Use of the Bray-Curtis similarity measure in cluster analysis of foraminiferal data

Transformation of data effectively limits the distortion by outlying values on the Bray-Curtis similarity measure. It represents an effective method of using cluster analysis in distinguishing biotopes of benthic foraminifera.     

Time-temperature-transformation (TTT) analysis of cation disordering in omphacite

The kinetics of cation disordering in a natural ordered (P2/n) omphacite have been followed at P=18 and 30 kb, T= 750–1,260° C, for times of between 1.5 min and 16 days in a piston-cylinder apparatus. Time-temperature-transformation (TTT) analysis of the experimental data, using the presence or absence of the 11¯1 reflection in single crystal X-ray precession photographs to indicate the extent of reaction, yields an equilibrium order/disorder temperature (T _ord) of 865±10° C, an activation enthalpy (1 bar) of 71±6 kcal mole^–1 and an activation volume of 9±4 cm³ mole^–1 (plus and minus figures represent the precision of a best fit between experimental data and TTT theory rather than absolute errors). The activation volume is consistent with a vacancy mechanism of cation diffusion. H₂O, added in the form of oxalic acid, appears to speed the process up slightly. The overall transformation mechanism is continuous, involving neither the nucleation of a disordered phase nor a change in antiphase-domain distribution. This is consistent with both first- and non-first-order character for the C2/cP2/n transformation, though a range of ordered states below T _ord is indicated by the weakening of h+k=odd reflections. A simple extrapolation of the disordering rates to geological conditions leads to the first estimate of how long disordered omphacites would take to order in nature, ranging from less than one year at T800° C to more than 10⁷ years at T<350° C.     

Nests of intermediate depth (70–160 km) earthquakes adjacent to active volcanoes during 1963–1982

Uniform maps of circumpacific convergence zones constructed by the same projection and scale reveal three main associations between intermediate depth seismicity and contemporaneous volcanic activity. First, in areas of high seismicity there are usually few active volcanoes. Second, in areas of low to moderate seismicity aseismic domains can often be recognized beneath the active volcanoes. Third, adjacent to the aseismic domains there are nests of seismicity located a few 10's of km away from the active volcanoes usually in the direction of the trench. More than 40 such nests are identified in the circumpacific and Indonesian arcs. These three associations may be related to melting near the upper surface of the underthrust slab. A fluid phase, either silicate melt or a hydrous fluid released by dehydration of the slab, would lower the strength of the slab and create aseismic zones beneath the active volcanoes. Nests of earthquakes can develop by stress concentration at the margins of the weak zones. Areas not volcanically active have little or no fluid phase and a higher level of seismicity.     

Trace metals in a tidal Mediterranean embayment

The Euvoikos gulf, and the strait of Euripos therein, is a restricted embayment on the eastern coast of Greece having a significant, unusual tidal phenomenon and receiving some domestic, trade and industrial wastes from the town of Chalkis and several coastal industries. The purpose of the present work was to study the influence of the tidal current and the anthropogenic inputs on the distributions of several trace elements (namely, Pb, Cu, Zn, Cr, Fe, Mn and Ni) in the seawaters (as dissolved and particulate species) and the sea-bottom sediments. Thorough mixing, resuspension and transport of fine particles and direct discharges are the major mechanisms affecting the distribution patterns.     

A world model of soil carbon dioxide

Mean growing season soil PCO₂ data were obtained for 19 regions of the world in nine countries. Bivariate and multiple linear regression analysis with soil log(PCO₂) as the dependent variable and TEMP, PRECIP, log(AET), and log(PET) as the four climatic independent variables demonstrated that AET was the best independent predictor of soil PCO₂. An improved soil PCO₂-AET model was developed by assuming (1) that as AET approaches zero, soil PCO₂ approaches the atmospheric value and (2) that there is an upper limit to soil PCO₂ at very high AET. This model has the form log(PCO₂) = ?3·47 + 2·09 (1 ?e^{?0·0172 AET}) where AET is in mm. It explains 67 per cent of the initial variation in the soil PCO₂ data, predicts a soil log(PCO₂) of ? 3·47 at AET = 0, and an upper limit of 3·5 per cent (log(PCO₂) = ? 1·45) for mean growing season soil PCO₂ at AET values of 2000 mm and above. The results of this study suggest that soil PCO₂ levels in tropical areas are, on average, higher than those in temperate, alpine, and arctic regions.     

Experimental investigations of trace element fractionation in iron meteorites,II: The influence of sulfur

We have investigated the partitioning of Ir. Ge, Ga, W, Cr, Au, P, and Ni between solid metal and metallic liquid as a function of temperature and S-concentration of the metallic liquid. Partition coefficients for siderophile elements such as Ir, W, Ga and Ge increase by factors of 10–100 as the Sconcentration of the metallic liquid increases from 0–30 wt%. Partition coefficients for other siderophile elements such as Ni, Au and P increase by only factors of 2–3. In contrast, partition coefficients for the more chalcophile element Cr decrease. These experimentally-determined partition coefficients have been used in conjunction with a fractional crystallization model to reproduce the geochemical behavior of Ni, P, Au and Ir during the magmatic evolution of groups IIAB, IIIAB, IVA and IVB iron meteorites. The mean S-concentration for each group increases in the order IVB, IVA, IIIAB, IIAB, in accord with cosmochemical prediction. However, we are unable to reproduce the geochemical behavior of Ge, Ga, W and Cr in an internally consistent way. We conclude that the magmatic histories of these iron meteorite groups are more complex than has been generally assumed.     

Size distribution of iron and manganese species in freshwaters

A recently established technique for size fractionation of particulate matter in freshwaters, based on low volume filtration through Nuclepore filters in the field, has been applied to the study of Fe and Mn species in 3 freshwater lakes and a stream feeding one of the lakes. The technique has also been used in a series of laboratory experiments to provide further insight into the process of particle formation. The results are complemented with scanning electron microscope examination of the particles.The raw data are transformed into mass size distributions, which are generally unimodal, with the major part of the mass confined to a single log unit size range. These size distributions are compared and contrasted with a theoretical model of particle behaviour in a lake. The results suggest that particulate Fe and Mn behave according to particle theory. The observed size distributions represent a balance between hydraulic input/output, aggregation, and gravitational settling, as well as chemical precipitation and dissolution processes. Overall particle aggregation is shown to be a slow process in the waters examined, with a time constant of the order of days. There is evidence for a fairly stable particle regime in the 0.05–0.4 μm size range.Deviations from the unimodal distribution in the epilimnion of the lakes indicate the association of Fe, but not Mn, with phytoplankton. In the waters examined Mn was most frequently found in solution, while Fe was predominantly particulate. These findings are interpreted in terms of the differing redox behaviour of the metals.