Measurements of the north polar cap of Mars and the Earth's northern hemisphere ice and snow cover

The boundaries of the polar caps of Mars have been measured on more than 3000 photographs since 1905 from the plate collection at the Lowell Observatory. For the Earth, the polar caps have been accurately mapped only since the mid 1960's when satellites were first available to synoptically view the polar regions. The polar caps of both planets wax and wane in response to changes in the seasons, and interannual differences in polar cap behavior on Mars as well as Earth are intimately linked to global energy balance. Data on the year to year variations in the extent of the north polar caps of Mars and Earth have been assembled and compared, although only 6 years of concurrent data were available for comparison.     

Monitoring selective availability dither frequencies and their effect on GPS data

Summary The signals transmitted by Block II satellites of the Global Positioning System (GPS) can be degraded to limit the highest accuracy of the system (10 m or better point positioning) to authorized users. This mode of degraded operation is called Selective Availability (S/A). S/A involves the degradation in the quality of broadcast orbits and satellite clock dithering. We monitored the dithered satellite oscillator and investigated the effect of this clock dithering on high accuracy relative positioning. The effect was studied over short 3-meter and zero-baselines with two GPS receivers. The equivalent S/A effects for baselines ranging from 0 to >10,000 km can be examined with short test baselines if the receiver clocks are deliberately mis-synchronized by a known and varying amount. Our results show that the maximum effect of satellite clock dithering on GPS double difference phase residuals grows as a function of the clock synchronization error according to: S/A _effect =0.04 cm/msec, and it increases as a function of baseline length like: S/A _effect =0.014 cm/100 km. These are equations for maximum observed values of post-fit residuals due to S/A. The effect on GPS baselines is likely to be smaller than the 0.14 mm for a baseline separation of 100 km. We therefore conclude, for our limited data set, and for the level of S/A during our tests, that S/A clock dithering has negligible effect on all terrestrial GPS baselines if double difference processing techniques are employed and if the GPS receivers remain synchronized to better than 10 msec. S/A may constitute a problem, however, if accurate point processing is required, or if GPS receivers are not synchronized. We suggest and test two different methods to monitor satellite frequency offsets due to S/A. S/A modulates GPS carrier frequencies in the range of-2 Hz to +2 Hz over time periods of several minutes. The methods used in this paper to measure the satellite clock dither could be applied by the civilian GPS community to continuously monitor S/A clock dithering. The monitored frequencies may aid high accuracy point positioning applications in a postprocessing mode (Malys and Ortiz 1989), and differential GPS with poorly synchronized receivers (Feigl et al. 1991).     

V792 Her=HD 155638: A totally eclipsing RS CVn binary

Photometry of HD 155638=V792 Her has been analyzed to determine the elements of this totally eclipsing RS CVn binary. The light variation outside eclipse was found to have a period of 27^d.07±0^d.07, which is slightly different from the 27^d.5384±0^d.0045 orbital period. Analysis of the eclipses was achieved by a modification of the Russell-Merrill technique. With the aid of radial velocity measures, absolute elements were obtained for the hot and cool stars, respectively;R _h=2.58R ,R _c=12.28R ,M _h=1.40M ,M _c=1.46M ,i=80^o.61 and velocity semi-amplitudesK _c=48.36 km s^–1±0.79 km s^–1, andK _h=50.50 km s^–1±0.33 km s^–1. The apparent magnitudes areV _h=9 ^m .73 andV _c=8 ^m .48. The distance to HD 155638 was estimated to be 310 parsecs.     

Properties of r-modes in the Sun

Global oscillations of the Sun (r-modes) with very long periods 1 month are reviewed and studied. Such modes would be trapped in an acoustic cavity formed either by most of the convective envelope or by most of the radiative interior. A turning point frequency giving cavity boundaries is defined and the run of eigenvalues for angular harmonics l 3 are plotted for a conventional solar convection zone. The r-modes show equipartition of oscillatory energy among shells which each contain one antinode in the radial dimension. Toroidal motion is dominant to at least the 14^th radial harmonic mode. Viscosity from convective turbulence is strong and would damp any mode in just a few solar rotations if it were the only significant nonadiabatic effect. Radial fine splitting which lifts the degeneracy in n is very small (20 nHz or less) for all n 14 trapped in the envelope. But, if splitting could be detected, we would have a valuable new constraint on solar convection theories.     

