Freshwater geographies: Experimenting with knowing and doing geography differently

The fair and effective governance of freshwater is an increasingly prominent issue in New Zealand. Emerging from a complex of cultural, economic and biophysical narratives, freshwater geographies are multiple, varied and increasingly acknowledged as worthy of interdisciplinary scrutiny. In this commentary, we reflect on a series of generative spaces that we – as group of postgraduate geographers (plus supporting staff) – created to engage with the multiplicity of freshwater meanings both within and beyond the academy. Through this evolving epistemic‐political project, we significantly reframed our own understandings about what freshwater ‘is’ and how it ought to be governed. By pursuing a deeper understanding of how the world gets made, we expand our ability to know and make it differently.     

Worst case scenario as stakeholder decision support: a 5- to 6-m sea level rise in the Rhone delta, France

Risk policy and public attitudes appear disconnected from research predicting warmer climate partially due to human activity. To step out of this stalled situation, a worst case scenario of a 5- to 6-m sea level rise (SLR) induced by the collapse of the WAIS and occurring during the period 2030–2130 is constructed and applied to the Rhone delta. Physical and socio-economic scenarios developed with data from the Rhone delta context are developed and submitted to stakeholders for a day-long workshop. Group process analysis shows a high level of trust and cooperation mobilized to face the 5–6 m SLR issue, despite potentially diverging interests. Two sets of recommendations stem from the scenario workshop. A conservative “wait and see” option is decided when the risk of the WAIS collapse is announced in 2030. After WAIS collapse generates an effective 1 m SLR rise by 2050, decisions are taken for total retreat and rendering of the Rhone delta to its hydrological function. The transposition of these results into present-day policy decisions could be considered. The methodology developed here could be applied to other risk objects and situations, and serve for policy exercises and crisis prevention.     

Oxygen isotopes composition of sapphires from the French Massif Central: implications for the origin of gem corundum in basaltic fields

Alluvial and colluvial gem sapphires are common in the basaltic fields of the French Massif Central (FMC) but sapphire-bearing xenoliths are very rare, found only in the Menet trachytic cone in Cantal. The O-isotope composition of the sapphires ranges between 4.4 and 13.9‰. Two distinct groups have been defined: the first with a restricted isotopic range between 4.4 and 6.8‰ (n = 22; mean δ¹⁸O = 5.6 ± 0.7‰), falls within the worldwide range defined for blue-green-yellow sapphires related to basaltic gem fields (3.0 < δ¹⁸O < 8.2‰, n = 150), and overlaps the ranges defined for magmatic sapphires in syenite (4.4 < δ¹⁸O < 8.3‰, n = 29). A second group, with an isotopic range between 7.6 and 13.9‰ (n = 9), suggests a metamorphic sapphire source such as biotite schist in gneisses or skarns. The δ¹⁸O values of 4.4–4.5‰ for the blue sapphire-bearing anorthoclasite xenolith from Menet is lower than the δ¹⁸O values obtained for anorthoclase (7.7–7.9‰), but suggest that these sapphires were derived from an igneous reservoir in the subcontinental spinel lherzolitic mantle of the FMC. The presence of inclusions of columbite-group minerals, pyrochlore, Nb-bearing rutile, and thorite in these sapphires provides an additional argument for a magmatic origin. In the FMC lithospheric mantle, felsic melts crystallized to form anorthoclasites, the most evolved peraluminous variant of the alkaline basaltic melt. The O-isotopic compositions of the first group suggests that these sapphires crystallized from felsic magmas under upper mantle conditions. The second group of isotopic values, typified for example by the Le Bras sapphire with a δ¹⁸O of 13.9‰, indicates that metamorphic sapphires from granulites were transported to the surface by basaltic magma.     

Youth empowerment and information and communication technologies: a case study of a remote Australian Aboriginal community

In spite of a ‘digital divide’, Aboriginal groups in Australia, as internationally, are increasingly using information and communication technologies (ICTs) to maintain their cultures, communicate, archive knowledge, empower their communities, develop skills and generate income. Each community uses the technologies differently in accordance with their particular needs and the opportunities available. The use of ICTs in Aboriginal youth empowerment is illustrated through a case study of an initiative undertaken by the Walkatjurra Cultural Centre in Leonora, remote Western Australia. A participatory process was used to engage the Centre’s young people and they were given individual assistance to develop their ICT related capacity. The community conceives this youth empowerment to be part of a broader youth participation process that will contribute to the Centre’s overall objectives.     

The Ashima/MIT Mars GCM and argon in the martian atmosphere

We investigate the ability of modern general circulation models (GCMs) to simulate transport in the martian atmosphere using measurements of argon as a proxy for the transport processes. Argon provides the simplest measure of transport as it is a noble gas with no sinks or sources on seasonal timescales. Variations in argon result solely from ‘freeze distillation’, as the atmosphere condenses at the winter poles, and from atmospheric transport. Comparison of all previously published models when rescaled to a common definition of the argon enhancement factor (EF) suggest that models generally do a poor job in predicting the peak enhancement in southern winter over the winter pole – the time when the capability of the model transport approaches are most severely tested. Despite observed peak EF values of ～6, previously published model predictions peaked at EF values of only 2–3. We introduce a new GCM that provides a better treatment of mass conservation within the dynamical core, includes more sophisticated tracer transport approaches, and utilizes a cube–sphere grid structure thus avoiding the grid-point convergence problem at the pole that exists for most current Mars GCMs. We describe this model – the Ashima Research/Massachusetts Institute of Technology Mars General Circulation Model (Ashima/MIT Mars GCM) and use it to demonstrate the significant sensitivity of peak EF to the choices of transport approach for both tracers and heat. We obtain a peak EF of 4.75 which, while over 50% higher than any prior model, remains well short of the observed value. We show that the polar EF value in winter is primarily determined by the competition between two processes: (1) mean meridional import of lower-latitude air not enriched in argon and (2) the leakage of enriched argon out of the polar column by eddies in the lowest atmospheric levels. We suggest possibilities for improving GCM representation of the CO₂ cycle and the general circulation that may further improve the simulation of the argon cycle. We conclude that current GCMs may be insufficient for detailed simulation of transport-sensitive problems like the water cycle and potentially also the dust cycle.     

