The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Sophie Opfergelt - One of the best experts on this subject based on the ideXlab platform.
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Soil redistribution and Weathering controlling the fate of geochemical and physical carbon stabilization mechanisms in Soils of an eroding landscape
Biogeosciences, 2014Co-Authors: Sophie Opfergelt, Sebastian Doetterl, Jeanthomas Cornelis, Johan Six, Samuel Bode, Pascal Boeckx, K Van OostAbstract:The role of eroding landscapes in organic carbon stabilization operating as C sinks or sources has been fre- quently discussed, but the underlying mechanisms are not fully understood. Our analysis aims to clarify the effects of Soil redistribution on physical and biogeochemical Soil or- ganic carbon (SOC) stabilization mechanisms along a hills- lope transect. The observed mineralogical differences seem partly responsible for the effectiveness of geochemical and physical SOC stabilization mechanisms as the mineral envi- ronment along the transect is highly variable and dynamic. The abundance of primary and secondary minerals and the Weathering status of the investigated Soils differ drastically along this transect. Extractable iron and aluminum compo- nents are generally abundant in aggregates, but show no strong correlation to SOC, indicating their importance for aggregate stability but not for SOC retention. We further show that pyrophosphate extractable Soil components, es- pecially manganese, play a role in stabilizing SOC within non-aggregated mineral fractions. The abundance of micro- bial residues and measured 14 C ages for aggregated and non- aggregated SOC fractions demonstrate the importance of the combined effect of geochemical and physical protection to stabilize SOC after burial at the depositional site. Mineral alteration and the breakdown of aggregates limit the protec- tion of C by minerals and within aggregates temporally. The 14 C ages of buried Soil indicate that C in aggregated frac- tions seems to be preserved more efficiently while C in non- aggregated fractions is released, allowing a re-sequestration of younger C with this fraction. Old 14 C ages and at the same time high contents of microbial residues in aggregates sug- gest either that microorganisms feed on old carbon to build up microbial biomass or that these environments consisting of considerable amounts of old C are proper habitats for mi- croorganisms and preserve their residues. Due to continuous Soil Weathering and, hence, weakening of protection mecha- nisms, a potential C sink through Soil burial is finally tempo- rally limited.
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silicon isotopes and the tracing of desilication in volcanic Soil Weathering sequences guadeloupe
Chemical Geology, 2012Co-Authors: Sophie Opfergelt, R B Georg, Bruno Delvaux, Y M Cabidoche, Kevin W Burton, Alex N HallidayAbstract:Abstract Silicon (Si) stable isotopes have the potential to become a useful Weathering proxy, given that light Si isotopes are preferentially incorporated into secondary clay minerals. Here we investigate how Si depletion in Soils and associated clay mineralogy influence the Si isotope fractionation associated with clay mineral formation. We report δ 30 Si compositions in bulk Soils and clay fractions relative to their parent andesite in three Soil Weathering sequences from Guadeloupe that were formed under contrasting climatic conditions. Strongly desilicated Soils containing kaolinite that formed in wet areas (high precipitation) are compared with less desilicated Soils containing smectite formed in drier conditions (low precipitation). Clay fractions are isotopically lighter than the parent andesite (δ 30 Si-0.23‰), and increasingly lighter with Si depletion in Soils, which supports the view that the Si isotope composition in secondary clay fractions is controlled by the degree of Soil desilication. It is shown that the Si isotope fractionation factor between the parent silicate material and the secondary clay minerals is smaller for Si-rich secondary clay minerals such as smectite and larger for Si-poor secondary clay minerals such as kaolinite. This study provides new insights to better define Si isotopes as a proxy for environmental conditions for clay neoformation.
