Models of solar irradiance variations: Current status     

Natalie A. Krivova  Sami K. Solanki 《Journal of Astrophysics and Astronomy》2008,29(1-2):151-158

Regular monitoring of solar irradiance has been carried out since 1978 to show that solar total and spectral irradiance varies at different time scales. Whereas variations on time scales of minutes to hours are due to solar oscillations and granulation, variations on longer time scales are driven by the evolution of the solar surface magnetic field. Here the most recent advances in modelling of solar irradiance variations on time scales longer than a day are briefly reviewed.  相似文献   

Sinks of iron and manganese in underground coal mine workings     

Natalie?A.?S.?KruseEmail author  Paul?L.?Younger 《Environmental Geology》2009,57(8):1893-1899

The sources and sinks of manganese in underground coal mine workings are poorly understood compared to those of iron. The geochemical system in the secondary egress drift of Caphouse Colliery near Horbury, UK, is an ideal system for studying these processes. Five locations along the drift and four secondary inflows to the drift were sampled 24 times through the year commencing May 2005. During the sampling period, the pH in the main channel varied from 6.73 to 7.93 and increased along the flow path. The secondary inflows to the drift from the strata were of higher alkalinity (mean = 385 mg/L as CaCO₃) than the main flow (mean = 330 mg/L as CaCO₃); the affects of mixing between the less alkaline main channel and the more alkaline secondary inflows and of carbon dioxide exsolution are evident in the form of carbonate and hydroxide precipitates. SEM and XRD analysis of precipitates collected from the drift confirm the presence of calcium and manganese carbonates and ferric hydroxide. PHREEQC speciation and solubility modelling confirms supersaturation of the water in the main channel with respect to ferric oxy-hydroxides; iron, manganese, magnesium and calcium carbonates; and manganese oxides. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Shock-induced kelyphite formation in the core of a complex impact crater     

Natalie?DesetaEmail author  Suporn?Boonsue  Roger?L.?Gibson  John?G.?Spray 《Contributions to Mineralogy and Petrology》2017,172(10):84

We present a compositional and textural analysis of shock-induced microtextures in garnet porphyroblasts in migmatitic garnet–cordierite–biotite paragneisses from the centre of the Vredefort impact structure, South Africa. Detailed imaging and major element analysis of deformation features in, and adjacent to, the garnet porphyroblasts record a complex, heterogeneous distribution of shock effects at the microscale. As the most competent silicate mineral in the assemblage, with the highest Hugoniot Elastic Limit and a wide pressure–temperature stability field, the porphyroblastic garnet preserves a more diverse shock deformation response compared to minerals such as quartz and feldspar, which underwent more comprehensive shock metamorphism and subsequent annealing. The garnet porphyroblasts display pre-impact fractures that are overprinted by later intra-granular Hertzian and distinctive planar fractures associated with the impact event. Shock-induced strain localization occurred along internal slip planes and defects, including pre-existing fractures and inclusion boundaries in the garnet. Symplectitic (kelyphitic) coronas commonly enclose the garnet porphyroblasts, and inhabit intra-granular fractures. The kelyphite assemblage in fractures with open communication beyond garnet grain boundaries is characterized by orthopyroxene—cordierite—sapphirine. Conversely, the kelyphite assemblage in closed-off intra-granular fractures is highly variable, comprising spatially restricted combinations of a secondary garnet phase with a majoritic component, Al-rich orthopyroxene, sapphirine and cordierite. The impedance contrast between garnet porphyroblasts and their inclusions further facilitated the formation of shock-induced features (Al-rich orthopyroxene coronas). Together, the textural and mineralogical data suggest that these features provide a record of oscillatory shock perturbations initiated under confining pressure beneath the transient crater floor. This occurred as the shocked rock volume underwent post-shock expansion, forming the core of the central uplift, and was followed by variable textural re-equilibration. This study thus provides a microtextural and mineralogical perspective of the shock regime within confined crust immediately prior to and during central uplift formation.  相似文献   

Sampling soil water along the pF curve for δ2H and δ18O analysis     

Natalie Orlowski  Lutz Breuer 《水文研究》2020,34(25):4959-4972

Soil water stable isotopes are widely used across disciplines (e.g., hydrology, ecology, soil science, and biogeochemistry). However, the full potential of stables isotopes as a tool for characterizing the origin, flow path, transport processes and residence times of water in different eco-, hydro-, and geological compartments has not yet been exploited. This is mainly due to the large variety of different methods for pore water extraction. While recent work has shown that matric potential affects the equilibrium fractionation, little work has examined how different water retention characteristics might affect the sampled water isotopic composition. Here, we present a simple laboratory experiment with two well-studied standard soils differing in their physico-chemical properties (e.g., clayey loam and silty sand). Samples were sieved, oven-dried and spiked with water of known isotopic composition to full saturation. For investigating the effect of water retention characteristics on the extracted water isotopic composition, we used pressure extractors to sample isotopically labelled soil water along the pF curve. After pressure extraction, we further extracted the soil samples via cryogenic vacuum extraction. The null hypothesis guiding our work was that water held at different tensions shows the same isotopic composition. Our results showed that the sampled soil water differed isotopically from the introduced isotopic label over time and sequentially along the pF curve. Our and previous studies suggest caution in interpreting isotope results of extracted soil water and a need to better characterize processes that govern isotope fractionation with respect to soil water retention characteristics. In the future, knowledge about soil water retention characteristics with respect to soil water isotopic composition could be applied to predict soil water fractionation effects under natural and non-stationary conditions. In this regard, isotope retention characteristics as an analog to water retention characteristics have been proposed as a way forward since matric potential affects the equilibrium fractionation between the bound water and the water vapour.  相似文献   

