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Sample records for silicate weathering rates

  1. Natural Weathering Rates of Silicate Minerals

    NASA Astrophysics Data System (ADS)

    White, A. F.

    2003-12-01

    Silicates constitute more than 90% of the rocks exposed at Earth's land surface (Garrels and Mackenzie, 1971). Most primary minerals comprising these rocks are thermodynamically unstable at surface pressure/temperature conditions and are therefore susceptible to chemical weathering. Such weathering has long been of interest in the natural sciences. Hartt (1853) correctly attributed chemical weathering to "the efficacy of water containing carbonic acid in promoting the decomposition of igneous rocks." Antecedent to the recent interest in the role of vegetation on chemical weathering, Belt (1874) observed that the most intense weathering of rocks in tropical Nicaragua was confined to forested regions. He attributed this effect to "the percolation through rocks of rain water charged with a little acid from decomposing vegetation." Chamberlin (1899) proposed that the enhanced rates of chemical weathering associated with major mountain building episodes in Earth's history resulted in a drawdown of atmospheric CO2 that led to periods of global cooling. Many of the major characteristics of chemical weathering had been described when Merrill (1906) published the groundbreaking volume Rocks, Rock Weathering, and Soils.The major advances since that time, particularly during the last several decades, have centered on understanding the fundamental chemical, hydrologic, and biologic processes that control weathering and in establishing quantitative weathering rates. This research has been driven by the importance of chemical weathering to a number environmentally and economically important issues. Undoubtedly, the most significant aspect of chemical weathering is the breakdown of rocks to form soils, a process that makes life possible on the surface of the Earth. The availability of many soil macronutrients such as magnesium, calcium, potassium, and PO4 is directly related to the rate at which primary minerals weather. Often such nutrient balances are upset by anthropogenic

  2. New estimates of silicate weathering rates and their uncertainties in global rivers

    NASA Astrophysics Data System (ADS)

    Moon, Seulgi; Chamberlain, C. P.; Hilley, G. E.

    2014-06-01

    This study estimated the catchment- and global-scale weathering rates of silicate rocks from global rivers using global compilation datasets from the GEMS/Water and HYBAM. These datasets include both time-series of chemical concentrations of major elements and synchronous discharge. Using these datasets, we first examined the sources of uncertainties in catchment and global silicate weathering rates. Then, we proposed future sampling strategies and geochemical analyses to estimate accurate silicate weathering rates in global rivers and to reduce uncertainties in their estimates. For catchment silicate weathering rates, we considered uncertainties due to sampling frequency and variability in river discharge, concentration, and attribution of weathering to different chemical sources. Our results showed that uncertainties in catchment-scale silicate weathering rates were due mostly to the variations in discharge and cation fractions from silicate substrates. To calculate unbiased silicate weathering rates accounting for the variations from discharge and concentrations, we suggest that at least 10 and preferably ∼40 temporal chemical data points with synchronous discharge from each river are necessary. For the global silicate weathering rate, we examined uncertainties from infrequent sampling within an individual river, the extrapolation from limited rivers to a global flux, and the inverse model selections for source differentiation. For this weathering rate, we found that the main uncertainty came from the extrapolation to the global flux and the model configurations of source differentiation methods. This suggests that to reduce the uncertainties in the global silicate weathering rates, coverage of synchronous datasets of river chemistry and discharge to rivers from tectonically active regions and volcanic provinces must be extended, and catchment-specific silicate end-members for those rivers must be characterized. With current available synchronous datasets, we

  3. Uncertainty in silicate mineral weathering rate estimates: source partitioning and policy implications

    NASA Astrophysics Data System (ADS)

    Futter, M. N.; Klaminder, J.; Lucas, R. W.; Laudon, H.; Köhler, S. J.

    2012-06-01

    Precise and accurate estimates of silicate mineral weathering rates are crucial when setting policy targets for long-term forest sustainability, critical load calculations and assessing consequences of proposed geo-engineering solutions to climate change. In this paper, we scrutinize 394 individual silicate mineral weathering estimates from 82 sites on three continents. We show that within-site differences of several hundred per cent arise when different methods are used to estimate weathering rates, mainly as a result of uncertainties related to input data rather than conceptually different views of the weathering process. While different methods tend to rank sites congruently from high to low weathering rates, large within-site differences in estimated weathering rate suggest that policies relying on quantitative estimates based upon a single method may have undesirable outcomes. We recommend the use of at least three independent estimates when making management decisions related to silicate mineral weathering rates.

  4. The effect of land plants on weathering rates of silicate minerals

    NASA Astrophysics Data System (ADS)

    Drever, James I.

    1994-05-01

    Land plants and their associated microbiota directly affect silicate mineral weathering in several ways: by generation of chelating ligands, by modifying pH through production of CO 2 or organic acids, and by altering the physical properties of a soil, particularly the exposed surface areas of minerals and the residence time of water. In laboratory experiments far from equilibrium, 1 mM oxalate (a strong chelator of Al) has a negligible effect on the dissolution rate of alkali feldspars, but some effect on calcic feldspars and olivine. By analogy to oxalate, the overall effect of organic ligands on the weathering rate of silicate minerals in nature is likely to be small, except perhaps in microenvironments adjacent to roots and fungal hyphae. The effect of pH on silicate mineral dissolution rate depends on pH: below pH 4-5, the rate increases with decreasing pH, in the circumneutral region the rate is pH-independent, and at pH values above around 8 the rate increases with increasing pH. Vegetation should thus cause an increase in weathering rate through the pH effect only where the pH is below 4-5. As an overall generalization, the effect of plants on weathering rate through changes in soil-solution chemistry is probably small for granitic rocks; it may be greater for more mafic rocks. It is the release of Ca and Mg from mafic rocks that has the greatest influence on the global CO 2 budget. The effect of changes in soil physical properties on weathering rate can be major. By binding fine particles, plants can greatly increase weathering rates in areas of high physical erosion. Where erosion rates are lower, the effect of plants is less clear. On long timescales plants may decrease chemical weathering by binding secondary products and isolating unweathered minerals from meteoric water. A major unknown in estimating the effect of the advent of land plants on weathering rates is the nature (thickness, particle size distribution, permeability) of the regolith on the

  5. The effect of land plants on weathering rates of silicate minerals

    SciTech Connect

    Drever, J.I. )

    1994-05-01

    Land plants and their associated microbiota directly affect silicate mineral weathering in several ways: by generation of chelating ligands, by modifying pH through production of CO[sub 2] or organic acids, and by altering the physical properties of a soil, particularly the exposed surface areas of minerals and the residence time of water. In laboratory experiments far from equilibrium, 1 mM oxalate (a strong chelator of Al) has a negligible effect on the dissolution rate of alkali feldspars, but some effect on calcic feldspars and olivine. By analogy to oxalate, the overall effect of organic ligands on the weathering rate of silicate minerals in nature is likely to be small, except perhaps in microenvironments adjacent to roots and fungal hyphae. The effect of pH on silicate mineral dissolution rate depends on pH: below pH 4-5, the rate increases with decreasing pH, in the circumneutral region the rate is pH-independent, and at pH values above around 8 the rate increases with increasing pH. Vegetation should thus cause an increase in weathering rate through the pH effect only where the pH is below 4-5. As an overall generalization, the effect of plants on weathering rate through changes in soil-solution chemistry is probably small for granitic rocks; it may be greater for more mafic rocks. It is the release of Ca and Mg from mafic rocks that has the greatest influence on the global CO[sub 2] budget.

  6. A framework for predicting global silicate weathering and CO2 drawdown rates over geologic time-scales.

    PubMed

    Hilley, George E; Porder, Stephen

    2008-11-01

    Global silicate weathering drives long-time-scale fluctuations in atmospheric CO(2). While tectonics, climate, and rock-type influence silicate weathering, it is unclear how these factors combine to drive global rates. Here, we explore whether local erosion rates, GCM-derived dust fluxes, temperature, and water balance can capture global variation in silicate weathering. Our spatially explicit approach predicts 1.9-4.6 x 10(13) mols of Si weathered globally per year, within a factor of 4-10 of estimates of global silicate fluxes derived from riverine measurements. Similarly, our watershed-based estimates are within a factor of 4-18 (mean of 5.3) of the silica fluxes measured in the world's ten largest rivers. Eighty percent of total global silicate weathering product traveling as dissolved load occurs within a narrow range (0.01-0.5 mm/year) of erosion rates. Assuming each mol of Mg or Ca reacts with 1 mol of CO(2), 1.5-3.3 x 10(8) tons/year of CO(2) is consumed by silicate weathering, consistent with previously published estimates. Approximately 50% of this drawdown occurs in the world's active mountain belts, emphasizing the importance of tectonic regulation of global climate over geologic timescales. PMID:18952842

  7. A framework for predicting global silicate weathering and CO2 drawdown rates over geologic time-scales

    PubMed Central

    Hilley, George E.; Porder, Stephen

    2008-01-01

    Global silicate weathering drives long-time-scale fluctuations in atmospheric CO2. While tectonics, climate, and rock-type influence silicate weathering, it is unclear how these factors combine to drive global rates. Here, we explore whether local erosion rates, GCM-derived dust fluxes, temperature, and water balance can capture global variation in silicate weathering. Our spatially explicit approach predicts 1.9–4.6 × 1013 mols of Si weathered globally per year, within a factor of 4–10 of estimates of global silicate fluxes derived from riverine measurements. Similarly, our watershed-based estimates are within a factor of 4–18 (mean of 5.3) of the silica fluxes measured in the world's ten largest rivers. Eighty percent of total global silicate weathering product traveling as dissolved load occurs within a narrow range (0.01–0.5 mm/year) of erosion rates. Assuming each mol of Mg or Ca reacts with 1 mol of CO2, 1.5–3.3 × 108 tons/year of CO2 is consumed by silicate weathering, consistent with previously published estimates. Approximately 50% of this drawdown occurs in the world's active mountain belts, emphasizing the importance of tectonic regulation of global climate over geologic timescales. PMID:18952842

  8. Evaluating sensitivity of silicate mineral dissolution rates to physical weathering using a soil evolution model (SoilGen2.25)

    NASA Astrophysics Data System (ADS)

    Opolot, E.; Finke, P. A.

    2015-08-01

    Silicate mineral dissolution rates depend on the interaction of a number of factors categorized either as intrinsic (e.g. mineral surface area, mineral composition) or extrinsic (e.g. climate, hydrology, biological factors, physical weathering). Estimating the integrated effect of these factors on the silicate mineral dissolution rates therefore necessitates the use of fully mechanistic soil evolution models. This study applies a mechanistic soil evolution model (SoilGen) to explore the sensitivity of silicate mineral dissolution rates to the integrated effect of other soil forming processes and factors. The SoilGen soil evolution model is a 1-D model developed to simulate the time-depth evolution of soil properties as a function of various soil forming processes (e.g. water, heat and solute transport, chemical and physical weathering, clay migration, nutrient cycling and bioturbation) driven by soil forming factors (i.e., climate, organisms, relief, parent material). Results from this study show that although soil solution chemistry (pH) plays a dominant role in determining the silicate mineral dissolution rates, all processes that directly or indirectly influence the soil solution composition equally play an important role in driving silicate mineral dissolution rates. Model results demonstrated a decrease of silicate mineral dissolution rates with time, an obvious effect of texture and an indirect but substantial effect of physical weathering on silicate mineral dissolution rates. Results further indicated that clay migration and plant nutrient recycling processes influence the pH and thus the silicate mineral dissolution rates. Our silicate mineral dissolution rates results fall between field and laboratory rates but were rather high and more close to the laboratory rates owing to the assumption of far from equilibrium reaction used in our dissolution rate mechanism. There is therefore need to include secondary mineral precipitation mechanism in our formulation

  9. Evaluating sensitivity of silicate mineral dissolution rates to physical weathering using a soil evolution model (SoilGen2.25)

    NASA Astrophysics Data System (ADS)

    Opolot, E.; Finke, P. A.

    2015-11-01

    Silicate mineral dissolution rates depend on the interaction of a number of factors categorized either as intrinsic (e.g. mineral surface area, mineral composition) or extrinsic (e.g. climate, hydrology, biological factors, physical weathering). Estimating the integrated effect of these factors on the silicate mineral dissolution rates therefore necessitates the use of fully mechanistic soil evolution models. This study applies a mechanistic soil evolution model (SoilGen) to explore the sensitivity of silicate mineral dissolution rates to the integrated effect of other soil-forming processes and factors. The SoilGen soil evolution model is a 1-D model developed to simulate the time-depth evolution of soil properties as a function of various soil-forming processes (e.g. water, heat and solute transport, chemical and physical weathering, clay migration, nutrient cycling, and bioturbation) driven by soil-forming factors (i.e., climate, organisms, relief, parent material). Results from this study show that although soil solution chemistry (pH) plays a dominant role in determining the silicate mineral dissolution rates, all processes that directly or indirectly influence the soil solution composition play an equally important role in driving silicate mineral dissolution rates. Model results demonstrated a decrease of silicate mineral dissolution rates with time, an obvious effect of texture and an indirect but substantial effect of physical weathering on silicate mineral dissolution rates. Results further indicated that clay migration and plant nutrient recycling processes influence the pH and thus the silicate mineral dissolution rates. Our silicate mineral dissolution rates results fall between field and laboratory rates but were rather high and more close to the laboratory rates possibly due to the assumption of far from equilibrium reaction used in our dissolution rate mechanism. There is therefore a need to include secondary mineral precipitation mechanism in our

  10. Chemical weathering rates of a soil chronosequence on granitic alluvium: I. Quantification of mineralogical and surface area changes and calculation of primary silicate reaction rates

    USGS Publications Warehouse

    White, A.F.; Blum, A.E.; Schulz, M.S.; Bullen, T.D.; Harden, J.W.; Peterson, M.L.

    1996-01-01

    Mineral weathering rates are determined for a series of soils ranging in age from 0.2-3000 Ky developed on alluvial terraces near Merced in the Central Valley of California. Mineralogical and elemental abundances exhibit time-dependent trends documenting the chemical evolution of granitic sand to residual kaolinite and quartz. Mineral losses with time occur in the order: hornblende > plagioclase > K-feldspar. Maximum volume decreases of >50% occur in the older soils. BET surface areas of the bulk soils increase with age, as do specific surface areas of aluminosilicate mineral fractions such as plagioclase, which increases from 0.4-1.5 m2 g-1 over 600 Ky. Quartz surface areas are lower and change less with time (0.11-0.23 m2 g-1). BET surface areas correspond to increasing external surface roughness (?? = 10-600) and relatively constant internal surface area (??? 1.3 m2 g-1). SEM observations confirm both surface pitting and development of internal porosity. A numerical model describes aluminosilicate dissolution rates as a function of changes in residual mineral abundance, grain size distributions, and mineral surface areas with time. A simple geometric treatment, assuming spherical grains and no surface roughness, predicts average dissolution rates (plagioclase, 10-17.4; K-feldspar, 10-17.8; and hornblende, 10-17.5 mol cm-1 s-1) that are constant with time and comparable to previous estimates of soil weathering. Average rates, based on BET surface area measurements and variable surface roughnesses, are much slower (plagioclase, 10-19.9; K-feldspar, 10-20.5; and hornblende 10-20.1 mol cm-2 s-1). Rates for individual soil horizons decrease by a factor of 101.5 over 3000 Ky indicating that the surface reactivities of minerals decrease as the physical surface areas increase. Rate constants based on BET estimates for the Merced soils are factors of 103-104 slower than reported experimental dissolution rates determined from freshly prepared silicates with low surface

  11. Basalt Weathering Rates Across Scales

    NASA Astrophysics Data System (ADS)

    Navarresitchler, A.; Brantley, S.

    2006-12-01

    Weathering of silicate minerals is a known sink for atmospheric CO2. An estimated 30%-35% of the consumption of CO2 from continental silicate weathering can be attributed to basalt weathering (Dessert et al., 2003). To assess basalt weathering rates we examine weathering advance rates of basalt (w, mm/yr) reported at four scales: denudation rates from basalt watersheds (tens of kilometers), rates of soil formation from soil profiles developed on basaltic parent material of known age (meters), rates of weathering rind formation on basalt clasts (centimeters), and laboratory dissolution rates (millimeters). Basalt weathering advance rates calculated for watersheds range between 0.36 and 9.8x10-3 mm/yr. The weathering advance rate for a basalt soil profile in Hawaii is 8.0x10-3 mm/yr while advance rates for clasts range from 5.6x10-6 to 2.4x10-4 mm/yr. Batch and mixed flow laboratory experiments performed at circum- neutral pH yield advance rates of 2.5x10^{-5} to 3.4x10-7 mm/yr when normalized to BET surface area. These results show increasing advance rates with both increasing scale (from laboratory to watersheds) and increasing temperature. If we assume that basalt weathers at an intrinsic rate that applies to all scales then we conclude that variations in weathering advance rates arise from variations in surface area measurement at different scales (D); therefore, basalt weathering is a fractal system. We measure a fractal dimension (dr) of basalt weathering of 2.2. For Euclidean geometries, measured surface area does not vary with the scale at which it is measured and dr equals 2. For natural surfaces, surface area is related to the scale at which it is measured. As scale increases, the minimum size of the surface irregularities that are measurable also increases. The ratio between BET and geometric normalized laboratory dissolution rates has been defined as a roughness parameter, λ, which ranges from ~10-100. We extend the definition of this roughness parameter

  12. Shaken and Stirred: A Combined Reaction-Diffusion and Random Rate Model for the Temporal Evolution and Earthquake-induced Hydrodynamics of Silicate Mineral Weathering

    NASA Astrophysics Data System (ADS)

    Evaristo, J. A.; Willenbring, J.

    2013-12-01

    The time dependency of silicate mineral weathering has been explored in the literature in terms of processes and features that are intrinsic and extrinsic to the mineral [1]. However, although the advent of sophisticated reactive transport models has allowed for coupling increasingly complex reaction and transport processes [2,3], a simple and fundamental understanding of the temporal evolution of weathering is lacking. Here, we propose that a purely deterministic approach may not be sufficient given the inherent differences in reactivity over space and time. Therefore, we explore how a combined reaction-diffusion and random rate model - informed by a stochastic distribution of weathering rates K (T-1) - might be able to explain not only the temporal evolution but also the hydrodynamics of weathering during earthquakes; the latter being purportedly described by time-dependent property permeability (L2). Preliminary model results show that (1) an increase in dimensionless quantity βrp, where β is the diffusion length (L-1) and rp is the distance between pores (L), leads to a decrease in minimum reaction rate with time from the relation Kmin ∝ e-βrp/rp ; (2) at a given porosity, a time-dependent decrease in reactivity arises as permeability decreases due to decreasing pore size (and therefore increasing rp), which in turn may be related to the time-dependent feedback between dissolution and precipitation; (3) while permeability is lower in older soils, transient stresses as during earthquakes [4], may induce more efficient "declogging" of pores in these soils than in younger soils due to higher hydrodynamic viscous shear stress, thereby, resulting in a coseismic change in stream discharge Q; and (4) subsequent weathering beyond t~Kmin-1 exhibits a fall in rates, marking the cessation of logarithmic decay possibly due to dissolution-precipitation feedback. [1] White and Brantley (2003), Chem. Geol. 202, 479. [2] Lichtner P.C. (1996), Mineralogical Society of

  13. Weathering and weathering rates of natural stone

    SciTech Connect

    Winkler, E.M. )

    1987-01-01

    Physical and chemical weathering were studied as separate processes in the past. Recent research, however, shows that most processes are physicochemical in nature. The rates at which calcite and silica weather by dissolution are dependent on the regional and local climatic environment. The weathering of silicate rocks leaves discolored margins and rinds, a function of the ricks permeability and of the climatic parameters. Salt action, the greatest disruptive factor, is complex and not yet fully understood in all its phases, but some of th causes of disruption are crystallization pressure, hydration pressure, and hygroscopic attraction of excess moisture. The decay of marble is complex, an interaction between dissolution, crack-corrosion, and the expansion-contraction cycles triggered by the release of residual stresses. Thin spalls of granites commonly found near the street level of buildings are generally caused by a combination of stress relief and salt action. To study and determine weathering rates of a variety of commercial stones, the National Bureau of Standards erected a Stone Exposure Test Wall in 1948. Of the many types of stone represented, only a few fossiliferous limestones permit a valid measurement of surface reduction in a polluted urban environment.

  14. Impact of atmospheric CO2 levels on continental silicate weathering

    NASA Astrophysics Data System (ADS)

    Beaulieu, E.; GoddéRis, Y.; Labat, D.; Roelandt, C.; Oliva, P.; Guerrero, B.

    2010-07-01

    Anthropogenic sources are widely accepted as the dominant cause for the increase in atmospheric CO2 concentrations since the beginning of the industrial revolution. Here we use the B-WITCH model to quantify the impact of increased CO2 concentrations on CO2 consumption by weathering of continental surfaces. B-WITCH couples a dynamic biogeochemistry model (LPJ) and a process-based numerical model of continental weathering (WITCH). It allows simultaneous calculations of the different components of continental weathering fluxes, terrestrial vegetation dynamics, and carbon and water fluxes. The CO2 consumption rates are estimated at four different atmospheric CO2 concentrations, from 280 up to 1120 ppmv, for 22 sites characterized by silicate lithologies (basalt, granite, or sandstones). The sensitivity to atmospheric CO2 variations is explored, while temperature and rainfall are held constant. First, we show that under 355 ppmv of atmospheric CO2, B-WITCH is able to reproduce the global pattern of weathering rates as a function of annual runoff, mean annual temperature, or latitude for silicate lithologies. When atmospheric CO2 increases, evapotranspiration generally decreases due to progressive stomatal closure, and the soil CO2 pressure increases due to enhanced biospheric productivity. As a result, vertical drainage and soil acidity increase, promoting CO2 consumption by mineral weathering. We calculate an increase of about 3% of the CO2 consumption through silicate weathering (mol ha-1 yr-1) for 100 ppmv rise in CO2. Importantly, the sensitivity of the weathering system to the CO2 rise is not uniform and heavily depends on the climatic, lithologic, pedologic, and biospheric settings.

