Eolian controlled modification of the martian south polar layered deposits

Data from the Mars Orbiter Laser Altimeter (MOLA) and Mars Orbiter Camera (MOC) aboard the Mars Global Surveyor (MGS) mission and the Thermal Emission Imaging System (THEMIS) aboard the Mars Odyssey mission have revealed unique surface features in a particular region of the South Polar Layered Deposits (SPLD). The dominant morphology is large-scale quasi-parallel grooves that extend for hundreds of kilometers with only tens of meters of vertical relief, that we have termed here the “Wire Brush” terrain. The grooves are also transected by disjointed, yet roughly continuous, low-relief sinuous ridges that cross roughly perpendicular to the trend-direction of the large-scale grooves and show only tens of meters of relief. We interpret these ridges to be eroded remnants of folded layers. At the northern end of the large-scale grooves there are non-symmetric mounds. They are frequently preceded by a significant depression and/or trailing grooves that are parallel to the Wire Brush trend. We find that a two-stage process involving winds that intermittently remove a low-density crust exposing the underlying ice to ablation is the interpretation that best explains the multitude of features observed here. These features appear to be currently inactive indicating higher winds in previous epochs.     

A population cartogram of New Zealand

The authors use 1981 census data to create a cartogram showing the counties of New Zealand in proportion to their population.     

Characterization of uraninite nanoparticles produced by Shewanella oneidensis MR-1

The reduction of uranium(VI) by Shewanella oneidensis MR-1 was studied to examine the effects of bioreduction kinetics and background electrolyte on the physical properties and reactivity to re-oxidation of the biogenic uraninite, UO_2(s). Bioreduction experiments were conducted with uranyl acetate as the electron acceptor and sodium lactate as the electron donor under resting cell conditions in a 30 mM NaHCO₃ buffer, and in a PIPES-buffered artificial groundwater (PBAGW). MR-1 was cultured in batch mode in a defined minimal medium with a specified air-to-medium volume ratio such that electron acceptor (O₂) limiting conditions were reached just when cells were harvested for subsequent experiments. The rate of U(VI) bioreduction was manipulated by varying the cell density and the incubation temperature (1.0 × 10⁸ cell ml⁻¹ at 20 °C or 2.0 × 10⁸ cell ml⁻¹ at 37 °C) to generate U(IV) solids at “fast” and “slow” rates in the two different buffers. The presence of Ca in PBAGW buffer altered U(VI) speciation and solubility, and significantly decreased U(VI) bioreduction kinetics. High resolution transmission electron microscopy was used to measure uraninite particle size distributions produced under the four different conditions. The most common primary particle size was 2.9-3.0 nm regardless of U(VI) bioreduction rate or background electrolyte. Extended X-ray absorption fine-structure spectroscopy was also used to estimate uraninite particle size and was consistent with TEM results. The reactivity of the biogenic uraninite products with dissolved oxygen was tested, and neither U(VI) bioreduction rate nor background electrolyte had any statistical effect on oxidation rates. With MR-1, uraninite particle size was not controlled by the bioreduction rate of U(VI) or the background electrolyte. These results for MR-1, where U(VI) bioreduction rate had no discernible effect on uraninite particle size or oxidation rate, contrast with our recent research with Shewanella putrefaciens CN32, where U(VI) bioreduction rate strongly influenced both uraninite particle size and oxidation rate. These two studies with Shewanella species can be viewed as consistent if one assumes that particle size controls oxidation rates, so the similar uraninite particle sizes produced by MR-1 regardless of U(VI) bioreduction rate would result in similar oxidation rates. Factors that might explain why U(VI) bioreduction rate was an important control on uraninite particle size for CN32 but not for MR-1 are discussed.     

The provenance of Australian uranium ore concentrates by elemental and isotopic analysis

Elemental and isotopic ratio analyses of U ore concentrate samples, from the 3 operating U mining facilities in Australia, were carried out to determine if significant variations exist between their products, thereby allowing the U ore concentrate’s origin to be identified. Elemental analyses were conducted using inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence spectrometry (XRF). Lead isotope ratios were measured using ICP-MS and U isotope analyses were conducted using thermal ionisation mass spectrometry (TIMS). Minute quantities of sample, such as that obtained from a swipe, were also examined for elemental concentrations using secondary ion mass spectrometry (SIMS). The results of multivariate statistical analysis show clear patterns in the trace elemental composition of the processed U ores, indicating that it is possible to use this feature as a unique identifier of an Australian U ore concentrate’s source. Secondary ion mass spectrometry analyses also allow individual particles to be differentiated using this ‘fingerprinting’ technique. Isotope ratios determined using TIMS reveal that there is a significant difference in the n(²³⁴U)/n(²³⁸U) isotope ratio between the U ore concentrate from each mine.     

