Unstable plasma irregular structures in the topside ionosphere and spread-<Emphasis Type="Italic">F</Emphasis>

The results of the Cosmos-900 satellite observ ations of plasma density inhomogeneities in the geomagnetic equator region and the longitudinal distributions of the equatorial spread-F, according to the Intercosmos-19 satellite data are presented. It is show n that the dependence of radiosignal propagation in the ionosphere on geophysical parameters is related to development of the electrostatic instability of the inhomo-geneous ionospheric plasma. The longitudinal dependence of the spread-F, can reflect the influence of the energetic sources, located outside the ionospheric layer that scatters a radio pulse, on the ionosphere. The manifestation of the longitudinal effect in the equatorial spread-F, in the Atlantic region can be explained by the influence of the cone instability on the plasma electrodynamics in the South Atlantic geomagnetic anomaly.     

Environmental hypoxia as a metabolic constraint on fish: the case of Atlantic cod, Gadus morhua

Hypoxia is known to provoke a wide range of effects on aquatic animals. Here we use laboratory and field data on Atlantic cod, Gadus morhua, to illustrate that many of these responses can be explained within the metabolic scope (MS) framework, i.e. taking into account the directive and limiting effects of dissolved oxygen (DO) on the ability of animals to acquire energy for growth and activity. A MS model for cod shows that scope for activity (swimming, feeding, etc.) is proportional to DO and becomes nil, jeopardising survival, when DO is < approximately 20% air saturation. Laboratory studies have confirmed this lethal threshold and demonstrated that growth and food ingestion were significantly reduced below 70% sat. This loss of appetite has been linked to a reduction of the peak value and an increase in duration of postprandial metabolism, in agreement with the MS model. Dwindling MS during hypoxia imposes an upper limit to swimming performance. Cod may also opt to reduce spontaneous swimming activity to spare oxygen for other activities such as digestion. In the Kattegat, the Baltic Sea, and the Gulf of St. Lawrence, eastern Canada, cod completely avoid waters where their MS is near zero. Furthermore, cod density increases exponentially with DO up to approximately 70% sat in the Gulf of St. Lawrence. Although hypoxia results in other direct and indirect effects as well, the MS framework allows modelling of many of the responses to hypoxia for individual cod that ought to be reflected at the population and community levels. The MS framework is also useful to compare species responses. We show that the impact of hypoxia on MS is similar, when expressed as a proportion of MS in normoxia, in cod, European sea bass (Dicentrarchus labrax), the common sole (Solea solea) and turbot (Psetta maxima). Data are required for other species to evaluate how general these findings are.     

Spectral characteristics of magnetogravity waves generated by high-energy mass source in the equatorial region of the atmosphere,Part I

The possibility of magnetogravity wave (MGW) propagation in the equatorial ionosphere taking into account the finite conductivity is analyzed. The dispersion relation shows the existence of two propagating MGW modes in ionospheric layer F2: high-frequency (HF MGW) and low frequency (LF MGW). The dispersion relations for them are executed and the characteristic frequencies and propagation velocities are determined. In this part of research the spectral features of disturbances in components of environment displacement for HF MGW, generated by a mass source, is carried out. The results are applied to estimate the values of density, pressure and magnetic field spectral components of magnetogravity disturbances caused by horizontal meteor sweep. They may be useful in the analysis of ionospheric disturbances excited by high energy geophysical sources.     

Effect of anisotropy of the earth on the impedance measurements

Summary Electromagnetic field response of a homogeneous uniaxially anisotropic conducting medium has been investigated in the presence of a vertical electric dipole placed at a heighth above the conducting surface. Expressions for the horizontal components of electric and magnetic fields and hence that of vertical impedance of the field, as a function of the distance of the place of observation from the source, have been derived. Numerical computations have been done and curves are given to illustrate the influence of anisotropy on the amplitude values of the impedance on the surface of the conducting medium.N.G.R.I. Contribution number 71–279.     

The bedrock topography of the botany basin,New South Wales

The bedrock topography of the Botany Basin has been determined from seismic‐sparker records made in Botany Bay and Bate Bay, and from seismic‐refraction and gravity measurements on the Kurnell Peninsula. Supplementary information has been obtained from boreholes both on land and in the sea.

The Cooks and Georges Rivers formerly constituted the main drainage of the Basin and flowed generally southeastwards (beneath the present Kurnell Peninsula) and joined the Port Hacking River east of Cronulla. The depth of the bedrock channel of the former Georges River is 75–80 m b.s.l. at Taren Point, 90–95 m beneath the Kurnell Peninsula and 110–115 m at its junction with the Port Hacking River channel. The bedrock channel of the former Cooks River is about 30 m b.s.l. at Kyeemagh, its present entrance to Botany Bay, and it joined the Georges River at a location now 90 m b.s.l. beneath the Kurnell Peninsula.

A second drainage system existed in the north and east of Botany Bay and generated the present mouth beneath which the bedrock is now 110 m b.s.l. This channel followed a southeasterly course parallel to the present northern shore of Botany Bay and was separated from that of the ‘Cooks and Georges Rivers’ by a bedrock ridge which extended from beneath Sydney Airport to the northern extremity of the Kurnell Peninsula. Over much of its length this divide had a depth of about 30 m b.s.l.

The formation of the Kurnell Peninsula tombolo led to the diversion of the ‘Cooks/Georges River’ through the mouth of Botany Bay and subsequently led to the development of the bay. This change in the drainage system occurred when the sea was less than 30 m below the present sea level.     

Anthropogenic transformations of the Arctic ecosystem of Lake Imandra: Tendencies for recovery after long period of pollution

Transformation of an Arctic aquatic ecosystem (a case study of Lake Imandra) under the impact of a mining industrial complex is considered. Water chemical composition and the ecosystem’s structural components (phyto- and zooplankton, zoobenthos, and ichthiofauna) are analyzed for the following periods: the preindustrial background (reference) conditions, industrial development of mineral resources and strong anthropogenic impact, industrial recession and decreased anthropogenic impact, and stabilization. The main regularities of the aquatic ecosystem successions under the conditions of anthropogenic loads and their decrease are established.     

Coastal processes and cliff recession between Gabicce and Pesaro (northern Adriatic Sea): a case history

Cliff recession on the high rocky coast between Gabicce and Pesaro Adriatic sea causes a wide range of mass movement processes on the whole slope, affecting both the bedrock and the overburden. The outcropping late Miocene rock formations are represented by marls, marly limestones, dark laminated mudstones and bedded sandstones and marls. Mass movements are common because of stratification and discontinuities in the rocks that, together with the presence of groundwater and weathering processes, reduce the overall strength of the slopes. A model for the evolution of this coastal area is proposed, which involves cyclic basal erosion, followed by mass movement that favours debris accumulation at the base of the cliff. The longshore currents have to then remove the material before a new cycle can begin.