Mercury levels in fish,invertebrates and sediment in a recently recorded polluted area (Nissum Broad,western Limfjord,Denmark)

High concentrations of mercury were measured in sediment and animals collected in the immediate vicinity of a closed-down chemical factory. Sediment contained up to 22 ppm (dry wt) of mercury, deposit-feeding bivalves between 1.4 and 4.4 ppm (wet wt), suspension-feeding bivalves between 0.9 and 1.9 ppm and predatory fish between 0.3 and 0.8 ppm. Outside the ‘hot spot’ area, the mercury concentration in sediment and mussels (Mytilus edulis) rapidly decreased with increasing distance from the former factory. Mercury concentration in flounders (Platichthys flesus) also decreased with distance from the source; the decline was, however, much less marked.     

Burrowing and avoidance behaviour in marine organisms exposed to pesticide-contaminated sediment

Behavioural effects of marine sediment contaminated with pesticides (6000 ppm parathion, 200 ppm methyl parathion, 200 ppm malathion) were studied in a number of marine organisms in laboratory tests and in situ. The burrowing behaviour in Macoma baltica, Cerastoderma edule, Abra alba, Nereis diversicolor and Scoloplos armiger was impaired in the contaminated sediment compared to control. The impairment was most pronounced in the laboratory tests, where almost no burrowing occured. In a very simple laboratory set-up, highly significant avoidance of the contaminated sediment was demonstrated for Crangon crangon and Solea solea, but not for Carcinus meanas and Pomatoschistus minutus. The validity of both behavioural tests was supported by in situ observations and investigations on the distribution of the species. It is concluded that both tests are useful tools in the assessment of the impact of contaminated sediments.     

Geochemistry of Caledonian metabasalts from some Norwegian ophiolite fragments

Major and trace element analyses of metabasalts from five of the Lower Palaeozoic Caledonian ophiolite fragments along a strike distance of some 800 km of the west Norwegian coast are presented. Characteristically the REE patterns show depletion of both LREE and HREE relative to intermediate REE, giving an upward convex shape, but nearly flat, LREE depleted or enriched patterns occur. The REE patterns of the metabasalts from three of these sequences, i.e. the Lykling, Solund and Stavfjorden ophiolite fragments show little within-sequence but large between-sequence variation. The REE patterns of the metabasalts from the Gullfjellet (Major Bergen Arc) and Skålvær ophiolite fragments, however, show significant within-sequence variations, indicative of local source heterogeneties.When incompatible trace elements such as Ta, Nb, Ce, P, Zr, Hf, Sm, Ti, Y and Yb are normalized against average MORB, the metabasalts can be subdivided into two major groups. One group, geographically comprising the ophiolite fragments north of Bergen (i.e. Solund, Stavfjorden og Skålvær) show trace element ratios similar to average MORB, whereas the other group, defined by the Gullfjellet and Lykling ophiolite fragments (from Bergen southwards) differ significantly with respect to Yb/Y, Ti/Y and Nb/Ce ratios. These features are discussed in terms of trace element patterns in basalts from oceanic islands, island arcs and back-arc basins, and it is tentatively concluded that they reflect partial melts from a mid-oceanic mantle, or probably a back-arc basin mantle, which differed chemically from that of the northwestern Norwegian ophiolite fragments.     

Seismicity of the north-eastern region (N.E.R.) of India

Summary The earthquake pattern in the N.E.R. of India is investigated on the background of tectonic conditions. The epicentre maps and the cross-sections indicate some regularities in the spatial distribution of foci, particularly the existence of a Benioff zone, dipping down to 200 km at an angle of 35°–40° to the East between 25° N and 21° N. The shallow and intermediate activities in the Indoburmese zone seem to be mutually related as evidenced by the coincidence of periods of quiescence and activity. The origin of the largest of the whole region (15 Aug. 1950, M=8.6) can be accommodated in the statistics only by assuming a very large preparatory area also encompassing the extended Mishmi region. This event seems to be a rather exceptional event with the return period larger than the sample used for investigation, i.e. 54 years. The problem of a gap in the region of the Upper Assam remains open, the lack of activity also be explained also by pure geological reasons, i.e. by the age of the stable geological formation. The maps and the statistics of extremes provide the estimate of probability of occurrence of large events for practical purpose.     

Palaeomagnetism of late Precambrian dolerite dykes from Varanger peninsula,north Norway

Palaeomagnetic investigations have been carried out on 12 dykes of Late Precambrian age from the Varanger peninsula, north Norway. The dykes are separated into two groups, the Kongsfjord dykes and the Båtsfjord dykes. In the Kongsfjord dykes, titanomagnetite is almost entirely erased, as a result of an extreme degree of alteration. Pyrrhotite is the dominating magnetic mineral, and only three stable specimen directions can be defined. In the Båtsfjord dykes, however, the most important magnetic constituent is nearly pure magnetite, and a two-axis magnetization structure is revealed. The directions of the major component conform to a Fisherian distribution, and are assumed to represent the relative Late Precambrian field. Superimposed on this magnetization is a minor component which is assumed to be of Caledonian origin, probably Ordovician. This latter remanence is in accordance with other Middle Palaeozoic results obtained in Western Europe. The upper age limit of the Late Precambrian field is discussed, and it is proposed that the polar shift from the Late Precambrian position to the main Palaeozoic group may have occurred as late as Middle Ordovician.     

Eisbedeckung und hypolimnische Sauerstoffanreicherung im Greifensee von 1950 bis 1980

Hypolimnetic oxygen in the highly eutrophic Swiss lake Greifensee (area 8 km², maximum depth 33 m) was almost entirely depleted during summer stratification. We found a strong empirical relation between wind action across the lake surface and hypolimnetic reoxygenation in the cold half year. Long periods of ice cover severely limited anemogenic reoxygenation.      

Wind flow over low arbitrary hills

A simplified model is given which computes the wind distribution over an arbitrary mountain range for a given upwind boundary-layer profile. The method has been adopted for the HP-41C calculator and results include the distribution of the amplification factor along the wind direction for various topographies.