  15. Silicate weathering in the Ganges alluvial plain

    NASA Astrophysics Data System (ADS)

    Frings, Patrick J.; Clymans, Wim; Fontorbe, Guillaume; Gray, William; Chakrapani, Govind J.; Conley, Daniel J.; De La Rocha, Christina

    2015-10-01

    The Ganges is one of the world's largest rivers and lies at the heart of a body of literature that investigates the interaction between mountain orogeny, weathering and global climate change. Three regions can be recognised in the Ganges basin, with the Himalayan orogeny to the north and the plateaus of peninsular India to the south together delimiting the Ganges alluvial plain. Despite constituting approximately 80% of the basin, weathering processes in the peninsula and alluvial plain have received little attention. Here we present an analysis of 51 water samples along a transect of the alluvial plain, including all major tributaries. We focus on the geochemistry of silicon and its isotopes. Area normalised dissolved Si yields are approximately twice as high in rivers of Himalaya origin than the plain and peninsular tributaries (82, 51 and 32 kmol SiO2 km-2 yr-1, respectively). Such dissolved Si fluxes are not widely used as weathering rate indicators because a large but variable fraction of the DSi mobilised during the initial weathering process is retained in secondary clay minerals. However, the silicon isotopic composition of dissolved Si (expressed as δ30Si) varies from + 0.8 ‰ in the Ganges mainstem at the Himalaya front to + 3.0 ‰ in alluvial plain streams and appears to be controlled by weathering congruency, i.e. by the degree of incorporation of Si into secondary phases. The higher δ30Si values therefore reflect decreasing weathering congruency in the lowland river catchments. This is exploited to quantify the degree of removal using a Rayleigh isotope mass balance model, and consequently derive initial silica mobilisation rates of 200, 150 and 107 kmol SiO2 km-2 yr-1, for the Himalaya, peninsular India and the alluvial plain, respectively. Because the non-Himalayan regions dominate the catchment area, the majority of initial silica mobilisation from primary minerals occurs in the alluvial plain and peninsular catchment (41% and 34%, respectively).

  16. Geochemistry of large river suspended sediments: Silicate weathering or recycling tracer?

    SciTech Connect

    Gaillardet, J.; Dupre, B.; Allegre, C.J.

    1999-12-01

    This study focuses on the major and trace element composition of suspended sediments transported by the world's largest rivers. Its main purpose is to answer the following question: is the degree of weathering of modern river-borne particles consistent with the estimated river dissolved loads derived from silicate weathering? In agreement with the well known mobility of elements during weathering of continental rocks, the authors confirm that river sediments are systematically depleted in Na, K, Ba with respect to the Upper Continental Crust. For each of these mobile elements, a systematics of weathering indexes of river-borne solids is attempted. A global consistency is found between all these indexes. Important variations in weathering intensities exist. A clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands. However, no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones. An inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments. Finally, chemical and physical weathering are compared through the use of a simple steady state model. The authors show that the weathering intensities of large river suspended sediments can only be reconciled with the (silicate-derived) dissolved load or rivers, by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles. A simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins. Finally, even if orogenic zones produce weakly weathered sediments, the authors emphasize the fact that silicate chemical weathering rates (and hence CO{sub 2} consumption rates by silicate

  17. Lithium Isotopes as Proxy of Continental Silicate Weathering

    NASA Astrophysics Data System (ADS)

    Liu, X. M.; Wanner, C.; Rudnick, R. L.; McDonough, W. F.

    2014-12-01

    Chemical weathering has an important influence on continental crust evolution, as weathering of basalt preferentially removes soluble elements, such as Mg and Ca, and can shift the crust towards more andesitic compositions, thus helping to solve the crustal composition paradox. The isotopic compositions of soluble elements (e.g., Li and Mg) provide a monitor of chemical weathering of the continents through time. Here we evaluate the factors influencing the abundance, [Li], and isotopic composition of riverine Li delivered to the oceans through analyses and modeling of [Li] and d7Li in streams and groundwaters draining a single continental lithology, the Columbia River Basalts (CRBs). The streams were sampled in different climate zones that lie on the dry and wet sides of the Cascades Mountains, and during two different seasons (summer and late winter) in order to evaluate climatic and seasonal influences on Li isotopes in rivers. Dissolved Li (δ7Li = +9.3 to +30.4) is systematically heavier than that of fresh or weathered CRBs, suspended loads (-5.9 to -0.3), and shallow groundwaters (+6.7 to +9.4). Continued isotopic fractionation between stream water and suspended and/or bed loads has a major influence on riverine δ7Li as indicated by the heavier Li in streams, compared to the shallow groundwaters that feed them. Seasonal δ7Li variation is observed only for streams west of the Cascades, where the difference in precipitation rate between the seasons is greatest. Reactive transport model simulations reveal that riverine δ7Li is strongly controlled by subsurface residence times and Li isotope fractionation occurring within rivers. The varying residence times for groundwaters feeding the western streams in summer (long residence times, higher δ7Li, greater weathering) and winter (short residence times, lower δ7Li, less weathering) explains the observed seasonal variations. A global, negative correlation between δ7Li and Li/Na for streams and rivers draining

  18. Geoengineering potential of artificially enhanced silicate weathering of olivine.

    PubMed

    Köhler, Peter; Hartmann, Jens; Wolf-Gladrow, Dieter A

    2010-11-23

    Geoengineering is a proposed action to manipulate Earth's climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate the potential of a specific geoengineering technique, carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification, because it influences the global climate via the carbon cycle. If important details of the marine chemistry are taken into consideration, a new mass ratio of CO(2) sequestration per olivine dissolution of about 1 is achieved, 20% smaller than previously assumed. We calculate that this approach has the potential to sequestrate up to 1 Pg of C per year directly, if olivine is distributed as fine powder over land areas of the humid tropics, but this rate is limited by the saturation concentration of silicic acid. In our calculations for the Amazon and Congo river catchments, a maximum annual dissolution of 1.8 and 0.4 Pg of olivine seems possible, corresponding to the sequestration of 0.5 and 0.1 Pg of C per year, but these upper limit sequestration rates come at the environmental cost of pH values in the rivers rising to 8.2. Open water dissolution of fine-grained olivine and an enhancement of the biological pump by the rising riverine input of silicic acid might increase our estimate of the carbon sequestration, but additional research is needed here. We finally calculate with a carbon cycle model the consequences of sequestration rates of 1-5 Pg of C per year for the 21st century by this technique. PMID:21059941

  19. Geoengineering potential of artificially enhanced silicate weathering of olivine

    PubMed Central

    Köhler, Peter; Hartmann, Jens; Wolf-Gladrow, Dieter A.

    2010-01-01

    Geoengineering is a proposed action to manipulate Earth’s climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate the potential of a specific geoengineering technique, carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification, because it influences the global climate via the carbon cycle. If important details of the marine chemistry are taken into consideration, a new mass ratio of CO2 sequestration per olivine dissolution of about 1 is achieved, 20% smaller than previously assumed. We calculate that this approach has the potential to sequestrate up to 1 Pg of C per year directly, if olivine is distributed as fine powder over land areas of the humid tropics, but this rate is limited by the saturation concentration of silicic acid. In our calculations for the Amazon and Congo river catchments, a maximum annual dissolution of 1.8 and 0.4 Pg of olivine seems possible, corresponding to the sequestration of 0.5 and 0.1 Pg of C per year, but these upper limit sequestration rates come at the environmental cost of pH values in the rivers rising to 8.2. Open water dissolution of fine-grained olivine and an enhancement of the biological pump by the rising riverine input of silicic acid might increase our estimate of the carbon sequestration, but additional research is needed here. We finally calculate with a carbon cycle model the consequences of sequestration rates of 1–5 Pg of C per year for the 21st century by this technique. PMID:21059941

  20. Weather Balloon Ascent Rate

    NASA Astrophysics Data System (ADS)

    Denny, Mark

    2016-05-01

    The physics of a weather balloon is analyzed. The surprising aspect of the motion of these balloons is that they ascend to great altitudes (typically 35 km) at a more or less constant rate. Such behavior is not surprising near the ground—say for a helium-filled party balloon rising from street level to the top of the Empire State building—but it is unexpected for a balloon that rises to altitudes where the air is rarefied. We show from elementary physical laws why the ascent rate is approximately constant.

  1. Grasslands, silicate weathering and diatoms: Cause and effect

    SciTech Connect

    Johansson, A.K. . Dept. of Geological Sciences)

    1993-03-01

    Diatoms are silica-limited, photosynthetic, single-celled eukaryotes that today occupy a wide variety of habitats both in freshwater and marine environments. Ultimately the silica they use is derived from the weathering of silicates on land. Although marine diatoms first appear in the Jurassic, the fossil record shows a remarkable correlation between the Mid-Miocene appearance of widespread grasslands and the drastic increase in diatom-rich deposits in freshwater, as well as in marine environments throughout the world. Grasses actively weather silicates, accumulating soluble silica into their leaves. Decomposing grasses release this soluble silica into the soil from whence it is transported into lakes and oceans and made available to diatoms. Grasses also probably increased chemical weathering, and hence the release of soluble silica, in previously weakly vegetated semi-arid areas. Increased weathering of silicates also led to cooler climates as evidenced by the Mid-Miocene [delta][sup 18]O record. The author suggests that the Tertiary expansion of grasslands is responsible for the explosive increase in diversity and abundance of diatoms in the oceans and freshwaters of the Mid-Miocene.

  2. An Evaluation of Ethyl Silicate-Based Grouts for Weathered Silicate Stones

    NASA Astrophysics Data System (ADS)

    Dolph, Brittany Helen

    Culturally significant monuments made of weathered siliceous stone often display sub-surface condition issues such as cracks and voids. These issues require grouts that are ideally compatible with the composition and properties of the substrate. Based on the successful application of ethyl silicates as consolidants in recent literature, this study examines possible formulation pathways for the development of a grout incorporating ethyl silicate. Tetraethylorthosilicate (TEOS), dibutyltin dilaurate (DBTL) as a catalyst, silicone oil (PDMS), various grades of ground quartz, sepiolite, and hollow glass spheres were used in differing concentrations to create samples. These were visually and physically assessed on workability, separation, shrinkage, cracking, strength, and flexibility. Quantitative analysis was performed on selected formulations using UV-Vis-NIR reflectance spectroscopy in coordination with a weight loss experiment to investigate kinetics, dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). Successful formulations tended to include oligomeric TEOS, crushed quartz of mixed grades, sepiolite powder, and PDMS, and show promise for future investigations.

  3. Direct measurement of the combined effects of lichen, rainfall, and temperature on silicate weathering

    SciTech Connect

    Brady, P.V.; Dorn, R.I.; Brazel, A.J.; Clark, J.; Moore, R.B.; Glidewell, T.

    1999-10-01

    A key uncertainty in models of the global carbonate-silicate cycle and long-term climate is the way that silicates weather under different climatologic conditions, and in the presence or absence of organic activity. Digital imaging of basalts in Hawaii resolves the coupling between temperature, rainfall, and weathering in the presence and absence of lichens. Activation energies for abiotic dissolution of plagioclase (23.1 {+-} 2.5 kcal/mol) and olivine (21.3 {+-} 2.7 kcal/mol) are similar to those measured in the laboratory, and are roughly double those measured from samples taken underneath lichen. Abiotic weathering rates appear to be proportional to rainfall. Dissolution of plagioclase and olivine underneath lichen is far more sensitive to rainfall.

  4. Submarine weathering of silicate minerals and the extent of pore water freshening at active continental margins

    NASA Astrophysics Data System (ADS)

    Scholz, Florian; Hensen, Christian; Schmidt, Mark; Geersen, Jacob

    2013-01-01

    In order to investigate how submarine weathering processes may affect the water balance of sediments at convergent plate margins, six sediment cores were retrieved off Central Chile at water depth between ˜800 and 4000 m. The sediment solid phase was analyzed for its major element composition and the pore fluids were analyzed for dissolved sulfate, sulfide, total alkalinity, major cations, chloride, bromide, iodide, hydrocarbons as well as the carbon isotopic composition of methane. Because of negligible weathering on land, surface sediments off Central Chile are rich in reactive silicate minerals and have a bulk composition similar to volcanic rocks in the adjacent Andes. Deep-sourced fluxes of alkalinity, cations and chloride indicate that silicate minerals are subject to weathering in the forearc during burial. Comparison of deep-sourced signals with data from nearby Ocean Drilling Program Sites reveals two different types of weathering processes: In shallow (tens of meters), methanic sediments of slope basins with high organic carbon burial rates, reactive silicate minerals undergo incongruent dissolution through reaction with CO2 from methanogenesis. At greater burial depth (hundreds of meters), silicate weathering is dominated by authigenic smectite formation. This process is accompanied by uptake of water into the clay interlayers thus leading to elevated salinities in the surrounding pore water. Deep-seated smectite formation is more widespread than shallow silicate dissolution, as it is independent from the availability of CO2 from methanogenesis. Although solute transport is not focused enough to form cold seeps in the proper sense, tectonically induced, diffuse fluid flow transfers the deep-seated signal of smectite formation into the shallow sediments. The temperature-controlled conversion of smectite to illite is considered the most important dehydration process in marine forearc environments (depth of kilometers). However, in agreement with other

  5. Silicate and carbonate mineral weathering in soil profiles developed on Pleistocene glacial drift (Michigan, USA): Mass balances based on soil water geochemistry

    NASA Astrophysics Data System (ADS)

    Jin, Lixin; Williams, Erika L.; Szramek, Kathryn J.; Walter, Lynn M.; Hamilton, Stephen K.

    2008-02-01

    Geochemistry of soil, soil water, and soil gas was characterized in representative soil profiles of three Michigan watersheds. Because of differences in source regions, parent materials in the Upper Peninsula of Michigan (the Tahquamenon watershed) contain only silicates, while those in the Lower Peninsula (the Cheboygan and the Huron watersheds) have significant mixtures of silicate and carbonate minerals. These differences in soil mineralogy and climate conditions permit us to examine controls on carbonate and silicate mineral weathering rates and to better define the importance of silicate versus carbonate dissolution in the early stage of soil-water cation acquisition. Soil waters of the Tahquamenon watershed are the most dilute; solutes reflect amphibole and plagioclase dissolution along with significant contributions from atmospheric precipitation sources. Soil waters in the Cheboygan and the Huron watersheds begin their evolution as relatively dilute solutions dominated by silicate weathering in shallow carbonate-free soil horizons. Here, silicate dissolution is rapid and reaction rates dominantly are controlled by mineral abundances. In the deeper soil horizons, silicate dissolution slows down and soil-water chemistry is dominated by calcite and dolomite weathering, where solutions reach equilibrium with carbonate minerals within the soil profile. Thus, carbonate weathering intensities are dominantly controlled by annual precipitation, temperature and soil pCO 2. Results of a conceptual model support these field observations, implying that dolomite and calcite are dissolving at a similar rate, and further dissolution of more soluble dolomite after calcite equilibrium produces higher dissolved inorganic carbon concentrations and a Mg 2+/Ca 2+ ratio of 0.4. Mass balance calculations show that overall, silicate minerals and atmospheric inputs generally contribute <10% of Ca 2+ and Mg 2+ in natural waters. Dolomite dissolution appears to be a major process

  6. Process-based modeling of silicate mineral weathering responses to increasing atmospheric CO2 and climate change

    NASA Astrophysics Data System (ADS)

    Banwart, Steven A.; Berg, Astrid; Beerling, David J.

    2009-12-01

    A mathematical model describes silicate mineral weathering processes in modern soils located in the boreal coniferous region of northern Europe. The process model results demonstrate a stabilizing biological feedback mechanism between atmospheric CO2 levels and silicate weathering rates as is generally postulated for atmospheric evolution. The process model feedback response agrees within a factor of 2 of that calculated by a weathering feedback function of the type generally employed in global geochemical carbon cycle models of the Earth's Phanerozoic CO2 history. Sensitivity analysis of parameter values in the process model provides insight into the key mechanisms that influence the strength of the biological feedback to weathering. First, the process model accounts for the alkalinity released by weathering, whereby its acceleration stabilizes pH at values that are higher than expected. Although the process model yields faster weathering with increasing temperature, because of activation energy effects on mineral dissolution kinetics at warmer temperature, the mineral dissolution rate laws utilized in the process model also result in lower dissolution rates at higher pH values. Hence, as dissolution rates increase under warmer conditions, more alkalinity is released by the weathering reaction, helping maintain higher pH values thus stabilizing the weathering rate. Second, the process model yields a relatively low sensitivity of soil pH to increasing plant productivity. This is due to more rapid decomposition of dissolved organic carbon (DOC) under warmer conditions. Because DOC fluxes strongly influence the soil water proton balance and pH, this increased decomposition rate dampens the feedback between productivity and weathering. The process model is most sensitive to parameters reflecting soil structure; depth, porosity, and water content. This suggests that the role of biota to influence these characteristics of the weathering profile is as important, if not

  7. Assessing Silicate Weathering in Permafrost-Dominated Catchments Using Lithium Isotopes: The Lena River, Siberia

    NASA Astrophysics Data System (ADS)

    Murphy, M. J.; Pogge von Strandmann, P.; Porcelli, D.; Katchinoff, J. A.; Moreras Martí, A.; Hirst, C. A.; Andersson, P. S.; Maximov, T. C.

    2015-12-01

    -dominated region, and provides rates on how quickly water-rock interaction can affect silicate weathering.

  8. Silicate weathering and CO2 consumption within agricultural landscapes, the Ohio-Tennessee River Basin

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Myriad studies have shown the extent of human alteration to global biogeochemical cycles. Yet, there is only a limited understanding of the influence that humans have over silicate weathering fluxes; fluxes that have regulated atmospheric carbon dioxide concentrations and global climate over geologi...

  9. Silicate versus carbonate weathering in Iceland: New insights from Ca isotopes

    NASA Astrophysics Data System (ADS)

    Jacobson, Andrew D.; Grace Andrews, M.; Lehn, Gregory O.; Holmden, Chris

    2015-04-01

    Several studies have measured riverine fluxes of Ca and carbonate alkalinity in Iceland with the aim of quantifying the role of basalt weathering in the long-term carbon cycle. A major assumption is that all of the Ca and alkalinity originates from the dissolution of Ca-bearing silicate minerals, such as plagioclase and clinopyroxene. However, hydrothermal calcite occurs throughout Iceland, and even trace levels are expected to impact river geochemistry owing to the mineral's high solubility and fast dissolution rate. To test this hypothesis, we used a new, high-precision Ca isotope MC-TIMS method (δ44/40Ca; 2σSD = ± 0.04 ‰) to trace sources of Ca in Icelandic rivers. We report elemental and Ca isotope data for rivers, high- and low-temperature groundwater, basalt, hydrothermal calcite (including Iceland Spar), and stilbite and heulandite, which are two types of zeolites commonly formed during low-grade metamorphism of basalt. In agreement with previous research, we find that rivers have higher δ44/40Ca values than basalt, with a maximum difference of ∼0.40‰. This difference may reflect isotope fractionation in the weathering zone, i.e., preferential uptake of 40Ca during clay mineral formation, adsorption, and other geochemical processes that cycle Ca. However, calcite δ44/40Ca values are also up to ∼0.40‰ higher than bedrock values, and on a diagram of δ44/40Ca versus Sr/Ca, nearly all waters plot within a plausible mixing domain bounded by the measured compositions of basalt and calcite, with glacial rivers plotting closer to calcite than non-glacial rivers. Calcite and heulandite form during hydrothermal alteration of basalt in the deep lava pile and often occur together in metabasalts now exposed at the surface. Because heulandite δ44/40Ca values are ∼1-2‰ lower than basalt, we suggest that 40Ca uptake by heudlandite explains the relatively high δ44/40Ca values of calcite and that calcite weathering in turn elevates riverine δ44/40Ca

  10. Rates of oxidative weathering on the surface of Mars

    NASA Technical Reports Server (NTRS)

    Burns, Roger G.

    1992-01-01

    Implicit in the mnemonic 'MSATT' (Mars surface and atmosphere through time) is that rates of surface processes on Mars through time should be investigated, including studies of the kinetics and mechanism of oxidative weathering reactions occurring in the Martian regolith. Such measurements are described. Two major elements analyzed in the Viking Lander XRF experiment that are most vulnerable to atmospheric oxidation are iron and sulfur. Originally, they occurred as Fe(2+)-bearing silicate and sulfide minerals in basaltic rocks on the surface of Mars. However, chemical weathering reactions through time have produced ferric- and sulfate-bearing assemblages now visible in the Martian regolith. Such observations raise several question about: (1) when the oxidative weathering reactions took place on Mars; (2) whether or not the oxidized regolith is a fossilized remnant of past weathering processes; (3) deducting chemical interactions of the ancient Martian atmosphere with its surface from surviving phases; (4) possible weathering reactions still occurring in the frozen regolith; and (5) the kinetics and mechanism of past and present-day oxidative reactions on Mars. These questions may be addressed experimentally by studying reaction rates of dissolution and oxidation of basaltic minerals, and by identifying reaction products forming on the mineral surfaces. Results for the oxidation of pyrrhotite and dissolved ferrous iron are reported.

  11. Initial effects of vegetation on Hawaiian basalt weathering rates

    SciTech Connect

    Cochran, M.F.; Berner, R.A. )

    1992-01-01

    Weathering of Ca and Mg silicates on land and ensuing precipitation and burial of Ca and Mg carbonates in marine sediments is the principal sink for carbon dioxide from the atmosphere/ocean system on geologic time scales. Model calculations of ancient atmospheric CO[sub 2] partial pressure depend strongly on the authors assumptions about the enhancement of silicate weathering rates first by primitive terrestrial biota, then by the appearance and evolution of the vascular plants. Aa and pahoehoe basalts were collected from Mauna Loa and Kilauea volcanoes on the island of Hawaii. Flows ranged in age (one year to several thousand years) and in ambient climate. Where possible, each flow was sampled beneath a suite of current plant covers: none, lichens, and higher plants. Rocks were embedded in epoxy to preserve the plant-rock interface, then sectioned and subjected to electron probe microanalysis. During initial weathering, vascular plants appeared to promote congruent dissolution of minerals (particularly olivine and Ca-rich plagioclase) and glass near the surfaces of underlying basalts. In the neighborhood of roots, primary cracks widened with time into networks of open channels. This effect was observed prior to the formation of measurable leached zones in exterior grains and prior to the appearance of secondary minerals. As a result, initial mass loss from young, plant-covered basalts appeared to be up to one or more orders of magnitude greater than from bare-rock controls. Despite earlier reports of substantial enhancement of Hawaiian basalt weathering rates by the lichen Stereocaulon vulcani, weathering observed beneath this lichen was comparable to that of unvegetated rocks.

  12. Dual-Rate Transmission Reduces Weather Effects

    NASA Technical Reports Server (NTRS)

    Posner, E. C.

    1984-01-01

    Scheme ensures maximum data received on average. Dual-rate scheme for maximizing data returned during spacecraft mission, adaptable, as is or with modifications, to high-frequency terrestrial data transmission. Data rate fixed in advance at minimum value guarantees reasonable prospect of success during bad weather. Dualrate strategy yields net data rate 2.5 times best achievable with single transmission rate.

  13. Silicate weathering and CO2 consumption within agricultural landscapes, the Ohio-Tennessee River Basin, USA

    NASA Astrophysics Data System (ADS)

    Fortner, S. K.; Lyons, W. B.; Carey, A. E.; Shipitalo, M. J.; Welch, S. A.; Welch, K. A.

