A life detection problem in a High Arctic microbial community

Fluorescent labeling of bacterial cell walls, DNA, and metabolic processes demonstrates high (potentially single molecule) sensitivity, is non-invasive, and in some cases can differentiate strains and species. Robust microscopes such as the custom instruments presented here can provide good image quality in the field and are potentially suitable for flight. However, ambiguous or false-positive results with bacterial stains can occur and can create difficulties in interpretation even on Earth. We present a “real” life detection problem in a sample of biofilms taken from the Canadian High Arctic. The samples consisted of numerous small sulfur-oxidizing bacteria and larger structures resembling fungi or diatoms. The identity of these latter structures remained ambiguous until electron microscopy and X-ray spectroscopy were performed, indicating that they were unusual sulfur minerals probably precipitated by the bacterial communities. While such mineral structures may possibly serve as biosignatures after the cells have disappeared, it is important that they not be mistaken for cells themselves. It is also possible that unusual mineral structures will be performed under extraterrestrial conditions, so great care is needed to differentiate cell structures from minerals.     

Stakeholder needs for ground penetrating radar utility location

In the UK alone there are millions of miles of underground utilities with often inaccurate, incomplete, or non-existent location records that cause significant health and safety problems for maintenance personnel, together with the potential for large, unnecessary, social and financial costs for their upkeep and repair. This has led to increasing use of Ground Penetrating Radar (GPR) for utility location, but without detailed consideration of the degree of location accuracy required by stakeholders — i.e. all those directly involved in streetworks ranging from utility owners to contractors and surveyors and government departments. In order to ensure that stakeholder requirements are incorporated into a major new UK study, entitled Mapping the Underworld, a questionnaire has been used to determine the current and future utility location accuracy requirements. The resulting data indicate that stakeholders generally require location tolerances better than 100 mm at depths usually extending down to 3 m, and more occasionally to 5 m, below surface level, providing significant challenges to GPR if their needs are to be met in all ground conditions. As well as providing much useful data on stakeholder needs, these data are also providing a methodology for assessment of GPR utility location in terms of the factor most important to them — the degree to which the equipment provides location within their own accuracy requirements.     

Microbial control of mineral–groundwater equilibria:Macroscale to microscale

macroscale processes that perturb general groundwater chemistry and therefore mineral–water equilibria; and microscale interactions, where attached organisms locally perturb mineral–water equilibria, potentially releasing limiting trace nutrients from the dissolving mineral. In the contaminated unconfined glacio-fluvial aquifer near Bemidji, Minnesota, USA, carbonate chemistry is influenced primarily at the macroscale. Under oxic conditions, respiration by native aerobic heterotrophs produces excess carbon dioxide that promotes calcite and dolomite dissolution. Aerobic microorganisms do not colonize dolomite surfaces and few occur on calcite. Within the anoxic groundwater, calcite overgrowths form on uncolonized calcite cleavage surfaces, possibly due to the consumption of acidity by dissimilatory iron-reducing bacteria. As molecular oxygen concentration increases downgradient of the oil pool, aerobes again dominate and residual hydrocarbons and ferrous iron are oxidized, resulting in macroscale carbonate-mineral dissolution and iron precipitation. Feldspars, in contrast, weather exclusively at the microscale near attached microorganisms, principally in the anoxic region of the plume. Native organisms preferentially colonize feldspars that contain trace phosphorus as apatite inclusions, apparently as a consequence of the low P concentration in the groundwater. These feldspars weather rapidly, whereas nearby feldspars without trace P are uncolonized and unweathered. Feldspar dissolution is accompanied by the precipitation of secondary minerals, sometimes on the bacterial cell wall itself. These observations suggest a tightly linked biogeochemical system whereby microbial processes control mineral diagenesis at many scales of interaction, and the mineralogy and mineral chemistry influence microbial ecology. Only the macroscale interaction, however, is easily observable by standard geochemical methods, and documentation of the microscale interactions requires microscopic examination of microorganisms on mineral surfaces and the locally intense diagenetic reactions that result. Received, May 1999/Revised, October 1999/Accepted, October 1999     

Evolution of pantellerite-trachyte-phonolite volcanoes by fractional crystallization of basanite magma in a continental rift setting,Marie Byrd Land,Antarctica

The Marie Byrd Land province includes 18 large (up to 1,800 km³) central volcanoes distributed across an active volcano-tectonic dome. The typical volcano structure consists of a basal 1,000–5,000 m of basanite surmounted by trachyte and subordinate intermediate rocks, plus phonolite, or pantellerite, or comendite. The volumes of felsic sections are large (~30–700 km³), but these rocks probably make up <10% of volcanic rock in the province. This paper describes pantellerite volcanoes in the Ames and Flood Ranges, which include a large and varied suite of these iron-rich, silica-poor rhyolites. Isotopic and trace element data, maintenance of isotopic equilibrium throughout the basalt-felsic range, and the results of modeling, all exclude significant crustal contamination and point to fractional crystallization as the process that controls magmatic evolution. The most unusual feature of these volcanoes is the apparent need to derive pantellerites from basanite, the long interval of fractionation at the base of the lithosphere and crust, involving kaersutite as the key phase in developing pantellerite, and a plumbing system that permitted coeval eruption of pantellerite and phonolite from the same edifice. Peralkalinity most likely developed in upper crustal reservoirs during the final 4–5% of magmatic history, by fractionating a high proportion of plagioclase under low pH₂O. Mantle plume activity appears to drive doming and volcanism. This, a stationary plate, and continental lithospheric structure seem to provide an optimal environment for the evolution of a diverse, large volume suite of felsic rocks by fractional crystallization.     

