Rural household demographics, livelihoods and the environment

This paper reviews and synthesizes findings from scholarly work on linkages among rural household demographics, livelihoods and the environment. Using the livelihood approach as an organizing framework, we examine evidence on the multiple pathways linking environmental variables and the following demographic variables: fertility, migration, morbidity and mortality, and lifecycles. Although the review draws on studies from the entire developing world, we find the majority of microlevel studies have been conducted in either marginal (mountainous or arid) or frontier environments, especially Amazonia. Though the linkages are mediated by many complex and often context-specific factors, there is strong evidence that dependence on natural resources intensifies when households lose human and social capital through adult morbidity and mortality, and qualified evidence for the influence of environmental factors on household decision-making regarding fertility and migration. Two decades of research on lifecycles and land cover change at the farm level have yielded a number of insights about how households make use of different land-use and natural resource management strategies at different stages. A thread running throughout the review is the importance of managing risk through livelihood diversification, ensuring future income security, and culture-specific norms regarding appropriate and desirable activities and demographic responses. Recommendations for future research are provided.     

Tidal disruption of globular clusters in dwarf galaxies with triaxial dark matter haloes

We use N -body simulations to study the tidal evolution of globular clusters (GCs) in dwarf spheroidal (dSph) galaxies. Our models adopt a cosmologically motivated scenario in which the dSph is approximated by a static Navarro, Frenk & White halo with a triaxial shape. We apply our models to five GCs spanning three orders of magnitude in stellar density and two in mass, chosen to represent the properties exhibited by the five GCs of the Fornax dSph. We show that only the object representing Fornax's least dense GC (F1) can be fully disrupted by Fornax's internal tidal field – the four denser clusters survive even if their orbits decay to the centre of Fornax. For a large set of orbits and projection angles, we examine the spatial and velocity distribution of stellar debris deposited during the complete disruption of an F1-like GC. Our simulations show that such debris appears as shells, isolated clumps and elongated overdensities at low surface brightness (≥26 mag arcsec⁻²), reminiscent of substructure observed in several Milky Way dSphs. Such features arise from the triaxiality of the galaxy potential and do not dissolve in time. The kinematics of the debris depends strongly on the progenitor's orbit. Debris associated with box and resonant orbits does not display stream motions and may appear 'colder'/'hotter' than the dSph's field population if the viewing angle is perpendicular/parallel to the progenitor's orbital plane. In contrast, debris associated with loop orbits shows a rotational velocity that may be detectable out to a few kpc from the galaxy centre. Chemical tagging that can distinguish GC debris from field stars may reveal whether the merger of GCs contributed to the formation of multiple stellar components observed in dSphs.     

Chemical and chronologic complexity in the convecting upper mantle: Evidence from the Taitao ophiolite, southern Chile