    2012-03-01

    Myriad studies have shown the extent of human alteration to global biogeochemical cycles. Yet, there is only a limited understanding of the influence that humans have over silicate weathering fluxes; fluxes that have regulated atmospheric carbon dioxide concentrations and global climate over geologic timescales. Natural landscapes have been reshaped into agricultural ones to meet food needs for growing world populations. These processes modify soil properties, alter hydrology, affect erosion, and consequently impact water-soil-rock interactions such as chemical weathering. Dissolved silica (DSi), Ca2+, Mg2+, NO3-, and total alkalinity were measured in water samples collected from five small (0.0065 to 0.383 km2) gauged watersheds at the North Appalachian Experimental Watershed (NAEW) near Coshocton, Ohio, USA. The sampled watersheds in this unglaciated region include: a forested site (70+ year stand), mixed agricultural use (corn, forest, pasture), an unimproved pasture, tilled corn, and a recently (<3 yr) converted no-till corn field. The first three watersheds had perennial streams, but the two corn watersheds only produced runoff during storms and snowmelt. For the perennial streams, total discharge was an important control of dissolved silicate transport. Median DSi yields (2210-3080 kg km-2 yr-1) were similar to the median of annual averages between 1979-2009 for the much larger Ohio-Tennessee River Basin (2560 kg km-2 yr-1). Corn watersheds, which only had surface runoff, had substantially lower DSi yields (<530 kg km-2 yr-1) than the perennial-flow watersheds. The lack of contributions from Si-enriched groundwater largely explained their much lower DSi yields with respect to sites having baseflow. A significant positive correlation between the molar ratio of (Ca2++Mg2+)/alkalinity to DSi in the tilled corn and the forested site suggested, however, that silicate minerals weathered as alkalinity was lost via enhanced nitrification resulting from fertilizer

  14. Hydrochemistry, weathering and weathering rates on Madeira island

    NASA Astrophysics Data System (ADS)

    Van der Weijden, Cornelis H.; Pacheco, Fernando A. L.

    2003-12-01

    Madeira island consists of Miocene to Pleistocene lavas and pyroclasts. Major rock types are alkali-basalts, basanites and hawaiites; principal soil types are leptosols, andosols and cambisols. Our main objective was to link the chemistry of ground waters to weathering reactions and rates. We collected 40 shallow groundwater samples, remote from human activities. With a few exceptions, the ranges of electrical conductivities were 29-176 μS/cm and of pH 5.8-8.5. The calculated PCO 2 was generally higher than the atmospheric value. The contribution of sea salt to the water chemistry was 30±9%. Corrected for sea salt, the cation concentrations (in meq/l) decrease in the order Ca 2+≈Mg 2+>Na +>>>K +. The concentrations of SO 42- and NO 3- are very low. We calculated that the total annual chemical denudation rate in the studied area amounts to 37±12 g/m 2, consuming 0.86±0.38 mol CO 2/m 2. To achieve our main objective, a set of mole balance equations— ( AX= B)—was used, where A is a composite matrix of coefficients, including ratios between stoichiometric coefficients as determined by the weathering reactions and coefficients accounting for unconstrained contributions, B is the vector with a water composition, and X is the set of mole fractions of dissolved primary minerals plus the residual concentrations of the unconstrained contributions. Olivine (Ol), pyroxene (Py) and plagioclase (Pl) were considered to be the major primary minerals, and smectite, vermiculite, halloysite, allophane, gibbsite and hematite the secondary minerals in the weathering reactions. Using iterative procedures, whereby mixtures of secondary products as well as the composition of plagioclase are allowed to change, we selected one best-fit set of weathering reactions for each spring by checking all possible solutions of the mole balances against predefined boundary conditions. At odds with Goldich (1938) sequence, our model results indicate—for most best-fit sets—a weathering rate

  15. The time scale of the silicate weathering negative feedback on atmospheric CO2

    NASA Astrophysics Data System (ADS)

    Colbourn, G.; Ridgwell, A.; Lenton, T. M.

    2015-05-01

    The ultimate fate of CO2 added to the ocean-atmosphere system is chemical reaction with silicate minerals and burial as marine carbonates. The time scale of this silicate weathering negative feedback on atmospheric pCO2 will determine the duration of perturbations to the carbon cycle, be they geological release events or the current anthropogenic perturbation. However, there has been little previous work on quantifying the time scale of the silicate weathering feedback, with the primary estimate of 300-400 kyr being traceable to an early box model study by Sundquist (1991). Here we employ a representation of terrestrial rock weathering in conjunction with the "GENIE" (Grid ENabled Integrated Earth system) model to elucidate the different time scales of atmospheric CO2 regulation while including the main climate feedbacks on CO2 uptake by the ocean. In this coupled model, the main dependencies of weathering—runoff, temperature, and biological productivity—were driven from an energy-moisture balance atmosphere model and parameterized plant productivity. Long-term projections (1 Myr) were conducted for idealized scenarios of 1000 and 5000 PgC fossil fuel emissions and their sensitivity to different model parameters was tested. By fitting model output to a series of exponentials we determined the e-folding time scale for atmospheric CO2 drawdown by silicate weathering to be ˜240 kyr (range 170-380 kyr), significantly less than existing quantifications. Although the time scales for reequilibration of global surface temperature and surface ocean pH are similar to that for CO2, a much greater proportion of the peak temperature anomaly persists on this longest time scale; ˜21% compared to ˜10% for CO2.

  16. Experimental Weathering of Silicates and Carbonates in a SO_2 Atmosphere: Implications for the Martian Surface Mineralogy

    NASA Astrophysics Data System (ADS)

    Chevrier, V. F.; Lozano, C. G.; Altheide, T. S.

    2012-03-01

    Weathering experiments of carbonates and silicates in a SO_2 atmosphere and water or water plus hydrogen peroxide result in differences in nature and abundance of secondary phases, favoring sulfites in the first case and sulfates in the second.

  17. 40K-40Ca systematics as a tracer of silicate weathering in the Himalayas

    NASA Astrophysics Data System (ADS)

    Davenport, J.; Caro, G.; France-Lanord, C.

    2015-12-01

    Increased weathering resulting from the uplift of the Himalayan Mountains has been cited as one cause (among others) of late Cenozoic cooling. Orogenic uplift generally results in the development of high relief and enhanced erosion, which in turn induces rapid chemical weathering and uptake of atmospheric CO2. Tracing these processes can be accomplished using techniques such as the budget of major element and/or Sr isotopes of the dissolved load. However, in the Himalaya, Sr isotopic compositions are extreme even in carbonate phases, making it difficult to produce realistic estimates of silicate and carbonate inputs to Himalayan rivers. In this study, we explore the potential of the 40K-40Ca system to quantify the relative contributions of silicate and carbonate weathering to river dissolved loads. To this end, we analysed a suite of 40 rivers draining the main litho-tectonic units of the Himalaya, sediments, bedrock, mineral separates and soil and gravel. Our results show that Himalayan carbonates exhibit no radiogenic 40Ca excess despite highly variable 87Sr/86Sr signatures (0.73-0.85). The silicate fraction of bedload sediments is variably radiogenic (+1 to +4), with ɛ40Ca correlating with the 87Sr/86Sr ratio. Analyses of plagioclase, biotite and muscovite separates from a HHC gneiss and greywacke show homogeneous ɛ40Ca despite highly variable K/Ca ratios, indicating recent metamorphic equilibration on a mineral scale. Thus, incongruent weathering of high K/Ca minerals should not represent a significant factor when considering the transfer of radiogenic calcium to the dissolved load. The ɛ40Ca signatures of dissolved river material are significantly influenced by silicate lithologies, and range from +0.1 in carbonate dominated catchments to >+2 ɛ-units in rivers draining predominantly silicate catchments. The silicate contributions estimated from our 40Ca results are in line with major element budgets when considering small catchments but largely exceeds

  18. Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

    NASA Astrophysics Data System (ADS)

    Lechler, Maria; Pogge von Strandmann, Philip A. E.; Jenkyns, Hugh C.; Prosser, Giacomo; Parente, Mariano

    2015-12-01

    An abrupt rise in temperature, forced by a massive input of CO2 into the atmosphere, is commonly invoked as the main trigger for Oceanic Anoxic Events (OAEs). Global warming initiated a cascade of palaeoenvironmental perturbations starting with increased continental weathering and an accelerated hydrological cycle that delivered higher loads of nutrients to coastal areas, stimulating biological productivity. The end-result was widespread anoxia and deposition of black shales: the hallmarks of OAEs. In order to assess the role of weathering as both an OAE initiator and terminator (via CO2 sequestration) during the Early Aptian OAE 1a (Selli Event, ∼120 Ma) the isotopic ratio of lithium isotopes was analysed in three sections of shallow-marine carbonates from the Pacific and Tethyan realms and one basinal pelagic section from the Tethyan domain. Because the isotopic composition of lithium in seawater is largely controlled by continental silicate weathering and high- and low-temperature alteration of basaltic material, a shift to lighter δ7Li values is expected to characterize OAEs. The studied sections illustrate this phenomenon: δ7Li values decrease to a minimum coincident with the negative carbon-isotope excursion that effectively records the onset of OAE 1a. A second negative δ7Li excursion occurs coeval with the minimum in strontium isotopes after the event. The striking similarity to the strontium-isotope record argues for a common driver. The formation and destruction (weathering) of an oceanic LIP could account for the parallel trend in both isotope systems. The double-spike in lithium isotopes is probably related to a change in weathering congruencies. Such a chemostratigraphy is consistent with the hypothesis that an increase in silicate weathering, in conjunction with organic-carbon burial, led to drawdown of atmospheric CO2 during the early Aptian OAE 1a.

  19. MINERAL WEATHERING RATES FROM SMALL-PLOT EXPERIMENTS, WMP SITE, BEAR BROOKS, MAINE

    EPA Science Inventory

    The pH-dependence of silicate mineral weathering rates was measured in small-plot experiments at the Bear Brooks Watershed Manipulation Project site in Maine, U.S.A. ix 2 m2 plots were acidified with solutions of HCL in deionized water at pH values of 2, 2.5, and 3. Acid applicat...

  20. Climatic and landscape controls on water transit times and silicate mineral weathering in the critical zone

    NASA Astrophysics Data System (ADS)

    Zapata-Rios, Xavier; McIntosh, Jennifer; Rademacher, Laura; Troch, Peter A.; Brooks, Paul D.; Rasmussen, Craig; Chorover, Jon

    2015-08-01

    The critical zone (CZ) can be conceptualized as an open system reactor that is continually transforming energy and water fluxes into an internal structural organization and dissipative products. In this study, we test a controlling factor on water transit times (WTT) and mineral weathering called Effective Energy and Mass Transfer (EEMT). We hypothesize that EEMT, quantified based on local climatic variables, can effectively predict WTT within—and mineral weathering products from—the CZ. This study tests whether EEMT or static landscape characteristics are good predictors of WTT, aqueous phase solutes, and silicate weathering products. Our study site is located around Redondo Peak, a rhyolitic volcanic resurgent dome, in northern New Mexico. At Redondo Peak, springs drain slopes along an energy gradient created by differences in terrain aspect. This investigation uses major solute concentrations, the calculated mineral mass undergoing dissolution, and the age tracer tritium and relates them quantitatively to EEMT and landscape characteristics. We found significant correlations between EEMT, WTT, and mineral weathering products. Significant correlations were observed between dissolved weathering products (Na+ and DIC), 3H concentrations, and maximum EEMT. In contrast, landscape characteristics such as contributing area of spring, slope gradient, elevation, and flow path length were not as effective predictive variables of WTT, solute concentrations, and mineral weathering products. These results highlight the interrelationship between landscape, hydrological, and biogeochemical processes and suggest that basic climatic data embodied in EEMT can be used to scale hydrological and hydrochemical responses in other sites.

  1. Silicate weathering and CO2 consumption within agricultural landscapes, the Ohio-Tennessee River Basin, USA

    NASA Astrophysics Data System (ADS)

    Fortner, S. K.; Lyons, W. B.; Carey, A. E.; Shipitalo, M. J.; Welch, S. A.; Welch, K. A.

    2011-09-01

    Myriad studies have shown the extent of human alteration to global biogeochemical cycles. Yet, there is only a limited understanding of the influence that humans have over silicate weathering fluxes; fluxes that have regulated atmospheric carbon dioxide concentrations and global climate over geologic timescales. Natural landscapes have been reshaped into agricultural ones to meet food needs for growing world populations. These processes modify soil properties, alter hydrology, affect erosion, and consequently impact water-soil-rock interactions such as chemical weathering. Dissolved silica (DSi), Ca2+, Mg2+, NO3-, and total alkalinity were measured in water samples collected from five small (0.65 to 38.3 ha) gauged watersheds at the North Appalachian Experimental Watershed (NAEW) near Coshocton, Ohio, USA. The sampled watersheds in this unglaciated region include: a forested site (70+ yr stand), mixed agricultural use (corn, forest, pasture), an unimproved pasture, tilled corn, and a recently (<3 yr) converted no-till corn field. The first three watersheds had perennial streams, but the two corn watersheds only produced runoff during storms and snowmelt. For the perennial streams, total discharge was an important control of dissolved silicate transport. Median DSi yields (22.1-30.8 kg ha-1 a-1) were similar to the median of annual averages between 1979-2009 for the much larger Ohio-Tennessee River Basin (25.6 kg ha-1 a-1). Corn watersheds, which only had surface runoff, had substantially lower DSi yields (<5.3 kg ha-1 a-1) than the perennial-flow watersheds. The lack of contributions from Si-enriched groundwater largely explained their much lower DSi yields with respect to sites having baseflow. A significant positive correlation between the molar ratio of (Ca2+ + Mg2)/alkalinity to DSi in the tilled corn and the forested site suggested, however, that silicate minerals weathered as alkalinity was lost via enhanced nitrification resulting from fertilizer additions

  2. Differential rates of feldspar weathering in granitic regoliths

    USGS Publications Warehouse

    White, A.F.; Bullen, T.D.; Schulz, M.S.; Blum, A.E.; Huntington, T.G.; Peters, N.E.

    2001-01-01

    time. Differential feldspar weathering in the low-permeability Panola bedrock environment is more dependent on relative feldspar solubilities than on differences in kinetic reaction rates. Such weathering is very sensitive to primary and secondary hydraulic conductivities (qp and qs), which control both the fluid volumes passing through the regolith and the thermodynamic saturation of the feldspars. Bedrock permeability is primarily intragranular and is created by internal weathering of networks of interconnected plagioclase phenocrysts. Saprolite permeability is principally intergranular and is the result of dissolution of silicate phases during isovolumetric weathering. A secondary to primary hydraulic conductivity ratio of qs/qp = 150 in the Panola bedrock results in kinetically controlled plagioclase dissolution but thermodynamically inhibited K-feldspar reaction. This result is in accord with calculated chemical saturation states for groundwater sampled in the Panola Granite. In contrast, greater secondary conductivities in the Davis Run saprolite, qs/qp = 800, produces both kinetically controlled plagioclase and K-feldspar dissolution. Faster plagioclase reaction, leading to bedrock weathering in the Panola Granite but not at Davis Run, is attributed to a higher anorthite component of the plagioclase and a wetter and warmer climate. In addition, the Panola Granite has an abnormally high content of disseminated calcite, the dissolution of which precedes the plagioclase weathering front, thus creating additional secondary permeability. Copyright ?? 2001 Elsevier Science Ltd.

  3. Estimation of weathering rates and CO2 drawdown based on solute load: Significance of granulites and gneisses dominated weathering in the Kaveri River basin, Southern India

    NASA Astrophysics Data System (ADS)

    Pattanaik, J. K.; Balakrishnan, S.; Bhutani, R.; Singh, P.

    2013-11-01

    The solute load of the Kaveri River (South India) and its tributaries draining diverse Precambrian terrains during pre-monsoon and monsoon periods was determined. Using average annual flow, total drainage area and atmospheric input corrected major ion concentrations of these rivers chemical weathering rates, annual fluxes of different ionic species to the ocean and CO2 consumption rates were estimated. Bicarbonate is the most dominant ion (27-79% of anion budget) in all the river samples collected during monsoon period followed by Ca2+, whereas, in case of pre-monsoon water samples Na+ is the most dominant ion (in meq/l). Two approaches were adopted to estimate silicate and carbonate weathering rates in the drainage basin. At Musuri silicate weathering rate (SWR) is 9.44 ± 0.29 tons/km2/a and carbonate weathering rate (CWR) is 1.46 ± 0.16 tons/km2/a. More than 90% of the total ionic budget is derived from weathering of silicates in the Kaveri basin. CO2 consumption rate in the basin for silicate weathering FCO2sil is 3.83 ± 0.12 × 105 mol/km2/a (upper limit), which is comparable with the Himalayan rivers at upper reaches. For carbonate weathering (FCO2carb) CO2 consumption rate is 0.15 ± 0.03 × 105 mol/km2/a in the Kaveri basin. The lower limit of CO2 consumption rate corrected for H2SO4 during silicate and carbonate weathering is FCO2sil is 3.24 × 1005 mol/km2/a and FCO2carb 0.13 × 105 mol/km2/a respectively. CO2 sequestered due to silicate weathering in the Kaveri basin is 25.41 (±0.82) × 109 mol/a which represents 0.21 (±0.01)% of global CO2 drawdown. This may be due to tropical climatic condition, high rainfall during both SW and NE monsoon and predominance of silicate rocks in the Kaveri basin.

  4. Northern latitude chemical weathering rates: clues from the Mackenzie River Basin, Canada

    NASA Astrophysics Data System (ADS)

    Millot, Romain; Gaillardet, J. érôme; Dupré, Bernard; Allègre, Claude Jean

    2003-04-01

    The main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate. More than 110 river water samples from the Mackenzie River system (northern Canada) have been sampled and analyzed for major and trace elements and Sr isotopic ratios in the dissolved phase. The three main morphological units are reflected in water chemistry. Rivers from the Canadian Shield are very dilute, dominated by silicate weathering (Millot et al., 2002), whereas the rivers of the Rocky and Mackenzie Mountains as well as the rivers of the sedimentary Interior Platform are dominated by carbonate weathering and are SO 4 rich. Compared to the rivers of the Mackenzie and Rocky Mountains, the rivers of the interior plains are organic, silica, and Na rich and constitute the dominant input term to the Mackenzie River mainstream. Rivers of the Canadian Shield area do not significantly contribute to the Mackenzie River system. Using elemental ratios and Sr isotopic ratios, a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering. Carbonate weathering rates are mostly controlled by runoff, which is higher in the mountainous part of the Mackenzie basin. These rates are comparable to the carbonate weathering rates of warmer areas of the world. It is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering, but its extent remains difficult to assess. Conversely to what was stated by Edmond and Huh (1997), overall silicate weathering rates in the Mackenzie basin are low, ranging from 0.13 to 4.3 tons/km 2/yr (Na + K + Ca + Mg), and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates. In contrast to what has been observed in other large river systems such as the Amazon and Ganges Rivers, silicate weathering rates appear 3 to 4

  5. Isolation and the interaction between a mineral-weathering Rhizobium tropici Q34 and silicate minerals.

    PubMed

    Wang, Rong Rong; Wang, Qi; He, Lin Yan; Qiu, Gang; Sheng, Xia Fang

    2015-05-01

    The purposes of this study were to isolate and evaluate the interaction between mineral-weathering bacteria and silicate minerals (feldspar and biotite). A mineral-weathering bacterium was isolated from weathered rocks and identified as Rhizobium tropici Q34 based on 16S rRNA gene sequence analysis. Si and K concentrations were increased by 1.3- to 4.0-fold and 1.1- to 1.7-fold in the live bacterium-inoculated cultures compared with the controls respectively. Significant increases in the productions of tartaric and succinic acids and extracellular polysaccharides by strain Q34 were observed in cultures with minerals. Furthermore, significantly more tartaric acid and polysaccharide productions by strain Q34 were obtained in the presence of feldspar, while better growth and more citric acid production of strain Q34 were observed in the presence of biotite. Mineral dissolution experiments showed that the organic acids and polysaccharides produced by strain Q34 were also capable of promoting the release of Si and K from the minerals. The results showed that the growth and metabolite production of strain Q34 were enhanced in the presence of the minerals and different mineral exerted distinct impacts on the growth and metabolite production. The bio-weathering process is probably a synergistic action of organic acids and extracellular polysaccharides produced by the bacterium. PMID:25716616

  6. Rates of oxidative weathering on the surface of Mars

    NASA Astrophysics Data System (ADS)

    Burns, R. G.; Fisher, D. S.

    1993-02-01

    A model of acid weathering is proposed for the iron-rich basalts on Mars. Aqueous oxidation of iron sulfides released SO4(2-) and H(+) ions that initiated the dissolution of basaltic ferromagnesian silicates and released Fe(2+) ions. The Fe(2+) ions eventually underwent ferrolysis reactions and produced insoluble hydrous ferric oxide phases. Measurements of the time-dependence of acid weathering reactions show that pyrrhotite is rapidly converted to pyrite plus dissolved ferrous iron, the rate of pyrite formation decreasing with rising pH and lower temperatures. On Mars, oxidation rates of dissolved Fe(2+) ions in equatorial melt-waters in contact with the atmosphere are estimated to lie in the range 0.3-3.0 ppb Fe/yr over the pH range 2 to 6. Oxidation of Fe(2+) ions is estimated to be extremely slow in brine eutectic solutions that might be present on Mars and to be negligible in the frozen regolith.

  7. Rates of oxidative weathering on the surface of Mars

    NASA Technical Reports Server (NTRS)

    Burns, Roger G.; Fisher, Duncan S.

    1993-01-01

    A model of acid weathering is proposed for the iron-rich basalts on Mars. Aqueous oxidation of iron sulfides released SO4(2-) and H(+) ions that initiated the dissolution of basaltic ferromagnesian silicates and released Fe(2+) ions. The Fe(2+) ions eventually underwent ferrolysis reactions and produced insoluble hydrous ferric oxide phases. Measurements of the time-dependence of acid weathering reactions show that pyrrhotite is rapidly converted to pyrite plus dissolved ferrous iron, the rate of pyrite formation decreasing with rising pH and lower temperatures. On Mars, oxidation rates of dissolved Fe(2+) ions in equatorial melt-waters in contact with the atmosphere are estimated to lie in the range 0.3-3.0 ppb Fe/yr over the pH range 2 to 6. Oxidation of Fe(2+) ions is estimated to be extremely slow in brine eutectic solutions that might be present on Mars and to be negligible in the frozen regolith.