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mechanisms of magnesium isotope fractionation in volcanic Soil Weathering sequences guadeloupe
Earth and Planetary Science Letters, 2012Co-Authors: Sophie Opfergelt, R B Georg, Bruno Delvaux, Y M Cabidoche, Kevin W Burton, Alex N HallidayAbstract:Magnesium (Mg) stable isotopes are increasingly used as a Weathering proxy in Soils and rivers, but the impact of the mineralogy of secondary phases on isotopefractionation remains obscure. A better understanding of the behaviour of Mg isotopes during Weathering processes is a mandatory step toward deployment of this new tracer for understanding chemical fluxes exported from the critical zone. Here we investigate isotopic variations in δ26Mg in bulk Soils and clay fractions relative to their parent andesite in three SoilWeatheringsequences from Guadeloupe formed under contrasting climatic conditions. Soils formed in drier conditions (low precipitation) contain smectite, whereas Soils formed under wet conditions (high rainfall) are characterized by halloysite and Fe-oxides or kaolinite. All clay fractions have Mg isotopic compositions (δ26Mg −0.41‰ to −0.10‰) similar to or heavier than their parent andesite (δ26Mg −0.47‰) supporting the preferential incorporation of heavy Mg isotopes in secondary Mg-bearing clay minerals with the first direct measurements on clay fractions. Soils with lighter Mg isotope compositions have greater quantities of exchangeable Mg. The data support a contribution from sea spray to the exchangeable Mg pool correlated to the SoilWeathering degree. This study highlights for the first time that the Soil δ26Mg not only depend on δ26Mg of the parent rock, and on any fractionation that might occur, but also on the Mg retention on the exchange complex, which could in turn be controlled by external inputs such as sea spray.
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impact of Soil Weathering degree on silicon isotopic fractionation during adsorption onto iron oxides in basaltic ash Soils cameroon
Geochimica et Cosmochimica Acta, 2009Co-Authors: Sophie Opfergelt, G De Bournonville, Damien Cardinal, Luc Andre, Severine Delstanche, Bruno DelvauxAbstract:The sequestration of silicon in Soil clay-sized iron oxides may affect the terrestrial cycle of Si. Iron oxides indeed specifically adsorb aqueous monosilicic acid (H4SiO40), thereby influencing Si concentration in Soil solution. Here we study the impact of H4SiO40 adsorption on the fractionation of Si isotopes in basaltic ash Soils differing in Weathering degree (from two Weathering sequences, Cameroon), hence in clay and Fe-oxide contents, and evaluate the potential isotopic impact on dissolved Si in surrounding Cameroon rivers. Adsorption was measured in batch experiment series designed as function of time (0-72 h) and initial concentration (ic) of Si in solution (0.61-1.18 mM) at 20 degrees C, constant pH (5.5) and ionic strength (I mM). After various Soil-solution contact times, the delta Si-30 vs. NBS28 compositions were determined in selected solutions by MC-ICP-MS (Nu Plasma) in medium resolution, operating in dry plasma with Mg doping with an average precision of +/-0.15 parts per thousand (+/-2 sigma(SEM)). The quantitative adsorption of H4SiO40 by Soil Fe-oxides left a solution depleted in light Si isotopes, which confirms previous study on synthetic Fe-oxides. Measured against its initial composition (delta Si-30 = +0.02 +/- 0.07 parts per thousand (+/-2 sigma(SD))), the solutions were systematically enriched in Si-30 reaching maximum delta Si-30 values ranging between +0.16 parts per thousand and +0.95 parts per thousand after 72 h contact time. The enrichment of the solution in heavy isotopes increased with increasing values of three parameters: Soil Weathering degree, iron oxide content, and proportion of short-range ordered Fe-oxide. The Si-isotopic signature of the solution was partly influenced by Si release, possibly through mineral dissolution and Si desorption from oxide surfaces, depending on Soil type, highlighting the complex pattern of natural Soils. Surrounding Cameroon rivers displayed a mean Si-isotopic signature of +1.19 parts per thousand. Our data imply that in natural environments, H4SiO40 adsorption by Soil clay-sized Fe-oxides at least partly impacts the Si-isotopic signature of the Soil solution exported to water streams. (C) 2009 Elsevier Ltd. All rights reserved.
