Modelling the effects of climatic and hydrological regime changes on the sediment dynamics of the Fraser River Basin,British Columbia,Canada

Future sediment dynamics may be affected by changing climates or hydrological regimes because of the close link between hydrology and sediment erosion, deposition, and transport. Previously, investigations of these potential changes have been constrained by a combination of limited observational data, hydrological drivers, and appropriate mechanistic models. Additionally, there is often ambiguity regarding how to disentangle the impacts of climate and hydrology from direct human factors such as reservoirs and land‐use change, which often exert more control over sediment dynamics. In this study, we utilize a recently developed, large‐scale, distributed, mechanistic sediment transport model to project future sediment erosion, deposition, and transportation within the Fraser River Basin in British Columbia, Canada—a basin with historical water flux and sediment load observations and limited anthropogenic influences upstream of its delta. The sediment model is driven by synthetic land‐surface hydrology derived from Scenarios A1B, A2, and B1 of the Special Report on Emissions Scenarios, which were provided by the Pacific Climate Impacts Consortium. Resulting simulations of water flux and sediment load from 1965 to 1994 are first validated against observational data then compared with future projections. Future projections show an overall increase in annual hillslope erosion and in‐channel transportation, a shift towards earlier spring peak erosion and transportation, and longer persistence of the sediment signal through the year. These shifts in timing and annual yield may have deleterious effects on spawning sockeye salmon and are insufficient to counteract future coastal retreat caused by sea‐level rise.     

An analytical solution for the transient response of saturated porous elastic solids

The general forms for the field equations governing the transient response of poroelastic media given by Biot and by Zienkiewicz are compared and relations between the material constants are obtained. A one-dimensional analytical solution is presented for the situation where the solid and fluid materials satisfy Biot'S dynamic compatibility relation. The transient response of porous media is illustrated for varying degrees of solid and fluid compressibility when subjected to step, cyclic and short duration spike surface tractions. The results obtained (for the special situation where the materials are dynamically compatible) exhibit the overall characteristics of wave propagation in porous media and will provide representative test problems which allow a quantitative evaluation of the accuracy of various numerical solution methods (e.g. finite element models).     

Pulsations in subdwarf B stars

Subdwarf B stars play a significant role in close binary evolution and in the hot star content of old stellar populations, in particular in giant elliptical galaxies. While the question of their origin poses several problems for stellar evolution theory, one of their most fascinating properties is the presence of multi-periodic 2–3 minute oscillations. Interpreting these oscillations optimally requires the correct identification of the modes. Partial identifications can be obtained using high-speed observations of radial velocity and colour variations. We review some of the several attempts to make such observations, most recently with the Multi-Site Spectroscopic Telescope campaign and withULTRACAM.     

A unique ultrarefractory inclusion from the Murchison meteorite

Abstract— Through freeze-thaw disaggregation of the Murchison meteorite, we have recovered a refractory inclusion, HIB-11, that is unique in terms of its texture, mineral compositions, and bulk composition. It consists of anhedral, Y-rich (1.6 wt% Y₂O₃) perovskite and lathlike spinel grains enclosed in a matrix of fine-grained, Sc-rich (10.5 wt% SC₂O₃ avg.), Ti-rich (12.6 wt% TiO₂ avg., reporting all Ti as TiO₂) clinopyroxene. The chondrite-normalized rare earth element (REE) pattern is complex, with light REE (LREE) at ～10× C1, abundances increasing from Gd through Ho (the latter at ～10⁴× C1), decreasing through Yb at 200× C1, and Lu at ～400× C1. The pattern reflects several stages of high-temperature volatility fractionation. Removal of Lu and Er from the source gas in the first condensation event was followed by partial to complete removal of the somewhat less refractory heavy REE, Gd through Ho, in the HIB-11 precursors by condensation from the fractionated residual gas in a second event. Both of these events probably reflect condensation of REE into ZrO₂ or a mixed Zr-, Sc-, Ti-, Y-oxide at temperatures too high for hibonite stability. A second, lower-temperature component, which was subsequently added, had fractionated (Nd-poor, Ce-rich) LREE abundances that resulted from condensation from a gas that had undergone prior removal of the more refractory LREE, resulting in enrichment in Ce and the most volatile REE, Eu and Yb. The aggregate was then melted and quickly cooled, forming a fine-grained spherule. This is the first reported inclusion in which the two most refractory REE, Lu and Er, are strongly fractionated from the other REE. An absence of mass fractionation among the Ti isotopes indicates that HIB-11 is not an evaporative residue, implying that volatility fractionation of trace elements took place during condensation. The fact that the two most refractory heavy REE could be separated from the other, only slightly less refractory heavy REE suggests that a wide variety of REE patterns is possible, and that ultrarefractory inclusions with other unusual REE patterns, important recorders of nebular condensation, may yet be discovered.     