Anion chemistry on Titan: A possible route to large N-bearing hydrocarbons

The reaction of CN^? with cyanoacetylene (HC₃N), has been studied as a function of the HC₃N pressure in a quadrupole tandem mass spectrometer. The mass spectra revealed the fast depletion of the CN^? parent ion and formation of larger anions of rapidly growing size. Most of the ions observed were found to belong to two series of products: (HC₃N)_x·C_2p+1N^? and (HC₃N)_x·C_2pN^? resulting from the sequential additions of HC₃N molecules and loss of HCN or HCCN molecules. The mechanism and energetics of the first two reaction steps are briefly discussed. The laboratory data are compared with those from the Cassini CAPS-ELS spectrometer. It is believed that the reactions observed could account for the growth of anions in Titan’s ionosphere.     

The lacustrine microbial carbonate factory of the successive Lake Bonneville and Great Salt Lake,Utah, USA

The Bonneville Basin is a continental lacustrine system accommodating extensive microbial carbonate deposits corresponding to two distinct phases: the deep Lake Bonneville (30 000 to 11 500 ¹⁴C bp ) and the shallow Great Salt Lake (since 11 500 ¹⁴C bp ). A characterization of these microbial deposits and their associated sediments provides insights into their spatio‐temporal distribution patterns. The Bonneville phase preferentially displays vertical distribution of the microbial deposits resulting from high‐amplitude lake level variations. Due to the basin physiography, the microbial deposits were restricted to a narrow shoreline belt following Bonneville lake level variations. Carbonate production was more efficient during intervals of relative lake level stability as recorded by the formation of successive terraces. In contrast, the Great Salt Lake microbial deposits showed a great lateral distribution, linked to the modern flat bottom configuration. A low vertical distribution of the microbial deposits was the result of the shallow water depth combined with a low amplitude of lake level fluctuations. These younger microbial deposits display a higher diversity of fabrics and sizes. They are distributed along an extensive ‘shore to lake’ transect on a flat platform in relation to local and progressive accommodation space changes. Microbial deposits are temporally discontinuous throughout the lake history showing longer hiatuses during the Bonneville phase. The main parameters controlling the rate of carbonate production are related to the interaction between physical (kinetics of the mineral precipitation, lake water temperature and runoff), chemical (Ca²⁺, Mg²⁺ and HCO₃^? concentrations, Mg/Ca ratio, dilution and depletion) and/or biological (trophic) factors. The contrast in evolution of Lake Bonneville and Great Salt Lake microbial deposits during their lacustrine history leads to discussions on major chemical and climatic changes during this interval as well as the role of physiography. Furthermore, it provides novel insights into the composition, structure and formation of microbialite‐rich carbonate deposits under freshwater and hypersaline conditions.     

Australian ‘gayborhoods’ and ‘lesborhoods’: a new method for estimating the number and prevalence of adult gay men and lesbian women living in each Australian postcode

ABSTRACT

Gay men and lesbian women often demonstrate unique settlement patterns, forming what have been referred to as ‘gayborhoods’. This study sought to provide the first postcode-level estimates of population size and prevalence of gay and lesbian people in Australia. Data on same-gender-partnered households from the Australian Census were combined with information from six different surveys conducted from 2011 to 2017. We estimated that in 2016 there were 132,203 gay men (1.5% of adult males; 95% CI: 1.4–1.6) and 79,931 lesbian women (0.9% of adult females; 95% CI: 0.8–1.0) in Australia. While many postcodes were sparsely populated by gay and lesbian people (40.1% had prevalences of <0.1%), 24.6% were moderately populated (prevalences in the 50-95th percentile) and 2.7% were highly populated (95th percentile). By jurisdiction, the Australian Capital Territory had the highest prevalences of gay men (2.1%; 95% CI: 2.0–2.2) and lesbian women (1.5%; 95% CI: 1.4–1.6). Although the majority of highly populated postcodes were found in major cities (83.7%), some were also found in regional and remote area (16.3%). This method can be applied in other countries to enhance populate estimates. The accompanying dataset can be used to guide service delivery, conduct geographically contextualised research and develop policies relevant to gay men and lesbian women in Australia.     

Extension at the coast of the Makran subduction zone (Iran)

In the Makran subduction zone, earthquake focal mechanisms and geodetic data indicate that the deforming prism currently experiences N–S compression. However, palaeostress inversions performed on normal faults observed along the coast reveal local stress components consistent with N‐S extension. Previously proposed mechanisms such as gravitational collapse are not favoured by N–S compression and surface uplift. We propose that the observed kinematics result from transient stress reversals following large earthquakes. During the interseismic period (now), the region experiences N–S compression. However, following a large reverse rupture on the subduction interface, stresses in the inner wedge relax, enabling a brief period of extensional faulting before a compressive stress state is re‐established. This mechanism, also observed in other subduction zones, requires low overall stresses in the upper plate and that the margin ruptures in large megathrust earthquakes that result in nearly complete stress drops.