Temperature dependence of the water-ice spectrum between 1 and 4 microns: Application to Europa,Ganymede and Saturn's rings

Reflection spectra of water ice from 1 to 4 μm are presented as a function of temperature. It is found that a feature at 6056 cm^?1 changes its intensity sufficiently that it can be used as a spectroscopic measure of the ice temperature. A temperature calibration curve of this feature down to 55 K is developed and is used to determine ice temperatures for the Galilean satellites Europa (95±10 K), Ganymede (103±10 K), and the rings of Saturn (80±5 K). The ice temperatures for the Galilean satellites are lower than their measured brightness temperatures, which can be explained by a higher albedo of the ice covered regions relative to the rest of the satellite and possibly a concentration of the ice near the polar caps.     

The Spatial Distribution of Gaseous Atomic Sodium in the Comae of Comets: Evidence for Direct Nucleus and Extended Plasma Sources

Sodium D-line emission (5890 and 5896 Å) has been observed in bright comets at small to moderate heliocentric distances for many years. We present here the first in depth study of a set of spatial profiles of the sodium D-line emission constructed from long-slit spectroscopic observations of Comets Bennett C/1969 Y1, Kohoutek C/1973 D1, and 1P/Halley. Preliminary analysis of these data lead to the suggestion by Combiet al.(1996,A Plasmagenic Source for Gaseous Sodium in Comets.Presented at Asteroids, Comets, Meteors) that a major fraction of the gaseous sodium was produced by an extended source in the tail and that the source was likely to be some charged species. Dissociative recombination of a molecular ion was suggested. The spatial profiles of sodium are not like typical neutral species. The inner region from the nucleus (<2 × 10⁴km) can be explained in terms of a model that accounts for collisional entrainment in the expanding coma and the heliocentric velocity dependent fluorescence rate and radiation pressure acceleration. This source comes either directly from the nucleus or has a very short-lived parent (?10³s). Away from the nucleus, down the tail and to the sides, the spatial profile slope flattens, indicating a second extended source. The striking similarity of the extended region of sodium spatial profiles with those of ions (H₂O⁺), both along and perpendicular to the tail, is highly suggestive that an ion source is responsible for the production of the extended component of gaseous sodium in the coma. The production rate of the highly variable extended source when present is four to five times that of the direct nucleus source. Observations (Schneideret al., 1991,Science253,1394–1397) and quantitative model analyses (Wilson and Schneider, 1994,Icarus111,31–34) have shown that a dissociative recombination of a sodium bearing molecular ion (NaX⁺) produces a peculiar component of the neutral sodium near Io. It displays a variable spatial morphology consistent with that of a molecular ion source “picked-up” in the plasma torus corotating with Jupiter's magnetic field. The rapid onset of the appearance of gaseous sodium in bright comets, its spatial distribution in the extended coma and near tail, and recent observations of sodium tails are all consistent with our original suggestion of this plasma source for sodium in comets.     

The investigation of fault-controlled groundwater recharge within a suburban area of Damascus,Syria

Al-Mazraa is a heavily populated suburb of Damascus (Syria) with agricultural activity. It is adjacent to the Cretaceous Qassioun Mountain Range, from which it is structurally separated by the Damascus fault. Al-Mazraa waterworks abstracts from a shallow Quaternary aquifer, whose recharge processes are unidentified. The functions of Qassioun Mountain, the Damascus fault, the agricultural activities, the ascending deeper groundwater, and the through-flowing Tora River are not well understood and they are, hence, subject to study. The application of hydrochemical parameters and ratios in combination with signatures of δD and δ¹⁸O revealed that recharge predominantly occurs in the outcropping Cretaceous rocks through subsurface passages rather than through influent conditions of the Tora River or through direct rainfall. Interestingly, high Na/Cl ratios indicate contact with volcanic rocks which exist within the Cretaceous anticline and also in the subsurface of the studied Quaternary aquifer. Evidence for deeper circulating groundwater is given, since replenishing waters are up to 4 °C warmer and have much lower nitrate concentrations than the groundwater in the study area. From these points, it is indicated that the Damascus fault is conductive in respect to groundwater, rather than being impermeable, as it is elsewhere.     

