Seasonal,hydrological, and land management factors controlling dissolved organic carbon concentrations in the loch fleet catchments,Southwest Scotland

Dissolved organic carbon (DOC) was measured at hourly or two-hourly intervals during more than 30 events in one forested and two moorland subcatchments of the Loch Fleet catchment in southwest Scotland. The dominantly peaty soils in the catchments resulted in small discharge-related DOC variations within individual events, with a maximum range of about 2 mg 1^?1. Seasonal variations were larger with an amplitude of 8-9 mg 1^?1 and maximum concentrations in the summer months. The forested stream had the highest mean DOC, twice as large as the comparable moorland stream in the preliming phase. Applications of lime to the catchments increased stream DOC concentrations, with the largest increases in the moorland catchments.     

Subglacial drainage system structure and morphology of Brewster Glacier,New Zealand

A global positioning system and ground penetrating radar surveys is used to produce digital elevation models of the surface and bed of Brewster Glacier. These are used to derive maps of subglacial hydraulic potential and drainage system structure using three different assumptions about the subglacial water pressure (P_w): (i) P_w = ice overburden; (ii) P_w = half ice overburden; (iii) P_w = atmospheric. Additionally, 16 dye‐tracing experiments at 12 locations were performed through a summer melt season. Dye return curve shape, together with calculations of transit velocity, dispersivity and storage, are used to infer the likely morphology of the subglacial drainage system. Taken together, the data indicate that the glacier is underlain by a channelised but hydraulically inefficient drainage system in the early summer in which water pressures are close to ice overburden. By mid‐summer, water pressures are closer to half‐ice overburden and the channelised drainage system is more hydraulically efficient. Surface streams that enter the glacier close to the location of major subglacial drainage pathways are routed quickly to the channels and then to the glacier snout. Streams that enter the glacier further away from the drainage pathways are routed slowly to the channels and then to the snout because they first flow through a distributed drainage system. Copyright © 2008 John Wiley & Sons, Ltd.     

Physical properties of Martian meteorites: Porosity and density measurements

Abstract— Martian meteorites are fragments of the Martian crust. These samples represent igneous rocks, much like basalt. As such, many laboratory techniques designed for the study of Earth materials have been applied to these meteorites. Despite numerous studies of Martian meteorites, little data exists on their basic structural characteristics, such as porosity or density, information that is important in interpreting their origin, shock modification, and cosmic ray exposure history. Analysis of these meteorites provides both insight into the various lithologies present as well as the impact history of the planet's surface. We present new data relating to the physical characteristics of twelve Martian meteorites. Porosity was determined via a combination of scanning electron microscope (SEM) imagery/image analysis and helium pycnometry, coupled with a modified Archimedean method for bulk density measurements. Our results show a range in porosity and density values and that porosity tends to increase toward the edge of the sample. Preliminary interpretation of the data demonstrates good agreement between porosity measured at 100× and 300× magnification for the shergottite group, while others exhibit more variability. In comparison with the limited existing data for Martian meteorites we find fairly good agreement, although our porosity values typically lie at the low end of published values. Surprisingly, despite the increased data set, there is little by way of correlation between either porosity or density with parameters such as shock effect or terrestrial residency. Further data collection on additional meteorite samples is required before more definitive statements can be made concerning the validity of these observations.     

Simulation of the Magnetothermal Instability

In many magnetized, dilute astrophysical plasmas, thermal conduction occurs almost exclusively parallel to magnetic field lines. In this case, the usual stability criterion for convective stability, the Schwarzschild criterion, which depends on entropy gradients, is modified. In the magnetized long mean free path regime, instability occurs for small wavenumbers when (∂ P/∂z) (∂ ln T/∂ z) > 0, which we refer to as the Balbus criterion. We refer to the convective-type instability that results as the magnetothermal instability (MTI). We use the equations of MHD with anisotropic electron heat conduction to numerically simulate the linear growth and nonlinear saturation of the MTI in plane-parallel atmospheres that are unstable according to the Balbus criterion. The linear growth rates measured from the simulations are in excellent agreement with the weak field dispersion relation. The addition of isotropic conduction, e.g. radiation, or strong magnetic fields can damp the growth of the MTI and affect the nonlinear regime. The instability saturates when the atmosphere becomes isothermal as the source of free energy is exhausted. By maintaining a fixed temperature difference between the top and bottom boundaries of the simulation domain, sustained convective turbulence can be driven. MTI-stable layers introduced by isotropic conduction are used to prevent the formation of unresolved, thermal boundary layers. We find that the largest component of the time-averaged heat flux is due to advective motions as opposed to the actual thermal conduction itself. Finally, we explore the implications of this instability for a variety of astrophysical systems, such as neutron stars, the hot intracluster medium of galaxy clusters, and the structure of radiatively inefficient accretion flows. J. M. Stone: Program in Applied and Computational Mathematics, Princeton University, Princeton, NJ 08544     

