The energetics and structure of the hydrogarnet defect in grossular: A computer simulation study

We have used computer simulation methods to model the structure and energetics of the hydrogarnet defect in grossular. The predicted structure is in good agreement with experimental data. The calculated energy for the reaction of water with grossular to form the hydrogarnet defect is 1.02 Ev (98 kJ mol^-1). This low energy of reaction suggests that such defects will be common in garnets where they could play an important role in effecting processes such as atomic transport.     

Dispersal of river sediments in coastal seas: Six contrasting cases

The fate of sediment seaward of river mouths involves at least four stages: supply via plumes; initial deposition; resuspension and transport by marine processes; and long-term net accumulation. The processes that operate at each stage, and relative roles of each stage in governing the long-term accumulation patterns, vary appreciably with river regime and coastal ocean environment. To illustrate the diversity and illuminate the process of dispersal, information is synthesized for six systems: Amazon, Changjiang, Mississippi, Columbia, Purari, and Huanghe. These systems differ markedly in terms of water discharge, sediment discharge, and coastal energy regime and much of the diversity of dispersal patterns is attributed to these differences as well as to the temporal sequencing of river discharge relative to oceanographic transport processes. Although the sediment: water ratio of the discharge of the Mississippi River is 70 times less than that of the Huanghe, both of these systems exhibit rapid deposition and accumulation of sediments near the river mouths. In contrast, sediments dispersed by, the other four systems are transported greater distances from the mouths by oceanographic processes, and are accumulating over relatively wide areas.     

Evaporation from the understorey in the Jarrah (Eucalyptus marginata Don ex Sm.) forest, southwestern Australia

Annual evaporation from groundflora, litter and soil of the jarrah forest was estimated from measurements of daily evaporation by ventilated chambers on several days over two separate 12-month periods. In the first year, when sampling ranged over 0.1 ha of forest, annual evaporation during daylight hours was estimated as 410 mm (0.32 rainfall). In the second year, sampling was more frequent, on a larger scale, and included the night hours. Annual evaporation was estimated at 360 mm (0.36 rainfall).

Similarly, in the second year, annual evaporation from two trees of the dominant middle storey species, Banksia grandis, was estimated at 7500 and 18,9001 respectively. The leaf area of these two trees was 9.6 and 22.4 m², respectively, so that annual evaporation, when expressed as mm³ per mm² leaf area, was similar for both trees (mean = 820 ± 30 mm). Applying that value to all Banksia trees in a hectare of forest, and using a measured estimate of leaf area index of 0.19, the estimated annual evaporation from the Banksia component was 155 mm (0.16 rainfall). For the upland part of the forest sampled, the combined annual evaporation from the lower and middle storeys accounted for about half (0.51) of the annual rainfall.

We conclude that reduced evaporation from the upper storey following clearing or thinning may be strongly counteracted by increased evaporation from the understorey due to increased availability of energy and water.     

Notes on late Cenomanian and Turonianammonites from Touraine,Western France

Recent collecting in the type area of the Turonian stage and adjacent parts of Touraine in western France provides new geographic and stratigraphic records as well as additional systematic information on species of the ammonite genera Puzosia, Watinoceras, Metoicoceras, Mammites, Prohauericeras, Collignoniceras, Lecointriceras, Subprionocyclus and Sciponoceras.     

Late glacial and late Holocene moraines in the Cerros Cuchpanga, central Peru

Small ice fields on the western cordillera northeast of Lima were expanded to three times their present size in the recent past, and the regional snow line was probably about 100 m lower than it is today. Outwash from the expanded glaciers formed deltas of silt in valley-bottom lakes. When the ice lobes retreated, the reduced outwash was trapped behind recessional moraines, and the clear meltwater infiltrated into the limestone bedrock and emerged at the heads of the deltas in spring pools. The delta surfaces then became covered with peat, and radiocarbon dates for the base of the peat (1100 ± 70 and 430 ± 70 yr B.P. for two different deltas) indicate that the maximum ice advance was older than those dates and, thus, older than the Little Ice Age of many north-temperate regions. Much older moraines date from expansion of the same local summit glaciers to even lower levels in the main valleys, which had previously been inundated by the cordilleran ice field. The cordilleran deglaciation and this expansion of local glaciers probably occurred between 12,000 and 10,000 yr ago, on the basis of slightly contradictory radiocarbon dates.     

A direct measurement of the distribution in depth of 26Al in the Estacado meteorite

The two-dimensional distribution of ²⁶Al across a slice of the Estacado meteorite was measured using non-destructive γ-γ coincidence counting. The maximum activity was found to be 60 ± 2 dpm kg^?1 and the variation across the slice rather small. The intensity and distribution are in moderate agreement with existing theoretical models if the pre-atmospheric shape of the meteorite had been a sphere of radius 0.35 ± 0.05 m, but it was more likely to have been slightly non-spherical.     

Frequency distribution of zinc concentrations in the common mussel,Mytilus edulis (L.)

The frequency distribution of zinc concentrations in a population of mussels (Mytilus edulis) from the moderately polluted Tyne estuary showed marked positive skewness. A peak was reached between 3 and 4 μmoles per dry gram of whole soft tissue followed by a long tail ending with a single exceptional value of 20.5 μmoles per g. The mean zinc concentration for the population was 5.13±2.66 (standard deviation). The skewness (g¹) value was 1.78 (SE+0.14 p?0.001). Within the population, there was a strong positive association between the log mean zinc concentration of a single collection and the log variance of the collection. The significance of this for biomonitoring procedures is discussed.