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the reserve of weatherable primary silicates impacts the accumulation of biogenic silicon in volcanic ash Soils
Biogeochemistry, 2008Co-Authors: Celine Henriet, Sophie Opfergelt, N De Jaeger, Marc Dorel, Bruno DelvauxAbstract:Banana plantlets (Musa acuminata cv Grande Naine) cultivated in hydroponics take up silicon proportionally to the concentration of Si in the nutrient solution (0-1.66 mM Si). Here we study the Si status of banana plantlets grown under controlled greenhouse conditions on five Soils developed from andesitic volcanic ash, but differing in Weathering stage. The mineralogical composition of Soils was inferred from X-ray diffraction, elemental analysis and selective chemical/mineralogical extractions. With increasing Weathering, the content of weatherable primary minerals decreased. Conversely, clay content increased and stable secondary minerals were increasingly dominant: gibbsite, Fe oxides, allophane, halloysite and kaolinite. The contents of biogenic Si in plant and Soil were governed by the reserve of weatherable primary minerals. The largest concentrations of biogenic Si in plant (6.9-7 g kg(-1)) and Soil (50-58 g kg(-1)) occurred in the least weathered Soils, where total Si content was above 225 g kg(-1). The lowest contents of biogenic Si in plant (2.8-4.3 g kg(-1)) and Soil (8-31 g kg(-1)) occurred in the most weathered desilicated Soils enriched with secondary oxides and clay minerals. Our data imply that Soil Weathering stage directly impacted the Soil-to-plant transfer of silicon, and thereby the stock of biogenic Si in a Soil-plant system involving a Si-accumulating plant. They further imply that Soil type can influence the silicon Soil-plant cycle and its hydrological output.
Bruno Delvaux - One of the best experts on this subject based on the ideXlab platform.
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the Weathering stage of tropical Soils affects the Soil plant cycle of silicon but depending on land use
Geoderma, 2019Co-Authors: Charles Vander Linden, Bruno DelvauxAbstract:Abstract Plants take up silicon (Si) from Soil solution, and form biogenic silica bodies (phytoliths) that return to Soil with plant debris. Since phytolith dissolution releases plant available Si, the Soil-plant Si cycle tremendously influences the global Si cycle. Si plant uptake ranges from 0.7 to 1470 kg ha−1 year−1 among different terrestrial ecosystems depending on Soil properties and processes, climate, plant species, and management practices. The humid tropics shelter a huge variety of Soils. Many of them are strongly weathered and desilicated, and exhausted in plant nutrients. Nevertheless, these Soils support evergreen forests with the greatest biodiversity and biomass because of an intense pumping of nutrients. This pumping involves non-essential Si, and further governs the Soil-plant Si cycle, which is perturbed after converting forest area into cropland. Here, we used literature data quantifying the Si Soil-plant cycle in natural forest areas and croplands established on Soils that differ in Weathering stage. We particularly focused on comparing forest to Si-accumulating rice crop. We show that the impact of Soil Weathering stage on the Soil-plant Si cycle markedly differs depending on land use in the tropics. In slightly or moderately weathered Soils, cultivated plants take up Si in larger amounts than forest trees do, likely because the former are stimulated to pump nutrients and dissolve Si from less soluble lithogenic and pedogenic silicates. With increasing Soil Weathering and desilication, Si plant uptake increases in natural forest ecosystems while it decreases in cultivated ecosystems. Four factors may explain this discrepancy: (i) since they are more soluble than lithogenic and pedogenic silicates, phytoliths make the pool of plant available Si; (ii) forest litter, which is densely exploited by roots, is a place of intense mineral pumping; (iii) deep rooting of forest trees enhances pumping too; (iv) crop harvesting exports Si out of cultivated ecosystems.
