The equilibrium speciation of dissolved components in freshwater and sea water at 25°C and 1 atm pressure

A data base summarising the stability constants of more than 500 complexes is used to calculate speciation pictures for 58 trace elements in model seawater (pH 8.2) and freshwaters (pH 6 and 9). Consideration of the results provides a general summary of the chemical periodicity of the speciation of trace components in natural waters. The polarising power of an element ((cation charge)²/(radius), z²/r) provides a useful index to the degree of hydrolysis in aqueous solution. The fully hydrolysed elements with a high polarising power form distinct groupings in the periodic table. The relative magnitudes of the acid dissociation constants are summarised by Pauling's rules and the speciation of the fully hydrolysed elements in natural waters largely depends on pH and, to a lesser extent, on interactions with the major cations. The remaining cations of low and intermediate polarising power can be subdivided according to their tendency to form covalent bonds. An empirical parameter Δβ(= logβ⁰_MF ? log β⁰_MCl) is used to define (a)-type (Δβ > 2), borderline (a)-type (2 >Δβ > 0), (b)-type (Δβ < ?2) and borderline (b)-type (0 >Δβ > ?2) cations. Again these various categories form coherent groupings on the periodic table. By considering the interactions of cations from the various categories with the inorganic ligands commonly encountered in natural waters it is possible to assign the ligands themselves to ‘hard’ (e.g. F^?, SO₄^2?), ‘intermediate’ (e.g. OH^?, CO^2?₃) and ‘soft’ categories (e.g. Cl^?). These concepts can be summarised by constructing a Complexation Field Diagram in which the various cations are located on a plot of $\text{z}{}^2\text{r}$ vs δβ. The extension of the model to include redox equilibria and additional ligands is described.     

Variability of the reverse-flow concentration technique of measuring plankton respiration

Results from the reverse-flow concentration method used to determine community plankton respiration vary significantly because of metabolic inactivation or losses of a portion of the concentrated sample during the filtering process. These losses seem to be nearly constant at concentrations greater than 150X. The within sample coefficient of variation is 20–40% and is primarily a result of clumping and inadequate mixing before subsampling. A rapid processing of the samples is critical for best results.     

Biaxiality in relation to visible twinning in experimentally deformed calcite

Moderate to strong biaxiality (2V = 10 °–45 °) in experimentally deformed calcite (in single crystals and in marble) is attributed to overlap between one or two thin {01¯12} twin lamellae and the enclosing host. A perfectly centered conoscopic figure (section normal to [0001]) is perceptibly asymmetric about the trace of the optic axial plane. This asymmetry is pronouned in thick sections (> 0.04 mm) and completely distrupts the biaxial configuration of the figure if the overlapping lamella exceeds about 0.0025 mm in thickness. In sections somewhat oblique to [0001] and cut at 20 ° or less to the plane of twinning the conoscopic figure may appear to be perfectly biaxial-expecially in thin sections ( 0.02 mm) enclosing thin ( 0.001 mm) but still visible twins.Similar values of 2V recorded for natural calcite likewise are attributed to twinning on a visible scale.     

Magnetisation history of lower old red sandstones from the Gamrie Outlier,Scotland

Red beds in the Lower Old Red Sandstone Gamrie Outlier on the southern margin of the Orcadian Basin originated through the diagenetic breakdown of iron silicates. The magnetic evidence indicates that haematite pigment was produced over a long time period because both normal and reversed components of magnetisation are present in individual specimens. A part of the magnetisation in these rocks is carried by coarse particle specularite but there is no evidence that this is DRM or PDRM. The composite nature of the magnetisation and its acquisition over a relatively long time period is also indicated by the fact that all sample/site mean directions are of the same polarity (reversed) but originated over a period when normal and reversed polarities were common. There is evidence that the production of early diagenetic pigment was necessary for the preservation of Devonian magnetisations in these sandstones.Another group of sandstones acquired their magnetisation in Permo-Carboniferous times and these occur in intimate association with those which retain the original composite Devonian direction. The stable NRM of these rocks is carried by specularite and they are thought to have been remagnetised because they originally contained a greater proportion of magnetite than those sandstones which retain the original magnetisation and also an unstable pigment magnetisation. In-situ oxidation of magnetite in Permo-Carboniferous times is thus thought to be responsible for the remagnetisation of these rocks.     

