Thermodynamic properties,low-temperature heat-capacity anomalies,and single-crystal X-ray refinement of hydronium jarosite, (H<Subscript>3</Subscript>O)Fe<Subscript>3</Subscript>(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)<Subscript>6</Subscript>

Crystals of hydronium jarosite were synthesized by hydrothermal treatment of Fe(III)–SO₄ solutions. Single-crystal XRD refinement with R₁=0.0232 for the unique observed reflections (|F_o| > 4_F) and wR₂=0.0451 for all data gave a=7.3559(8) Å, c=17.019(3) Å, V^o=160.11(4) cm³, and fractional positions for all atoms except the H in the H₃O groups. The chemical composition of this sample is described by the formula (H₃O)_0.91Fe_2.91(SO₄)₂[(OH)_5.64(H₂O)_0.18]. The enthalpy of formation (H^o_f) is –3694.5 ± 4.6 kJ mol^–1, calculated from acid (5.0 N HCl) solution calorimetry data for hydronium jarosite, -FeOOH, MgO, H₂O, and -MgSO₄. The entropy at standard temperature and pressure (S^o) is 438.9±0.7 J mol^–1 K^–1, calculated from adiabatic and semi-adiabatic calorimetry data. The heat capacity (C_p) data between 273 and 400 K were fitted to a Maier-Kelley polynomial C_p(T in K)=280.6 + 0.6149T–3199700T^–2. The Gibbs free energy of formation is –3162.2 ± 4.6 kJ mol^–1. Speciation and activity calculations for Fe(III)–SO₄ solutions show that these new thermodynamic data reproduce the results of solubility experiments with hydronium jarosite. A spin-glass freezing transition was manifested as a broad anomaly in the C_p data, and as a broad maximum in the zero-field-cooled magnetic susceptibility data at 16.5 K. Another anomaly in C_p, below 0.7 K, has been tentatively attributed to spin cluster tunneling. A set of thermodynamic values for an ideal composition end member (H₃O)Fe₃(SO₄)₂(OH)₆ was estimated: G^o_f= –3226.4 ± 4.6 kJ mol^–1, H^o_f=–3770.2 ± 4.6 kJ mol^–1, S^o=448.2 ± 0.7 J mol^–1 K^–1, C_p (T in K)=287.2 + 0.6281T–3286000T^–2 (between 273 and 400 K).     

Sulfur geochemistry of hydrothermal waters in Yellowstone National Park,Wyoming, USA. III. An anion-exchange resin technique for sampling and preservation of sulfoxyanions in natural waters

A sampling protocol for the retention, extraction, and analysis of sulfoxyanions in hydrothermal waters has been developed in the laboratory and tested at Yellowstone National Park and Green Lake, NY. Initial laboratory testing of the anion-exchange resin Bio-Rad™ AG1-X8 indicated that the resin was well suited for the sampling, preservation, and extraction of sulfate and thiosulfate. Synthetic solutions containing sulfate and thiosulfate were passed through AG1-X8 resin columns and eluted with 1 and 3 M KCl, respectively. Recovery ranged from 89 to 100%. Comparison of results for water samples collected from five pools in Yellowstone National Park between on-site IC analysis (U.S. Geological Survey mobile lab) and IC analysis of resin-stored sample at SUNY-Stony Brook indicates 96 to 100% agreement for three pools (Cinder, Cistern, and an unnamed pool near Cistern) and 76 and 63% agreement for two pools (Sulfur Dust and Frying Pan). Attempts to extract polythionates from the AG1-X8 resin were made using HCl solutions, but were unsuccessful. Bio-Rad™ AG2-X8, an anion-exchange resin with weaker binding sites than the AG1-X8 resin, is better suited for polythionate extraction. Sulfate and thiosulfate extraction with this resin has been accomplished with KCl solutions of 0.1 and 0.5 M, respectively. Trithionate and tetrathionate can be extracted with 4 M KCl. Higher polythionates can be extracted with 9 M hydrochloric acid. Polythionate concentrations can then be determined directly using ion chromatographic methods, and laboratory results indicate recovery of up to 90% for synthetic polythionate solutions using AG2-X8 resin columns.     

Exploring the Moon in the 21st century

Ian Crawford and Mahesh Anand report on a wide-ranging RAS Discussion Meeting on the future of lunar exploration, held in the Geological Society Lecture Theatre at Burlington House on Friday 11 November 2005.     

Polygon-to-Polygon Spatial Accessibility Using Different Aggregation Approaches: A Case Study of National Forests in the US Mountain West Region

Spatial accessibility is an enduring topic of spatial analysis that is intimately tied to issues of spatial representation and scale. A variety of methods to measure accessibility have been developed with most research focusing on metropolitan‐sized spatial extents using census‐defined aggregation units and relying on vector point representation to calculate Euclidean or network distances as key ingredients in measure formulations. Less research considers broader scales where both origin and destination points are treated as polygons. This research develops alternative gravity‐based measures of polygon‐to‐polygon accessibility for a case study of county‐level accessibility to national forests in the western US. Different methods of county and forest representation are implemented using census block centroids and a lattice approach for disaggregation and re‐aggregation. Other characteristics that are analyzed include origin‐destination linkage definitions, population weighting, and distance thresholds. Correlation analysis is used to assess relationships of alternative measures with a simple percentage measure and with each other. Low correlations would suggest that measures capture different aspects of accessibility that are related to their qualitative characteristics. Results show the alternative measures to be dissimilar from the percentage measure; however, high correlations among alternative measures suggest that there is little to differentiate certain disaggregated measures in spite of their richer qualitative interpretation.     

