Fractionation of oxygen isotopes in phosphate during its interactions with iron oxides

Iron (III) oxides are ubiquitous in near-surface soils and sediments and interact strongly with dissolved phosphates via sorption, co-precipitation, mineral transformation and redox-cycling reactions. Iron oxide phases are thus, an important reservoir for dissolved phosphate, and phosphate bound to iron oxides may reflect dissolved phosphate sources as well as carry a history of the biogeochemical cycling of phosphorus (P). It has recently been demonstrated that dissolved inorganic phosphate (DIP) in rivers, lakes, estuaries and the open ocean can be used to distinguish different P sources and biological reaction pathways in the ratio of ¹⁸O/¹⁶O (δ¹⁸O_P) in PO₄³⁻. Here we present results of experimental studies aimed at determining whether non-biological interactions between dissolved inorganic phosphate and solid iron oxides involve fractionation of oxygen isotopes in PO₄. Determination of such fractionations is critical to any interpretation of δ¹⁸O_P values of modern (e.g., hydrothermal iron oxide deposits, marine sediments, soils, groundwater systems) to ancient and extraterrestrial samples (e.g., BIF’s, Martian soils). Batch sorption experiments were performed using varied concentrations of synthetic ferrihydrite and isotopically-labeled dissolved ortho-phosphate at temperatures ranging from 4 to 95 °C. Mineral transformations and morphological changes were determined by X-Ray, Mössbauer spectroscopy and SEM image analyses.Our results show that isotopic fractionation between sorbed and aqueous phosphate occurs during the early phase of sorption with isotopically-light phosphate (P¹⁶O₄) preferentially incorporated into sorbed/solid phases. This fractionation showed negligible temperature-dependence and gradually decreased as a result of O-isotope exchange between sorbed and aqueous-phase phosphate, to become insignificant at greater than ∼100 h of reaction. In high-temperature experiments, this exchange was very rapid resulting in negligible fractionation between sorbed and aqueous-phase phosphate at much shorter reaction times. Mineral transformation resulted in initial preferential desorption/loss of light phosphate (P¹⁶O₄) to solution. However, the continual exchange between sorbed and aqueous PO₄, concomitant with this mineralogical transformation resulted again in negligible fractionation between aqueous and sorbed PO₄ at long reaction times (>2000 h). This finding is consistent with results obtained from natural marine samples. Therefore, ¹⁸O values of dissolved phosphate (DIP) in sea water may be preserved during its sorption to iron-oxide minerals such as hydrothermal plume particles, making marine iron oxides a potential new proxy for dissolved phosphate in the oceans.     

Soil water content in southern England derived from a cosmic‐ray soil moisture observing system – COSMOS‐UK

Cosmic‐ray soil moisture sensors have the advantage of a large measurement footprint (approximately 700 m in diameter) and are able to operate continuously to provide area‐averaged near‐surface (top 10–20 cm) volumetric soil moisture content at the field scale. This paper presents the application of this technique at four sites in southern England over almost 3 years. Results show the soil moisture response to contrasting climatic conditions during 2011–2014 and are the first such field‐scale measurements made in the UK. These four sites are prototype stations for a UK COsmic‐ray Soil Moisture Observing System, and particular consideration is given to sensor operating conditions in the UK. Comparison of these soil water content observations with the Joint UK Land Environment Simulator 10‐cm soil moisture layer shows that these data can be used to test and diagnose model performance and indicate the potential for assimilation of these data into hydro‐meteorological models. The application of these large‐area soil water content measurements to evaluate remotely sensed soil moisture products is also demonstrated. Numerous applications and the future development of a national COsmic‐ray Soil Moisture Observing System network are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

��A�䨡 lava flows in the Deccan Volcanic Province, India, and their significance for the nature of continental flood basalt eruptions