  8. 40K-40Ca systematics as a Tracer of Silicate Weathering: A Himalayan case study

    NASA Astrophysics Data System (ADS)

    Davenport, Jesse; Caro, Guillaume; France-Lanord, Christian

    2015-04-01

    This study investigates the use of the 40K-40Ca system as a tracer to better quantify the contributions of silicate and carbonate lithologies in the dissolved load of major Himalayan rivers. Previous work using Sr isotopes as a proxy for silicate weathering has been complicated by the redistribution of radiogenic 87Sr between silicate and carbonate lithologies, particularly in the Lesser Himalaya, where dolomites exhibit 87Sr/86Sr ratios as high as 0.85. The 40Ca signature of carbonates, on the other hand, appears to be remarkably resistant to metamorphism and dolomitization [1]. It was therefore anticipated that the 40K-40Ca system could circumvent issues associated with such secondary events, and yield more robust constraints on the relative contribution of silicate vs. carbonate lithologies in dissolved river loads. The main difficulty in applying the 40K-40Ca decay scheme as a tracer lies in the analytical precision required to measure small variations (~1 ɛ-unit) on the large 40Ca isotope (96.9%). This difficulty can now be overcome using the Finnigan Triton TIMS, which allows measurements of the 40Ca/44Ca ratio with external precision of 0.35 ɛ-unit in multidynamic mode. Using this method, we generated high-precision 40Ca data on carbonates/dolomites, bedload sediments, dissolved load, and clay samples originating from and representing the main litho-tectonic units of the Himalaya. Our results show that metamorphosed dolomites from the Lesser Himalaya (LH) exhibit no radiogenic 40Ca excess despite highly variable 87Sr/86Sr signatures (0.73-0.85). Thus, all Himalayan carbonates appear to be characterized by a homogeneous ɛ40Ca=0. In contrast, silicate material is radiogenic, with ɛ40Ca averaging +1 in the Tethyan Sedimentary Series (TSS), +1.6 in the High Himalaya crystalline (HHC) and +4 ɛ-units in the LH. Results obtained from a series of 35 Himalayan rivers (including the Brahmaputra, Ganga and its main tributaries) show that ɛ40Ca in the

  9. Rock-weathering rates as functions of time

    USGS Publications Warehouse

    Colman, Steven M.

    1981-01-01

    The scarcity of documented numerical relations between rock weathering and time has led to a common assumption that rates of weathering are linear. This assumption has been strengthened by studies that have calculated long-term average rates. However, little theoretical or empirical evidence exists to support linear rates for most chemical-weathering processes, with the exception of congruent dissolution processes. The few previous studies of rock-weathering rates that contain quantitative documentation of the relation between chemical weathering and time suggest that the rates of most weathering processes decrease with time. Recent studies of weathering rinds on basaltic and andesitic stones in glacial deposits in the western United States also clearly demonstrate that rock-weathering processes slow with time. Some weathering processes appear to conform to exponential functions of time, such as the square-root time function for hydration of volcanic glass, which conforms to the theoretical predictions of diffusion kinetics. However, weathering of mineralogically heterogeneous rocks involves complex physical and chemical processes that generally can be expressed only empirically, commonly by way of logarithmic time functions. Incongruent dissolution and other weathering processes produce residues, which are commonly used as measures of weathering. These residues appear to slow movement of water to unaltered material and impede chemical transport away from it. If weathering residues impede weathering processes then rates of weathering and rates of residue production are inversely proportional to some function of the residue thickness. This results in simple mathematical analogs for weathering that imply nonlinear time functions. The rate of weathering becomes constant only when an equilibrium thickness of the residue is reached. Because weathering residues are relatively stable chemically, and because physical removal of residues below the ground surface is slight

  10. Hf and Nd isotopes in marine sediments: Constraints on global silicate weathering

    NASA Astrophysics Data System (ADS)

    Bayon, G.; Burton, K. W.; Soulet, G.; Vigier, N.; Dennielou, B.; Etoubleau, J.; Ponzevera, E.; German, C. R.; Nesbitt, R. W.

    2009-01-01

    The combined use of Lu-Hf and Sm-Nd isotope systems potentially offers a unique perspective for investigating continental erosion, but little is known about whether, and to what extent, the Hf-Nd isotope composition of sediments is related to silicate weathering intensity. In this study, Hf and Nd elemental and isotope data are reported for marine muds, leached Fe-oxide fractions and zircon-rich turbidite sands collected off the Congo River mouth, and from other parts of the SE Atlantic Ocean. All studied samples from the Congo fan (muds, Fe-hydroxides, sands) exhibit indistinguishable Nd isotopic composition (ɛ Nd ~ - 16), indicating that Fe-hydroxides leached from these sediments correspond to continental oxides precipitated within the Congo basin. In marked contrast, Hf isotope compositions for the same samples exhibit significant variations. Leached Fe-hydroxide fractions are characterized by ɛ Hf values (from - 1.1 to + 1.3) far more radiogenic than associated sediments (from - 7.1 to - 12.0) and turbidite sands (from - 27.2 to - 31.6). ɛ Hf values for Congo fan sediments correlate very well with Al/K (i.e. a well-known index for the intensity of chemical weathering in Central Africa). Taken together, these results indicate that (1) silicate weathering on continents leads to erosion products having very distinctive Hf isotope signatures, and (2) a direct relationship exists between ɛ Hf of secondary clay minerals and chemical weathering intensity. These results combined with data from the literature have global implications for understanding the Hf-Nd isotope variability in marine precipitates and sediments. Leached Fe-hydroxides from Congo fan sediments plot remarkably well on an extension of the 'seawater array' (i.e. the correlation defined by deep-sea Fe-Mn precipitates), providing additional support to the suggestion that the ocean Hf budget is dominated by continental inputs. Fine-grained sediments define a diffuse trend, between that for igneous

  11. Determining mineral weathering rates based on solid and solute weathering gradients and velocities: Application to biotite weathering in saprolites

    USGS Publications Warehouse

    White, A.F.

    2002-01-01

    Chemical weathering gradients are defined by the changes in the measured elemental concentrations in solids and pore waters with depth in soils and regoliths. An increase in the mineral weathering rate increases the change in these concentrations with depth while increases in the weathering velocity decrease the change. The solid-state weathering velocity is the rate at which the weathering front propagates through the regolith and the solute weathering velocity is equivalent to the rate of pore water infiltration. These relationships provide a unifying approach to calculating both solid and solute weathering rates from the respective ratios of the weathering velocities and gradients. Contemporary weathering rates based on solute residence times can be directly compared to long-term past weathering based on changes in regolith composition. Both rates incorporate identical parameters describing mineral abundance, stoichiometry, and surface area. Weathering gradients were used to calculate biotite weathering rates in saprolitic regoliths in the Piedmont of Northern Georgia, USA and in Luquillo Mountains of Puerto Rico. Solid-state weathering gradients for Mg and K at Panola produced reaction rates of 3 to 6 x 10-17 mol m-2 s-1 for biotite. Faster weathering rates of 1.8 to 3.6 ?? 10-16 mol m-2 s-1 are calculated based on Mg and K pore water gradients in the Rio Icacos regolith. The relative rates are in agreement with a warmer and wetter tropical climate in Puerto Rico. Both natural rates are three to six orders of magnitude slower than reported experimental rates of biotite weathering. ?? 2002 Elsevier Science B.V. All rights reserved.

  12. Effects of climate and mineral supply rates on long-term chemical weathering rates in granitic landscapes

    NASA Astrophysics Data System (ADS)

    Riebe, C. S.; Kirchner, J. W.; Finkel, R. C.

    2003-12-01

    We used cosmogenic nuclide and geochemical mass balance methods to measure long-term rates of chemical weathering and physical erosion of granitic terrain. Our 43 study sites encompass widely varying climates and denudation rates; mean annual temperatures vary from 2 to 32\\deg C, average annual precipitation spans a 20-fold range (from 22 to 420 cm/yr), and denudation rates vary by 32-fold across our sites. Long-term chemical weathering rates for these 43 sites range from 0 to 173 t km-2 yr-1, in several cases exceeding the highest granitic weathering rates on record from previous work. Chemical weathering rates are highest at sites with rapid denudation rates, consistent with strong coupling between rates of chemical weathering and mineral supply from physical erosion of rock. To account for effects of mineral supply in analyzing how climate affects chemical weathering, we introduce the "Weathering Intensity Factor" (WIF), the ratio of chemical weathering rate to physical erosion rate. WIF's increase systematically with average annual precipitation and mean annual temperature, both for the soil as a whole, and for individual component elements including Si, Na, and Ca. Between 59 and 79 percent of the variance in WIF's can be explained by a simple Arrhenius-like relationship based on mean annual temperature and average annual precipitation. Moreover, when we couple this Arrhenius relationship with our measurements of long-term erosion rates, we obtain a simple prediction equation that explains between 79 and 93 percent of the variance in long-term chemical weathering rates. The temperature-dependence of WIF is roughly half what one would expect from laboratory measurements of activation energies for feldspar weathering. Our results imply that the strength of climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought, at least in actively eroding, unglaciated terrain similar to our study sites. Our results

  13. Silicate Weathering and Pervasive Authigenic Carbonate Precipitation Coupled to Methanogenesis in the Krishna-Godavari Basin, Offshore India

    NASA Astrophysics Data System (ADS)

    Solomon, E. A.; Spivack, A. J.; Kastner, M.; Torres, M. E.

    2014-12-01

    The cycling of methane in marine sediments has been actively studied for the past several decades, but less attention has been paid to the cycling of CO2 produced in methanogenic sediments. The National Gas Hydrate Program Expedition 01 cored 10 sites with the Joides Resolution drillship in the Krishna-Godavari basin, located on the southeastern margin of India. A comprehensive suite of pore water solute concentrations and isotope ratios were analyzed to investigate the distribution and concentration of gas hydrate along the margin, in situ diagenetic and metabolic reactions, fluid migration and flow pathways, and fluid and gas sources. This represents one of the most comprehensive pore water geochemical datasets collected at a continental margin to date, and provides the necessary tracers to better understand the processes and sinks controlling CO2 in margin sediments. Our results show that the CO2 produced through net microbial methanogenesis is effectively neutralized through silicate weathering throughout the sediment column drilled at each site (~100-300 m), buffering the pH of the sedimentary pore water and generating excess alkalinity through the same reaction sequence as continental silicate weathering. Most of the excess alkalinity produced through silicate weathering in the Krishna-Godavari basin is sequestered in Ca- and Fe-carbonates as a result of ubiquitous calcium release from weathering detrital silicates and Fe-reduction within the methanogenic sediments. Formation of secondary hydrous silicates (e.g. smectite) related to incongruent primary silicate dissolution acts as a significant sink for pore water Mg, K, Li, Rb, and B. The consumption of methane through anaerobic oxidation of methane, sequestration of methane in gas hydrate, and sequestration of dissolved inorganic carbon in authigenic carbonates keeps methanogenesis as a thermodynamically feasible catabolic pathway. Our results combined with previous indications of silicate weathering in

  14. BET surface area distributions in polar stream sediments: Implications for silicate weathering in a cold-arid environment

    USGS Publications Warehouse

    Marra, Kristen R.; Elwood Madden, Megan E; Soreghan, Gerilyn S.; Hall, Brenda L

    2014-01-01

    BET surface area values are critical for quantifying the amount of potentially reactive sediments available for chemical weathering and ultimately, prediction of silicate weathering fluxes. BET surface area values of fine-grained (<62.5 μm) sediment from the hyporheic zone of polar glacial streams in the McMurdo Dry Valleys, Antarctica (Wright and Taylor Valleys) exhibit a wide range (2.5–70.6 m2/g) of surface area values. Samples from one (Delta Stream, Taylor Valley) of the four sampled stream transects exhibit high values (up to 70.6 m2/g), which greatly exceed surface area values from three temperate proglacial streams (0.3–12.1 m2/g). Only Clark stream in Wright Valley exhibits a robust trend with distance, wherein surface area systematically decreases (and particle size increases) in the mud fraction downstream, interpreted to reflect rapid dissolution processes in the weathering environment. The remaining transects exhibit a range in variability in surface area distributions along the length of the channel, likely related to variations in eolian input to exposed channel beds, adjacent snow drifts, and to glacier surfaces, where dust is trapped and subsequently liberated during summer melting. Additionally, variations in stream discharge rate, which mobilizes sediment in pulses and influences water:rock ratios, the origin and nature of the underlying drift material, and the contribution of organic acids may play significant roles in the production and mobilization of high-surface area sediment. This study highlights the presence of sediments with high surface area in cold-based glacier systems, which influences models of chemical denudation rates and the impact of glacial systems on the global carbon cycle.

  15. Evidence for stable Sr isotope fractionation by silicate weathering in a small sedimentary watershed in southwestern Taiwan

    NASA Astrophysics Data System (ADS)

    Chao, Hung-Chun; You, Chen-Feng; Liu, Hou-Chun; Chung, Chuan-Hsiung

    2015-09-01

    Radiogenic Sr isotopes (87Sr/86Sr) are robust for provenance identification in hydrology, affected mainly by the age of background lithologies and the degree of chemical weathering. However, there is limited knowledge concerning the fractionation mechanism of stable Sr isotopes (88Sr/86Sr) in rivers. In this study, river water was collected on a weekly to monthly basis throughout dry and wet seasons. Furthermore, to study the variations of radiogenic and stable Sr isotopes during intense weathering, a major flooding event (2000 mm precipitation in three days, Typhoon Morakot), water was captured within a small drainage catchment system (161 km2) along the Hou-ku River in southwestern Taiwan. For a better constraint on the end member compositions, bedload sediments, suspended particles, and several host rocks were sampled for a systematic investigation. The carbonate and silicate phases of these solids were chemically separated. Dissolved major elements indicate that the watersheds were predominated by silicate weathering. Stable Sr isotopes show no significant variation (δ88Sr = 0.24-0.31‰) temporally and spatially with an average of 0.28‰. Additionally, all solids showed lower δ88Sr values than the river water while the host rocks had higher δ88Sr values (δ88Sr = 0.20-0.26‰) than the residual weathering products (δ88Sr = 0.08-0.22‰), indicating preferential leaching of heavy Sr into the hydrosphere and leaving light Sr in the residual solids. Results of laboratory acid leaching experiments reveal that dissolution of high δ88Sr value minerals occurred at an early stage of weathering. The variation of weathering intensity does not alter stable Sr isotopes in silicate weathering dominated river water, which contains higher stable Sr isotopes than the associated sediments. The silicatic sedimentary rocks preferentially released higher stable Sr isotopes into the hydrosphere during chemical weathering, thus leaving lower stable Sr isotopes in the residual

  16. Sensitivity of mineral dissolution rates to physical weathering : A modeling approach

    NASA Astrophysics Data System (ADS)

    Opolot, Emmanuel; Finke, Peter

    2015-04-01

    There is continued interest on accurate estimation of natural weathering rates owing to their importance in soil formation, nutrient cycling, estimation of acidification in soils, rivers and lakes, and in understanding the role of silicate weathering in carbon sequestration. At the same time a challenge does exist to reconcile discrepancies between laboratory-determined weathering rates and natural weathering rates. Studies have consistently reported laboratory rates to be in orders of magnitude faster than the natural weathering rates (White, 2009). These discrepancies have mainly been attributed to (i) changes in fluid composition (ii) changes in primary mineral surfaces (reactive sites) and (iii) the formation of secondary phases; that could slow natural weathering rates. It is indeed difficult to measure the interactive effect of the intrinsic factors (e.g. mineral composition, surface area) and extrinsic factors (e.g. solution composition, climate, bioturbation) occurring at the natural setting, in the laboratory experiments. A modeling approach could be useful in this case. A number of geochemical models (e.g. PHREEQC, EQ3/EQ6) already exist and are capable of estimating mineral dissolution / precipitation rates as a function of time and mineral mass. However most of these approaches assume a constant surface area in a given volume of water (White, 2009). This assumption may become invalid especially at long time scales. One of the widely used weathering models is the PROFILE model (Sverdrup and Warfvinge, 1993). The PROFILE model takes into account the mineral composition, solution composition and surface area in determining dissolution / precipitation rates. However there is less coupling with other processes (e.g. physical weathering, clay migration, bioturbation) which could directly or indirectly influence dissolution / precipitation rates. We propose in this study a coupling between chemical weathering mechanism (defined as a function of reactive area

  17. Electrochemical Acceleration of Carbonate and Silicate Weathering for CO2 Mitigation

    NASA Astrophysics Data System (ADS)

    Rau, G. H.; Carroll, S.

    2011-12-01

    Carbonate and many silicate minerals dissolve in strong acids, and such acids are commonly generated at the anode of a conventional saline water electrolysis cell. It was therefore reasoned that encasing such an anode with base minerals would lead to enhanced mineral dissolution and hence increased hydroxide (base) generation at the cathode, formed in course of splitting water, generating H2 and OH-. Subsequent exposue of the alkalized solution to CO2 (e.g., as in air) would lead to absorption of the CO2 and formation of stable dissolved or solid (bi)carbonates for carbon sequestration. Previously, it has been demonstrated that mineral carbonate encasement of a seawater electrolysis cell anode indeed generated basic solutions in excess of pH 9 that were subsequently neutralized via contact with air CO2, increasing the carbon content of the initial seawater by 30% (Rau, G.H. 2008. Environ Sci. Techol. 42, 8935-). To test such a weathering/CO2 capture scheme using silicate minerals, either powdered wollastonite or ultramafic rock standard (UM-4) was encased around the anode of an electrolysis cell composed of graphite electrodes and a 0.25M Na2SO4 electrolyte solution. After 0.5 to 1.5 hrs of electricity application (3.5Vdc, 5-10mA), the electrolyte pH rose to as much as 11.1 (initial and blank solution pH's <6.6). Subequent bubbling of these basic solutions with air lowered pH by at least 2 units and increased dissolve carbon content (primarily bicarbonate) by as much as 50X that of the blanks. While Ca2+ and Mg2+ concentrations were elevated, these were insufficient to balance the majority of the bicarbonate anions formed in solution. This suggests that in these experiments the silicate minerals acted as a neutralizer of the anolyte acid, H2SO4, forming mostly insoluble CaSO4 and MgSO4 at the anode. This then allowed NaOH normally produced at the cathode to accumulate in solution, in turn reacting with air CO2 to form NaHCO3. Longer electrolysis times and

  18. Long-term stability of global erosion rates and weathering during late-Cenozoic cooling.

    PubMed

    Willenbring, Jane K; von Blanckenburg, Friedhelm

    2010-05-13

    Over geologic timescales, CO(2) is emitted from the Earth's interior and is removed from the atmosphere by silicate rock weathering and organic carbon burial. This balance is thought to have stabilized greenhouse conditions within a range that ensured habitable conditions. Changes in this balance have been attributed to changes in topographic relief, where varying rates of continental rock weathering and erosion are superimposed on fluctuations in organic carbon burial. Geological strata provide an indirect yet imperfectly preserved record of this change through changing rates of sedimentation. Widespread observations of a recent (0-5-Myr) fourfold increase in global sedimentation rates require a global mechanism to explain them. Accelerated uplift and global cooling have been given as possible causes, but because of the links between rates of erosion and the correlated rate of weathering, an increase in the drawdown of CO(2) that is predicted to follow may be the cause of global climate change instead. However, globally, rates of uplift cannot increase everywhere in the way that apparent sedimentation rates do. Moreover, proxy records of past atmospheric CO(2) provide no evidence for this large reduction in recent CO(2) concentrations. Here we question whether this increase in global weathering and erosion actually occurred and whether the apparent increase in the sedimentation rate is due to observational biases in the sedimentary record. As evidence, we recast the ocean dissolved (10)Be/(9)Be isotope system as a weathering proxy spanning the past approximately 12 Myr (ref. 14). This proxy indicates stable weathering fluxes during the late-Cenozoic era. The sum of these observations shows neither clear evidence for increased erosion nor clear evidence for a pulse in weathered material to the ocean. We conclude that processes different from an increase in denudation caused Cenozoic global cooling, and that global cooling had no profound effect on spatially and

  19. Revisiting classical silicate dissolution rate laws under hydrothermal conditions

    NASA Astrophysics Data System (ADS)

    Pollet-Villard, Marion; Daval, Damien; Saldi, Giuseppe; Knauss, Kevin; Wild, Bastien; Fritz, Bertrand

    2015-04-01

    apparent modification of silicate dissolution rate over time. In addition, we evidenced that the relation between K-spar dissolution rate and ΔG depends on the crystallographic orientation of the altered surface, and differs from the transition state theory currently implemented into geochemical codes. Importantly, this theoretical curve overestimates the dissolution rates measured in close-to-equilibrium conditions. Taken together, the new findings show promise as a means for improving the accuracy of geochemical simulations. [1] Schott, J., Pokrovsky, O. S., and Oelkers, E. H., 2009. The Link Between Mineral Dissolution/Precipitation Kinetics and Solution Chemistry. Rev Mineral Geochem 70, 207-258. [2] Daval, D., Hellmann, R., Saldi, G. D., Wirth, R., and Knauss, K. G., 2013. Linking nm-scale measurements of the anisotropy of silicate surface reactivity to macroscopic dissolution rate laws: New insights based on diopside. Geochim Cosmochim Acta 107, 121-134.

  20. Effects of silicate weathering on water chemistry in forested, upland, felsic terrane of the USA

    SciTech Connect

    Stauffer, R.E.; Wittchen, B.D. )

    1991-11-01

    The authors use data from the US EPA National Surface Water Survey (NSWS), the USGS Bench-Mark Station monitoring program, and the National Acid Deposition Program (NADP) to evaluate the role of weathering in supplying base cations to surface waters in forested, upland, felsic terrane of the northeastern, northcentral, and northwestern (Idaho batholith) US. Multivariate regression reveals differential effects of discharge on individual base cations and silica, but no secular trend in the Ca/Na denudation rate over 24 yr (1965-1988) for the Wild River catchment in the White Mountains. Because the turn-over time for Na in the soil-exchange complex is only ca. 1.5 yr, the long-term behavior of the ratios Ca/Na and Si/Na in waters leaving this catchment indicates that weathering is compensating for base cation export. In every subregion, Ca and Mg concentrations in lakes are statistically linked to nonmarine Na, but the median Ca/Na ratio is greater than the ratio in local plagioclase. The authors attribute this inequality to nonstoichiometric weathering of calcium in juvenile (formerly glaciated) terrane, not to leaching of exchangeable cations by So{sub 4} because intraregional and cross-regional statistical analysis reveals no effect of atmospherically derived sulfate ion. The median base cation denudation rates (meq m{sup {minus}2}yr{sup {minus}1}) for these American lake regions are: Maine granites (108); western Adirondack felsic gneiss (85); Vermilion batholith (42); Idaho batholith (52). The regional rates are high enough to compensate for present wet deposition of acidifying anions except in some vulnerable lake watersheds in the western Adirondacks.