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silicon isotopes and the tracing of desilication in volcanic Soil Weathering sequences guadeloupe
Chemical Geology, 2012Co-Authors: Sophie Opfergelt, R B Georg, Bruno Delvaux, Y M Cabidoche, Kevin W Burton, Alex N HallidayAbstract:Abstract Silicon (Si) stable isotopes have the potential to become a useful Weathering proxy, given that light Si isotopes are preferentially incorporated into secondary clay minerals. Here we investigate how Si depletion in Soils and associated clay mineralogy influence the Si isotope fractionation associated with clay mineral formation. We report δ 30 Si compositions in bulk Soils and clay fractions relative to their parent andesite in three Soil Weathering sequences from Guadeloupe that were formed under contrasting climatic conditions. Strongly desilicated Soils containing kaolinite that formed in wet areas (high precipitation) are compared with less desilicated Soils containing smectite formed in drier conditions (low precipitation). Clay fractions are isotopically lighter than the parent andesite (δ 30 Si-0.23‰), and increasingly lighter with Si depletion in Soils, which supports the view that the Si isotope composition in secondary clay fractions is controlled by the degree of Soil desilication. It is shown that the Si isotope fractionation factor between the parent silicate material and the secondary clay minerals is smaller for Si-rich secondary clay minerals such as smectite and larger for Si-poor secondary clay minerals such as kaolinite. This study provides new insights to better define Si isotopes as a proxy for environmental conditions for clay neoformation.
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mechanisms of magnesium isotope fractionation in volcanic Soil Weathering sequences guadeloupe
Earth and Planetary Science Letters, 2012Co-Authors: Sophie Opfergelt, R B Georg, Bruno Delvaux, Y M Cabidoche, Kevin W Burton, Alex N HallidayAbstract:Magnesium (Mg) stable isotopes are increasingly used as a Weathering proxy in Soils and rivers, but the impact of the mineralogy of secondary phases on isotopefractionation remains obscure. A better understanding of the behaviour of Mg isotopes during Weathering processes is a mandatory step toward deployment of this new tracer for understanding chemical fluxes exported from the critical zone. Here we investigate isotopic variations in δ26Mg in bulk Soils and clay fractions relative to their parent andesite in three SoilWeatheringsequences from Guadeloupe formed under contrasting climatic conditions. Soils formed in drier conditions (low precipitation) contain smectite, whereas Soils formed under wet conditions (high rainfall) are characterized by halloysite and Fe-oxides or kaolinite. All clay fractions have Mg isotopic compositions (δ26Mg −0.41‰ to −0.10‰) similar to or heavier than their parent andesite (δ26Mg −0.47‰) supporting the preferential incorporation of heavy Mg isotopes in secondary Mg-bearing clay minerals with the first direct measurements on clay fractions. Soils with lighter Mg isotope compositions have greater quantities of exchangeable Mg. The data support a contribution from sea spray to the exchangeable Mg pool correlated to the SoilWeathering degree. This study highlights for the first time that the Soil δ26Mg not only depend on δ26Mg of the parent rock, and on any fractionation that might occur, but also on the Mg retention on the exchange complex, which could in turn be controlled by external inputs such as sea spray.