Exposure of the ca. 6 Ma Taitao ophiolite, Chile, located 50 km south of the Chile Triple Junction, allows detailed chemical and isotopic study of rocks that were recently extracted from the depleted mantle source of mid-ocean ridge basalts (DMM). Ultramafic and mafic rocks are examined for isotopic (Os, Sr, Nd, and O), and major and trace element compositions, including the highly siderophile elements (HSE). Taitao peridotites have compositions indicative of variable extents of partial melting and melt extraction. Low δ¹⁸O values for most whole rock samples suggest some open-system, high-temperature water–rock interaction, most likely during serpentinization, but relict olivine grains have δ¹⁸O values consistent with primary mantle values. Most of the peridotites analyzed for Nd–Sr isotopes have compositions consistent with estimates for the modern DMM, although several samples are characterized by ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd indicative of crustal contamination, most likely via interactions with seawater. The peridotites have initial ¹⁸⁷Os/¹⁸⁸Os ratios that range widely from 0.1168 to 0.1288 (γ_Os = −8.0 to +1.1), averaging 0.1239 (γ_Os = −2.4), which is comparable to the average for modern abyssal peridotites. A negative correlation between the Mg^# of relict olivine grains and Os isotopic compositions of whole rock peridotites suggests that the Os isotopic compositions reflect primary mantle Re/Os fractionation produced by variable extents of partial melting at approximately 1.6 Ga. Recent re-melting at or near the spatially associated Chile Ridge further modified these rocks, and Re, and minor Pt and Pd were subsequently added back into some rocks by late-stage melt–rock or fluid–rock interactions.In contrast to the peridotites, approximately half of the mafic rocks examined have whole rock δ¹⁸O values within the range of mantle compositions, and their Nd and Sr isotopic compositions are all generally within the range of modern DMM. These rocks have initial ¹⁸⁷Os/¹⁸⁸Os ratios, calculated for 6 Ma, that range from 0.126 (γ_Os = −1) to as high as 0.561 (γ_Os = +342). The Os isotopic systematics of each of these rocks may reflect derivation from mixed lithologies that include the peridotites, but may also include pyroxenites with considerably more radiogenic Os than the peridotites. This observation supports the view that suprachondritic Os present in MORB derives from mixed mantle source lithologies, accounting for some of the worldwide dichotomy in ¹⁸⁷Os/¹⁸⁸Os between MORB and abyssal peridotites.The collective results of this study suggest that this >500 km³ block of the mantle underwent at least two stages of melting. The first stage occurred at 1.6 Ga, after which the block remained isolated and unmixed within the DMM. A final stage of melting recently occurred at or near the Chile Ridge, resulting in the production of at least some of the mafic rocks. Convective stirring of this mantle domain during a >1 Ga period was remarkably inefficient, at least with regard to Os isotopes.     

X-ray absorption contrast images of binary chemical reactions

Low-divergence synchrotron-sourced X-rays enable a radiographic imaging scheme for full characterization of binary chemical reactions and characterization by type of more complex reactions, in situ, in diamond anvil cells (DAC). Spatially resolved reactants are induced to react by laser heating of their interface. The spatially intermediate products are observed through X-ray absorption contrast. Limits to the technique include the ability to maintain controlled experiment geometry during compression and the ability to resolve chemical differences between reactants and products by X-ray absorption. The ability to make in situ observations at experimental pressure and temperature obviates the problem with quenching techniques for capturing liquid compositions in experiments with dimensions smaller than the diffusion length during quenching time. Partially molten Fe-alloy systems, of poor quenchability, are examined at DAC pressures and temperatures for relevance to Earth's core constitution and evolution. Determinations of eutectic melting in Fe–FeS match known results. Of the probable light elements that may alloy with Fe in the Earth's liquid outer core, Fe–FeS experiments show only modest quenching problems, but C and Si alloy experiments are highly vulnerable to quenching artifacts. The observed reactivity of FeS, Fe₃C, FeSi, and FeO(OH) with Fe in DAC makes the observed non-reactivity between Fe and FeO more significant, reducing the probability that oxygen alone is the major alloy in Earth's molten outer core.     

High-pressure melting relations in Fe-C-S systems: Implications for formation, evolution, and structure of metallic cores in planetary bodies