  1. Effects of silicate weathering on water chemistry in forested, upland, felsic terrane of the USA

    NASA Astrophysics Data System (ADS)

    Stauffer, Robert E.; Wittchen, Bruce D.

    1991-11-01

    We use data from the US EPA National Surface Water Survey (NSWS), the USGS Bench-Mark Station monitoring program, and the National Acid Deposition Program (NADP) to evaluate the role of weathering in supplying base cations to surface waters in forested, upland, felsic terrane of the northeastern, northcentral, and northwestern (Idaho batholith) United States. Multivariate regression reveals differential effects of discharge on individual base cations and silica, but no secular trend in the Ca/Na denudation rate over 24 yr (1965-1988) for the Wild River catchment in the White Mountains. Because the turn-over time for Na in the soil-exchange complex is only ca. 1.5 yr, the long-term behavior of the ratios Ca/Na and Si/Na in waters leaving this catchment indicates that weathering is compensating for base cation export. In every subregion, Ca and Mg concentrations in lakes are statistically linked to nonmarine Na, but the median Ca/Na ratio is greater than the ratio in local plagioclase. We attribute this inequality to nonstoichiometric weathering of calcium in juvenile (formerly glaciated) terrane, not to leaching of exchangeable cations by SO 4, because intraregional and cross-regional statistical analysis reveals no effect of atmospherically derived sulfate ion. The median base cation denudation rates (meq m -2 yr -1) for these American lake regions are: Maine granites (108); western Adirondack felsic gneiss (85); Vermilion batholith (42); Idaho batholith (52). The regional rates are high enough to compensate for present wet deposition of acidifying anions except in some vulnerable lake watersheds in the western Adirondacks.

  2. Chemical weathering in the Krishna Basin and Western Ghats of the Deccan Traps, India: Rates of basalt weathering and their controls

    NASA Astrophysics Data System (ADS)

    Das, A.; Krishnaswami, S.; Sarin, M. M.; Pande, K.

    2005-04-01

    Rates of chemical and silicate weathering of the Deccan Trap basalts, India, have been determined through major ion measurements in the headwaters of the Krishna and the Bhima rivers, their tributaries, and the west flowing streams of the Western Ghats, all of which flow almost entirely through the Deccan basalts. Samples ( n = 63) for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002. The Total dissolved solid (TDS) in the samples range from 27 to 640 mg l -1. The rivers draining the Western Ghats that flow through patches of cation deficient lateritic soils have lower TDS (average: 74 mg l -1), whereas the Bhima (except at origin) and its tributaries that seem to receive Na, Cl, and SO 4 from saline soils and anthropogenic inputs have values in excess of 170 mg l -1. Many of the rivers sampled are supersaturated with respect to calcite. The chemical weathering rates (CWR) of "selected" basins, which exclude rivers supersaturated in calcite and which have high Cl and SO 4, are in range of ˜3 to ˜60 t km -2 y -1. This yields an area-weighted average CWR of ˜16 t km -2 y -1 for the Deccan Traps. This is a factor of ˜2 lower than that reported for the Narmada-Tapti-Wainganga (NTW) systems draining the more northern regions of the Deccan. The difference can be because of (i) natural variations in CWR among the different basins of the Deccan, (ii) "selection" of river basin for CWR calculation in this study, and (iii) possible contribution of major ions from sources, in addition to basalts, to rivers of the northern Deccan Traps. Silicate weathering rates (SWR) in the selected basins calculated using dissolved Mg as an index varies between ˜3 to ˜60 t km -2 y -1, nearly identical to their CWR. The Ca/Mg and Na/Mg in these rivers, after correcting for rain input, are quite similar to those in average basalts of the region, suggesting near congruent release of Ca, Mg, and Na from basalts to rivers. Comparison of

  3. Transport properties of interfacial Si-rich layers formed on silicate minerals during weathering: Implications for environmental concerns

    NASA Astrophysics Data System (ADS)

    Daval, Damien; Rémusat, Laurent; Bernard, Sylvain; Wild, Bastien; Micha, Jean-Sébastien; Rieutord, François; Fernandez-Martinez, Alejandro

    2015-04-01

    The dissolution of silicate minerals is of primary importance for various processes ranging from chemical weathering to CO2 sequestration. Whether it determines the rates of soil formation, CO2 uptake and its impact on climate change, channeling caused by hydrothermal circulation in reservoirs of geothermal power plants, durability of radioactive waste confinement glasses or geological sequestration of CO2, the same strategy is commonly applied for determining the long term evolution of fluid-rock interactions. This strategy relies on a bottom-up approach, where the kinetic rate laws governing silicate mineral dissolution are determined from laboratory experiments. However, a long-standing problem regarding this approach stems from the observation that laboratory-derived dissolution rates overestimate their field counterparts by orders of magnitude, casting doubt on the accuracy and relevance of predictions based on reactive-transport simulations. Recently [1], it has been suggested that taking into account the formation of amorphous Si-rich surface layers (ASSL) as a consequence of mineral dissolution may contribute to decrease the large gap existing between laboratory and natural rates. Our ongoing study is aimed at deciphering the extent to which ASSL may represent a protective entity which affects the dissolution rate of the underlying minerals, both physically (passivation) and chemically (by promoting the formation of a local chemical medium which significantly differs from that of the bulk solution). Our strategy relies on the nm-scale measurement of the physicochemical properties (diffusivity, thickness and density) of ASSL formed on cleavages of a model mineral (wollastonite) and their evolution as a function of reaction progress. Our preliminary results indicate that the diffusivity of nm-thick ASSL formed on wollastonite surface is ~1,000,000 times smaller than that reported for an aqueous medium, as estimated from the monitoring of the progression of a

  4. Silicate or Carbonate Weathering: Fingerprinting Sources of Dissolved Inorganic Carbon Using δ13C in a Tropical River, Southern India

    NASA Astrophysics Data System (ADS)

    Bhagat, H.; Ghosh, P.

    2015-12-01

    Rivers are an inherently vital resource for the development of any region and their importance is highlighted by the presence of many ancient human civilizations adjacent to river systems. δ13C - Si/HCO3 systematics has been applied to large south Indian rivers which drain the Deccan basaltic traps in order to quantify their relative contributions from silicate and carbonate weathering. This study investigates δ13C - Si/HCO3 systematics of the Cauvery River basin which flows through silicate lithology in the higher reaches and carbonate lithology with pedogenic and marine carbonates dominating the terrain in the lower reaches of the basin. The samples for the present study were collected at locations within the watershed during Pre-Monsoon and Monsoon Season 2014. The measurements of stable isotope ratios of δ13CDIC and were accomplished through a Thermo Scientific GasBench II interface connected to a MAT 253 IRMS. We captured a large spatial variation in δ13C and Si/HCO3 values during both seasons; Pre-Monsoon δ13C values ranges between -17.57‰ to -4.02‰ and during Monsoon it varies between -9.19‰ to +0.61‰. These results indicate a two end-member mixing component i.e. a silicate and a carbonate end member; governing the weathering interactions of the Cauvery River. Within the drainage basin, we identified silicate and carbonate dominating sources by using contributions of DIC and δ13C. Si/HCO3 values for Pre-Monsoon ranges between 0.028 - 0.67 and for Monsoon it varies between 0.073 - 0.80. Lighter δ13C composition was observed at sampling sites at higher altitude in contrast to sampling sites at flood plain which show relatively enriched δ13C which indicate mixing of soil derived CO2 with C4 plants. Result suggests dominance of carbonate weathering during the Monsoon Period, while silicate weathering is pronounced during Pre- Monsoon period.

  5. Hydrochemistry of inland rivers in the north Tibetan Plateau: Constraints and weathering rate estimation.

    PubMed

    Wu, Weihua

    2016-01-15

    The geographic region around the northern and northeastern Tibetan Plateau is the source of several inland rivers (e.g. Tarim River) of worldwide importance that are generated in the surrounding mountains systems of Tianshan, Pamir, Karakorum, and Qilian. To characterize chemical weathering and atmospheric CO2 consumption in these regions, water samples from the Tarim, Yili, Heihe, Shule, and Shiyang Rivers were collected and analyzed for major ion concentrations. The hydrochemical characteristics of these inland rivers pronouncedly distinguish them from large exorheic rivers (e.g., the Yangtze River and the Yellow River), as reflected in very high total dissolution solids (TDS) values. TDS was 115-4345 mg l(-1) with an average of 732 mg l(-1), which is an order of magnitude higher than the mean value for world rivers (65 mg l(-1)). The Cheerchen River, Niya River, Keliya River and the terminal lakes of the Tarim River and the Heihe River have TDS values higher than 1 gl(-1), indicating saline water that cannot be directly consumed. Therefore, the problem of sufficient and safe drinking water has become increasingly prominent in the northwestern China arid zone. According to an inversion model, the contribution from evaporite dissolution to the dissolved loads in these rivers is 12.5%-99% with an average of 54%. The calculated silicate and carbonate weathering rates are 0.02-4.62 t km(-2)y(-1) and 0.01-11.7 t km(-2)y(-1) for these rivers. To reduce the influence of lithology, only the silicate weathering rates in different parts of the Tibetan Plateau are compared. A rough variation tendency can be seen in the rates: northern regional (0.15-1.73 t km(-2)y(-1))weathering rates did not show a noticeable correlation with a single influencing factor, such as temperature, elevation, vegetation, and physical

  6. Evidence for non-Gaussian distribution of rock weathering rates

    NASA Astrophysics Data System (ADS)

    Emmanuel, S.

    2015-07-01

    The weathering of rocks influences the geochemistry of the oceans, the erosion of landscapes and manmade structures, and even the global climate. Although a high degree of variance is often observed in rate measurements, little is understood about the statistical characteristics of weathering rate distributions. This preliminary study demonstrates that the weathering rates of limestone, determined from measurements of an ancient eroded limestone edifice, can exhibit highly non-Gaussian behavior. While a Gaussian model produced a poor fit with the data, an alternative model - the generalized extreme value (GEV) framework - was capable of capturing the asymmetric long tailed distribution, in good agreement with the measured curve. Furthermore, the non-Gaussian distribution of these field rates was found to have similar characteristics to the distribution of rates measured over much smaller microscopic regions of limestone surfaces in laboratory experiments. Such similar behavior could be indicative of analogous chemical and mechanical weathering processes acting over a range of different spatial and temporal scales. Moreover, highly asymmetric rate distributions with high variance could be characteristic of rates not only in carbonate rocks, but in other rock types too, suggesting that the use of a small number of measurements to determine field weathering rates may be insufficient to fully characterize the range of rates in natural systems.

  7. Space weathering of near-Earth and main belt silicate-rich asteroids: observations and ion irradiation experiments

    NASA Astrophysics Data System (ADS)

    Marchi, S.; Brunetto, R.; Magrin, S.; Lazzarin, M.; Gandolfi, D.

    2005-12-01

    In this paper we report the results of a comparison between ion irradiation experiments (N^+, Ar^+, Ar++) on silicates, a large spectral data set of silicate-rich (S-type) asteroids, and ordinary chondrite meteorites (OCs). Ion irradiation experiments - conducted on Fe-poor olivine, Fe-poor orthopyroxene, bulk silicate-rich rocks and one OC - have been monitored by means of reflectance spectroscopy (0.3-2.5 μm). All these experiments produce reddening and darkening of reflectance spectra. The observational data consist of a set of visible and near-infrared (0.4-2.4 μm) spectra of S-type asteroids, that belong to main belt (MBAs) and near-Earth (NEOs) populations. By analyzing the spectra of OCs, MBAs, and NEOs, we find a similar mineralogy between most asteroids and meteorites, but different distributions of spectral slopes. We interpret these findings in the frame of space weathering induced by solar wind ion irradiation.

  8. Effect of carbonic anhydrase on silicate weathering and carbonate formation at present day CO2 concentrations compared to primordial values

    PubMed Central

    Xiao, Leilei; Lian, Bin; Hao, Jianchao; Liu, Congqiang; Wang, Shijie

    2015-01-01

    It is widely recognized that carbonic anhydrase (CA) participates in silicate weathering and carbonate formation. Nevertheless, it is still not known if the magnitude of the effect produced by CA on surface rock evolution changes or not. In this work, CA gene expression from Bacillus mucilaginosus and the effects of recombination protein on wollastonite dissolution and carbonate formation under different conditions are explored. Real-time fluorescent quantitative PCR was used to explore the correlation between CA gene expression and sufficiency or deficiency in calcium and CO2 concentration. The results show that the expression of CA genes is negatively correlated with both CO2 concentration and ease of obtaining soluble calcium. A pure form of the protein of interest (CA) is obtained by cloning, heterologous expression, and purification. The results from tests of the recombination protein on wollastonite dissolution and carbonate formation at different levels of CO2 concentration show that the magnitudes of the effects of CA and CO2 concentration are negatively correlated. These results suggest that the effects of microbial CA in relation to silicate weathering and carbonate formation may have increased importance at the modern atmospheric CO2 concentration compared to 3 billion years ago. PMID:25583135

  9. Effect of carbonic anhydrase on silicate weathering and carbonate formation at present day CO2 concentrations compared to primordial values

    NASA Astrophysics Data System (ADS)

    Xiao, Leilei; Lian, Bin; Hao, Jianchao; Liu, Congqiang; Wang, Shijie

    2015-01-01

    It is widely recognized that carbonic anhydrase (CA) participates in silicate weathering and carbonate formation. Nevertheless, it is still not known if the magnitude of the effect produced by CA on surface rock evolution changes or not. In this work, CA gene expression from Bacillus mucilaginosus and the effects of recombination protein on wollastonite dissolution and carbonate formation under different conditions are explored. Real-time fluorescent quantitative PCR was used to explore the correlation between CA gene expression and sufficiency or deficiency in calcium and CO2 concentration. The results show that the expression of CA genes is negatively correlated with both CO2 concentration and ease of obtaining soluble calcium. A pure form of the protein of interest (CA) is obtained by cloning, heterologous expression, and purification. The results from tests of the recombination protein on wollastonite dissolution and carbonate formation at different levels of CO2 concentration show that the magnitudes of the effects of CA and CO2 concentration are negatively correlated. These results suggest that the effects of microbial CA in relation to silicate weathering and carbonate formation may have increased importance at the modern atmospheric CO2 concentration compared to 3 billion years ago.

  10. High-Silica Rock Coatings on Mars: Constraining Secondary Silicate Mineralogy and Chemical Weathering Processes on Mars.

    NASA Astrophysics Data System (ADS)

    Kraft, M. D.; Michalski, J. R.; Sharp, T. G.

    2003-12-01

    Thermal Emission Spectrometer (TES) data have been fundamental to understanding Martian surface mineralogy. These data, however, require careful modeling based on laboratory spectroscopic measurements, and modeling of some minerals for Mars has been equivocal. Due to high degrees of spectral similarity, it is difficult to distinguishing silicate glass, clay minerals, zeolites, palagonitized glass, and other secondary products such as amorphous silica as components of surface rock spectra. Deciphering the nature of secondary mineral products on Mars is of key importance to understanding the role of water at the Martian surface over time. It is of central interest to distinguish primary glass from secondary silicate minerals, and secondary minerals from one another to better constrain the degree and mechanisms of aqueous alteration. Observations of Martian surface materials indicate some degree of atmosphere-water-rock interaction. These include nanophase ferric-iron oxides from visible/near-infrared spectroscopy, concentrated hematite deposits identified with TES, high water contents of rocks measured by the Alpha Proton X-ray Spectrometer, sulfate and halide minerals inferred from lander geochemical measurements, and carbonate minerals identified in Martian dust with TES data. Mass balance suggests that if there are oxides, salts, and carbonates there must also be secondary silicate phases present on Mars, which may be identifiable with TES. Identifying the types, distribution, and abundance (or absence) of secondary silicates will enable better constrains to be placed on Martian chemical weathering processes and the role water has played at the Martian surface. We suggest that rock coatings dominated by amorphous silica are geologically reasonable for Mars and may be consistent with TES data. Laboratory measurements of silica-coated rocks show that thin, micrometer-scale silica coatings have a substantial impact on rock spectra. Consequently, if authegenic

  11. Chemical weathering in a tropical watershed, Luquillo Mountains, Puerto Rico III: Quartz dissolution rates

    USGS Publications Warehouse

    Schulz, M.S.; White, A.F.

    1999-01-01

    The paucity of weathering rates for quartz in the natural environment stems both from the slow rate at which quartz dissolves and the difficulty in differentiating solute Si contributed by quartz from that derived from other silicate minerals. This study, a first effort in quantifying natural rates of quartz dissolution, takes advantage of extremely rapid tropical weathering, simple regolith mineralogy, and detailed information on hydrologic and chemical transport. Quartz abundances and grain sizes are relatively constant with depth in a thick saprolite. Limited quartz dissolution is indicated by solution rounding of primary angularity and by the formation of etch pits. A low correlation of surface area (0.14 and 0.42 m2 g-1) with grain size indicates that internal microfractures and pitting are the principal contributors to total surface area. Pore water silica concentration increases linearly with depth. On a molar basis, between one and three quarters of pore water silica is derived from quartz with the remainder contributed from biotite weathering. Average solute Si remains thermodynamically undersaturated with respect to recently revised estimates of quartz solubility (17-81 ??M). Etch pitting is more abundant on grains in the upper saprolite and is associated with pore waters lower in dissolved silica. Rate constants describing quartz dissolution increase with decreasing depth (from 10-14.5-10-15.1 mol m-2 s-1), which correlate with both greater thermodynamic undersaturation and increasing etch pit densities. Unlike for many aluminosilicates, the calculated natural weathering rates of quartz fall slightly below the rate constants previously reported for experimental studies (10-12.4-10-14.2 mol m-2 s-1). This agreement reflects the structural simplicity of quartz, dilute solutes, and near-hydrologic saturation.

  12. Fundamental Study on Temperature Dependence of Deposition Rate of Silicic Acid - 13270

    SciTech Connect

    Shinmura, Hayata; Niibori, Yuichi; Mimura, Hitoshi

    2013-07-01

    The dynamic behavior of the silicic acid is one of the key factors to estimate the condition of the repository system after the backfill. This study experimentally examined the temperature dependence of dynamic behavior of supersaturated silicic acid in the co-presence of solid phase, considering Na ions around the repository, and evaluated the deposition rate constant, k, of silicic acid by using the first-order reaction equation considering the specific surface area. The values of k were in the range of 1.0x10{sup -11} to 1.0x10{sup -9} m/s in the temperature range of 288 K to 323 K. The deposition rate became larger with increments of temperature under the Na ion free condition. Besides, in the case of Na ions 0.6 M, colloidal silicic acid decreased dramatically at a certain time. This means that the diameter of the colloidal silicic acid became larger than the pore size of filter (0.45 μm) due to bridging of colloidal silicic acid. Furthermore, this study estimated the range of altering area and the aperture of flow-path in various value of k corresponding to temperature by using advection-dispersion model. The concentration in the flow-path became lower with increments of temperature, and when the value of k is larger than 1.0x10{sup -11} m/s, the deposition range of supersaturated silicic acid was estimated to be less than 20 m around the repository. In addition, the deposition of supersaturated silicic acid led the decrement of flow-path aperture, which was remarkable under the condition of relatively high temperature. Such a clogging in flow paths is expected as a retardation effect of radionuclides. (authors)

  13. hydrochemistry of the Andeans and sub-andeans Amazon basins - Weathering and CO2 consumption rates.

    NASA Astrophysics Data System (ADS)

    Moquet, Jean-Sébastien; Crave, Alain; Viers, Jérome; Guyot, Jean-Loup; Lagane, Christelle; Sven Lavado Casimiro, Waldo; Pombosa, Rodrigo; Noriega, Luis; Chavary, Eduardo

    2010-05-01

    Measuring mountain weathering rates, estimating their role on C cycle and identifying the parameters which control them are key to better constrain the knowledge of the continental-ocean-atmosphere interactions over geological timescale. The Andes, in contrast to the Himalaya, have received poor attention in terms of chemical weathering. Several authors have worked on the Amazon river basin, but it is difficult to assess the role of the Andes (10% of the surface area of the Amazon river basin) by only sampling the Amazon at mouth or sampling its largest tributaries. As shown by earlier works, the Upper-Amazon basins are the main matter source of the Amazon basin. The studied area participates at more than 70% of the Amazon weathering rates while it contributes to the total discharge on 30% for 27% of the total area. The studied area is comprised between latitude 0°47'N and 20°28'S and between longitude 79°36'W and 58°45'W and can be divided in three major hydrosystems (the Napo river at North, the Maranon-Ucayali rivers on the central part and the upper Madeira at south) which can be separated on Andes and sub-Andes parts. This work presents the results of the HYBAM research program (present-day hydro-geodynamics of the Amazon Basin) on the upper Amazon basin. The concentration of major elements was analyzed on a monthly basis, sampling at 26 gauging stations which include the Andean basins of the Amazon River and a part of the downstream catchment domain. The objectives of this work are i) calculate the major elements fluxes and their spatial distribution, ii) estimate the present-day rate of rock weathering, as well as the flux of atmospheric/soil CO2 consumption from total rock and silicate weathering, and iii) constrain the major environmental factor which controls the dissolved matter production using unique high temporal and spatial resolution data sampling. The main difficulty of studying large river geochemistry is to separate the main sources of the

  14. Experimental Determination of Ca-Silicate Dissolution Rates: A Source of Calcium for Geologic CO2

    SciTech Connect

    Carroll, S A; Knauss, K G

    2001-04-11

    The international scientific community recognizes that greenhouse gases have the potential to influence climate, and that potential changes in sea level and weather patterns would be largely deleterious. Because CO{sub 2} is emitted in such large quantities and its atmospheric concentration has been consistently rising throughout the recent past, it is only prudent to focus attention on reducing its emission and on developing strategies for its removal from the atmosphere [1]. A variety of removal methods have been suggested ranging from deep-sea disposal, to recycling to methanol, and to conversion to solid carbonate [2]. Problems appear to remain with all these strategies, and more work is needed to develop an acceptable, efficient method or set of methods. The idea of converting the gas to solid carbonate is particularly appealing, because on a human time scale, this is permanent disposal. The reaction of CO{sub 2} and water with unstable silicate minerals to produce more stable silicates (e.g., clays) and solid carbonates is the natural weathering process which is a dominant part of the long-term global geochemical cycling process (e.g., [3]). The Earth's large deposits of limestone and dolomite (the two primary forms of carbonate rock) represent the Earth's natural response to volcanic CO{sub 2} emissions over much of planetary history. Recently, the suggestion was made to utilize the reaction of CO{sub 2} with silicate minerals that occurs naturally during chemical-weathering within deep sedimentary basins [4] or in aquifers [1] as a basis for removal.