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impact of Soil Weathering degree on silicon isotopic fractionation during adsorption onto iron oxides in basaltic ash Soils cameroon
Geochimica et Cosmochimica Acta, 2009Co-Authors: Sophie Opfergelt, G De Bournonville, Damien Cardinal, Luc Andre, Severine Delstanche, Bruno DelvauxAbstract:The sequestration of silicon in Soil clay-sized iron oxides may affect the terrestrial cycle of Si. Iron oxides indeed specifically adsorb aqueous monosilicic acid (H4SiO40), thereby influencing Si concentration in Soil solution. Here we study the impact of H4SiO40 adsorption on the fractionation of Si isotopes in basaltic ash Soils differing in Weathering degree (from two Weathering sequences, Cameroon), hence in clay and Fe-oxide contents, and evaluate the potential isotopic impact on dissolved Si in surrounding Cameroon rivers. Adsorption was measured in batch experiment series designed as function of time (0-72 h) and initial concentration (ic) of Si in solution (0.61-1.18 mM) at 20 degrees C, constant pH (5.5) and ionic strength (I mM). After various Soil-solution contact times, the delta Si-30 vs. NBS28 compositions were determined in selected solutions by MC-ICP-MS (Nu Plasma) in medium resolution, operating in dry plasma with Mg doping with an average precision of +/-0.15 parts per thousand (+/-2 sigma(SEM)). The quantitative adsorption of H4SiO40 by Soil Fe-oxides left a solution depleted in light Si isotopes, which confirms previous study on synthetic Fe-oxides. Measured against its initial composition (delta Si-30 = +0.02 +/- 0.07 parts per thousand (+/-2 sigma(SD))), the solutions were systematically enriched in Si-30 reaching maximum delta Si-30 values ranging between +0.16 parts per thousand and +0.95 parts per thousand after 72 h contact time. The enrichment of the solution in heavy isotopes increased with increasing values of three parameters: Soil Weathering degree, iron oxide content, and proportion of short-range ordered Fe-oxide. The Si-isotopic signature of the solution was partly influenced by Si release, possibly through mineral dissolution and Si desorption from oxide surfaces, depending on Soil type, highlighting the complex pattern of natural Soils. Surrounding Cameroon rivers displayed a mean Si-isotopic signature of +1.19 parts per thousand. Our data imply that in natural environments, H4SiO40 adsorption by Soil clay-sized Fe-oxides at least partly impacts the Si-isotopic signature of the Soil solution exported to water streams. (C) 2009 Elsevier Ltd. All rights reserved.
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the reserve of weatherable primary silicates impacts the accumulation of biogenic silicon in volcanic ash Soils
Biogeochemistry, 2008Co-Authors: Celine Henriet, Sophie Opfergelt, N De Jaeger, Marc Dorel, Bruno DelvauxAbstract:Banana plantlets (Musa acuminata cv Grande Naine) cultivated in hydroponics take up silicon proportionally to the concentration of Si in the nutrient solution (0-1.66 mM Si). Here we study the Si status of banana plantlets grown under controlled greenhouse conditions on five Soils developed from andesitic volcanic ash, but differing in Weathering stage. The mineralogical composition of Soils was inferred from X-ray diffraction, elemental analysis and selective chemical/mineralogical extractions. With increasing Weathering, the content of weatherable primary minerals decreased. Conversely, clay content increased and stable secondary minerals were increasingly dominant: gibbsite, Fe oxides, allophane, halloysite and kaolinite. The contents of biogenic Si in plant and Soil were governed by the reserve of weatherable primary minerals. The largest concentrations of biogenic Si in plant (6.9-7 g kg(-1)) and Soil (50-58 g kg(-1)) occurred in the least weathered Soils, where total Si content was above 225 g kg(-1). The lowest contents of biogenic Si in plant (2.8-4.3 g kg(-1)) and Soil (8-31 g kg(-1)) occurred in the most weathered desilicated Soils enriched with secondary oxides and clay minerals. Our data imply that Soil Weathering stage directly impacted the Soil-to-plant transfer of silicon, and thereby the stock of biogenic Si in a Soil-plant system involving a Si-accumulating plant. They further imply that Soil type can influence the silicon Soil-plant cycle and its hydrological output.
Corey R. Lawrence - One of the best experts on this subject based on the ideXlab platform.