Assessing global trends in Mars magma compositions using ground truth

Global magmatic trends inferred from gamma-ray, visible/near-infrared, and thermal infrared spectrometers on Mars-orbiting spacecraft have been used to constrain planetary petrogenetic processes and global thermal evolution models. Inferred magmatic trends include temporal variations in the relative proportions of low-Ca and high-Ca pyroxenes, and in the abundances of potassium (and total alkalis), silica, FeO* (total iron expressed as FeO), and thorium. These patterns are evaluated for consistency with the compositions of surface igneous rocks of different ages analyzed by Mars rovers and of martian meteorites. Trends of decreasing low-Ca pyroxene/total pyroxene ratios and of decreasing potassium (and total alkalis), with time are generally supported by surface rock analyses. However, significant differences in the GRS-measured silica in Amazonian volcanoes and in martian meteorites of equivalent age result from contamination by silica-rich dust and are problematic for a silica trend. Comparison of FeO* in Noachian and Amazonian surface data shows no decrease. An inferred temporal trend in thorium is in conflict with the complex enrichment and depletion patterns of incompatible trace elements in martian meteorites of various ages. A dearth of analyses of Hesperian-age surface rocks precludes a firm evaluation of inferred Noachian-Hesperian trends and Hesperian-Amazonian trends, but abundant Noachian rocks and a few Hesperian rocks at rover sites, and Amazonian martian meteorites, collectively representing at least 16 surface locations, afford useful comparisons with orbital remote-sensing data.     

Stable carbon and nitrogen isotope signatures indicate recovery of marine biota from sewage pollution at Moa Point,New Zealand

Stable carbon and nitrogen isotopes have been used to assess sewage contamination of a sewage outfall, discharging milli-screened effluent into Moa Point Bay, New Zealand, and monitor the recovery of flora and fauna after the outfall's closure. An initial study characterising the extent of the discharge and the effects on seaweed (Ulva lactuca L.), blue mussels (Mytilus galloprovincialis) and limpets (Cellana denticulata) from the area, showed effects of the sewage discharge on flora and fauna were localised within in the bay. The immediate area surrounding the discharge area was found to contain limited biodiversity, with an abundance of Ulva lactuca, a bright green lettuce-like seaweed, typically found in areas with high nutrient input, limpets and small blue mussels. The nitrogen isotopic signature (delta15N) is shown to be a good tracer of sewage pollution in seaweed and associated grazers (i.e. limpets) as a result of the increased contribution of urea and ammonia to seawater nitrogen derived from the effluent. The carbon isotopic signature (delta13C) is suggested as a more appropriate sewage tracer for mussels, which filter feed the effluent's particulate organic matter from the water. Lower carbon:nitrogen ratios were found in Ulva lactuca sampled from around the outfall region compared to uncontaminated control sites. However carbon:nitrogen ratios do not vary significantly amongst shellfish species.After closure, monitoring continued for 9 months and showed that the carbon and nitrogen isotopic signatures of algae (Ulva lactuca L.) returned to similar control site levels within 3 months. Limpet and blue mussels (Cellana denticulata and Mytilus galloprovincialis) showed slower recovery times than the Ulva lactuca, with detectable levels of the sewage-derived carbon and nitrogen remaining in the animal's tissue for up to 9 months.     

HIGH SPATIAL AND TEMPORAL RESOLUTION OPTICAL SEARCH FOR EVIDENCE OF METEOROID FRAGMENTATION

A digital image intensified CCD camera with an electronically gated image intensifier was used to produce very short duration images of meteors. The observational system employed a 0.40 m F/4.5 Newtonian telescope to obtain high spatial resolution. A second intensified CCD camera was used to yield height information using parallax. At a typical meteor height one pixel (for the vertically oriented system) corresponded to about 1.1 m. A sampling of 59 mainly sporadic meteors was analyzed. There is clear variability from meteor to meteor, with many meteors (nearly 50%) showing only a small amount of wake, while some meteors (approximately 20%) have the off segments completely filled in.     

Decoding the spectra of SDSS early-type galaxies: new indicators of age and recent star formation

We apply principal component analysis (PCA) to a sample of early-type galaxies from the Sloan Digital Sky Survey (SDSS) in order to infer differences in their star formation histories from their unresolved stellar populations. We select a   z < 0.1  volume-limited sample comprising ∼7000 early-type galaxies from SDSS/Data Release 4. Out of the first few principal components (PC), we study four which give information about stellar populations and velocity dispersion. We construct two parameters (η and ζ) as linear combinations of PC1 and PC2. The four components can be presented as 'optimal filters' to explore in detail the properties of the underlying stellar populations. By comparing various photospectroscopic observables – including near-ultraviolet (NUV) photometry from Galaxy Evolution Explorer (GALEX) – we find ζ to be most sensitive to recent episodes of star formation, and η to be strongly dependent on the average age of the stellar populations. Both η and ζ also depend on metallicity. We apply these optimal filters to composite spectra assembled by Bernardi et al. The distribution of the η component of the composites appear to be indistinguishable between high- and low-density regions, whereas the distribution of ζ parameters have a significant skew towards lower values for galaxies in low-density regions. This result suggests that galaxies in lower density environments are less likely to present weak episodes of recent star formation. In contrast, a significant number of galaxies from our high-density subsample – which includes clusters (both outer regions and centres) and groups – underwent small but detectable recent star formation at high metallicity, in agreement with recent estimates targeting elliptical galaxies in Hickson Compact Groups and in the field.