Improved time control on Cretaceous coastal deposits: new results from Sr isotope measurements using laser ablation

Sr-isotope measurements of unaltered oyster shell calcite using laser-ablation multi-collector ICPMS techniques represent a powerful tool capable of establishing a chronostratigraphic framework for fossil near-shore deposits. This approach is tested on two shoal-water successions from the Portuguese Algarve and Lusitanian basins covering Late Barremian to Albian strata. ⁸⁷Sr/⁸⁶Sr values derived from low-Mg calcite of oyster shells fluctuate between 0.70717 ± 0.00001 and 0.70746 ± 0.00002; absolute values as well as stratigraphic trends match well with the global open-marine seawater signal. The new Sr-isotope results in combination with existing bio- and chemostratigraphic records allow for identification of an Early Aptian biocalcification crisis at both studied localities and show that this event has severely affected coastal environments along the evolving Atlantic. Siliciclastic intervals in the Algarve section are interpreted as near-shore equivalents of enhanced detrital shedding into shelf and deep-sea environments as a consequence of increased chemical weathering rates during humid climate episodes.     

Distribution of brine in grain boundaries during static recrystallization in wet, synthetic halite: insight from broad ion beam sectioning and SEM observation at cryogenic temperature

We report observations from room temperature static recrystallization experiments (annealing times from minutes to year) of cold-pressed, synthetic, coarse-grained, wet sodium chloride, prepared by broad ion beam polishing and SEM observations at cryogenic temperature to observe directly the brine in grain boundaries. At all stages of annealing, the majority of the brine in the samples is connected in 2D sections along grain boundaries. Another part of the brine is in isolated brine inclusion arrays along grain boundaries and in brine inclusions left behind by migrating brine-filled grain boundaries. Most of these boundaries are mobile because the aggregate is coarsening. We interpret that the boundaries without observable brine films (<15 nm) and brine inclusion arrays are healed and immobile. Evolution of grain boundary structure involves three major processes. First, dissolution on one side of the grain boundary and precipitation on the other side, resulting in grain boundary migration. Second, the development of facets formed by low-index crystallographic planes of the grains bounding the grain boundary brine. When both sides of a grain boundary are able to develop low-index facets in a thick brine film, the resulting impingement boundary is interpreted to be immobile and may prevent the new grain from migrating into a deformed neighbor. When one side of a faceted boundary consists of low-index crystallographic planes and the other side passively follows this faceted shape along irrational surfaces, the boundary is mobile. Third, the healing of grain boundary brine films, producing solid–solid grain boundaries without resolvable brine films.     

Use of major and selected trace elements to describe mixing processes in a water reservoir

Data on temperature, major constituents and some trace elements, measured in the dissolved and particulate phases, were used to identify the hydrodynamics of a reservoir (the Bicaz reservoir, Romania). Results revealed that the reservoir experiences two thermal stratifications per year (summer and winter). However, the summer stratification is delayed by the high river inflow of June–July. Two layers were identified, a surface and a deep layer, whose location and impact vary with time. The surface layer originates from the river inflow (intrusion layer) and the deep current is produced by the outflow (velocity current). According to season, the river inflow either supplies the deep current or remains recordable up to the dam. Consequently, the structure of the water column, and thus the biogeochemical processes within it, are governed both by thermal stratification and by these layers.     

Experimental investigation of shock metamorphic effects in a metapelitic granulite: The importance of shock impedance contrast between components

Shock recovery experiments were performed at 12.5, 25, 34, 40, and 56 GPa at 25 °C, and at 18 and 25 GPa at 400 °C, on a high‐grade, migmatitic, garnet‐cordierite metapelite from the Etivé aureole, Scotland. Objectives for this study were to (1) characterize shock effects in a complex polymineralic rock with a significant proportion of hydrous ferromagnesian minerals, both as a function of variable shock pressure and preshock temperature, and (2) to explore the effects of shock impedance contrast between component minerals on the respective abundances and distribution of these features. At any shock pressure, the order of decreasing intensity of shock metamorphic effects in component phases is: cordierite (Crd)→biotite (Bt)→plagioclase (Pl)→K‐feldspar (Kfs)→quartz (Qtz)→garnet (Grt)→orthopyroxene (Opx). Samples shocked to pressures below 40 GPa (25 °C) were typically characterized by marked heterogeneous distribution of shock effects on both intragranular and intergranular scales. Shock heterogeneity is mainly attributed to shock impedance contrast between contiguous phases, and manifests as shock amplification locally where shock impedance contrast is greatest, and shock suppression where impedance contrast is least. The heterogeneous distribution of shock metamorphic effects in both experiments and natural rocks is a signature of extreme disequilibrium at the submillimeter scale. The heterogeneous distribution of shock metamorphic effects mitigates against the use of shock effects in minerals exclusively as regional shock pressure barometers, and ought to be augmented by additional constraints on shock pressure from numerical models.