Methane,carbon monoxide and methylchloroform in the southern hemisphere

New observational data on CH₄, CO and CH₃CCl₃ in the southern hemisphere are reported. The data are analysed for long term trends and seasonal cycles. CH₃CCl₃ data are used to scale the OH fields incorporated in a two dimensional model, which in turn, is used to constrain the magnitude of a global CH₄ source function. The possible causes of observed seasonality of CH₃CCl₃, CH₄ and CO are identified, and several other aspects of observed CH₄ variability are discussed.Possible future research directions are also given.     

Variations in the distribution of magma in the lower crust and at the Moho beneath the East Pacific Rise at 9°-10°N

Measurements of the seafloor deformation under ocean waves (compliance) reveal an asymmetric lower crustal partial melt zone (shear velocity less than 1.8 km/s) beneath the East Pacific Rise axis between 9° and 10°N. At 9°48′N, the zone is less than 8 km wide and is centered beneath the rise axis. The zone shifts west of the rise axis as the rise approaches the westward-stepping 9°N overlapping spreading center discontinuity and is anomalously wide at the northern tip of the discontinuity. The ratio of the compliance determined shear velocity to the compressional velocities (estimated by seismic tomography) suggests that the melt is well-connected in high-aspect ratio cracks rather than in isolated sills. The shear and compressional velocities indicate less than 18% melt in the lower crust on average. The compliance measurements also reveal a separate lower crustal partial melt zone 10 km east of the rise axis at 9°48′N and isolated melt bodies near the Moho beneath four of the 39 measurement sites (three on-axis and one off-axis). The offset of the central melt zone from the rise axis correlates strongly with the offset of the overlying axial melt lens and the inferred center of mantle melting, but its shape appears to be controlled by crustal processes.     

Floodplain formation processes and archaeological implications at the Grand Banks site,lower Grand River,southern, Ontario

Processes of floodplain development and the record of Princess Point cultural occupation (A.D. 500–1000) were examined at the Grand Banks site in the lower Grand River of southern Ontario. The Princess Point Complex of the early Late Woodland is significant because it represents the first shift to horticulture in this region in which inhabitants made significant use of floodplains. The floodplain of the lower Grand River has been constructed primarily via vertical accretion of sediment in a low energy environment conducive to limited erosion and slow burial of middle and late Holocene sediments. At this site, cultural materials are preferentially preserved in two buried soils each corresponding to relatively stable periods of valley infilling at or before 3200 B.P. and 1500 B.P. (¹⁴C years). Initial formation of the floodplain and subsequent stability of the floodplain surface can be tied to middle Holocene, and later, base-level fluctuations in Lake Erie. Understanding floodplain development is crucial in determining the linkages between settlement pattern and chronology, and, conversely, the archaeological record in floodplain settings provides important contemporary data for modeling floodplain geomorphological processes. © 1997 John Wiley & Sons, Inc.     

A rock test cell with true triaxial capability

Conventional so-called triaxial test cells apply the axial stress to a cylindrical sample using steel platens, with the confining stress developed via an annulus of hydraulic fluid retained by a liner in a pressure cell. This does not allow differentiation between the two principal stresses around the core and inhibits the realism with which the rocks can be tested, for example in determining the effect of the intermediate principal stress on the strength of the sample.This paper describes the development and application of a new test cell – believed to be the first in the world – which enables truly triaxial stresses to be applied to cylindrical core samples, opening up the possibility to test rocks routinely in a more realistic manner. An array of 24 trapped tubes replace the single annulus which usually generates the uniform radial stress. Selective pressurization of the tubes enables differential radial stresses to be generated, while axial stresses are applied as before through steel platens. The first results of multi-state failure and permeability stress sensitivity of samples tested in the cell are presented. These demonstrate the influence of the intermediate principal stress on measured rock properties and the orientation of induced fracture planes.     

Eco‐physiological repercussions of dietary arachidonic acid in cell membranes of active tissues of the Gray whale

The radiation of the mammalian land species that became the baleen whales happened about 27–34 Mya. Mammals require omega 6 fatty acids for reproduction. With this long exposure to the omega 3‐rich marine food chain, the Gray whale (Eschrichtius robustus) might be expected to have lost its requirement for omega 6 fatty acids. We report an unexpectedly high content of omega 6 arachidonic acid (ArA) in the Gray whale liver and muscle lipids. This whale migrates 10,000 km from the cold polar, omega 3 oil‐rich food chain to that of the breeding lagoons of the tropical waters. The food web of tropical waters is a source of omega 6 fatty acids, which are hardly present in the cold polar food web. We suggest the reason for this longest of migrations from cold to warm waters is to meet the requirement for omega 6 fatty acids for mammalian reproduction and brain growth. This extreme conservation of omega 6 fatty acids in Gray whale biology has critical implications for mammalian biology and especially for whale conservation.