Note on the genesis of brucite in contact metamorphism of dolomite

Consideration of available thermodynamic data and the published results of direct experiments relating to (1) formation. of periclase from dolomite and (2) hydration of periclase to brucite, permits the following conclusions to be drawn: (1) At very low partial pressures of CO₂ (perhaps of the order of 1 bar) and relatively high partial pressures of water (up to 2000 bars), dolomite can break down directly to brucite and calcite at temperatures above about 400° C, and below temperatures on the brucite dehydration curve. (2) The reaction dolomite calcite + periclase + CO₂ in contact metamorphism near granitic bodies is likely to occur only at low partial pressures of CO₂ (perhaps 10 or 20 bars); this can be achieved without direct formation of brucite, by maintaining a partial pressure of water of the order of 1000 bars or more. (3) At low CO₂ pressures dolomite may re-form in the cooling stages of metamorphism by reaction between calcite, brucite, and CO₂ at temperatures below about 400° C.     

Generalisation of a Nonlinear Dynamo Model

In order to gain a better understanding of the physical processes underlying fast dynamo action it is instructive to investigate the structure of both the magnetic field and the velocity field after the dynamo saturates. Previously, computational results have been presented (Cattaneo, Hughes and Kim, 1996) that indicate, in particular, that Lagrangian chaos is suppressed in the dynamical regime of the dynamo. Here we extend their model by removing the assumption of neglecting the inertial term. This allows for an investigation into the effect of this term on the evolution of the dynamo via a comparison of the two models. Our results indicate that this term plays a crucial role in the physics of the dynamo.     

Crystal bending in metamorphic calcite,and its relations to associated twinning

This paper deals with the incidence and geometry of lattice bending in calcite of naturally strained marble and possible relations in time to associated {01¯12} twinning, as revealed by microscopic examination with a universal stage. Microscopic technique and graphic treatment of data with a view to identifying the relation in time of bending to twinning, and possible glide mechanisms involved in the bending process are reviewed as a basis for present and subsequent investigation of this general topic.In most instances development of surviving thin e twins postdates bending of the host crystal (such twins everywhere are rationally oriented). Rarely (in contrast with experimental experience) some thin twins are slightly irrational (L_e lamellae) and apparently developed in the final stages of bending. Thick twins (a few tens of microns wide) on the other hand rather commonly predate or are synchronous with bending.The geometry of bending (external rotation) — especially for rotation less than 25° —commonly is compatible with models (based on experimental experience) of simple translation in the strained domains. The commonest translation system so identified is on {10¯11}, with sense of shear, where recognizable, either negative or positive. Translation on {02¯21} is relatively rare. Unexpectedly there is rather strong but not conclusive evidence of translation on {0001} parallel to an a axis. This mechanism, hitherto never identified with certainty, is now here documented unequivocally in a crystal of calcite experimentally strained at 300° C, 5 kb.     

A review of the distribution of metamorphism in the ancient Rhodesian craton

During the early development of the Rhodesian craton the regional metamorphism of some of the oldest rocks of Bulawayan and Shamvalan age, was apparently progressive and is expressed in terms of a clearly defined metamorphic zonation established under conditions of relatively high geothermal gradients in which very low grades typical of the central craton pass into extremely high grades that define the cratonic margin particularly within the Zambezi and the Limpopo belts. The distribution of the associated early granitic rocks relates to the metamorphic pattern, thus implying that both metamorphism and granite development were due to thermal highs centred on the Limpopo mobile belt and possibly the Zambezi belt.     

Diagenetic development of unstable and stable magnetization in the St. Bees Sandstone (Triassic) of northern England

Thermal demagnetization of red and drab sandstones from the St. Bees Sandstone shows a wide range of directional stability. After the removal of a metastable secondary magnetization at temperatures up to 300°C red sandstones may show stable or unstable magnetization. Experiments indicate that both the stable and unstable magnetization is carried by coarse haematite particles (specularite).Drab sandstones, which have been subject to reduction and dissolution of haematite are generally unstable but specimens with a stable NRM occur and this must be carried by specularite because the pigment has been removed from these specimens.The stable magnetization is believed to have developed during deposition and early diagenesis by the oxidation of detrital iron oxides. Pole positions correspond to known Triassic poles and there are abundant normal and reversed zones typical of the Lower Triassic.The unstable magnetization of the red sandstones is apparently due to the development of authigenic overgrowths of haematite on the detrital specularites. This phase of authigenesis may have taken place over a long time, and after significant changes in the ambient geomagnetic field resulting in complex magnetizations in individual grains and hence whole rocks.     

Chlorinated cooling waters in the marine environment: Development of effluent guidelines

The effects of free chlorine and chloramine on stage I lobster larvae and juvenile killifish were investigated in continuous flow bioassay units. In comparing mortality and changes in standard respiration rates during and after exposure to either chlorine form, significant respiratory stress was observed with exposure to sublethal levels. Sublethal responses to free and combined chlorine should be considered when establishing regulations for chlorine residuals in cooling waters.