  15. Rates of consumption of atmospheric CO2 through the weathering of loess during the next 100 yr of climate change

    NASA Astrophysics Data System (ADS)

    Goddéris, Y.; Brantley, S. L.; François, L. M.; Schott, J.; Pollard, D.; Déqué, M.; Dury, M.

    2013-01-01

    Quantifying how C fluxes will change in the future is a complex task for models because of the coupling between climate, hydrology, and biogeochemical reactions. Here we investigate how pedogenesis of the Peoria loess, which has been weathering for the last 13 kyr, will respond over the next 100 yr of climate change. Using a cascade of numerical models for climate (ARPEGE), vegetation (CARAIB) and weathering (WITCH), we explore the effect of an increase in CO2 of 315 ppmv (1950) to 700 ppmv (2100 projection). The increasing CO2 results in an increase in temperature along the entire transect. In contrast, drainage increases slightly for a focus pedon in the south but decreases strongly in the north. These two variables largely determine the behavior of weathering. In addition, although CO2 production rate increases in the soils in response to global warming, the rate of diffusion back to the atmosphere also increases, maintaining a roughly constant or even decreasing CO2 concentration in the soil gas phase. Our simulations predict that temperature increasing in the next 100 yr causes the weathering rates of the silicates to increase into the future. In contrast, the weathering rate of dolomite - which consumes most of the CO2 - decreases in both end members (south and north) of the transect due to its retrograde solubility. We thus infer slower rates of advance of the dolomite reaction front into the subsurface, and faster rates of advance of the silicate reaction front. However, additional simulations for 9 pedons located along the north-south transect show that the dolomite weathering advance rate will increase in the central part of the Mississippi Valley, owing to a maximum in the response of vertical drainage to the ongoing climate change. The carbonate reaction front can be likened to a terrestrial lysocline because it represents a depth interval over which carbonate dissolution rates increase drastically. However, in contrast to the lower pH and shallower

  16. Resolving the gap between laboratory and field rates of feldspar weathering

    NASA Astrophysics Data System (ADS)

    Gruber, Chen; Zhu, Chen; Georg, R. Bastian; Zakon, Yevgeny; Ganor, Jiwchar

    2014-12-01

    Weathering rates of silicate minerals observed in the laboratory are in general up to five orders of magnitude higher than those inferred from field studies. The differences between experimental conditions in the laboratory and natural conditions in the field have been thoroughly discussed in previous studies, however, the discrepancy was never fully resolved. It has been shown in past work that if the field conditions are fully simulated in standard laboratory experiments, it is not possible to measure the slow rates of mineral dissolution that are observed in the field using standard laboratory experiments. Therefore, a novel method that uses the change of Si isotopes ratio in spiked solutions is used in the present study to measure weathering rates of feldspar under close-to-natural conditions. A single-point batch experiment (SPBE) of albite dissolution was performed in the present study with an “untreated” albite sample. During the SPBE the dissolution rate was affected by the change of deviation from equilibrium and by the change in the mineral surface reactivity. In order to quantify the effect of the change in surface reactivity on the measured dissolution rates, two multi-point batch experiments (MPBE) were conducted. In those experiments, surface reactivity was found to depend on the amount of dissolved mineral. The decrease in surface reactivity as a function of the amount of dissolved mineral may be described using empirical power laws. Another MPBE was used to measure far-from-equilibrium dissolution rate of albite using a sample that lost most of the highly reactive sites and highly reactive fine crystal during the initial stage of the experiment. Therefore, the change of its surface reactivity is small over the duration of the laboratory experiment (henceforth, “treated” albite sample). Another SPBE was conducted to quantify the effect of deviation from equilibrium on albite dissolution rate under close-to-equilibrium using the

  17. Rates of consumption of atmospheric CO2 through the weathering of loess during the next 100 yr of climate change

    NASA Astrophysics Data System (ADS)

    Goddéris, Y.; Brantley, S. L.; François, L. M.; Schott, J.; Pollard, D.; Déqué, M.

    2012-08-01

    Quantifying how C fluxes will change in the future is a complex task for models because of the coupling between climate, hydrology, and biogeochemical reactions. Here we investigate how pedogenesis of the Peoria loess, which has been weathering for the last 13 kyr, will respond over the next 100 yr of climate change. Using a cascade of numerical models for climate (ARPEGE), vegetation (CARAIB) and weathering (WITCH) we explore the effect of an increase in CO2 of 315 ppmv (1950) to 700 ppmv (2100 projection). The increasing CO2 results in an increase in temperature along the entire transect. In contrast, drainage increases slightly for a focus pedon in the South but decreases strongly in the North. These two variables largely determine the behavior of weathering. In addition, although CO2 production rate increases in the soils in response to global warming, the rate of diffusion back to the atmosphere also increases, maintaining a roughly constant or even decreasing CO2 concentration in the soil gas phase. Our simulations predict that temperature increasing in the next 100 yr causes the weathering rates of the silicates to increase into the future. In contrast, the weathering rate of dolomite - which consumes most of the CO2-decreases due to its retrograde solubility in both end members (South and North) of the transect. We thus infer slower rates of advance of the dolomite reaction front into the subsurface, and faster rates of advance of the silicate reaction front. However, additional simulations for 9 pedons located along the North-South transect show that dolomite weathering will increase in the central part of the Mississippi Valley, owing to a maximum in the response of vertical drainage to the ongoing climate change. The carbonate reaction front can be likened to a terrestrial lysocline because it represents a depth interval over which carbonate dissolution rates increase drastically. However, in contrast to the lower pH and shallower lysocline expected in

  18. Rates of Space Weathering in Lunar Regolith Grains

    NASA Technical Reports Server (NTRS)

    Zhang, S.; Keller, L. P.

    2012-01-01

    While the processes and products of lunar space weathering are reasonably well-studied, their accumulation rates in lunar soils are poorly constrained. Previously, we showed that the thickness of solar wind irradiated rims on soil grains is a smooth function of their solar flare particle track density, whereas the thickness of vapor-deposited rims was largely independent of track density [1]. Here, we have extended these preliminary results with data on additional grains from other mature soils.

  19. Chemical weathering in a tropical watershed, Luquillo Mountains, Puerto Rico: II. Rate and mechanism of biotite weathering

    USGS Publications Warehouse

    Murphy, S.F.; Brantley, S.L.; Blum, A.E.; White, A.F.; Dong, H.

    1998-01-01

    Samples of soil, saprolite, bedrock, and porewater from a lower montane wet forest, the Luquillo Experimental Forest (LEF) in Puerto Rico, were studied to investigate the rates and mechanisms of biotite weathering. The soil profile, at the top of a ridge in the Rio Icacos watershed, consists of a 50-100-cm thick layer of unstructured soil above a 600-800 cm thick saprolite developed on quartz diorite. The only minerals present in significant concentration within the soil and saprolite are biotite, quartz, kaolinite, and iron oxides. Biotite is the only primary silicate releasing significant K and Mg to porewaters. Although biotite in samples of the quartz diorite bedrock is extensively chloritized, chlorite is almost entirely absent in the saprolite phyllosilicates. Phyllosilicate grains are present as 200-1000 ??m wide books below about 50 cm depth. X-ray diffraction (XRD) and electron microprobe analyses indicate that the phyllosilicate grains contain a core of biotite surrounded by variable amounts of kaolinite. Lattice fringe images under transmission electron microscope (TEM) show single layers of biotite altering to two layers of kaolinite, suggesting dissolution of biotite and precipitation of kaolinite at discrete boundaries. Some single 14-A?? layers are also observed in the biotite under TEM. The degree of kaolinitization of individual phyllosilicate grains as observed by TEM decreases with depth in the saprolite. This TEM work is the first such microstructural evidence of epitaxial growth of kaolinite onto biotite during alteration in low-temperature environments. The rate of release of Mg in the profile, calculated as a flux through the soil normalized per watershed land area, is approximately 500 mol hectare-1 yr-1 (1.6 ?? 10-9 molMg m-2soil s-1). This rate is similar to the flux estimated from Mg discharge out the Rio Icacos (1000 mol hectare-1 yr-1, or 3.5 ?? 10-9 molMg m-2soil s-1), indicating that scaling up from the soil to the watershed is

  20. Origins of Deviations from Transition-State Theory: Formulating a New Kinetic Rate Law for Dissolution of Silicates

    SciTech Connect

    Andreas Luttge; Jonathan Icenhower

    2005-12-20

    Present models for dissolution of silicate minerals and glasses, based on Transition-State Theory (TST), overestimate the reaction rate as solution compositions approach saturation with respect to the rate-governing solid.

  1. The Rise of Late Tertiary and Quaternary Erosion and Weathering Rates revisited (Ralph Alger Bagnold Medal Lecture)

    NASA Astrophysics Data System (ADS)

    von Blanckenburg, Friedhelm

    2010-05-01

    The analyses of both modern river loads and chemical and physical hillslope denudation show that rates of weathering and erosion are tightly interlinked. An increase in silicate weathering through increased mountain erosion should therefore lead to global cooling by increased drawdown of atmospheric CO2. A five-fold increase of global sediment delivery was suggested for the last 5 Million years from a global compilation of sedimentation rates (1), and was also specifically suggested for the European Alps (2) and the India-Asia collisional area (3). While much research effort is currently being directed at explaining this increase, we should have been suspicious because this apparent increase in global erosion rate was not accompanied by a similar concomitant decrease in atmospheric CO2 as recorded by ocean alkalinity proxies. One possibility is that the increase in Neogene sedimentation rates is an artifact introduced by the discrepant time scale over which sedimentation is measured (4). The older the age, the longer the observational integration time will be, which in turn include longer periods of hiatus, and hence decreasing sedimentation rates with geologic time. An analysis of the records named above for time scale bias indeed suggests the possibility that erosion in these mountain belts might have been constant throughout the Neogene. An independent test of this hypothesis is provided by marine records of the isotopes of Beryllium (5). Be-10 is a rare radioactive cosmogenic nuclide, is produced mostly in the atmosphere and introduced to the surface oceans with a flux that can be considered to be globally uniform when averaged over time scales exceeding those of climate cycles. Be-9, in contrast, is stable, and enters the oceans from the continents mainly by river particulates (which are dissolved to some extent in the water column and during early diagenesis), in the dissolved form, and in minor amounts from dust. Should the global erosion rates have

  2. Increases in leach rate due to possible cracking in silicate glasses

    SciTech Connect

    Sang, J.C.; Barkatt, A.; Talmy, I.G.; Norr, M.K.

    1993-12-31

    Comparative studies of two multi-component silicate glasses have confirmed the observation that glasses with a relatively low SiO{sub 2} + AlO{sub 3/2} content may exhibit temporary increases in leach rate during the initial stages of their exposure to water. SEM studies of the leached glass surfaces strongly support the assumption that this phenomenon is due to cracking of the leached glass and a consequent increase of the exposed surface area.

  3. Effects of Climate on Long-term Rates of Physical Erosion and Chemical Weathering: Evidence from Cosmogenic Nuclides and Geochemical Mass Balance

    NASA Astrophysics Data System (ADS)

    Kirchner, J. W.; Riebe, C. S.; Ferrier, K. L.; Finkel, R. C.

    2004-12-01

    Cosmogenic nuclides such as 10Be and 26Al have recently become important tools for measuring long-term denudation rates. We have recently shown how cosmogenic nuclide measurements of denudation fluxes can be partitioned into their physical and chemical components, using the enrichment of insoluble tracers in regolith relative to its parent rock. We used these methods to measure long-term rates of physical erosion and chemical weathering for 42 sites, encompassing widely varying climates and denudation rates. Across these sites, mean annual temperatures vary from 2 to 25 ° C, average annual precipitation spans a 20-fold range (from 22 to 420 cm/yr), and denudation rates vary by 32-fold (from 23 to 755 t km-2 yr-2). Our measurements show that chemical weathering rates are tightly coupled with physical erosion rates, such that the relationship between climate and chemical weathering rates may be obscured by site-to-site differences in the rate that minerals are supplied to soil by physical erosion of rock. The relative importance of chemical weathering can be quantified using the "Weathering Intensity Factor" (WIF), the ratio of the chemical weathering rate to the physical erosion rate. Over 60 percent of the variance in WIF's can be explained by a simple Arrhenius-like relationship based on mean annual temperature and average annual precipitation. The temperature-dependence of WIF is roughly half of what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter-comparisons of short-term average weathering rates from the field. Our results imply that the strength of climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought, at least in actively eroding, unglaciated granitic terrain similar to our study sites.

  4. The Beryllium-10(meteoric)/ Beryllium-9 ratio as a new tracer of weathering and erosion rates

    NASA Astrophysics Data System (ADS)

    von Blanckenburg, F.; Bouchez, J.; Wittmann, H.; Dannhaus, N.

    2012-04-01

    A perfect clock of the stability of the Earth surface is one that combines a first isotope the flux of which depends on the release rate during erosion, and a second isotope produced at constant rate. The ratio of the meteoric cosmogenic nuclide 10Be to stable 9Be, suggested to serve as proxy for weathering and erosion over the late Cenozoic [1], is such a system. We provide a quantitative framework for its use. In a weathering zone some of the 9Be, present typically in 2ppm concentrations in silicate minerals, is released and partitioned between a reactive phase (adsorbed to clay and hydroxide surfaces, given the high partition coefficients at intermediate pH), and into the dissolved phase. The combined mass flux of both phases is defined by the soil formation rate and a mineral dissolution rate - and is hence proportional to the chemical weathering rate and the denudation rate. At the same time, the surface of the weathering zone is continuously exposed to fallout of meteoric 10Be. This 10Be percolates into the weathering zone where it mixes with dissolved 9Be. Both isotopes may exchange with the adsorbed Be, given that equilibration rate of Be is fast relative to soil residence times. Hence a 10Be/9Be(reactive) ratio results from which the total denudation rate can be calculated. A prerequisite is that the flux of meteoric 10Be is known from field experiments or from global production models [2]. In rivers, when reactive Be and dissolved Be equilibrate, a catchment-wide denudation rate can be determined from both sediment and a sample of filtered river water. We have tested this approach in sediment-bound Be [3] and dissolved Be in water [4] of the Amazon and Orinoco basin. The reactive Be was extracted from sediment by combined hydroxylamine and HCl leaches. In the Amazon trunk stream, the Orinoco, Apure, and La Tigra river 10Be/9Be(dissolved) agrees well with 10Be/9Be(reactive), showing that in most rivers these two phases equilibrate. 10Be/9Be ratios range

  5. Controls on silicate dissolution rates in neutral and basic pH solutions at 25°C

    NASA Astrophysics Data System (ADS)

    Brady, Patrick V.; Walther, John V.

    1989-11-01

    The pH-dependence of far from equilibrium steady-state dissolution rates of silicates can be understood by considering the detachment rates of their oxide components through surface protonation-deprotonation reactions. At high pH, where Si surface sites are deprotonated and therefore carry negative charge, detachment of silicon appears to control overall silicate dissolution rates. At low pH, near the zero point of charge of SiO 2 (where surface charge is dominated by the other oxide components), detachment of the non-silicon structure-forming oxides apparently controls dissolution rates of multi-oxide silicates. Correlations between metal-oxygen site potentials and pH-dependent surface detachment reactions permit estimation of dissolution rates of a large number of silicates from pH 5 to pH 12.

  6. Chemical and Biological Catalytic Enhancement of Weathering of Silicate Minerals and industrial wastes as a Novel Carbon Capture and Storage Technology

    NASA Astrophysics Data System (ADS)

    Park, A. H. A.

    2014-12-01

    Increasing concentration of CO2 in the atmosphere is attributed to rising consumption of fossil fuels around the world. The development of solutions to reduce CO2 emissions to the atmosphere is one of the most urgent needs of today's society. One of the most stable and long-term solutions for storing CO2 is via carbon mineralization, where minerals containing metal oxides of Ca or Mg are reacted with CO2 to produce thermodynamically stable Ca- and Mg-carbonates that are insoluble in water. Carbon mineralization can be carried out in-situ or ex-situ. In the case of in-situ mineralization, the degree of carbonation is thought to be limited by both mineral dissolution and carbonate precipitation reaction kinetics, and must be well understood to predict the ultimate fate of CO2 within geological reservoirs. While the kinetics of in-situ mineral trapping via carbonation is naturally slow, it can be enhanced at high temperature and high partial pressure of CO2. The addition of weak organic acids produced from food waste has also been shown to enhance mineral weathering kinetics. In the case of the ex-situ carbon mineralization, the role of these ligand-bearing organic acids can be further amplified for silicate mineral dissolution. Unfortunately, high mineral dissolution rates often lead to the formation of a silica-rich passivation layer on the surface of silicate minerals. Thus, the use of novel solvent mixture that allows chemically catalyzed removal of this passivation layer during enhanced Mg-leaching surface reaction has been proposed and demonstrated. Furthermore, an engineered biological catalyst, carbonic anhydrase, has been developed and evaluated to accelerate the hydration of CO2, which is another potentially rate-limiting step of the carbonation reaction. The development of these novel catalytic reaction schemes has significantly improved the overall efficiency and sustainability of in-situ and ex-situ mineral carbonation technologies and allowed direct

  7. Uranium thorium chronometry of weathering rinds: Rock alteration rate and paleo-isotopic record of weathering fluids

    NASA Astrophysics Data System (ADS)

    Pelt, E.; Chabaux, F.; Innocent, C.; Navarre-Sitchler, A. K.; Sak, P. B.; Brantley, S. L.

    2008-11-01

    The potential of 238U- 234U- 230Th chronometry for constraining the formation rate of weathering rinds developed on fresh rocks is assessed by analyzing a weathering rind on a basaltic clast from a 125 kyr old Costa Rican alluvial terrace. Eighteen subsamples were collected from one section of the clast by drilling cores (4 mm in diameter and 5 mm depth) along two transects straddling the core-rind boundary. Variations of major and trace element concentrations along the two transects point out (a) intense loss of alkaline and alkaline-earth elements, (b) conservative behaviour of elements such as Zr, Hf and Th, and (c) external input of U into the rind without any evidence of U loss during basalt weathering. In addition, variations in U concentrations along the transects show that the main U-Th fractionation process associated with the weathering of the basaltic clast is an external input of U (without addition nor loss of Th) in the basalt rind transition zone, and that, once deposited U is immobile in the weathering rind. In the frame of this interpretation scheme, a weathering rate of 0.5 ± 0.2 mm/kyr can be calculated for the studied clast, which is consistent with geological and isotopic evidence constraining the depositional ages of the terraces. In addition, the variations in the ( 234U/ 238U) ratio along the analysed transects as well as the increase in Sr isotopic ratios within the weathering rind are best explained by temporal variation of the U activity ratios and Sr isotope ratios of the soil solutions brought into the rind. This work highlights how well detailed U-Th chronological studies of weathering rinds can (1) constrain the formation rates of weathering systems, and (2) record the time variation of isotopic composition of weathering fluids.

  8. The rate and causes of lunar space weathering: Insights from Lunar Reconnaissance Orbiter Wide Angle Camera ultraviolet observations

    NASA Astrophysics Data System (ADS)

    Denevi, B. W.; Robinson, M. S.; Sato, H.; Hapke, B. W.; McEwen, A. S.; Hawke, B. R.

    2011-12-01

    Lunar Reconnaissance Orbiter Wide Angle Camera global ultraviolet and visible imaging provides a unique opportunity to examine the rate and causes of space weathering on the Moon. Silicates typically have a strong decrease in reflectance toward UV wavelengths (<~450 nm) due to strong bands at 250 nm and in the far UV. Metallic iron is relatively spectrally neutral, and laboratory spectra suggest that its addition to mature soils in the form of submicroscopic iron (also known as nanophase iron) flattens silicate spectra, significantly reducing spectral slope in the ultraviolet. Reflectance at ultraviolet wavelengths may be especially sensitive to the surface coatings that form due to exposure to space weathering because scattering from the surfaces of grains contributes a larger fraction to the reflectance spectrum at short wavelengths. We find that the UV slope (as measured by the 320/415 nm ratio) is a more sensitive measure of maturity than indexes based on visible and near-infrared wavelengths. Only the youngest features (less than ~100 Ma) retain a UV slope that is distinct from mature soils of the same composition. No craters >20 km have UV slopes that approach those observed in laboratory spectra of fresh lunar materials (powdered lunar rocks). While the 320/415 nm ratio increases by ~18% from powdered rocks to mature soils in laboratory samples, Giordano Bruno, the freshest large crater, only shows a 3% difference between fresh and mature materials. At the resolution of our UV data (400 m/pixel), we observe some small (<5 km) craters that show a ~14% difference in 320/415 nm ratio from their mature surroundings. UV observations show that Reiner Gamma has had significantly lower levels of space weathering than any of the Copernican craters we examined, and was the only region we found with a UV slope that approached laboratory values for fresh powdered rock samples. This is consistent with the hypothesis that its high albedo is due to magnetic shielding from

  9. The Weathering of Antarctic Meteorites: Climatic Controls on Weathering Rates and Implications for Meteorite Accumulation

    NASA Technical Reports Server (NTRS)

    Benoit, P. H.; Akridge, J. M. C.; Sears, D. W. G.; Bland, P. A.

    1995-01-01

    Weathering of meteorites includes a variety of chemical and mineralogical changes, including conversion of metal to iron oxides, or rust. Other changes include the devitrification of glass, especially in fusion crust. On a longer time scale, major minerals such as olivine, pyroxene, and feldspar are partially or wholly converted to various phyllosilicates. The degree of weathering of meteorite finds is often noted using a qualitative system based on visual inspection of hand specimens. Several quantitative weathering classification systems have been proposed or are currently under development. Wlotzka has proposed a classification system based on mineralogical changes observed in polished sections and Mossbauer properties of meteorite powders have also been used. In the current paper, we discuss induced thermoluminescence (TL) as an indicator of degree of weathering of individual meteorites. The quantitative measures of weathering, including induced TL, suffer from one major flaw, namely that their results only apply to small portions of the meteorite.

  10. Kinetically limited weathering at low denudation rates in semiarid climatic conditions

    NASA Astrophysics Data System (ADS)

    Schoonejans, Jérôme; Vanacker, Veerle; Opfergelt, Sophie; Ameijeiras-Mariño, Yolanda; Christl, Marcus

    2016-02-01

    Biogeochemical cycling within the Critical Zone depends on the interactions between minerals and fluids controlling chemical weathering and physical erosion rates. In this study, we explore the role of water availability in controlling soil chemical weathering in semiarid climatic conditions. Weathering rates and intensities were evaluated for nine soil profiles located on convex ridge crests of three mountain ranges in the Spanish Betic Cordillera. We combine a geochemical mass balance with 10Be cosmogenic nuclides to constrain chemical weathering intensities and long-term denudation rates. As such, this study presents new data on chemical weathering and 10Be-derived denudation for understudied semiarid climate systems. In the Betic Cordillera, chemical weathering intensities are relatively low (~5 to 30% of the total denudation of the soil) and negatively correlated with the magnitude of the water deficit in soils. Chemical mass losses are inversely related to denudation rates (14-109 mm/kyr) and positively to soil thickness (14-58 cm); these results are consistent with kinetic limitation of chemical weathering rates. A worldwide compilation of chemical weathering data suggests that soil water balance may regulate the coupling between chemical weathering and physical erosion by modulating soil solute fluxes. Therefore, future landscape evolution models that seek to link chemical weathering and physical erosion should include soil water flux as an essential driver of weathering.