Molybdenum Mass Fractions and Stable Isotope Compositions of Sedimentary Carbonate and Silicate Reference Materials     

Natalie Gaspers  Tom&#x; Magna  Luk&#x; Ackerman 《Geostandards and Geoanalytical Research》2020,44(2):363-374

A double‐spike method in combination with MC‐ICP‐MS was applied to obtain molybdenum (Mo) mass fractions and stable isotope compositions in a suite of sedimentary silicate (marine, lake, stream, estuarine, organic‐rich sediment, shales, slate, chert) and carbonate reference materials (coral, dolomite, limestones, carbonatites), and a manganese nodule reference material, poorly characterised for stable Mo isotope compositions. The Mo contents vary between 0.076 and 364 μg g^?1, with low‐Mo mass fractions (< 0.29 μg g^?1) found almost exclusively in carbonates. Intermediate Mo contents (0.73–2.70 μg g^?1) are reported for silicate sediments, with the exception of chert JCh‐1 (0.24 μg g^?1), organic‐rich shale SGR‐1b (36.6 μg g^?1) and manganese nodule NOD‐A‐1 (364 μg g^?1). The Mo isotope compositions (reported as δ⁹⁸Mo relative to NIST SRM 3134) range from ?1.77 to 1.03‰, with the intermediate precision varying between ± 0.01 and ± 0.12‰ (2s) for most materials. Low‐temperature carbonates show δ⁹⁸Mo values ranging from 0.21 to 1.03‰ whereas δ⁹⁸Mo values of ?1.77 and ?0.17‰ were obtained for carbonatites CMP‐1 and COQ‐1, respectively. Silicate materials have δ⁹⁸Mo values varying from ?1.56 to 0.73‰. The range of δ⁹⁸Mo values in reference materials may thus reflect the increasingly important relevance of Mo isotope investigations in the fields of palaeoceanography, weathering, sedimentation and provenance, as well as the magmatic realm.  相似文献   

The stable isotopes of natural waters at the Marcell Experimental Forest     

Jonathan M. Stelling  Stephen D. Sebestyen  Natalie A. Griffiths  Carl P. J. Mitchell  Mark B. Green 《水文研究》2021,35(10):e14336

We present a new data set from the Marcell Experimental Forest (MEF) that compiles water isotope measurements from multiple research catchments, some of which have been studied since the 1960s. The MEF is located in northern Minnesota, USA, and is home to heavily studied and monitored forests, streams, bogs, and fens. Peat-forming systems (bogs and fens) are an important component of the MEF landscape and have a profound impact on the water cycle in these catchments. Within the last decade, analysis of stable isotopes of water (expressed as δD and δ¹⁸O) has been implemented to characterize the different components of the water budget, and to allow researchers to look at catchment and peatland-specific hydrologic effects in the watershed. This δD and δ¹⁸O data set of natural waters from MEF catchments is primarily composed of measurements from three peatlands (S1, S2, S6) during an 11-year period. More recently collection and analysis were expanded to also include samples from the Spruce and Peatland Responses Under Changing Environments (SPRUCE) project in the S1 bog, peatlands S3, S4, S5, as well as nearby lakes. We establish a local meteoric water line by analyzing the isotopic composition of precipitation, which fills a void in regional meteoric water lines for Minnesota. Furthermore, we establish baseline isotopic composition for bog outlet streams, bog porewater, aquifer groundwater, overland flow, subsurface stormflow, and snowpack, as well as runoff from the SPRUCE experimental chambers. These data are publicly available and will be expanded upon in the future.  相似文献   

The value of recreational fishing in the Great Barrier Reef, Australia: A pooled revealed preference and contingent behaviour model   总被引：2，自引：0，他引：2  

Prabha Prayaga  John Rolfe  Natalie Stoeckl   《Marine Policy》2010,34(2):244-251

Given the focus on protecting natural assets in the Great Barrier Reef Marine Park in Australia, it is important for managers and policy makers to understand the value of recreational fishing in the area, and how changes in management may affect those recreational values. Travel cost methods were used to estimate the value of recreational fishing in the Capricorn Coast in Central Queensland using data from on-site surveys conducted at boat ramps. The study also uses contingent behaviour models to estimate the change in the value of recreational fishing as conditions vary. Results indicate that there are high values associated with recreational fishing activity along the Capricorn Coast, and that the demand for recreational fishing is inelastic and that values are relatively insensitive to changes in catch rates.  相似文献   

