Implications for mantle dynamics from the high melting temperature of perovskite

Recent studies have implied that (Mg, Fe)SiO(3)-perovskite, a likely dominant mineral phase in the lower mantle, may have a high melting temperature. The implications of these findings for the dynamics of the lower mantle were investigated with the use of numerical convection models. The results showed that low homologous temperatures (0.3 to 0.5) would prevail in the modeled lower mantle, regardless of the effective Rayleigh number and internal heating rates. High-temperature ductile creep is possible under relatively cold conditions. In models with low rates of internal heating, local maxima of viscosity developed in the mid-lower mantle that were similar to those obtained from inversion of geoid, topography, and plate velocities.     

A methylaspartate cycle in haloarchaea

Access to novel ecological niches often requires adaptation of metabolic pathways to cope with new environments. For conversion to cellular building blocks, many substrates enter central carbon metabolism via acetyl-coenzyme A (acetyl-CoA). Until now, only two such pathways have been identified: the glyoxylate cycle and the ethylmalonyl-CoA pathway. Prokaryotes in the haloarchaea use a third pathway by which acetyl-CoA is oxidized to glyoxylate via the key intermediate methylaspartate. Glyoxylate condensation with another acetyl-CoA molecule yields malate, the final assimilation product. This cycle combines reactions that originally belonged to different metabolic processes in different groups of prokaryotes, which suggests lateral gene transfer and evolutionary tinkering of acetate assimilation. Moreover, it requires elevated intracellular glutamate concentrations, as well as coupling carbon assimilation with nitrogen metabolism.     

Partitioning behavior of Alkan-1-ols between milkfat and aqueous phases as influenced by temperature

Partitioning of volatile compounds between lipid and aqueous phases may influence flavor perception and availability to participate in flavor-generating reactions. The objective of this research was to characterize the partitioning of short-chain alkan-1-ols between milkfat and aqueous phases, as influenced by temperature, as compared to an octan-1-ol/water biphasic system (Log P). Temperature has a positive, but nonlinear, influence on Log P values for alkan-1-ols. There is an approximately 1 log decrease in Log P values of milkfat/water as compared to octan-1-ol/water systems; similar trends were observed across chain length. Temperature has a greater effect on alkan-1-ol partitioning in milkfat/water systems than octan-1-ol/water. The latter observation is primarily attributed to the solidification of milkfat at temperatures below 40 degrees C and the resulting reduction in liquid lipid solvent volume.     

Reduction of decomposition rates of scots pine needle litter due to heavy-metal pollution

Decomposition of unpolluted Scots pine needle litter was studied in two heavy-metal-pollution gradients in Sweden; one near a brass mill and the other around a primary smelter. In the latter area locally collected polluted Scots pine needle litter was also incubated. Decomposition rates were strongly influenced by the metal pollution and a decrease in the rate of mass-loss occurred. In the brass-mill gradient this occurred until about 1 km from the pollution source which corresponded to about 500 µg Cu and 1 000 µg Zn g^?1 soil. Data are presented to indicate that lignin decomposition was more sensitive to pollution than decomposition of whole litter and affected further away from the pollution sources. At the smelter sites, the metal-polluted needle litter decomposed more slowly than the unpolluted needle litter, and this difference was enhanced close to the smelter. The results indicate that heavy metals accumulated in needles prior to shedding have a long-term impact on the subsequent decomposition of the litter. Both litter quality and soil factors thus contribute to the reduced litter decomposition rate in metal-polluted forests. A new non-linear model with decreasing decay rate was used in the statistical evaluation. The model can be used to characterize the effects of pollution on decomposition rate.     

Bacterial community structure in lake sediments of microcosms contaminated with nonylphenol

The impact of nonylphenol, an estrogenic degradation product of alkylphenol polyethoxylates, on the bacterial community structure in contaminated sediments of aquatic microcosms was investigated over a period of 20 weeks using a 16S rDNA-based molecular phylogenetic approach. All microcosms showeda strong seasonal fluctuation of the dominant as well as the active bacterial microflora independent of their degree of contamination with nonylphenol. These changes were correlated with the dynamic of the total organic carbon content (TOC), ranging from 4–39 g/kg sediment dry weight and the redox potential in the sediment. Even at the highest observed nonylphenol concentration (3.4 mg/kg sediment dry weight) the bacterial community structure was mostly unchanged.