared to those found through the Fourier transform. Discrete wavelet transforms were able to efficiently decouple the test signals, while the continuous wavelet transform and the Fourier transform could not.