Ulysses observations of the planetary depletion layer at Jupiter

The repeated samplings of the Jovian magnetosheath during the Ulysses encounter with Jupiter provided an opportunity to probe the planetary depletion layer. Of the 10 complete crossings of the Jovian magnetopause, only three contained clear signatures of an overlying depletion layer. All of these occurred on the flanks of the magnetosphere near the dusk terminator; crossings on the dayside were ambiguous or clearly lacked a depletion layer signature. In this paper we present a detailed analysis of the observations by the Ulysses solar wind plasma and magnetometer experiments and discuss conditions favorable and unfavorable for depletion layer observation.     

Standards for multilateral and worldwide exchange of geothermal data

Standards for the exchange of machine-readable data are discussed at five levels covering (1) physical characteristics of the medium used in the exchange, (2) overall structure of the data file, (3) format of individual records, (4) types of information contained in a record, and (5) authority files for information definition. The standards are used by the National Geothermal information Resource for compilations of geothermal energy data.This paper was presented at the International Geological Correlation Program (IGCP) Project 98 entitled Standards for Computer Applications in Resource Studies held at Loen, Norway, September 27–October 1, 1976.     

Rock fragment distributions and regolith evolution in the Ouachita Mountains,Arkansas, USA

Rock fragments in the regolith are a persistent property that reflects the combined influences of geologic controls, erosion, deposition, bioturbation, and weathering. The distribution of rock fragments in regoliths of the Ouachita Mountains, Arkansas, shows that sandstone fragments are common in all layers, even if sandstone is absent in parent material. Shale and sandstone fragments are produced at the bedrock weathering front, but the shale weathers rapidly and intact fragments are rare in the solum. Sandstone is weathered from ridgetop outcrops and transported downslope. Some of these fragments are moved downward, by faunalturbation and by transport into pits associated with rotting tree stumps. Upward movement by treethrow is common, resulting in a net concentration of rocks near the surface. However, the highest fragment concentrations are in the lower regolith, indicating active production at the weathering front. The regolith is a dynamic feature, reflecting the influences of vertical and horizontal processes, of active weathering at the bedrock interface, and of surficial sediment movements. The role of trees in redistributing rock fragments suggests that significant regolith mixing occurs over time scales associated with forest vegetation communities, and that forest soils have likely been extensively mixed within Holocene and historic time. Copyright © 2005 John Wiley & Sons, Ltd.     

Development of modified flyash as a permeable reactive barrier medium for a former manufactured gas plant site, Northern Ireland

A sequential biological permeable reactive barrier (PRB) was determined to be the best option for remediating groundwater that has become contaminated with a wide range of organic contaminants (i.e., benzene, toluene, ethylbenzene, xylene and polyaromatic hydrocarbons), heavy metals (i.e., lead and arsenic), and cyanide at a former manufactured gas plant after 150 years of operation in Portadown, Northern Ireland. The objective of this study was to develop a modified flyash that could be used in the initial cell within a sequential biological PRB to filter complex contaminated groundwater containing ammonium. Flyash modified with lime (CaOH) and alum was subjected to a series of batch tests which investigated the modified cation exchange capacity (CEC) and rate of removal of anions and cations from the solution. These tests showed that a high flyash composition medium (80%) could remove 8.65 mol of ammonium contaminant for every kilogram of medium. The modified CEC procedure ruled out the possibility of cation exchange as the major removal mechanism. The medium could also adsorb anions as well as cations (i.e., Pb and Cr), but not with the same capacity. The initial mechanism for Pb and Cr removal is probably precipitation. This is followed by sorption, which is possibly the only mechanism for the removal of dichromate anions. Scanning electron microscopic analysis revealed very small (<1 μm) cubic highly crystalline precipitates on the flyash, although this new crystalline zeolite growth did not occur rapidly enough to enable productive zeolite formation. Surface area measurements showed that biofilm growth on the medium could be a major factor in the comparative reduction of surface area between real and synthetic contaminant groundwaters. The modified flyash was found to be a highly sorptive granular material that did not inhibit microbiological activity, however, leaching tests revealed that the medium would fail as a long-term barrier material.     

Formation and evolution of carbonate chimneys at the Lost City Hydrothermal Field

The Lost City Hydrothermal Field at 30°N, near the Mid-Atlantic Ridge, is an off-axis, moderate temperature, high-pH (9-10.8), serpentinite-hosted vent system. The field is hosted on ∼1.5 Ma crust, near the summit of the Atlantis Massif. Within the field, actively venting carbonate chimneys tower up to 60 m above the seafloor, making them the tallest vent structures known. The chemistry of the chimneys and vent fluids is controlled by serpentinization reactions between seawater and underlying peridotite. Mixing of <40-91 °C calcium-rich vent fluids with seawater results in the precipitation of variable mixtures of aragonite, calcite, and brucite. The resultant deposits range from tall, graceful pinnacles to fragile flanges and delicate precipitates that grow outward from fissures in the bedrock. In this study, mineralogy, petrographic analyses, major and trace element concentrations, and Sr isotopic compositions are used to propose a model for the growth and chemical evolution of carbonate chimneys in a serpentinite-hosted environment. Our results show that nascent chimneys are characterized by a porous, interlacing network of aragonite, and brucite minerals that form extremely fragile structures. The chemistry of these young deposits is characterized by ∼10 wt% Ca and up to 27 wt% Mg, extremely low trace metal concentrations, and ⁸⁷Sr/⁸⁶Sr isotope ratios near 0.70760. During aging of the chimneys, progressive reactions with seawater result in the dissolution of brucite, the conversion of aragonite to calcite, and infilling of pore spaces with calcite. The oldest chimneys are dominated by calcite, with bulk rock values of up to 36 wt% Ca and <1 wt% Mg. These older structures contain higher concentrations of trace metals (e.g., Mn and Ti), and have Sr isotope ratios near seawater values (0.70908). Exposed ultramafic rocks are prevalent along the Mid-Atlantic, Arctic, and Indian Ocean ridge networks and it is likely that other Lost City-type systems exist.     