Staying cool in a changing climate: Reaching vulnerable populations during heat events   总被引：1，自引：0，他引：1  

Natalie R. Sampson  Carina J. Gronlund  Miatta A. Buxton  Linda Catalano  Jalonne L. White-Newsome  Kathryn C. Conlon  Marie S. O’Neill  Sabrina McCormick  Edith A. Parker 《Global Environmental Change》2013,23(2):475-484

The frequency and intensity of hot weather events are expected to increase globally, threatening human health, especially among the elderly, poor, and chronically ill. Current literature indicates that emergency preparedness plans, heat health warning systems, and related interventions may not be reaching or supporting behavior change among those most vulnerable in heat events. Using a qualitative multiple case study design, we comprehensively examined practices of these populations to stay cool during hot weather (“cooling behaviors”) in four U.S. cities with documented racial/ethnic and socio-economic disparities and diverse heat preparedness strategies: Phoenix, Arizona; Detroit, Michigan; New York City, New York; and Philadelphia, Pennsylvania. Based on semi-structured in-depth interviews we conducted with 173 community members and organizational leaders during 2009–2010, we assessed why vulnerable populations do or do not participate in health-promoting behaviors at home or in their community during heat events, inquiring about perceptions of heat-related threats and vulnerability and the role of social support. While vulnerable populations often recognize heat's potential health threats, many overlook or disassociate from risk factors or rely on experiences living in or visiting warmer climates as a protective factor. Many adopt basic cooling behaviors, but unknowingly harmful behaviors such as improper use of fans and heating and cooling systems are also adopted. Decision-making related to commonly promoted behaviors such as air conditioner use and cooling center attendance is complex, and these resources are often inaccessible financially, physically, or culturally. Interviewees expressed how interpersonal, intergenerational relationships are generally but not always protective, where peer relationships are a valuable mechanism for facilitating cooling behaviors among the elderly during heat events. To prevent disparities in heat morbidity and mortality in an increasingly changing climate, we note the implications of local context, and we broadly inform heat preparedness plans, interventions, and messages by sharing the perspectives and words of community members representing vulnerable populations and leaders who work most closely with them.  相似文献   

Igneous and shock processes affecting chassignite amphibole evaluated using chlorine/water partitioning and hydrogen isotopes          下载免费PDF全文

Paul A. Giesting  Susanne P. Schwenzer  Justin Filiberto  Natalie A. Starkey  Ian A. Franchi  Allan H. Treiman  Andy G. Tindle  Monica M. Grady 《Meteoritics & planetary science》2015,50(3):433-460

Amphibole in chassignite melt inclusions provides valuable information about the volatile content of the original interstitial magma, but also shock and postshock processes. We have analyzed amphibole and other phases from NWA 2737 melt inclusions, and we evaluate these data along with published values to constrain the crystallization Cl and H₂O content of phases in chassignite melt inclusions and the effects of shock on these amphibole grains. Using a model for the Cl/OH exchange between amphibole and melt, we estimate primary crystallization OH contents of chassignite amphiboles. SIMS analysis shows that amphibole from NWA 2737 currently has 0.15 wt% H₂O. It has lost ~0.6 wt% H₂O from an initial 0.7–0.8 wt% H₂O due to intense shock. Chassigny amphibole had on average 0.3–0.4 wt% H₂O and suffered little net loss of H₂O due to shock. NWA 2737 amphibole has δD ≈ +3700‰; it absorbed Martian atmosphere‐derived heavy H in the aftermath of shock. Chassigny amphibole, with δD ≤ +1900‰, incorporated less heavy H. Low H₂O/Cl ratios are inferred for the primitive chassignite magma, which had significant effects on melting and crystallization. Volatiles released by the degassing of Martian magma were more Cl‐rich than on Earth, resulting in the high Cl content of Martian surface materials.  相似文献   

Neoliberalism,Mineral Development and Indigenous People: a framework for analysis     

Cathy Howlett  Monica Seini  Diana McCallum  Natalie Osborne 《The Australian geographer》2011,42(3):309-323

There have been suggestions in recent literature that neoliberalism and globalisation present positive opportunities for Indigenous communities engaging in resource development projects on their traditional lands. This paper will present evidence from preliminary research on the neoliberal restructuring that has endured for those Indigenous communities of Queensland who have engaged with mineral development opportunities. Initial findings indicate that the State has devolved some of its responsibilities to the mining company in relation to Indigenous development and service provision. This paper develops a theoretical and analytical framework to enable an examination of the implications of this voluntary devolution of responsibility for Indigenous development and service provision and questions whether this represents a positive opportunity for Indigenous people in the region.  相似文献