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root driven Weathering impacts on mineral organic associations in deep Soils over pedogenic time scales
Geochimica et Cosmochimica Acta, 2019Co-Authors: Mariela Garcia Arredondo, Corey R. Lawrence, Marjorie S Schulz, Malak M Tfaily, Ravi K Kukkadapu, Morris E Jones, Kristin Boye, Marco KeiluweitAbstract:Abstract Plant roots are critical Weathering agents in deep Soils, yet the impact of resulting mineral transformations on the vast deep Soil carbon (C) reservoir are largely unknown. Root-driven Weathering of primary minerals may cause the formation of reactive secondary minerals, which protect mineral-organic associations (MOAs) for centuries or millennia. Conversely, root-driven Weathering may also transform secondary minerals, potentially enhancing the bioavailability of C previously protected in MOAs. Here we examined the impact of root-driven Weathering on MOAs and their capacity to store C over pedogenic time scales. To accomplish this, we examined deep horizons (100–160 cm) that experienced root-driven Weathering in four Soils of increasing ages (65–226 kyr) of the Santa Cruz marine terrace chronosequence. Specifically, we compared discrete rhizosphere zones subject to root-driven Weathering, with adjacent zones that experienced no root growth. Using a combination of radiocarbon, mass spectrometry, 57Fe Mossbauer spectroscopy, high-resolution mass spectrometry, and X-ray spectromicroscopy approaches, we characterized transformations of MOAs in relation to changes in C content, Δ14C values, and chemistry across the chronosequence. We found that the onset of root-driven Weathering (65–90 kyr) increased the amount of C associated with poorly crystalline iron (Fe) and aluminum (Al) phases, particularly highly disordered nano-particulate goethite (np-goethite). This increase coincided with greater C concentrations, lower Δ14C values, and greater abundance of what is likely microbially-derived C. Continued root-driven Weathering (137–226 kyr) did not significantly change the amount of C associated with crystalline Fe and Al phases, but resulted in a decline in the amount of C associated with poorly crystalline Fe and Al phases. This decline coincided with a decrease in C concentrations, an increase in Δ14C values, and a shift toward plant-derived C. In contrast, Soil not affected by root-driven Weathering showed comparatively low amounts of C bound to poorly crystalline Fe and Al phases regardless of Soil age and, correspondingly, lower C concentrations. Our results demonstrate that root-driven formation and disruption of MOAs are direct controls on both C accrual and loss in deep Soil. This finding suggests that root impacts on Soil C storage are dependent on Soil Weathering stage, a consideration that is critical for future predictions of the vulnerability of deep Soil C to global change.
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Modeling the influence of organic acids on Soil Weathering
Geochimica et Cosmochimica Acta, 2014Co-Authors: Corey R. Lawrence, Jennifer W. Harden, Kate MaherAbstract:Abstract Biological inputs and organic matter cycling have long been regarded as important factors in the physical and chemical development of Soils. In particular, the extent to which low molecular weight organic acids, such as oxalate, influence geochemical reactions has been widely studied. Although the effects of organic acids are diverse, there is strong evidence that organic acids accelerate the dissolution of some minerals. However, the influence of organic acids at the field-scale and over the timescales of Soil development has not been evaluated in detail. In this study, a reactive-transport model of Soil chemical Weathering and pedogenic development was used to quantify the extent to which organic acid cycling controls mineral dissolution rates and long-term patterns of chemical Weathering. Specifically, oxalic acid was added to simulations of Soil development to investigate a well-studied chronosequence of Soils near Santa Cruz, CA. The model formulation includes organic acid input, transport, decomposition, organic-metal aqueous complexation and mineral surface complexation in various combinations. Results suggest that although organic acid reactions accelerate mineral dissolution rates near the Soil surface, the net response is an overall decrease in chemical Weathering. Model results demonstrate the importance of organic acid input concentrations, fluid flow, decomposition and secondary mineral precipitation rates on the evolution of mineral Weathering fronts. In particular, model Soil profile evolution is sensitive to kaolinite precipitation and oxalate decomposition rates. The Soil profile-scale modeling presented here provides insights into the influence of organic carbon cycling on Soil Weathering and pedogenesis and supports the need for further field-scale measurements of the flux and speciation of reactive organic compounds.