Wind erodibility of soils at Fort Irwin,California (Mojave Desert), USA,before and after trampling disturbance: implications for land management

Recently disturbed and ‘control’ (i.e. less recently disturbed) soils in the Mojave Desert were compared for their vulnerability to wind erosion, using a wind tunnel, before and after being experimentally trampled. Before trampling, control sites had greater cyanobacterial biomass, soil surface stability, threshold friction velocities (TFV; i.e. the wind speed required to move soil particles), and sediment yield than sites that had been more recently disturbed by military manoeuvres. After trampling, all sites showed a large drop in TFVs and a concomitant increase in sediment yield. Simple correlation analyses showed that the decline in TFVs and the rise in sediment yield were significantly related to cyanobacterial biomass (as indicated by soil chlorophyll a). However, chlorophyll a amounts were very low compared to chlorophyll a amounts found at cooler desert sites, where chlorophyll a is often the most important factor in determining TFV and sediment yield. Multiple regression analyses showed that other factors at Fort Irwin were more important than cyanobacterial biomass in determining the overall site susceptibility to wind erosion. These factors included soil texture (especially the fine, medium and coarse sand fractions), rock cover, and the inherent stability of the soil (as indicated by subsurface soil stability tests). Thus, our results indicate that there is a threshold of biomass below which cyanobacterial crusts are not the dominant factor in soil vulnerability to wind erosion. Most undisturbed soil surfaces in the Mojave Desert region produce very little sediment, but even moderate disturbance increases soil loss from these sites. Because current weathering rates and dust inputs are very low, soil formation rates are low as well. Therefore, soil loss in this region is likely to have long‐term effects. Published in 2006 by John Wiley & Sons, Ltd.     

Flood hazard in Ratnapura, Sri Lanka: Individual attitudes vs collective action

In Ratnapura monsoonal flooding is a chronic problem of which the residents are acutely aware. Responses to structured interviews indicated that a wide range of actions are employed to reduce flood impact, although these actions are not perceived as specific adjustments to flooding. The only widely acknowledged means of mitigating the flood threat is government action. Dependency on government action reflects the government's role in dispensing aid to flood victims. While relief programmes do reduce personal, short-term losses, they simultaneously encourage resettlement in high-risk areas. In seeking a viable, long-term management policy, the Sri Lankan government recently adopted a plan to move the municipality of Ratnapura to invulnerable high ground. In making the decision to relocate, however, the attitudes of the residents were not evaluated, and government officials seemed unconcerned that residents viewed relocation as an unacceptable solution to the problem. Although individual attitudes concerning residential satisfaction in the context of the flood hazard varied with factors such as income, length of residency and land tenure, an overwhelming number of residents adamantly maintained that they would not move to the new town.     

Comment on “Chemical osmosis,reverse chemical osmosis,and the origin of subsurface brines” by Donald L. Graf

Graf (1982) has discussed possible mechanisms for ground water pressure differences large enough to drive subsurface reverse osmosis. Osmotic pressure differences were calculated assuming ideal membrane properties. However, consideration of non-ideal membrane properties indicates that actual subsurface osmotic pressure differences will be considerably smaller than those calculated by Graf (1980), and thus reverse osmosis may occur under more commonly observed hydrogeologic conditions.     

Diel activity cycles of two Chesapeake Bay fishes,the striped blenny (Chasmodes bosquianus) and the oyster toadfish (Opsanus tau)

Diel activity cycles of toadfish and striped blennies were identified in the laboratory by means of mechanoelectric detector units. Data for both species were collected over 72-h periods. Daytime and nighttime activity rates were compared statistically. In addition, five 3-h segments (3 during the day and 2 at night) were selected for statistical comparison. both species are more active at night than during the day. The toadfish appears to be more strictly nocturnal than does the blenny, with the peak in its activity occurring in the 3-h segment following dusk. Blenny activity increases throughout the night, reaching a peak during the 3-h segment before dawn. It then ebbs to a low in the afternoon.     

Mineralisation from Vall de Ribes area (Eastern Pyrenees,Spain)

Vein mineralisation with no preferred orientation, cutting lower Palaeozoic rocks, and local replacement deposits in dolomite show a zoning in tungsten-bismuth, arsenic and antimony minerals away from the adjacent late-Hercynian Costabona granite. A local reversed zoning is related to higher temperatures indicated by fluid inclusion study. Many of the minerals have not previously been reported from this area.