TEM evidence for intracellular accumulation of lead by bacteria in subsurface environments

We monitored near-surface atmospheric fallout (15-cm above ground) and soil solution (at 15, 35 and 55 cm below ground) derived nanoparticles over an 8-month period by collecting the particles directly onto TEM grids in anthropogenically-influenced (vineyard) and pristine (native forest) sites in France. Particle clusters trapped on the grid were selected randomly and individual particles were binned into eight different groups (euhedral clays, weathered clays, salts, oxi-hydroxides, bacteria, non-living organic matter, aggregates and undetermined). Bacteria represent 9–23% of the collected nanoparticle area (ave. 9.4% and 18% for two atmospheric collection sites and ave. 23% for soil infiltration samples). Bacteria were most often associated with non-living organic matter and comprised a variety of morpho-types. Interestingly, 45% of all the bacteria analyzed by transmission electron microscopy and electron dispersive spectroscopy (TEM-EDX) showed the presence of intracellular grains significantly enriched in lead and phosphorus. Intracellular sequestration of Pb into polyphosphate bodies has been observed in the laboratory, but this is the first observation of this phenomenon in a natural environment. Furthermore, this suggests that microbial-bound Pb may be an important transport mechanism in subsurface environments.     

Formation of Zn–Ca phyllomanganate nanoparticles in grass roots

It is now well established that a number of terrestrial and aquatic microorganisms have the capacity to oxidize and precipitate Mn as phyllomanganate. However, this biomineralization has never been shown to occur in plant tissues, nor has the structure of a natural Mn(IV) biooxide been characterized in detail. We show that the graminaceous plant Festuca rubra (red fescue) produces a Zn-rich phyllomanganate with constant Zn:Mn and Ca:Mn atomic ratios (0.46 and 0.38, respectively) when grown on a contaminated sediment. This new phase is so far the Zn-richest manganate known to form in nature (chalcophanite has a Zn:Mn ratio of 0.33) and has no synthetic equivalent. Visual examination of root fragments under a microscope shows black precipitates about ten to several tens of microns in size, and their imaging with backscattered and secondary electrons demonstrates that they are located in the root epidermis. In situ measurements by Mn and Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) with a micro-focused beam can be quantitatively described by a single-phase model consisting of Mn(IV) octahedral layers with 22% vacant sites capped with tetrahedral and octahedral Zn in proportions of 3:1. The layer charge deficit is also partly balanced by interlayer Mn and Ca. Diffracting crystallites have a domain radius of 33 Å in the ab plane and contain only 1.2 layers (8.6 Å) on average. Since this biogenic Mn oxide consists mostly of isolated layers, basal 00l reflections are essentially absent despite its lamellar structure. Individual Mn layers are probably held together in the Mn–Zn precipitates by stabilizing organic molecules. Zinc biomineralization by plants likely is a defense mechanism against toxicity induced by excess concentrations of this metal in the rhizosphere.     

The age of the martian meteorite Northwest Africa 1195 and the differentiation history of the shergottites

Samarium-neodymium isotopic analyses of unleached and acid-leached mineral fractions from the recently identified olivine-bearing shergottite Northwest Africa 1195 yield a crystallization age of 347 ± 13 Ma and an value of +40.1 ± 0.9. Maskelynite fractions do not lie on the Sm-Nd isochron and appear to contain a martian surface component with low ¹⁴⁷Sm/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd ratios that was added during shock. The Rb-Sr system is disturbed and does not yield an isochron. Terrestrial Sr appears to have affected all of the mineral fractions, although a maximum initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7016 is estimated by passing a 347 Ma reference line through the maskelynite fraction that is least affected by contamination. The high initial value and the low initial ⁸⁷Sr/⁸⁶Sr ratio, combined with the geologically young crystallization age, indicate that Northwest Africa 1195 is derived from a source region characterized by a long-term incompatible-element depletion.The age and initial Sr and Nd isotopic compositions of Northwest Africa 1195 are very similar to those of Queen Alexandra Range 94201, indicating these samples were derived from source regions with similar Sr-Nd isotopic systematics. These similarities suggest that these two meteorites share a close petrogenetic relationship and might have been erupted from a common volcano. The meteorites Yamato 980459, Dar al Gani 476, Sayh al Uhaymir 005/008, and Dhofar 019 also have relatively old ages between 474 and 575 Ma and trace element and/or isotopic systematics that are indicative of derivation from incompatible-element-depleted sources. This suggests that the oldest group of meteorites is more closely related to one another than they are to the younger meteorites that are derived from less incompatible-element-depleted sources. Closed-system fractional crystallization of this suite of meteorites is modeled with the MELTS algorithm using the bulk composition of Yamato 980459 as a parent. These models reproduce many of the major element and mineralogical variations observed in the suite. In addition, the rare earth element systematics of these meteorites are reproduced by fractional crystallization using the proportions of phases and extents of crystallization that are calculated by MELTS. Other shergottites that demonstrate enrichments in incompatible-elements and have evolved Sr and Nd isotopic systematics have some geochemical systematics that are similar to those observed in the depleted group. Most notably, although they exhibit a very limited range of incompatible trace element and isotopic compositions, they have highly variable major element compositions. This is also consistent with evolution from a common mantle source region by variable amounts of fractional crystallization. If this scenario is correct, it suggests that the combined effects of source composition and fractional crystallization are likely to account for the major element, trace element, and isotopic diversity of all shergottites.     