Storylines: an alternative approach to representing uncertainty in physical aspects of climate change

Investigating the relationships between climate extremes and crop yield can help us understand how unfavourable climatic conditions affect crop production. In this study, two statistical models, multiple linear regression and random forest, were used to identify rainfall extremes indices affecting wheat yield in three different regions of the New South Wales wheat belt. The results show that the random forest model explained 41–67% of the year-to-year yield variation, whereas the multiple linear regression model explained 34–58%. In the two models, 3-month timescale standardized precipitation index of Jun.–Aug. (SPI_JJA), Sep.–Nov. (SPI_SON), and consecutive dry days (CDDs) were identified as the three most important indices which can explain yield variability for most of the wheat belt. Our results indicated that the inter-annual variability of rainfall in winter and spring was largely responsible for wheat yield variation, and pre-growing season rainfall played a secondary role. Frequent shortages of rainfall posed a greater threat to crop growth than excessive rainfall in eastern Australia. We concluded that the comparison between multiple linear regression and machine learning algorithm proposed in the present study would be useful to provide robust prediction of yields and new insights of the effects of various rainfall extremes, when suitable climate and yield datasets are available.     

The nonillusory effects of neoliberalisation: Linking geographies of poverty, inequality, and violence

This paper steps into recent debates concerning the (f)utility of neoliberalism as an ‘actually existing’ concept by reminding the reader that without a Marxian political economy approach, one that specifically includes neoliberalisation as part of its theoretical edifice, we run the risk of obfuscating the reality of capitalism’s festering poverty, rising inequality, and ongoing geographies of violence as something unknowable and ‘out there’. By failing to acknowledge such nonillusory effects of neoliberalisation and refusing the explanatory power neoliberalism holds in relating similar constellations of experiences across space as a potential basis for emancipation, we precipitously ensure the prospect of a violent future.     

Hydrogen incorporation in enstatite in the system MgO–SiO2–H2O–NaCl

The incorporation of hydrogen in enstatite in a hydrous system containing various amounts of NaCl was investigated at 25 kbar. The hydrogen content in enstatite shows a clear negative correlation to the NaCl-concentration in the system. The most favourable explanation is the reduction of water fugacity due to dilution. Other reasons for the limited hydrogen incorporation at high NaCl levels, such as a significant influence of Na⁺ on the defect chemistry or an exchange between OH^- and Cl⁻in enstatite, appear much less important. A partition coefficient D _Na ^En/Fluid = 0.0013 could be determined, demonstrating that Na is less incompatible in enstatite than H. The new results support the idea that dissolved components have to be considered when the total hydrogen storage capacity in nominally anhydrous minerals is estimated, especially in geological settings with high levels of halogens, such as subduction zones.     

Ti-in-zircon thermometry: applications and limitations

The titanium concentrations of 484 zircons with U-Pb ages of ∼1 Ma to 4.4 Ga were measured by ion microprobe. Samples come from 45 different igneous rocks (365 zircons), as well as zircon megacrysts (84) from kimberlite, Early Archean detrital zircons (32), and zircon reference materials (3). Samples were chosen to represent a large range of igneous rock compositions. Most of the zircons contain less than 20 ppm Ti. Apparent temperatures for zircon crystallization were calculated using the Ti-in-zircon thermometer (Watson et al. 2006, Contrib Mineral Petrol 151:413–433) without making corrections for reduced oxide activities (e.g., TiO₂ or SiO₂), or variable pressure. Average apparent Ti-in-zircon temperatures range from 500° to 850°C, and are lower than either zircon saturation temperatures (for granitic rocks) or predicted crystallization temperatures of evolved melts (∼15% melt residue for mafic rocks). Temperatures average: 653 ± 124°C (2 standard deviations, 60 zircons) for felsic to intermediate igneous rocks, 758 ± 111°C (261 zircons) for mafic rocks, and 758 ± 98°C (84 zircons) for mantle megacrysts from kimberlite. Individually, the effects of reduced or , variable pressure, deviations from Henry’s Law, and subsolidus Ti exchange are insufficient to explain the seemingly low temperatures for zircon crystallization in igneous rocks. MELTs calculations show that mafic magmas can evolve to hydrous melts with significantly lower crystallization temperature for the last 10–15% melt residue than that of the main rock. While some magmatic zircons surely form in such late hydrous melts, low apparent temperatures are found in zircons that are included within phenocrysts or glass showing that those zircons are not from evolved residue melts. Intracrystalline variability in Ti concentration, in excess of analytical precision, is observed for nearly all zircons that were analyzed more than once. However, there is no systematic change in Ti content from core to rim, or correlation with zoning, age, U content, Th/U ratio, or concordance in U-Pb age. Thus, it is likely that other variables, in addition to temperature and , are important in controlling the Ti content of zircon. The Ti contents of igneous zircons from different rock types worldwide overlap significantly. However, on a more restricted regional scale, apparent Ti-in-zircon temperatures correlate with whole-rock SiO₂ and HfO₂ for plutonic rocks of the Sierra Nevada batholith, averaging 750°C at 50 wt.% SiO₂ and 600°C at 75 wt.%. Among felsic plutons in the Sierra, peraluminous granites average 610 ± 88°C, while metaluminous rocks average 694 ± 94°C. Detrital zircons from the Jack Hills, Western Australia with ages from 4.4 to 4.0 Ga have apparent temperatures of 717 ± 108°C, which are intermediate between values for felsic rocks and those for mafic rocks. Although some mafic zircons have higher Ti content, values for Early Archean detrital zircons from a proposed granitic provenance are similar to zircons from many mafic rocks, including anorthosites from the Adirondack Mts (709 ± 76°C). Furthermore, the Jack Hills zircon apparent Ti-temperatures are significantly higher than measured values for peraluminous granites (610 ± 88°C). Thus the Ti concentration in detrital zircons and apparent Ti-in-zircon temperatures are not sufficient to independently identify parent melt composition. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.