  11. Weather.

    ERIC Educational Resources Information Center

    Web Feet K-8, 2000

    2000-01-01

    This subject guide to weather resources includes Web sites, CD-ROMs and software, videos, books, audios, magazines, and professional resources. Related disciplines are indicated, age levels are specified, and a student activity is included. (LRW)

  12. Stable carbon isotopes in dissolved inorganic carbon: extraction and implications for quantifying the contributions from silicate and carbonate weathering in the Krishna River system during peak discharge.

    PubMed

    Laskar, Amzad H; Gandhi, Naveen; Thirumalai, Kaustubh; Yadava, Madhusudan G; Ramesh, Rengaswamy; Mahajan, Ramakant R; Kumar, Dharmendra

    2014-06-01

    We present a comparative study of two offline methods, a newly developed method and an existing one, for the measurement of the stable carbon isotopic composition (δ(13)C) of dissolved inorganic carbon (DIC; δ(13)CDIC) in natural waters. The measured δ(13)CDIC values of different water samples, prepared from laboratory Na2CO3, ground and oceanic waters, and a laboratory carbonate isotope standard, are found to be accurate and reproducible to within 0.5 ‰\\ (1σ). The extraction of CO2 from water samples by these methods does not require pre-treatment or sample poisoning and can be applied to a variety of natural waters to address carbon cycling in the hydrosphere. In addition, we present a simple method (based on a two-end-member mixing model) to estimate the silicate-weathering contribution to DIC in a river system by using the concentration of DIC and its δ(13)C. This approach is tested with data from the Krishna River system as a case study, thereby quantifying the contribution of silicate and carbonate weathering to DIC, particularly during peak discharge. PMID:24450598

  13. Soil production rates on silicate parent material in high-mountains: different approaches - different results?

    NASA Astrophysics Data System (ADS)

    Egli, Markus; Dahms, Dennis; Norton, Kevin

    2013-04-01

    High-mountain soils develop in particularly sensitive environments. Consequently, deciphering and predicting what drives the rates of soil formation in such environments is a major challenge. In terms of soil production from chemical weathering, the predominating perception for high-mountain soils and cold environments often is that the chemical weathering 'portion' of soil development is temperature-inhibited, often to the point of non-occurrence. Several concepts exist to determine long-term rates of soil formation and development. We present three different approaches: (1) quantification of soil formation from minimally eroded soils of known age using chronosequences (known surface age and soil thickness - SAST), (2) determination of soil residence times (SRT) and production rates through chemical weathering using (un)stable isotopes (e.g. 230Th / 234U activity ratios), and (3) a steady state approach using cosmogenic isotopes (e.g. 10Be). Data form different climate zones, and particularly from high-mountains (alpine environment), were compared. The SAST and steady state approach gave quite similar results for alpine environments (European Alps and the Wind River Range (Rocky Mountains USA)). Soil formation rates in mountain areas (but having a temperate climate) using the SRT approach, did not differ greatly from the SAST and Steady State approaches. Independent of the chosen approach, the results seem moderately comparable. Soil formation rates in high-mountain areas (alpine climate) ranged from very low to extremely high values and showed a clear decreasing tendency with time. Very young soils have up to 3 - 4 orders of magnitude higher rates of development than old soils (105 to 106 years). This is due to the fact that weathering is kinetically limited in regions having young surfaces and supply limited on old surfaces. Soil production rates cannot be infinitely high. Consequently, a speed limit must exist. In the literature, this limit has been set at

  14. ORIGINS OF DEVIATIONS FROM TRANSITION-STATE THEORY: FORMULATING A NEW KINETIC RATE LAW FOR DISSOLUTION OF SILICATES

    EPA Science Inventory

    Present models for dissolution of silicate minerals and glasses, based on transition-state theory TST), overestimate the reaction rate as solution compositions approach saturation with respect to the rate-governing solid. Therefore, the reactivity of key materials in the environm...

  15. Characterizing englacial and subglacial weathering processes in a silicate-carbonate system at Robertson Glacier, Canada: Combining field measurements and remote sensing

    NASA Astrophysics Data System (ADS)

    Rutledge, A. M.; Christensen, P. R.

    2012-12-01

    Geologic weathering processes in cold environments, especially processes acting on subglacial and englacial sediments and rocks, are not well characterized due to the difficulty of accessing these environments. However, subglacial and englacial weathering of geologic materials contributes to the solute flux in meltwater and provides a potential source of energy to chemotrophic microbes, and is thus an important component to understand. In this study, we characterize the weathering products present in a glaciated silicate-carbonate system using infrared spectroscopy, x-ray diffraction, and geochemical analyses. We use Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data to determine whether glacial weathering products can be detected from remotely detected infrared spectra. The major goals of the project are to quantify weathering inputs to the glacial energy budget, and to link in situ sampling with remote sensing capabilities. Robertson Glacier, Alberta, Canada (115°20'W, 50°44'N) provides an excellent field site for this technique as it is accessible, and its retreating stage allows sampling of fresh subglacial and englacial sediments. This site is also of great significance to microbiology studies due to the recent detection of methanogens in the local subglacial till. Samples of glacially altered rock and sediments were collected on a downstream transect of the glacier in September 2011. Infrared laboratory spectroscopy and x-ray diffraction were used to determine the composition and abundance of minerals present. Infrared imagery of the region was collected at the time of sampling with the ASTER satellite instrument. Geochemical data were also collected at each location, and ice and water samples were analyzed for major and minor elements. pH values decreased in the downstream direction, and Ca+2 and SO4-2 in solution increased downstream. This is initially consistent with earlier studies of similar systems; however, the majority of

  16. High continental weathering rate during Early Cambrian: Evidence from Os isotopic composition of Early Cambrian Ocean

    NASA Astrophysics Data System (ADS)

    Jiang, S.-Y.; Yang, J.-H.; Ling, H.-F.; Feng, H.-Z.; Chen, Y.-Q.; Chen, J.-H.

    2003-04-01

    The paleo-ocean environmental change during the Precambrian-Cambrian transition is a key issue related to the causes for an explosive radiation of different metazoan phyla during Early Cambrian. The chemical and isotopic compositions of marine sediments and chemical precipitates such as carbonates, phosphorites, siliceous rocks, and black shales record the changing composition and physical conditions of the seawater in which these rocks accumulated. Organic carbon-rich black shales from marine environments are commonly enriched in a number of trace elements such as Ni, Mo, V, Co, Cr, Au, U, As, Pb, Zn, Cu, Re, and platinum-group-elements (PGE). Recent researches have demonstrated that Re-Os isotopes and PGE contents in black shales are useful proxies for seawater chemistry. It is believed that Re and Os in orgainc-carbon rich black shales are mostly hydrogeneous in origin which were largely sequestered from seawater at the time of deposition. In South China, the Lower Cambrian black shale sequence of the Niutitang Formation (and lateral equivalents) exists broadly several thousands kilometers. The lowermost sequence of this formation contain a thin sulfide ore horizon with an apparently unique and extreme case of metal enrichments such as Mo, Ni, Se, Re, Os, As, Hg, Sb, Ag, Au, Pt, and Pd. In this study, we conducted a preliminary investigation of Re-Os isotopes and Plantium Group Element (PGE) distribution patterns of the balck shales and intercalated Ni-Mo polymetallic sulfide bed from Guizhou and Hunan Provinces. The high rOs(t) values of the black shales indicate that the Early Cambrian ocean in Yangtze Platform had a highly radiogenic Os, possibly as a result of high continental weathering rate at that time. The Ni-Mo polymetallic sulfide ores within the black shales have lower rOs(t) values than the black shales, and they show similar REE and PGE patterns as the hydrothermal siliceous rocks within the Lower Cambrian strata, which suggest that the Ni

  17. Quantifying present-day and long-term shale weathering rates across a latitudinal climosequence

    NASA Astrophysics Data System (ADS)

    Dere, A. L. D.; Andrews, E.; White, T. S.

    2015-12-01

    A transect of shale sites was established across the Northern Hemisphere as part of the Susquehanna Shale Hills Critical Zone Observatory (SSHO) to investigate the role of climate in shale weathering. Mean annual temperature and precipitation vary across sites located in Wales, New York, Pennsylvania, Virginia, Tennessee, Alabama and Puerto Rico. Long-term weathering rates were quantified by comparing bulk soil geochemistry with original parent shale composition and cosmogenic 10Be inventories to estimate weathering duration. Present-day weathering rates were obtained by burying approximately 2 cm by 1 cm shale chips at multiple depths in soil pit walls. Shale chip samples were exhumed after two and five years of burial, washed and mass loss measured. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to determine surface chemistry and physical alteration of the recovered shale. Long-term weathering rates increase with increasing temperature across the transect. Similarly, after two years of burial, exhumed shale chip weathering rates increased from 2.9 ± 0.9 in Wales to 11.2 ± 3.7 m Ma-1 in Puerto Rico. Average weathering rates after two years of burial were similar in Virginia, Tennessee and Alabama (8.6 - 10.6 m Ma-1). Many shale chips in Alabama and Puerto Rico, however, retained soil particles even after washing, therefore total mass loss, and thus weathering rates, at these sites could be even greater. After five years of burial, mass loss across the Appalachian sites was greatest in Tennessee while weathering rates were overall generally similar to two year rates (3.0 to 12.6 m Ma-1). Evidence of physical and chemical changes, especially Na and Mg loss, from shale chip surfaces was greater on shale chips buried at warmer and wetter sites. Quantifying weathering rates as a function of climate at multiple scales will contribute to understanding the effects of global climate change on soil formation rates in the Critical

  18. Understanding silicate hydration from quantitative analyses of hydrating tricalcium silicates

    PubMed Central

    Pustovgar, Elizaveta; Sangodkar, Rahul P.; Andreev, Andrey S.; Palacios, Marta; Chmelka, Bradley F.; Flatt, Robert J.; d'Espinose de Lacaillerie, Jean-Baptiste

    2016-01-01

    Silicate hydration is prevalent in natural and technological processes, such as, mineral weathering, glass alteration, zeolite syntheses and cement hydration. Tricalcium silicate (Ca3SiO5), the main constituent of Portland cement, is amongst the most reactive silicates in water. Despite its widespread industrial use, the reaction of Ca3SiO5 with water to form calcium-silicate-hydrates (C-S-H) still hosts many open questions. Here, we show that solid-state nuclear magnetic resonance measurements of 29Si-enriched triclinic Ca3SiO5 enable the quantitative monitoring of the hydration process in terms of transient local molecular composition, extent of silicate hydration and polymerization. This provides insights on the relative influence of surface hydroxylation and hydrate precipitation on the hydration rate. When the rate drops, the amount of hydroxylated Ca3SiO5 decreases, thus demonstrating the partial passivation of the surface during the deceleration stage. Moreover, the relative quantities of monomers, dimers, pentamers and octamers in the C-S-H structure are measured. PMID:27009966

  19. Understanding silicate hydration from quantitative analyses of hydrating tricalcium silicates.

    PubMed

    Pustovgar, Elizaveta; Sangodkar, Rahul P; Andreev, Andrey S; Palacios, Marta; Chmelka, Bradley F; Flatt, Robert J; d'Espinose de Lacaillerie, Jean-Baptiste

    2016-01-01

    Silicate hydration is prevalent in natural and technological processes, such as, mineral weathering, glass alteration, zeolite syntheses and cement hydration. Tricalcium silicate (Ca3SiO5), the main constituent of Portland cement, is amongst the most reactive silicates in water. Despite its widespread industrial use, the reaction of Ca3SiO5 with water to form calcium-silicate-hydrates (C-S-H) still hosts many open questions. Here, we show that solid-state nuclear magnetic resonance measurements of (29)Si-enriched triclinic Ca3SiO5 enable the quantitative monitoring of the hydration process in terms of transient local molecular composition, extent of silicate hydration and polymerization. This provides insights on the relative influence of surface hydroxylation and hydrate precipitation on the hydration rate. When the rate drops, the amount of hydroxylated Ca3SiO5 decreases, thus demonstrating the partial passivation of the surface during the deceleration stage. Moreover, the relative quantities of monomers, dimers, pentamers and octamers in the C-S-H structure are measured. PMID:27009966

  20. Understanding silicate hydration from quantitative analyses of hydrating tricalcium silicates

    NASA Astrophysics Data System (ADS)

    Pustovgar, Elizaveta; Sangodkar, Rahul P.; Andreev, Andrey S.; Palacios, Marta; Chmelka, Bradley F.; Flatt, Robert J.; D'Espinose de Lacaillerie, Jean-Baptiste

    2016-03-01

    Silicate hydration is prevalent in natural and technological processes, such as, mineral weathering, glass alteration, zeolite syntheses and cement hydration. Tricalcium silicate (Ca3SiO5), the main constituent of Portland cement, is amongst the most reactive silicates in water. Despite its widespread industrial use, the reaction of Ca3SiO5 with water to form calcium-silicate-hydrates (C-S-H) still hosts many open questions. Here, we show that solid-state nuclear magnetic resonance measurements of 29Si-enriched triclinic Ca3SiO5 enable the quantitative monitoring of the hydration process in terms of transient local molecular composition, extent of silicate hydration and polymerization. This provides insights on the relative influence of surface hydroxylation and hydrate precipitation on the hydration rate. When the rate drops, the amount of hydroxylated Ca3SiO5 decreases, thus demonstrating the partial passivation of the surface during the deceleration stage. Moreover, the relative quantities of monomers, dimers, pentamers and octamers in the C-S-H structure are measured.

  1. Estimating The Rate of Technology Adoption for Cockpit Weather Information Systems

    NASA Technical Reports Server (NTRS)

    Kauffmann, Paul; Stough, H. P.

    2000-01-01

    In February 1997, President Clinton announced a national goal to reduce the weather related fatal accident rate for aviation by 80% in ten years. To support that goal, NASA established an Aviation Weather Information Distribution and Presentation Project to develop technologies that will provide timely and intuitive information to pilots, dispatchers, and air traffic controllers. This information should enable the detection and avoidance of atmospheric hazards and support an improvement in the fatal accident rate related to weather. A critical issue in the success of NASA's weather information program is the rate at which the market place will adopt this new weather information technology. This paper examines that question by developing estimated adoption curves for weather information systems in five critical aviation segments: commercial, commuter, business, general aviation, and rotorcraft. The paper begins with development of general product descriptions. Using this data, key adopters are surveyed and estimates of adoption rates are obtained. These estimates are regressed to develop adoption curves and equations for weather related information systems. The paper demonstrates the use of adoption rate curves in product development and research planning to improve managerial decision processes and resource allocation.

  2. Hot spring siliceous stromatolites from Yellowstone National Park: assessing growth rate and laminae formation.

    PubMed

    Berelson, W M; Corsetti, F A; Pepe-Ranney, C; Hammond, D E; Beaumont, W; Spear, J R

    2011-09-01

    Stromatolites are commonly interpreted as evidence of ancient microbial life, yet stromatolite morphogenesis is poorly understood. We apply radiometric tracer and dating techniques, molecular analyses and growth experiments to investigate siliceous stromatolite morphogenesis in Obsidian Pool Prime (OPP), a hot spring in Yellowstone National Park. We examine rates of stromatolite growth and the environmental and/or biologic conditions that affect lamination formation and preservation, both difficult features to constrain in ancient examples. The "main body" of the stromatolite is composed of finely laminated, porous, light-dark couplets of erect (surface normal) and reclining (surface parallel) silicified filamentous bacteria, interrupted by a less-distinct, well-cemented "drape" lamination. Results from dating studies indicate a growth rate of 1-5 cm year(-1) ; however, growth is punctuated. (14)C as a tracer demonstrates that stromatolite cyanobacterial communities fix CO(2) derived from two sources, vent water (radiocarbon dead) and the atmosphere (modern (14)C). The drape facies contained a greater proportion of atmospheric CO(2) and more robust silica cementation (vs. the main body facies), which we interpret as formation when spring level was lower. Systematic changes in lamination style are likely related to environmental forcing and larger scale features (tectonic, climatic). Although the OPP stromatolites are composed of silica and most ancient forms are carbonate, their fine lamination texture requires early lithification. Without early lithification, whether silica or carbonate, it is unlikely that a finely laminated structure representing an ancient microbial mat would be preserved. In OPP, lithification on the nearly diurnal time scale is likely related to temperature control on silica solubility. PMID:21777367

  3. Short Communication: Evidence for non-Gaussian distribution of rock weathering rates

    NASA Astrophysics Data System (ADS)

    Emmanuel, S.

    2015-09-01

    The weathering of rocks influences the geochemistry of the oceans, the erosion of landscapes and man-made structures, and even the global climate. Although a high degree of variance is often observed in rate measurements, little is understood about the statistical characteristics of weathering rate distributions. This preliminary study demonstrates that the weathering rates of limestone, determined from measurements of an ancient eroded limestone edifice, can exhibit highly non-Gaussian behavior. While a Gaussian model produced a poor fit with the data, an alternative model - the generalized extreme value (GEV) framework - was capable of capturing the asymmetric long-tailed distribution, in good agreement with the measured curve. Furthermore, the non-Gaussian distribution of these field rates was found to have similar characteristics to the distribution of rates measured over much smaller microscopic regions of limestone surfaces in laboratory experiments. Such similar behavior could be indicative of analogous chemical and mechanical weathering processes acting over a range of spatial and temporal scales. Moreover, highly asymmetric rate distributions with high variance could be characteristic of rates not only in carbonate rocks, but also in other rock types, suggesting that the use of a small number of measurements to determine field weathering rates may be insufficient to fully characterize the range of rates in natural systems.

  4. Direct Determination of the Space Weathering Rates in Lunar Soils and Itokawa Regolith from Sample Analyses

    NASA Technical Reports Server (NTRS)

    Keller, L. P.; Berger, E. L.; Christoffersen, R.; Zhang, S.

    2016-01-01

    Space weathering effects on airless bodies result largely from micrometeorite impacts and solar wind interactions. Decades of research have provided insights into space weathering processes and their effects, but a major unanswered question still remains: what is the rate at which these space weathering effects are acquired in lunar and asteroidal regolith materials? To determine the space weathering rate for the formation of rims on lunar anorthite grains, we combine the rim width and type with the exposure ages of the grains, as determined by the accumulation of solar flare particle tracks. From these analyses, we recently showed that space weathering effects in mature lunar soils (both vapor-deposited rims and solar wind amorphized rims) accumulate and attain steady state in 10(sup 6)-10(sup 7) y. Regolith grains from Itokawa also show evidence for space weathering effects, but in these samples, solar wind interactions appear to dominate over impactrelated effects such as vapor-deposition. While in our lunar work, we focused on anorthite, given its high abundance on the lunar surface, for the Itokawa grains, we focused on olivine. We previously studied 3 olivine grains from Itokawa and determined their solar flare track densities and described their solar wind damaged rims]. We also analyzed olivine grains from lunar soils, measured their track densities and rim widths, and used this data along with the Itokawa results to constrain the space weathering rate on Itokawa. We observe that olivine and anorthite have different responses to solar wind irradiation.

  5. Weathering rates of marble in laboratory and outdoor conditions

    SciTech Connect

    Yerrapragada, S.S.; Chirra, S.R.; Jaynes, J.H.; Bandyopadhyay, J.K.; Gauri, K.L.; Li, S.

    1996-09-01

    In the modern urban atmosphere SO{sub 2} and NO{sub 2} attack calcite (CaCO{sub 3}) in marble exposed at rain-sheltered surfaces creating largely gypsum (CaSO{sub 4}{center_dot}2H{sub 2}O) crusts that eventually exfoliate. In combination with CO{sub 2} these gases erode the marble at unsheltered surfaces. the authors report the development of mathematical models to predict the rate of growth of crust and the rate of surface recession. To determine the rate of growth of crust the kinetic rate constant, diffusion rate, and the order of reaction were determined by the application of the shrinking-core model applied to data generated in laboratory experiments. Based on these parameters /and average ambient levels of 10 parts per billion (ppb) SO{sub 2} and 25 ppb NO{sub 2} in Louisville, Ky., the rate of crust formation for this metro area was calculated to be 1.8 {micro}m in the first year. However, the rate of recession was modeled from data obtained by exposing marble slabs to rainfalls. A surface recession of 15 {micro}m/yr was calculated. The models predicted well the rate of growth of crust observed at several sites in Louisville and the predicted surface recession compared well with values reported in the literature.

  6. Quantifying the VNIR Effects of Nanophase Iron Generated through the Space Weathering of Silicates: Reconciling Modeled Data with Laboratory Observations

    NASA Astrophysics Data System (ADS)

    Legett, C., IV; Glotch, T. D.; Lucey, P. G.

    2015-12-01

    Space weathering is a diverse set of processes that occur on the surfaces of airless bodies due to exposure to the space environment. One of the effects of space weathering is the generation of nanophase iron particles in glassy rims on mineral grains due to sputtering of iron-bearing minerals. These particles have a size-dependent effect on visible and near infrared (VNIR) reflectance spectra with smaller diameter particles (< 50 nm) causing both reddening and darkening of the spectra with respect to unweathered material (Britt-Pieters particle behavior), while larger particles (> 300 nm) darken without reddening. Between these two sizes, a gradual shift between these two behaviors occurs. In this work, we present results from the Multiple Sphere T-Matrix (MSTM) scattering model in combination with Hapke theory to explore the particle size and iron content parameter spaces with respect to VNIR (700-1700 nm) spectral slope. Previous work has shown that the MSTM-Hapke hybrid model offers improvements over Mie-Hapke models. Virtual particles are constructed out of an arbitrary number of spheres, and each sphere is assigned a refractive index and extinction coefficient for each wavelength of interest. The model then directly solves Maxwell's Equations at every wave-particle interface to predict the scattering, extinction and absorption efficiencies. These are then put into a simplified Hapke bidirectional reflectance model that yields a predicted reflectance. Preliminary results show an area of maximum slopes for iron particle diameters < 80 nm and iron concentrations of ~1-10wt% in an amorphous silica matrix. Further model runs are planned to better refine the extent of this region. Companion laboratory work using mixtures of powdered aerogel and nanophase iron particles provides a point of comparison to modeling efforts. The effects on reflectance and emissivity values due to particle size in a nearly ideal scatterer (aerogel) are also observed with comparisons to

  7. Spatial patterns and controls of soil chemical weathering rates along a transient hillslope

    USGS Publications Warehouse

    Yoo, K.; Mudd, S.M.; Sanderman, J.; Amundson, Ronald; Blum, A.