Newly identified ??a?? lava flows outcrop intermittently over an area of ~110?km² in the western Deccan Volcanic Province (DVP), India. They occur in the upper Thakurvadi Formation in the region south of Sangamner. The flows, one of which is compound, are 15?C25?m thick, and exhibit well-developed basal and flow-top breccias. The lavas have microcrystalline groundmasses and are porphyritic or glomerocrystic and contain phenocrysts of olivine, clinopyroxene or plagioclase feldspar. They are chemically similar to compound p??hoehoe flows at a similar stratigraphic horizon along the Western Ghats. Petrographic and geochemical differences between ??a?? flows at widely spaced outcrops at the same stratigraphic horizon suggest that they are the product of several eruptions, potentially from different sources. Their presence in the DVP could suggest relative proximity to vents. This discovery is significant because ??a?? lavas are generally scarce in large continental flood basalt provinces, which typically consist of numerous inflated compound p??hoehoe lobes and sheet lobes. Their scarcity is intriguing, and may relate to either their occurrence only in poorly preserved or exposed proximal areas or to the flat plateau-like topography of flood basalt provinces that may inhibit channelization and ??a?? formation, or both. In this context, the ??a?? flow fields described here are inferred to be the products of eruptions that produced unusually high-effusion-rate lavas compared to typical flood basalt eruptions. Whether these phases were transitional to lower intensity, sustained eruptions that fed extensive low effusion rate p??hoehoe flow fields remains unclear.     

Vegetation-related dry deposition of global PM2.5 from satellite observations

Journal of Geographical Sciences - Vegetation plays an important role in the dry deposition of particles with significant spatial variability, but the magnitude remains unclear at the global scale....     

A multi-criteria evaluation model of earthquake vulnerability in Victoria,British Columbia

Researchers have recently examined the geographic variability of the vulnerability of populations to earthquakes. These studies focus mainly on the complex modelling of geophysical processes or identification of socio-economically disadvantaged populations. However, no studies to date have integrated different components of vulnerability with metrics of travel distance to hospitals and trauma centres (systemic vulnerability). We argue that this previously unaccounted component is an important conceptual and practical aspect of earthquake vulnerability. Accordingly, this paper presents a multi-criteria model for combining physical, social, and systemic components, moving towards a more comprehensive assessment of vulnerability. An analytic hierarchy process is used to produce a place-specific index of social vulnerability, which we combine with soil liquefaction and amplification index and a road network model for access to hospitals and trauma services. Using a geographic information system, we implemented this model for the Greater Victoria region (483 km², 2011 population: 345,000) in British Columbia, Canada. Clustering of total vulnerability was found in outlying areas, highlighting the importance of access to trauma centres. We conclude by identifying challenges in measuring earthquake vulnerability and advocate integration of systemic vulnerability components in natural hazards research.     

Stable isotope evidence for magmatic fluid input during large-scale Na–Ca alteration in the Cloncurry Fe oxide Cu–Au district, NW Queensland, Australia

Sodic–calcic alteration is common in mineralized hydrothermal systems, yet the relative importance of igneous vs. basinal fluid sources remains controversial. One of the most extensive volumes of sodic–calcic rocks occurs near Cloncurry, NW Queensland, and was formed by overlapping hydrothermal systems that were active synchronously with emplacement of mid‐crustal batholithic granitoids (c. 1.55–1.50 Ga). Altered rocks contain albite–oligoclase, actinolite, diopside, titanite and magnetite. Alteration was localized by: (A) composite veins and breccias containing crystallized magma intimately intergrown with hydrothermal precipitates; (B) intrusions that host setting A veins and breccias; and (C) extensive breccia and vein systems linked to regional fault systems. Isotope analyses of actinolites in settings A and B indicate calculated δ¹⁸O_H2O (+8.2 to +10.6‰) and variably depleted δD_H2O (?130 to ?54‰) compared with typical magmatic fluids, whereas those from setting C typically indicate calculated δ¹⁸O_H2O (+8.0 to +12.8‰) and δD_H2O (?29 to ?99‰). The lowest δD_H2O values are interpreted as representing residual fluids after significant (> 90%) open‐system magmatic degassing. Overall the stable isotope, field, geochronological and geobarometric data suggest that these sodic–calcic alteration systems were formed by the episodic incursion of magmatic fluids that underwent minor isotopic modification as a result of varying degrees of interaction with country rocks.