Participation in payments for ecosystem services: Case studies from the Lacandon rainforest, Mexico

Understanding people’s willingness to participate in projects and programmes of payments for ecosystem services (PES) has not been a key analytical concern of the scholarly literature around this new field of environmental policy and practice. This paper analyses participation in four communities benefiting from payments for biodiversity and carbon fixation in Mexico, and contrasts the results for each case with neighbouring communities that do not receive payments. We take a holistic approach that accounts for procedural rules, actors’ interactions, institutions and values, and individuals’ characteristics. We show that the nature of PES rules and the effectiveness of communication with government officers and NGOs influence resource managers’ ability and willingness to participate. We highlight community size, resource managers’ ability to diversify livelihood activities and local perspectives on the conservation of common forests, particularly sacred values and intergenerational concerns on forest conservation, as critical participation drivers. This analysis provides insights on why and how these new institutions may be attractive for some resource managers and permits to draw some recommendations for the future design of PES projects and programmes.     

Laboratory and field evaluation of a flushable oxic limestone drain for treatment of net-acidic drainage from a flooded anthracite mine, Pennsylvania, USA

This paper demonstrates the use of dissolution-rate data obtained in the laboratory to indicate the potential quality of effluent from a field-scale oxic limestone drain (OLD) treatment system for neutralization of dilute acidic mine drainage (AMD). Effluent from the Reevesdale Mine South Dip Tunnel, a large source of AMD and base flow to the Wabash Creek and Little Schuylkill River in the Southern Anthracite Coalfield of east-central Pennsylvania, is representative of AMD with low concentrations but high loadings of dissolved Fe, Al and other metals because of a high flow rate. In January 2003, rapid neutralization of the AMD from the Reevesdale Mine was achieved in laboratory tests of its reaction rate with crushed limestone in closed, collapsible containers (Cubitainers). The tests showed that net-alkaline effluent could be achieved with retention times greater than 3 h and that effluent alkalinities and associated dissolution rates were equivalent for Fe(OH)₃-coated and uncoated limestone. On the basis of the laboratory results, a flushable OLD containing 1450 metric tons of high-purity calcitic limestone followed by two 0.7-m deep wetlands were constructed at the Reevesdale Mine. During the first year of operation, monthly data at the inflow, outflow and intermediate points within the treatment system were collected (April 2006–2007). The inflow to the treatment system ranged from 6.8 to 27.4 L/s, with median pH of 4.7, net acidity of 9.1 mg/L CaCO₃, and concentrations of dissolved Al, Fe and Mn of 1.0, 1.9 and 0.89 mg/L, respectively. The corresponding effluent from the OLD had computed void-volume retention times of 4.5–18 h, with median pH of 6.6, net acidity of −93.2 mg/L CaCO₃, and concentrations of dissolved Al, Fe and Mn of <0.1, 0.08 and 0.52 mg/L, respectively. The wetlands below the OLD were effective for retaining metal-rich solids flushed at monthly or more frequent intervals from the OLD, but otherwise had little effect on the effluent quality. During the first year of operation, approximately 43 metric tons of limestone were dissolved and 2 metric tons of Al, Fe and Mn were precipitated within the OLD. However, because of the accumulation of these metals within the OLD and possibly other debris from the mine, the effectiveness of the treatment system declined. Despite the installation of a flush-pipe network at the base of the OLD to remove precipitated solids, the limestone bed clogged near the inflow. Consequently, a large fraction of the AMD bypassed the treatment system. To promote flow through the OLD, the flush pipes were open continuously during the last 4 months of the study; however, this effluent was only partially treated because short-circuiting through the pipes decreased contact between the effluent and limestone. A reconfiguration of the flow path through the limestone bed from horizontal to vertical upward could increase the limestone surface area exposed to the metal-laden influent, increase the cross-sectional area perpendicular to flow, decrease the flow path for solids removal, and, consequently, decrease potential for clogging.