Long-term effects of tributyltin compounds on the baltic amphipod, Gammarus oceanicus

Amphipod larvae, Gammarus oceanicus, were exposed for 8 weeks to bis(tributyltin) oxide (TBTO) or tributyltin fluoride (TBTF), or for 5 weeks to leachates from tributyltin-containing antibiofouling paints. No larvae survived 8 weeks' exposure to 3 μg/litre TBTO or TBTF. Differential larval survival occurred during exposure to 0·3 gmg/litre of these same compounds. Paint leachates were shown to cause similar toxicity responses at comparable aqueous tributyltin concentrations. An examination of sublethal responses showed slight decreases in growth for larvae exposed to TBTO and to paint leachates, although responses at tributyltin levels below 1 μg/litre were not marked. Whole-animal oxygen consumption rates were not affected by low tributyltin exposure levels. While these studies demonstrate low level toxicity of tributyltins, effects on oxygen consumption and growth do not indicate a mode of action for these compounds.     

Ludlow (Silurian) stromatoporoid biostromes from Gotland, Sweden: facies, depositional models and modern analogues

Stacked stromatoporoid‐dominated biostromes of the Ludlow‐age Hemse Group (Silurian) in eastern Gotland, Sweden, are 0·5–5 m thick and a few tens of metres to >1 km in lateral extent. They form one of the world's richest Palaeozoic stromatoporoid deposits. This study compiles published and new data to provide an overall facies model for these biostromes, which is assessed in relation to possible modern analogues. Some biostromes have predominantly in‐place fossils and are regarded as reefs, but lack rigid frameworks because of abundant low‐profile non‐framebuilding stromatoporoids; other biostromes consist of stromatoporoid‐rich rudstones interpreted here as storm deposits. Variation between these two `end‐members' occurs both between interlayered biostromes and also vertically and laterally within individual biostromes. Such variation produces problems of applying established reef classification terms and demonstrates the need for the development of terminology that recognizes taphonomic destruction of reef fabrics. An approach to such terminology is found in all four categories of a recent biostrome classification scheme that are easily recognized in the Hemse biostrome facies: autobiostromes (>60% in place); autoparabiostromes (a mixture of in‐place and overturned reef‐building organisms, 20–60% in place); parabiostromes (builders are overturned and damaged, <20% in place); and allobiostromes (transported and detrital reef material, nothing in place). These categories provide a broad taphofacies scheme for the Hemse biostromes, which are mostly autoparabiostrome to allobiostrome. The biostromes developed on crinoidal grainstone sheets and expanded laterally across relatively flat substrates in a marine setting of low siliciclastic input. Planar erosion surfaces commonly terminate biostrome tops. Three broadly similar modern analogues are identified, each of which has elements in common with the Hemse biostromes, but none of which is an exact equivalent: (a) laterally expanded and coalesced back‐barrier patch reefs behind the Belize barrier, an area influenced by limited accommodation space; (b) a hurricane‐influenced shelf, interpreted for Grand Cayman, where reef cores consist of rubble and lack substantial framework; the wide distribution of rounded pebbles and cobbles of stromatoporoids in the Hemse biostromes most probably resulted from hurricanes; (c) coral carpets in 5–15 m water depth of the northern Red Sea, where lateral expansion of low‐diversity frames dominated by Porites coral has produced low‐profile biostromes up to 8 m thick and several km long. Such carpets accumulated large amounts of carbonate, with little export, as in the Hemse biostromes, although the latter did not build frameworks because of the nature of growth of the stromatoporoids. The notable lack of algae in the Hemse biostrome facies is also a feature of Red Sea coral carpets; nevertheless, coral carpets are ecologically different. Hemse biostromes lack evidence of a barrier reef system, although this may not be exposed; the facies assemblage is consistent with either a storm/hurricane‐influenced mid‐ to upper ramp or back‐barrier system.     

Stability constants of phosphoric acid in seawater of 5–40‰ salinity and temperatures of 5–25°C

The stability constants K₁ and K₁₂ of phosphoric acid were determined for artificial seawater of six different salinities (5, 10, 20, 30, 35, 40‰) and in 0.2, 0.4 and 0.7 M NaCl at three temperatures (5, 15, 25°C). The results are compared with those of Kester and Pytkowicz (1967), Atlas et al. (1976) and Dickson and Riley (1979). The ionic product of water, K_w, was determined in sodium chloride media at 5, 15 and 25°C. Complex formation among Ca²⁺, Mg²⁺, HPO₄^2? and PO₄^3? is discussed.     