Transport of elemental mercury in the unsaturated zone from a waste disposal site in an arid region

Mercury contained in buried landfill waste may be released via upward emission to the atmosphere or downward leaching to groundwater. Data from the US Geological Survey’s Amargosa Desert Research Site (ADRS) in arid southwestern Nevada reveal another potential pathway of Hg release: long-distance (10² m) lateral migration of elemental Hg (Hg⁰) through the unsaturated zone. Gas collected from multiple depths from two instrumented boreholes that sample the entire 110-m unsaturated zone thickness and are located 100 and 160 m away from the closest waste burial trench exhibit gaseous Hg concentrations of up to 33 and 11 ng m⁻³, respectively. The vertical distribution of gaseous Hg in the borehole closest to the disposal site shows distinct subsurface peaks in concentration at depths of 1.5 and 24 m that cannot be explained by radial diffusive transport through a heterogeneous layered unsaturated zone. The inability of current models to explain gaseous Hg distribution at the ADRS highlights the need to advance the understanding of gas-phase contaminant transport in unsaturated zones to attain a comprehensive model of landfill Hg release.     

Splintered networks: The colonial and contemporary waters of Jakarta

This paper queries the relevance of the ‘splintering urbanism’ thesis to postcolonial cities of the South, and responds to calls for the production of a decentered theory of urbanization through a case study of Jakarta. Drawing on archival and interview data, the paper demonstrates that Jakarta has, since its inception, been characterized by a high degree of differentiation of access to water supply, and of fragmentation of water supply networks. We document the origins of this fragmentation in the colonial era, and trace the legacy of the colonial constructions within the postcolonial city. Moreover, we demonstrate that the introduction of private sector management (in 1988) has not significantly disrupted, and certainly not caused, this pattern. In short, we provide evidence to support our claim that Jakarta’s water supply system is ‘splintered’ rather than ‘splintering’, and demonstrate that this phenomenon was not caused by the rise (or fall) of the ‘modern infrastructural ideal’. In order to explain this sustained fragmentation of infrastructure and access, the paper develops a conceptual framework of postcolonial governmentality that emphasizes the interrelationship between materiality, governmentality, identity, and urbanization, in particular through demonstrating how contested and evolving process of social differentiation are linked to the differentiation of water supply infrastructures and of urban spaces. Although we are wary of any simplistic comparisons between the colonial past and present, we argue that the optic of postcolonial governmentality provides a powerful lens for dissecting the power relations that continue to structure access to water supply and urban space in cities in the South.     

Holocene climate and environmental history of East Greenland inferred from lake sediments

Prediction of future Arctic climate and environmental changes, as well as associated ice-sheet behavior, requires placing present-day warming and reduced ice extent into a long-term context. Here we present a record of Holocene climate and glacier fluctuations inferred from the paleolimnology of small lakes near Istorvet ice cap in East Greenland. Calibrated radiocarbon dates of organic remains indicate deglaciation of the region before ~10,500 years BP, after which time the ice cap receded rapidly to a position similar to or less extensive than present, and lake sediments shifted from glacio-lacustrine clay to relatively organic-rich gyttja. The lack of glacio-lacustrine sediments throughout most of the record suggests that the ice cap was similar to or smaller than present throughout most of the Holocene. This restricted ice extent suggests that climate was similar to or warmer than present, in keeping with other records from Greenland that indicate a warm early and middle Holocene. Middle Holocene magnetic susceptibility oscillations, with a ~200-year frequency in one of the lakes, may relate to solar influence on local catchment processes. Following thousands of years of restricted extent, Istorvet ice cap advanced to within 365 m of its late Holocene limit at ~AD 1150. Variability in the timing of glacial and climate fluctuations, as well as of sediment organic content changes among East Greenland lacustrine records, may be a consequence of local factors, such as elevation, continentality, water depth, turbidity, and seabirds, and highlights the need for a detailed spatial array of datasets to address questions about Holocene climate change.     

The geomagnetic field over the past 5 million years

The modern geomagnetic field is usually expressed as a spherical harmonic expansion. Although the palaeomagnetic record is very incomplete in both space and time, sufficient data are available from a span of ages to generate time-averaged spherical harmonic field models with many degrees of freedom. Here three data sets are considered: directional measurements from lavas, inclination measurements from ocean sediments, and intensity measurements from lavas. Individual data are analysed, as well as site-averages, using the same methods that have been developed for the modern field, to give models for the past 5 Myr. The normal-polarity field model has an axial-dipole intensity similar to that of the modern-day field, whilst the equatorial-dipole component is very much smaller. The field is not axisymmetric, but shows flux concentrations at the core's surface under Canada and Siberia similar to those observed in the field over historical timescales. Tests on synthetic data show that it is unlikely that these similarities result from the overprinting of the palaeomagnetic field due to inadequate cleaning of the samples. The reverse-polarity field model does not show such obvious features, but this may be due to the sparsity of the data.
The patterns observed in the normal-polarity field, with persistent features in the northern hemisphere and a smooth southern hemisphere, could be explained if the present pattern of secular variation is typical of the past several million years. This would reveal itself as large variations over time in the direction of the magnetic vector in regions of high secular variation, with relatively little change over quieter regions. However, we have been unable to find any evidence for a geographical pattern of secular variation in the data.