We present new high-pressure temperature experiments on melting phase relations of Fe-C-S systems with applications to metallic core formation in planetary interiors. Experiments were performed on Fe-5 wt% C-5 wt% S and Fe-5 wt% C-15 wt% S at 2-6 GPa and 1050-2000 °C in MgO capsules and on Fe-13 wt% S, Fe-5 wt% S, and Fe-1.4 wt% S at 2 GPa and 1600 °C in graphite capsules. Our experiments show that: (a) At a given P-T, the solubility of carbon in iron-rich metallic melt decreases modestly with increasing sulfur content and at sufficiently high concentration, the interaction between carbon and sulfur can cause formation of two immiscible melts, one rich in Fe-carbide and the other rich in Fe-sulfide. (b) The mutual solubility of carbon and sulfur increases with increasing pressure and no super-liquidus immiscibility in Fe-rich compositions is likely expected at pressures greater than 5-6 GPa even for bulk compositions that are volatile-rich. (c) The liquidus temperature in the Fe-C-S ternary is significantly different compared to the binary liquidus in the Fe-C and Fe-S systems. At 6 GPa, the liquidus of Fe-5 wt% C-5 wt% S is 150-200 °C lower than the Fe-5 wt% S. (d) For Fe-C-S bulk compositions with modest concentration of carbon, the sole liquidus phase is iron carbide, Fe₃C at 2 GPa and Fe₇C₃ at 6 GPa and metallic iron crystallizes only with further cooling as sulfur is concentrated in the late crystallizing liquid. Our results suggest that for carbon and sulfur-rich core compositions, immiscibility induced core stratification can be expected for planets with core pressure less than ∼6 GPa. Thus planetary bodies in the outer solar system such as Ganymede, Europa, and Io with present day core-mantle boundary (CMB) pressures of ∼8, ∼5, and 7 GPa, respectively, if sufficiently volatile-rich, may either have a stratified core or may have experienced core stratification owing to liquid immiscibility at some stage of their accretion. A similar argument can be made for terrestrial planetary bodies such as Mercury and Earth’s Moon, but no such stratification is predicted for cores of terrestrial planets such as Earth, Venus, and Mars with the present day core pressure in the order ?136 GPa, ?100 GPa, and ?23 GPa. (e) Owing to different expected densities of Fe-rich (and carbon-bearing) and sulfur-rich metallic melts, their settling velocities are likely different; thus core formation in terrestrial planets may involve rain of more than one metallic melt through silicate magma ocean. (f) For small planetary bodies that have core pressures <6 GPa and have a molten core or outer core, settling of denser carbide-rich liquid or flotation of lighter, sulfide-rich melt may contribute to an early, short-lived geodynamo.     

Impact of flooded rice paddy on remotely sensed evapotranspiration in the Krishna River basin,India

Evapotranspiration (ET) is one of the major water exchange processes between the earth's surface and the atmosphere. ET is a combined process of evaporation from open water bodies, bare soil and plant surfaces, and transpiration from vegetation. Remote sensing-based ET models have been developed to estimate spatially distributed ET over large regions, however, many of them reportedly underestimate ET over semi-arid regions (Jamshidi et al., Journal of Hydrometeorology, 2019, 20, 947–964). In this work, we show that underestimation of ET can occur due to the open water evaporation from flooded rice paddies ignored in the existing ET models. To address the gap in ET estimation, we have developed a novel approach that accounts for the missing ET component over flooded rice paddies. Our method improved ET estimates by a modified Penman-Monteith algorithm that considered the fraction of open water evaporation from flooded rice paddies. Daily ET was calculated using ground based meteorological data and the MODIS satellite data over the Krishna River Basin. Seasonal and annual ET values over the Krishna Basin were compared with two different ET algorithms. ET estimates from these two models were also compared for different crop combinations. Results were validated with flux tower-based measurements from other studies. We have identified a 17 mm/year difference in average annual ET over the Krishna River Basin with this new ET algorithm. This is very critical in basin scale water balance analysis and water productivity studies.     

An expanded surface-water palaeotemperature inference model for use with fossil midges from eastern Canada

Using an expanded surface sample data set, representing lakes distributed across a transect from southernmost Canada to the Canadian High Arctic, a revised midge-palaeotemperature inference model was developed for eastern Canada. Modelling trials with weighted averaging (with classical and inverse deshrinking; with and without tolerance downweighting) and weighted averaging partial least squares (WA-PLS) regression, with and without square-root transformation of the species data, were used to identify the best model. Comparison of measured and predicted temperatures revealed that a 2 component WA-PLS model for square-root transformed percentage species data provided the model with the highest explained variance (r =0.88) and the lowest error estimate (RMSEP _jack =2.26 °C). Comparison of temperature inferences based on the new and old models indicates that the original model may have seriously under-estimated the magnitude of late-glacial temperature oscillations in Atlantic Canada. The new inferences suggest that summer surface water temperatures in Splan Pond, New Brunswick were approximately 10 to 12 °C immediately following deglaciation and during the Younger Dryas. During the Allerod and early Holocene, surface water temperatures of 20 to 24 °C were attained. The new model thus provides the basis for more accurate palaeotemperature reconstructions throughout easternmost Canada.     

Statistical analysis of short-term water stress conditions at Riggs Creek OzFlux tower site

Theoretical and Applied Climatology - A large range of indices and proxies are available to describe the water stress conditions of an area subject to different applications, which have varying...