Calorimetric study of the thermodynamics of formation of MgSO4 and NaSO4− ion pairs at the ionic strength of seawater

The formation of the ion pairs MgSO₄ and NaSO₄^? was investigated calorimetrically at 0.75 M ionic strength, 25°C, 1 atm. Simultaneous determinations of enthalpy changes, ΔH₁⁰, and stability constants, K₁, were not possible, and values of K₁ determined independently had to be introduced for the calculation of ΔH₁⁰. The values of ΔH₁⁰ obtained were 1–3 kJ mol^?1 for MgSO₄ and 0 kJ mol^?1 for NaSO₄^?.     

A study of apparently nearby stars with coinciding spectral type and apparent magnitude

At visual inspection of objective-prism plates one frequently detects a pair or higher multiple of apparently identical stellar spectra so close together that they form a conspicuous configuration for the eye. An attempt to analyse this type of objects has given no positive indication that it should be identified with any unique physical phenomenon. A series of explanations is presented. A minor fraction of the objects may constitute widely separated binary components, the identity of which is physically conditioned by the process of formation. For the majority, however, it seems more probable that they form parts of cluster remnants or very small clusters, and that the coincidence of the spectral types is in the first instance to consider as a fortunate random effect that facilitates the detection of the hidden cluster. Although there are several interpretations of the appearance of such ‘miniclusters’, I find it particularly important to take the possibility into consideration that the number of open clusters (and associations) may be considerably greater than one has hitherto assumed—from observational as well as from theoretical point of view.     

Organizations: INMARSAT: improving maritime communications

Improving maritime communications is the raison d'être of INMARSAT, of which 40 countries are now members. INMARSAT operates the world's only commercial satellite system devoted to international mobile communications. This article describes the system and the services which can be provided through it, and covers the policy issues of interest to INMARSAT. It concludes by considering the future of maritime mobile communications via satellite.     

A new type of magnetograph

A solar magnetograph without electronics or any moving parts has been designed. The principle is the use of a subtracting double-dispersion optical system. The exposure time is of the order of 1 sec.Preliminary results obtained at the Swedish Astrophysical Observatory at Anacapri indicate that this method could be convenient to use in space vehicles when aiming at high spatial resolution of solar magnetic fields.     

Validation of very high cloud droplet number concentrations in air masses transported thousands of kilometres over the ocean

The microstructure of orographic clouds related to the aerosol present was studied during the second Aerosol Characterisation Experiment (ACE‐2). Very high cloud droplet number concentrations (almost 3000 cm⁻³) were observed. These high concentrations occurred when clouds formed on a hill slope at Tenerife in polluted air masses originating in Europe that had transported the order of 1000 km over the Atlantic Ocean. The validity of the measured droplet number concentrations was investigated by comparing with measurements of the aerosol upstream of the cloud and cloud interstitial aerosol. Guided by distributions of the ratios between the measurements, three criteria of typically 30% in maximum deviation were applied to the measurements to test their validity. Agreement was found for 88% of the cases. The validated data set spans droplet number concentrations of 150–3000 cm⁻³. The updraught velocity during the cloud formation was estimated to 2.2 m s⁻¹ by model calculations, which is typical of cumuliform clouds. The results of the present study are discussed in relation to cloud droplet number concentrations previously reported in the literature. The importance of promoting the mechanistic understanding of the aerosol/cloud interaction and the use of validation procedures of cloud microphysical parameters is stressed in relation to the assessment of the indirect climatic effect of aerosols.     

A mechanism for the build-up of flare energy

It is shown how the kinetic energy of the rotational motion of a sunspot can be transferred to electromagnetic energy in filamentary currents. The time needed for preconditioning the solar atmosphere for a flare varies within wide limits. For small flares it may be of the order of minutes; for large flares, of the order of hours or days.Presently Guest Investigator at the Mount Wilson and Palomar Observatories.