Stable Carbon and Nitrogen Isotopic

The perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, are part of the coldest and driest ecosystem on earth. To understand lacustrine carbon and nitrogen cycling in this end-member ecosystem, and to define paleolimnological proxies for ice-covered lakes, we measured the stable carbon and nitrogen isotopic composition of particulate organic matter (POM) and benthic organic matter (BOM) within the lakes of Taylor Valley. The ¹³C compositions of seasonally ice-free edges of the lakes (moats) are enriched relative to under-ice organic matter. Thus, the organic carbon isotopic composition of buried sediments may be a proxy for sample position within the lake. In the moats, ¹³C values are governed by limited CO₂diffusion across benthic cyanobacterial cell membranes. During a high glacial melt (2001–2002) season, both ¹³C_POM and ¹³C_BOM in the moats were more depleted than during previous low melt years. We propose that this occurred in response to higher [CO₂]_(aq) and/or reduced growth rates resulting from turbidity-induced light limitation. Though moats and under-ice environments are usually poorly connected, during the 2001–2002 season, the enrichment of the ¹³C_POM values at 6 m depth in the stream-proximal sites relative to deep-profile sites implies enhanced connectivity between these environments. The ¹³C compositions of BOM and POM profiles in Lake Hoare and Lake Fryxell indicate that these lakes are dominated by benthic productivity. In contrast, in Lake Bonney, the similarity of the ¹³C values of BOM and POM indicates the pelagic component dominance in the carbon cycle.     

The importance of chemical data for the study of interstellar shocks

Shock waves perturb the chemical state of the interstellar gas. We consider the effects of C-shocks on the composition of molecular clouds, for a range of values of the pre-shock gas density and magnetic induction. The time required to re-establish equilibrium in the post-shock gas depends on the initial conditions and can become very large. The significance of the two known chemical phases of dark clouds and of bistability is considered in this context.     

Integrated investigation of the mixed origin of lunar sample 72161,11

Sample 72161,11 (dark mantle at LRV-3) has a graphic mean grain size (M _z) of 3.88 ø, inclusive graphic standard deviation (σ _I) of 1.29, and a total carbon content of 204µg C g^?1 sample, and is, therefore, quite mature. However, the agglutinate content is only 30% in the 90–177µm particles, indicating an apparent departure from steady state. Analyses of C, CH₄, and H₂ concentrations in size fractions larger than 149µm show that the volume correlated component of these species increases with increasing grain size. In a homogeneous agglutinate population the volume correlated component is expected to be independent of grain size. The observed increase can be interpreted in terms of the mixing of a dominant local population of coarser agglutinates, with high carbon and hydrogen, with an imported population of finer agglutinates relatively poor in carbon and hydrogen. When analyses of size-fractions from the bulk sample are considered, these effects are apparently obliterated by the admixture of coarse-grained material low in agglutinates. It seems likely that this low agglutinate content is a consequence of the breakdown of the fragile, large agglutinates in the imported material during their movement to the sample site.     

An astrobiological perspective on Meridiani Planum

Sedimentary rocks exposed in the Meridiani Planum region of Mars record aqueous and eolian deposition in ancient dune and interdune playa-like environments that were arid, acidic, and oxidizing. On Earth, microbial populations have repeatedly adapted to low pH and both episodic and chronic water limitation, suggesting that, to a first approximation, the Meridiani plain may have been habitable during at least part of the interval when deposition and early diagenesis took place. On the other hand, the environmental conditions inferred for Meridiani deposition would have posed a challenge for prebiotic chemical reactions thought to have played a role in the origin of life on Earth. Orbital observations suggest that the combination of sulfate minerals and hematite found in Meridiani rocks may be unusual on the martian surface; however, there is reason to believe that acidity, aridity, and oxidizing conditions were broadly distributed on ancient Mars. When these conditions were established and how much environmental heterogeneity existed on early Mars remain to be determined. Because sulfates and iron oxides can preserve detailed geochemical records of environmental history as well as chemical, textural and microfossil signatures of biological activity, Meridiani Planum is an attractive candidate for Mars sample return.     

An Eruv for St Ives? Religion,identity, place and conflict on the Sydney north shore

Religious identity, when marked by physical changes to urban landscapes, has been a cause of tension and conflict in many cities. In the Sydney suburb of St Ives, an attempt to create an eruv, a symbolic and only partly physical boundary around orthodox Jewish space, was vigorously opposed and eventually defeated through the planning system. The religious and physical significance of the eruv resulted in diverse rationales of opposition, centred on the physical and environmental impact, the conceptual nature of boundaries and the role of religion and ‘modernity’ in everyday suburban life. The place of an eruv was opposed with reference to spatial imaginaries of the nation, the suburb and the secular public, as religion and worship intersected with the politics of urban citizenship and belonging. Each of these spatial imaginaries was constructed by opponents in such a way as to deny a place for an eruv in St Ives, and reinforced through the application of planning instruments which eventually refused permission for an eruv. To many residents, public space was seen to be at risk, raising complex questions over amenity, the politics and perception of difference and what is in or out of place. The planning framework adjudicating such development proposals must transcend such imaginaries in the production of public spaces in multicultural cities.     

Social Networks as Livelihood Strategies for Small-scale Traders on the Thai–Lao Border

ABSTRACT

Small scale cross-border trade on the Thai–Lao border has come under increasing pressure with the construction of a new Mekong bridge that has expanded formal trade between the two countries. Most small-scale traders are women who, with assistance from family and friends, have developed small businesses from childhood, and created social networks across the border with other traders, and relevant actors such as drivers and government officials. Such networks, trust, experience and familiarity enabled superior access to information and trading concessions that have enabled the continued success of small-scale trade, the maintenance of complex cross-border livelihoods, and the ability of traders across an increasingly regulated border to deal with constraints and risks. A few established traders have developed trade networks and social relationships involving supply chains across several countries.