An analysis of Apollo lunar soil samples 12070,889, 12030,187, and 12070,891: Basaltic diversity at the Apollo 12 landing site and implications for classification of small‐sized lunar samples

Lunar mare basalts provide insights into the compositional diversity of the Moon's interior. Basalt fragments from the lunar regolith can potentially sample lava flows from regions of the Moon not previously visited, thus, increasing our understanding of lunar geological evolution. As part of a study of basaltic diversity at the Apollo 12 landing site, detailed petrological and geochemical data are provided here for 13 basaltic chips. In addition to bulk chemistry, we have analyzed the major, minor, and trace element chemistry of mineral phases which highlight differences between basalt groups. Where samples contain olivine, the equilibrium parent melt magnesium number (Mg#; atomic Mg/[Mg + Fe]) can be calculated to estimate parent melt composition. Ilmenite and plagioclase chemistry can also determine differences between basalt groups. We conclude that samples of approximately 1–2 mm in size can be categorized provided that appropriate mineral phases (olivine, plagioclase, and ilmenite) are present. Where samples are fine‐grained (grain size <0.3 mm), a “paired samples t‐test” can provide a statistical comparison between a particular sample and known lunar basalts. Of the fragments analyzed here, three are found to belong to each of the previously identified olivine and ilmenite basalt suites, four to the pigeonite basalt suite, one is an olivine cumulate, and two could not be categorized because of their coarse grain sizes and lack of appropriate mineral phases. Our approach introduces methods that can be used to investigate small sample sizes (i.e., fines) from future sample return missions to investigate lava flow diversity and petrological significance.     

Distribution of Palaeozoic tectonic superimposed unconformities in the Tarim Basin,NW China: significance for the evolution of palaeogeomorphology and sedimentary response

Seismic and drilling well data were used to examine the occurrence of multiple stratigraphic unconformities in the Tarim Basin, NW China. The Early Cambrian, the Late Ordovician and the late Middle Devonian unconformities constitute three important tectonic sequence boundaries within the Palaeozoic succession. In the Tazhong, Tabei, Tadong uplifts and the southwestern Tarim palaeo‐uplift, unconformities obviously belong to superimposed unconformities. A superimposed unconformity is formed by superimposition of unconformities of multiple periods. Areas where superimposed unconformities develop are shown as composite belts of multiple tectonic unconformities, and as higher uplift areas of palaeo‐uplifts in palaeogeomorphologic units. The contact relationship of unconformities in the lower uplift areas is indicative of truncation‐overlap. A slope belt is located below the uplift areas, and the main and secondary unconformities are characterized by local onlap reflection on seismic profiles. The regional dynamics controlled the palaeotectonic setting of the Palaeozoic rocks in the Tarim Basin and the origin and evolution of the basin constrained deposition. From the Sinian to the Cambrian, the Tarim landmass and its surrounding areas belonged to an extensional tectonic setting. Since the Late Ordovician, the neighbouring north Kunlun Ocean and Altyn Ocean was transformed from a spreading ocean basin to a closed compressional setting. The maximum compression was attained in the Late Ordovician. The formation of a tectonic palaeogeomorphologic evolution succession from a cratonic margin aulacogen depression to a peripheral foreland basin in the Early Caledonian cycle controlled the deposition of platform, platform margin, and deep‐water basin. Tectonic uplift during the Late Ordovician resulted in a shallower basin which was followed by substantial erosion. Subsequently, a cratonic depression and peripheral or back‐arc foreland basin began their development in the Silurian to Early–Middle Devonian interval. In this period, the Tabei Uplift, the Northern Depression and the southern Tarim palaeo‐uplift showed obvious control on depositional systems, including onshore slope, shelf and deep‐water basin. The southern Tarim Plate was in a continuous continental compressional setting after collision, whereas the southern Tianshan Ocean began to close in the Early Ordovician and was completely closed by the Middle Devonian. At the same time, further compression from peripheral tectonic units in the eastern and southern parts of the Tarim Basin led to the expansion of palaeo‐uplift in the Late Devonian–Early Carboniferous interval, and the connection of the Tabei Uplift and Tadong Uplift, thus controlling onshore, fluvial delta, clastic coast, lagoon‐bay and shallow marine deposition. Copyright © 2015 John Wiley & Sons, Ltd.     