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aeolian controls of Soil geochemistry and Weathering fluxes in high elevation ecosystems of the rocky mountains colorado
Geochimica et Cosmochimica Acta, 2013Co-Authors: Corey R. Lawrence, Richard L Reynolds, Michael E Ketterer, Jason C NeffAbstract:Abstract When dust inputs are large or have persisted for long periods of time, the signature of dust additions are often apparent in Soils. The of dust will be greatest where the geochemical composition of dust is distinct from local sources of Soil parent material. In this study the influence of dust accretion on Soil geochemistry is quantified for two different Soils from the San Juan Mountains of southwestern Colorado, USA. At both study sites, dust is enriched in several trace elements relative to local rock, especially Cd, Cu, Pb, and Zn. Mass-balance calculations that do not explicitly account for dust inputs indicate the accumulation of some elements in Soil beyond what can be explained by Weathering of local rock. Most observed elemental enrichments are explained by accounting for the long-term accretion of dust, based on modern isotopic and geochemical estimates. One notable exception is Pb, which based on mass-balance calculations and isotopic measurements may have an additional source at one of the study sites. These results suggest that dust is a major factor influencing the development of Soil in these settings and is also an important control of Soil Weathering fluxes. After accounting for dust inputs in mass-balance calculations, Si Weathering fluxes from San Juan Mountain Soils are within the range observed for other temperate systems. Comparing dust inputs with mass-balanced based flux estimates suggests dust could account for as much as 50–80% of total long-term chemical Weathering fluxes. These results support the notion that dust inputs may sustain chemical Weathering fluxes even in relatively young continental settings. Given the widespread input of far-traveled dust, the Weathering of dust is likely and important and underappreciated aspect of the global Weathering engine.
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the contemporary physical and chemical flux of aeolian dust a synthesis of direct measurements of dust deposition
Chemical Geology, 2009Co-Authors: Corey R. Lawrence, Jason C NeffAbstract:Abstract The deposition of aeolian, or windblown, dust is widely recognized as an important physical and chemical flux to ecosystems. Dust deposition adds exogenous mineral and organic material to terrestrial surfaces and can be important for the biogeochemical cycling of nutrients. There have been many studies that characterize the physical and chemical composition of dust. However, few studies have synthesized these observations in order to examine patterns geochemical fluxes. We have compiled observations of dust deposition rates, particle size distributions (PSD), mineralogy and bulk elemental and organic chemistry. The rates of dust deposition observed across the globe vary from almost 0 to greater than 450 g m− 2 yr− 1. Sites receiving dust deposition can be partitioned into broad categories based on there distance from dust source regions. When compared to global dust models our results suggest some models may underestimate dust deposition rates at the regional and local scales. The distance from the source region that dust is deposited also influences the particle size distributions, mineralogy, and chemical composition of dust; however, more consistent dust sampling and geochemical analyses are needed to better constrain these spatial patterns. On average, the concentrations of most major elements (Si, Al, Fe, Mg, Ca, K) in aeolian dust tend to be similar (± 20%) to the composition of the upper continental crust (UCC), but there is substantial variability from sample to sample. In contrast, some elements tend to be depleted (Na) or enriched (Ti) in dust, likely as a result of Soil Weathering processes prior to dust emissions. Trace elements, especially heavy metals, are consistently enriched in dust relative to the UCC. Ecologically important nutrients, such as N and P, are also present in dust deposition. The geochemical flux attributable to dust deposition can be substantial in ecosystems located proximal to dust source regions. We calculate estimates of elemental flux rates based on the average chemical composition of aeolian dust and varying rates of deposition. These estimated flux rates are useful as a rough gauge of the degree to which dust deposition may influence biogeochemical cycling in terrestrial ecosystems and should be utilized to better constrain deposition estimates of global dust models.
Alex N Halliday - One of the best experts on this subject based on the ideXlab platform.