A petrological,mineralogical, and chemical analysis of the lunar mare basalt meteorite LaPaz Icefield 02205, 02224, and 02226

Abstract— LaPaz Icefield (LAP) 02205, 02226, and 02224 are paired stones of a crystalline basaltic lunar meteorite with a low‐Ti (3.21–3.43% TiO₂) low‐Al (9.93–10.45% Al₂O₃), and low‐K (0.11–0.12% K₂O) composition. They consist mainly of zoned pyroxene and plagioclase grains, with minor ilmenite, spinel, and mesostasis regions. Large, possibly xenocrystic, forsteritic olivine grains (<3% by mode) contain small trapped multiphase melt inclusions. Accessory mineral and mesostasis composition shows that the samples have experienced residual melt crystallization with silica oversaturation and late‐stage liquid immiscibility. Our section of LAP 02224 has a vesicular fusion crust, implying that it was at one time located sufficiently close to the lunar surface environment to have accumulated solar‐wind‐implanted gases. The stones have a comparable major element composition and petrography to low‐Ti, low‐Al basalts collected at the Apollos 12 and 15 landing sites. However, the LAP stones also have an enriched REE bulk composition and are more ferroan (Mg numbers in the range of 31 to 35) than similar Apollo samples, suggesting that they represent members of a previously unsampled fractionated mare basalt suite that crystallized from a relatively evolved lunar melt.     

The Antarctic achondrite,Grove Mountains 021663: An olivine‐rich winonaite

Abstract– The Grove Mountains (GRV) 021663 meteorite was collected from the Grove Mountains region of Antarctica. The meteorite is composed primarily of olivine (Fa_5.4), orthopyroxene (Fs_4.7Wo_3.0), chromian diopside (En_53.6Fs_2.4Wo₄₄), troilite, kamacite, and plagioclase (Ab_74.5Or₄An_21.5). Minor phases include schreibersite and K‐feldspar. The meteorite is highly weathered (W3) and weakly shocked (S2). We determine a whole rock oxygen isotopic composition of δ¹⁸O = 7.50‰, δ¹⁷O = 3.52‰. Comparisons of these data with other primitive achondrites have resulted in the reclassification of this meteorite as a member of the winonaite group. The occurrences of troilite, metal, and schreibersite in GRV 021663 indicate that these minerals were once completely molten. Euhedral inclusions of pyroxene within plagioclase further suggest that these may have crystallized from a silicate melt, while the depletion of plagioclase, metal, and troilite indicates that GRV 021663 could represent a residuum following partial melting on its parent asteroid. Trace element distributions in silicate minerals do not, however, confirm this scenario. As with other winonaite meteorites, the formation of GRV 021663 probably relates to brecciation and mixing of heterogeneous lithologies, followed by varying degrees of thermal metamorphism on the parent body asteroid. Peak metamorphic conditions may have resulted in localized partial melting of metal and silicate mineralogies, but our data are not conclusive.     

Characterization of halophiles in natural MgSO4 salts and laboratory enrichment samples: Astrobiological implications for Mars

The presence of sulfate salts and limited subsurface water (ice) on Mars suggests that any liquid water on Mars today will occur as (magnesium) sulfate-rich brines in regions containing sources of magnesium and sulfur. The Basque Lakes of British Columbia, Canada, represent a hypersaline terrestrial analogue site, which possesses chemical and physical properties similar to those observed on Mars. The Basque Lakes also contain diverse halophilic organisms representing all three Kingdoms of life, growing in surface and near-subsurface environments. Of interest from an astrobiological perspective, crushed magnesium sulfate samples that were analyzed using a modified Lowry protein assay contained biomass in every crystal inspected, with biomass values from 0.078 to 4.21 mg_biomass/g_salt; average=0.74±0.7 mg_biomass/g_salt. Bacteria and Archaea cells were easily observed even in low-biomass samples using light microscopy, and bacteria trapped within magnesium sulfate crystals were observed using confocal microscopy. Regions within the salt also contained bacterial pigments, e.g., carotenoids, which were separate from the cells, indicating that cell lysis might have occurred during entrapment within the salt matrix. These biosignatures, cells, and any ‘soluble’ organic constituents were primarily found trapped within fluid inclusions or fluid-filled void spaces between intergrown crystals. Diffuse reflectance infrared Fourier transform spectroscopy (reflectance IR) analysis of enrichment cultures, containing cyanobacteria, Archaea, or dissimilatory sulfate-reducing bacteria, highlighted molecular biosignature features between 550-1650 and 2400-3000 cm⁻¹. Spectra from natural salts demonstrated that we can detect biomass within salt crystals using the most sensitive biosignatures, which are the 1530-1570 cm⁻¹, C-N, N-H, -COOH absorptions and the 1030-1050 cm⁻¹ C-OH, C-N, PO₄³⁻ bond features. The lowest detection limit for a biosignature absorption feature using reflectance IR was with a natural sample that possessed 0.78 mg_biomass/g_salt. In a model cell, i.e., a 0.5 by 1 μm bacillus, this biomass value corresponds to approximately 7.8×10⁸ cells/g_salt. Based on its ability to detect biomass entrapped within natural sulfate salts, reflectance IR may make an effective remote-sensing tool for finding enrichments of organic carbon within outcrops and surficial sedimentary deposits on Mars.