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silicon isotopes and the tracing of desilication in volcanic Soil Weathering sequences guadeloupe
Chemical Geology, 2012Co-Authors: Sophie Opfergelt, R B Georg, Bruno Delvaux, Y M Cabidoche, Kevin W Burton, Alex N HallidayAbstract:Abstract Silicon (Si) stable isotopes have the potential to become a useful Weathering proxy, given that light Si isotopes are preferentially incorporated into secondary clay minerals. Here we investigate how Si depletion in Soils and associated clay mineralogy influence the Si isotope fractionation associated with clay mineral formation. We report δ 30 Si compositions in bulk Soils and clay fractions relative to their parent andesite in three Soil Weathering sequences from Guadeloupe that were formed under contrasting climatic conditions. Strongly desilicated Soils containing kaolinite that formed in wet areas (high precipitation) are compared with less desilicated Soils containing smectite formed in drier conditions (low precipitation). Clay fractions are isotopically lighter than the parent andesite (δ 30 Si-0.23‰), and increasingly lighter with Si depletion in Soils, which supports the view that the Si isotope composition in secondary clay fractions is controlled by the degree of Soil desilication. It is shown that the Si isotope fractionation factor between the parent silicate material and the secondary clay minerals is smaller for Si-rich secondary clay minerals such as smectite and larger for Si-poor secondary clay minerals such as kaolinite. This study provides new insights to better define Si isotopes as a proxy for environmental conditions for clay neoformation.
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mechanisms of magnesium isotope fractionation in volcanic Soil Weathering sequences guadeloupe
Earth and Planetary Science Letters, 2012Co-Authors: Sophie Opfergelt, R B Georg, Bruno Delvaux, Y M Cabidoche, Kevin W Burton, Alex N HallidayAbstract:Magnesium (Mg) stable isotopes are increasingly used as a Weathering proxy in Soils and rivers, but the impact of the mineralogy of secondary phases on isotopefractionation remains obscure. A better understanding of the behaviour of Mg isotopes during Weathering processes is a mandatory step toward deployment of this new tracer for understanding chemical fluxes exported from the critical zone. Here we investigate isotopic variations in δ26Mg in bulk Soils and clay fractions relative to their parent andesite in three SoilWeatheringsequences from Guadeloupe formed under contrasting climatic conditions. Soils formed in drier conditions (low precipitation) contain smectite, whereas Soils formed under wet conditions (high rainfall) are characterized by halloysite and Fe-oxides or kaolinite. All clay fractions have Mg isotopic compositions (δ26Mg −0.41‰ to −0.10‰) similar to or heavier than their parent andesite (δ26Mg −0.47‰) supporting the preferential incorporation of heavy Mg isotopes in secondary Mg-bearing clay minerals with the first direct measurements on clay fractions. Soils with lighter Mg isotope compositions have greater quantities of exchangeable Mg. The data support a contribution from sea spray to the exchangeable Mg pool correlated to the SoilWeathering degree. This study highlights for the first time that the Soil δ26Mg not only depend on δ26Mg of the parent rock, and on any fractionation that might occur, but also on the Mg retention on the exchange complex, which could in turn be controlled by external inputs such as sea spray.
Jon Petter Gustafsson - One of the best experts on this subject based on the ideXlab platform.
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phosphorus in 2d spatially resolved p speciation in two swedish forest Soils as influenced by apatite Weathering and podzolization
Geoderma, 2020Co-Authors: Gbotemi A Adediran, Jon Petter Gustafsson, J Marius R Tuyishime, Delphine Vantelon, Wantana KlysubunAbstract:Abstract The cycling and long-term supply of phosphorus (P) in Soils are of global environmental and agricultural concern. To advance the knowledge, a detailed understanding of both the vertical and lateral variation of P chemical speciation and retention mechanism(s) is required, a knowledge that is limited in postglacial forest Soils. We combined the use of synchrotron X-ray fluorescence microscopy with multi-elemental co-localisation analysis and P K-edge XANES spectroscopy to reveal critical chemical and structural Soil properties. We established a two-dimensional (2D) imagery of P retention and speciation at a microscale spatial resolution in two forest Soil profiles formed in glaciofluvial and wave-washed sand. The abundance and speciation of P in the upper 40 cm was found to be influenced by Soil Weathering and podzolization, leading to spatial variability in P speciation on the microscale ( 600 μm) hot spots of inclusions in aluminosilicates or as discrete micro-sized apatite grains. The subSoil apatite represents a pool of P that trees can potentially acquire and thus add to the biogeochemically active P pool in temperate forest Soils.