    2009-01-01

    Hillslopes have been intensively studied by both geomorphologists and soil scientists. Whereas geomorphologists have focused on the physical soil production and transport on hillslopes, soil scientists have been concerned with the topographic variation of soil geochemical properties. We combined these differing approaches and quantified soil chemical weathering rates along a grass covered hillslope in Coastal California. The hillslope is comprised of both erosional and depositional sections. In the upper eroding section, soil production is balanced by physical erosion and chemical weathering. The hillslope then transitions to a depositional slope where soil accumulates due to a historical reduction of channel incision at the hillslope's base. Measurements of hillslope morphology and soil thickness were combined with the elemental composition of the soil and saprolite, and interpreted through a process-based model that accounts for both chemical weathering and sediment transport. Chemical weathering of the minerals as they moved downslope via sediment transport imparted spatial variation in the geochemical properties of the soil. Inverse modeling of the field and laboratory data revealed that the long-term soil chemical weathering rates peak at 5 g m- 2 yr- 1 at the downslope end of the eroding section and decrease to 1.5 g m- 2 yr- 1 within the depositional section. In the eroding section, soil chemical weathering rates appear to be primarily controlled by the rate of mineral supply via colluvial input from upslope. In the depositional slope, geochemical equilibrium between soil water and minerals appeared to limit the chemical weathering rate. Soil chemical weathering was responsible for removing 6% of the soil production in the eroding section and 5% of colluvial influx in the depositional slope. These were among the lowest weathering rates reported for actively eroding watersheds, which was attributed to the parent material with low amount of weatherable

  8. Chemical weathering rates of a soil chronosequence on granitic alluvium: III. Hydrochemical evolution and contemporary solute fluxes and rates

    USGS Publications Warehouse

    White, A.F.; Schulz, M.S.; Vivit, D.V.; Blum, A.E.; Stonestrom, D.A.; Harden, J.W.

    2005-01-01

    Although long-term changes in solid-state compositions of soil chronosequences have been extensively investigated, this study presents the first detailed description of the concurrent hydrochemical evolution and contemporary weathering rates in such sequences. The most direct linkage between weathering and hydrology over 3 million years of soil development in the Merced chronosequence in Central California relates decreasing permeability and increasing hydrologic heterogeneity to the development of secondary argillic horizons and silica duripans. In a highly permeable, younger soil (40 kyr old), pore water solutes reflect seasonal to decadal-scale variations in rainfall and evapotranspiration (ET). This climate signal is strongly damped in less permeable older soils (250 to 600 kyr old) where solutes increasingly reflect weathering inputs modified by heterogeneous flow. Elemental balances in the soils are described in terms of solid state, exchange and pore water reservoirs and input/output fluxes from precipitation, ET, biomass, solute discharge and weathering. Solute mineral nutrients are strongly dependent on biomass variations as evidenced by an apparent negative K weathering flux reflecting aggradation by grassland plants. The ratios of solute Na to other base cations progressively increase with soil age. Discharge fluxes of Na and Si, when integrated over geologic time, are comparable to solid-state mass losses in the soils, implying similar past weathering conditions. Similarities in solute and sorbed Ca/Mg ratios reflect short-term equilibrium with the exchange reservoir. Long-term consistency in solute ratios, when contrasted against progressive decreases in solid-state Ca/Mg, requires an additional Ca source, probably from dry deposition. Amorphous silica precipitates from thermodynamically-saturated pore waters during periods of high evapotranspiration and result in the formation of duripans in the oldest soils. The degree of feldspar and secondary

  9. Assessing Wind Farm Reliability Using Weather Dependent Failure Rates

    NASA Astrophysics Data System (ADS)

    Wilson, G.; McMillan, D.

    2014-06-01

    Using reliability data comprising of two modern, large scale wind farm sites and wind data from two onsite met masts, a model is developed which calculates wind speed dependant failure rates which are used to populate a Markov Chain. Monte Carlo simulation is then exercised to simulate three wind farms which are subjected to controlled wind speed conditions from three separate potential UK sites. The model then calculates and compares wind farm reliability due to corrective maintenance and component failure rates influenced by the wind speed of each of the sites. Results show that the components affected most by changes in average daily wind speed are the control system and the yaw system. A comparison between this model and a more simple estimation of site yield is undertaken. The model takes into account the effects of the wind speed on the cost of operation and maintenance and also includes the impact of longer periods of downtime in the winter months and shorter periods in the summer. By taking these factors into account a more detailed site assessment can be undertaken. There is significant value to this model for operators and manufacturers.

  10. Temperature dependence of basalt weathering

    NASA Astrophysics Data System (ADS)

    Li, Gaojun; Hartmann, Jens; Derry, Louis A.; West, A. Joshua; You, Chen-Feng; Long, Xiaoyong; Zhan, Tao; Li, Laifeng; Li, Gen; Qiu, Wenhong; Li, Tao; Liu, Lianwen; Chen, Yang; Ji, Junfeng; Zhao, Liang; Chen, Jun

    2016-06-01

    The homeostatic balance of Earth's long-term carbon cycle and the equable state of Earth's climate are maintained by negative feedbacks between the levels of atmospheric CO2 and the chemical weathering rate of silicate rocks. Though clearly demonstrated by well-controlled laboratory dissolution experiments, the temperature dependence of silicate weathering rates, hypothesized to play a central role in these weathering feedbacks, has been difficult to quantify clearly in natural settings at landscape scale. By compiling data from basaltic catchments worldwide and considering only inactive volcanic fields (IVFs), here we show that the rate of CO2 consumption associated with the weathering of basaltic rocks is strongly correlated with mean annual temperature (MAT) as predicted by chemical kinetics. Relations between temperature and CO2 consumption rate for active volcanic fields (AVFs) are complicated by other factors such as eruption age, hydrothermal activity, and hydrological complexities. On the basis of this updated data compilation we are not able to distinguish whether or not there is a significant runoff control on basalt weathering rates. Nonetheless, the simple temperature control as observed in this global dataset implies that basalt weathering could be an effective mechanism for Earth to modulate long-term carbon cycle perturbations.

  11. Effect of variability in weather conditions on conductor temperature and the dynamic rating of transmission lines

    SciTech Connect

    Foss, S.D.; Lin, S.H. ); Maraio, R.A.; Schrayshuen, H. )

    1988-10-01

    Simultaneous weather and conductor data were collected from these locations situated in New York State and Western Massachusetts. The two New York State locations represent the termination points of a 230 kV seventy-mile overhead line. The transmission line consists of a Drake 795 kcmil ACSR conductor. Data were monitored using on-line sensor equipment developed by the Research and Development Department of the Niagara Mohawk Power Corporation. The purposes of the investigation were to analyze variability in weather conditions, conductor temperature and calculated dynamic ratings that exist along transmission lines. Reported here are variabilities in air temperature, wind speed, conductor current, conductor surface temperature and calculated dynamic ratings.

  12. Hydrologic regulation of chemical weathering and the geologic carbon cycle.

    PubMed

    Maher, K; Chamberlain, C P

    2014-03-28

    Earth's temperature is thought to be regulated by a negative feedback between atmospheric CO2 levels and chemical weathering of silicate rocks that operates over million-year time scales. To explain variations in the strength of the weathering feedback, we present a model for silicate weathering that regulates climatic and tectonic forcing through hydrologic processes and imposes a thermodynamic limit on weathering fluxes, based on the physical and chemical properties of river basins. Climate regulation by silicate weathering is thus strongest when global topography is elevated, similar to the situation today, and lowest when global topography is more subdued, allowing planetary temperatures to vary depending on the global distribution of topography and mountain belts, even in the absence of appreciable changes in CO2 degassing rates. PMID:24625927

  13. Measuring U-series Disequilibrium in Weathering Rinds to Study the Influence of Environmental Factors to Weathering Rates in Tropical Basse-Terre Island (French Guadeloupe)

    NASA Astrophysics Data System (ADS)

    Guo, J.; Ma, L.; Sak, P. B.; Gaillardet, J.; Chabaux, F. J.; Brantley, S. L.

    2015-12-01

    Chemical weathering is a critical process to global CO2 consumption, river/ocean chemistry, and nutrient import to biosphere. Weathering rinds experience minimal physical erosion and provide a well-constrained system to study the chemical weathering process. Here, we applied U-series disequilibrium dating method to study weathering advance rates on the wet side of Basse-Terre Island, French Guadeloupe, aiming to understand the role of the precipitation in controlling weathering rates and elucidate the behavior and immobilization mechanisms of U-series isotopes during rind formation. Six weathering clasts from 5 watersheds with mean annual precipitation varying from 2000 to 3000 mm/yr were measured for U-series isotope ratios and major element compositions on linear core-to-rind transects. One sample experienced complete core-to-rind transformation, while the rest clasts contain both rinds and unweathered cores. Our results show that the unweathered cores are under U-series secular equilibrium, while all the rind materials show significant U-series disequilibrium. For most rinds, linear core-to-rind increases of (230Th/232Th) activity ratios suggest a simple continuous U addition history. However, (234U/238U) and (238U/232Th) trends in several clasts show evidences of remobilization of Uranium besides the U addition, complicating the use of U-series dating method. The similarity between U/Th ratios and major elements trends like Fe, Al, P in some transects and the ongoing leaching experiments suggest that redox and organic colloids could control the mobilization of U-series isotopes in the rinds. Rind formation ages and weathering advance rate (0.07-0.29mm/kyr) were calculated for those rinds with a simple U-addition history. Our preliminary results show that local precipitation gradient significantly influenced the weathering advance rate, revealing the potential of estimating weathering advance rates at a large spatial scale using the U-series dating method.

  14. Space weathering of silicate regoliths with various FeO contents: New insights from laser irradiation experiments and theoretical spectral simulations

    NASA Astrophysics Data System (ADS)

    Moroz, Lyuba V.; Starukhina, Larissa V.; Rout, Surya Snata; Sasaki, Sho; Helbert, Jörn; Baither, Dietmar; Bischoff, Addi; Hiesinger, Harald

    2014-06-01

    To investigate effects of micrometeorite bombardment on optical spectra and composition of planetary and asteroid regoliths with low Fe contents, we irradiated samples of a Fe-poor plagioclase feldspar (andesine-labradorite) using a nanosecond pulsed laser. We measured reflectance spectra of irradiated and non-irradiated areas of the samples (pressed pellets) between 0.5 and 18 μm and performed SEM/EDS and TEM studies of the samples. Bulk FeO content of 0.72 wt.% in the samples is comparable, for example, to FeO content in silicates on the surface of Mercury, that was recently mapped by NASA's MESSENGER mission and will be spectrally mapped by remote sensing instruments MERTIS and SYMBIO-SYS on board the ESA BepiColombo spacecraft. We also employed theoretical spectral modeling to characterize optical alteration caused by formation of nano- and submicrometer Fe0 inclusions within space-weathered surface layers and grain rims of a Fe-poor regolith. The laser-irradiated surface layer of plagioclase reveals significant melting, while reflectance spectra show mild darkening and reddening in the visible and near-infrared (VNIR). Our spectral modeling indicates that the optical changes observed in the visible require reduction of bulk FeO (including Fe from mineral impurities found in the sample) and formation of nanophase (np) Fe0 within the glassy surface layer. A vapor deposit, if present, is optically too thin to contribute to optical modification of the investigated samples or to cause space weathering-induced optical alteration of Fe-poor regoliths in general. Due to low thickness of vapor deposits, npFe0 formation in the latter can cause darkening and reddening only for a regolith with rather high bulk Fe content. Our calculations show that only a fraction of bulk Fe is likely to be converted to npFe0 in nanosecond laser irradiation experiments and probably in natural regolith layers modified by space weathering. The previously reported differences in response of

  15. Correlation-study about the ambient dose rate and the weather conditions

    NASA Astrophysics Data System (ADS)

    Furuya, Masato; Hatano, Yuko; Aoyama, Tomoo; Igarashi, Yasuhito; Kita, Kazuyuki; Ishizuka, Masahide

    2016-04-01

    The long-term radiation risks are believed to be heavily affected by the resuspension process. We therefore focus on the surface-atmosphere exchange process of released radioactive materials in this study. Radioactive materials were deposited on the soil and float in the air, and such complicated process are influenced by the weather conditions deeply. We need to reveal the correlation between the weather conditions and the ambient dose rate. In this study, we study the correlation between the weather conditions and the ambient dose rate with the correction of the decrease due to the radioactive decay. We found that there is a negative correlation between the ambient dose rate and the soil water content by the correlation coefficient. Using this result, we reconstruct the ambient dose rate from the weather conditions by the multiple regression analysis and found that the reconstructed data agree with the observation very well. Using Kalman filter, which can be sequentially updates the state estimate, we obtained such a good agreement.

  16. URBAN WET-WEATHER FLOW MICROBIAL CONTAMINATION: HIGH-RATE TREATMENT APPROACHES

    EPA Science Inventory

    fThis presentation is on high-rate disinfection of wet-weather flow (WWF) and pretreatment processes of suspended solids to enhance the disinfection. A discussion of pretreatment processes and of the newest disinfection technologies used for WWF is included, along with the feasib...

  17. Hydroecological Connections: Hyporheic Zone Weathering of Silicate Minerals Controls Diatom Biodiversity in Microbial Mats in Glacial Meltwater Streams of the McMurdo Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    McKnight, D. M.; Dyson, I.; Esposito, R. M.; Gooseff, M. N.; Lyons, W. B.; Welch, K. A.

    2015-12-01

    The McMurdo Dry Valleys of Antarctica is comprised of alpine and terminal glaciers, large expanses of patterned ground, and ice-covered lakes in the valley floors, which are linked by glacial meltwater streams that flow during the austral summer. As part of the McMurdo Dry Valleys Long-Term Ecological research project, we have observed stream ecosystem response to a sustained 18 year cool period with low flows, which has been recently interrupted by three "flood events" during sunny, warm summers. Many of these streams contain thriving microbial mats comprised of cyanobacteria and endemic diatoms, the most diverse group of eukaryotic organisms in the valleys. Of the 45 diatom taxa, some common taxa are heavily silicified, Hantzschia amphioxys f. muelleri, while others are only lightly silicified. By comparing diatom communities in streams which flow every summer with those in streams that only flow during flood events, we found that hydrologic flow regime acts as a strong environmental filter on diatom community composition. Following the first flood event in 2001/02, mat biomass was two-fold lower due to scouring and recovered over several years, with lesser declines following the subsequent floods. In the longer streams, the diatom community composition remained stable through the flood events, whereas in two of the shorter streams, Green and Bowles Creeks, the diatom community shifted after the first flood event to a greater abundance of lightly silicified taxa. Water quality monitoring and reactive transport modeling have shown that rapid weathering of silicate minerals in the hyporheic zone accounts for the downstream increases in Si concentration which are observed in the longer streams. One mechanism driving this greater abundance of lightly silicified diatoms in shorter streams could be the greater dilution of the Si supply from hyporheic weathering in shorter streams under high flows. Given that the stream diatom community is well preserved in the 40

  18. Chemically Accelerated Carbon Mineralization: Chemical and Biological Catalytic Enhancement of Weathering of Silicate Minerals as Novel Carbon Capture and Storage

    SciTech Connect

    2010-07-01

    IMPACCT Project: Columbia University is developing a process to pull CO2 out of the exhaust gas of coal-fired power plants and turn it into a solid that can be easily and safely transported, stored above ground, or integrated into value-added products (e.g. paper filler, plastic filler, construction materials, etc.). In nature, the reaction of CO2 with various minerals over long periods of time will yield a solid carbonate—this process is known as carbon mineralization. The use of carbon mineralization as a CO2 capture and storage method is limited by the speeds at which these minerals can be dissolved and CO2 can be hydrated. To facilitate this, Columbia University is using a unique process and a combination of chemical catalysts which increase the mineral dissolution rate, and the enzymatic catalyst carbonic anhydrase which speeds up the hydration of CO2.

  19. Experimental high strain-rate deformation products of carbonate-silicate rocks: Comparison with terrestrial impact materials

    NASA Astrophysics Data System (ADS)

    van der Bogert, C. H.; Schultz, P. H.; Spray, J. G.

    2008-09-01

    Introduction. The response of carbonate to impact processes has thus far been investigated using a combination of thermodynamic modelling, shock experiments, and impact experiments. Localized shear deformation was suggested to play an important role in the failure of carbonate during some shock experiments [1,2], and was invoked to explain significant degassing of carbonates during oblique impact experiments [3]. The results of the impact experiments are at odds with experiments [4] that show back-reaction of CO2 with CaO and MgO could significantly reduce CO2 degassing during impact events. We performed a frictional-welding experiment in order to investigate the effects of high strain-rate deformation on carbonate-silicate target materials, exclusive of shock deformation effects, and to investigate the differing results of other experiments. Samples and Techniques. A frictional melting experiment was performed using dolomitic marble and quartzite samples to simulate conditions during an impact into carbonate-silicate target rocks. The experiment followed the method of Spray (1995) [5]. The 1.5 cm3 samples were mounted onto separate steel cylinders with epoxy. Using a Blacks FWH-3 axial friction-welding rig, the samples were brought into contact at room temperature and under dry conditions with ~5 MPa applied pressure. Contact was maintained for two seconds at 750 rpm for a sustained strain-rate of 102 to 103 s-1. Results. Vapor or fine dust escaped from the interface during the experiment. Immediately after sample separation, the interfaces were incandescent. Once cooled, opaque white material adhered to both the quartzite and dolomitic marble samples. Quartzite sample. Material was injected into cracks that formed in the quartzite sample. Cooling and crystallization of the friction products resulted in the formation of submicron-sized minerals such as periclase and Ca- and Ca,Mg-silicates (Fig. 1) including merwinite and åkermanite. While periclase was observed

  20. Subcritical crack growth and mechanical weathering: a new consideration of how moisture influences rock erosion rates.

    NASA Astrophysics Data System (ADS)

    Eppes, Martha-Cary; Keanini, Russell; Hancock, Gregory S.

    2016-04-01

    The contributions of moisture to the mechanical aspects of rock weathering and regolith production are poorly quantified. In particular, geomorphologists have largely overlooked the role of subcritical crack growth processes in physical weathering and the fact that moisture strongly influences the rates of those processes. This influence is irrespective of the function that moisture plays in stress loading mechanisms like freezing or hydration. Here we present a simple numerical model that explores the efficacy of subcritical crack growth in granite rock subaerially exposed under a range of moisture conditions. Because most weathering-related stress loading for rocks found at, or near, Earth's surface (hereafter surface rocks) is cyclic, we modeled crack growth using a novel combination of Paris' Law and Charles' Law. This combination allowed us to apply existing empirically-derived data for the stress corrosion index of Charles' Law to fatigue cracking. For stress, we focused on the relatively straightforward case of intergranular stresses that arise during solar-induced thermal cycling by conductive heat transfer, making the assumption that such stresses represent a universal minimum weathering stress experienced by all surface rocks. Because all other tensile weathering-related stresses would be additive in the context of crack growth, however, our model can be adapted to include other stress loading mechanisms. We validated our calculations using recently published thermal-stress-induced cracking rates. Our results demonstrate that 1) weathering-induced stresses as modeled herein, and as published by others, are sufficient to propagate fractures subcritically over long timescales with or without the presence of water 2) fracture propagation rates increase exponentially with respect to moisture, specifically relative humidity 3) fracture propagation rates driven by thermal cycling are strongly dependent on the magnitude of diurnal temperature ranges and the

  1. The role of nitrification in silicate hydrolysis in soils near Santa Cruz, CA

    NASA Astrophysics Data System (ADS)

    Kyker-Snowman, E.; White, A.; Lawrence, C. R.; Schulz, M. S.

    2013-12-01

    In some ecosystems, nitrification (microbial conversion of ammonium to nitrate) may supplant carbonic acid as a source of acidity and drive silicate weathering. Recent studies have explored the impact that ammonium fertilizer addition to soils has on weathering of various mineral types (Pacheco et al. 2013) and demonstrated directly that ammonium addition to soils can increase carbonate weathering (Gandois et al. 2011). Some evidence points to a role for nitrification in silicate weathering at a series of coastal grassland terraces near Santa Cruz, CA. Weathering rates in these soils have been estimated using the byproducts of silicate hydrolysis (Cl--adjusted Na+ and other cations). If carbonic acid from dissolved CO2 is the source of acidity in silicate hydrolysis, bicarbonate should balance the cations produced during weathering. However, in the Santa Cruz soils nitrate is the dominant anion balancing cation concentrations. High concentrations of CO2 (>1%) at depths greater than 1m may provide additional support for nitrification-based silicate hydrolysis at Santa Cruz. We evaluate the role of nitrification in silicate weathering for soils from the Santa Cruz Marine Terrace Chronosequence using a column ammonium-addition experiment and a basic weathering model. The column experiment uses ammonium inputs in excess of natural inputs and measures weathering products in eluted fluids over time. The model incorporates more realistic estimates of ammonium input and explores whether the observed concentrations of cations, nitrate and CO2 seen at Santa Cruz can be explained by nitrification-driven acidity or if other inputs need to be considered. Gandois, L, Perrin, A-S, and Probst, A. 2011. Impact of nitrogenous fertiliser-induced proton release on cultivated soils with contrasting carbonate contents: A column experiment. Geochimica et Cosmochimica Acta 75 pp. 1185-1198. Pacheco, F, Landim, P, and Szocs, T. 2013. Anthropogenic impacts on mineral weathering: A

  2. Determining rates of chemical weathering in soils - Solute transport versus profile evolution

    USGS Publications Warehouse

    Stonestrom, D.A.; White, A.F.; Akstin, K.C.

    1998-01-01

    SiO2 fluxes associated with contemporary solute transport in three deeply weathered granitoid profiles are compared to bulk SiO2 losses that have occurred during regolith development. Climates at the three profiles range from Mediterranean to humid to tropical. Due to shallow impeding alluvial layers at two of the profiles, and seasonally uniform rainfall at the third, temporal variations in hydraulic and chemical state variables are largely attenuated below depths of 1-2 m. This allows current SiO2 fluxes below the zone of seasonal variations to be estimated from pore-water concentrations and average hydraulic flux densities. Mean-annual SiO2 concentrations were 0.1-1.5 mM. Hydraulic conductivities for the investigated range of soil-moisture saturations ranged from 10-6 m s-1. Estimated hydraulic flux densities for quasi-steady portions of the profiles varied from 6 x 10-9 to 14 x 10-9 m s-1 based on Darcy's law and field measurements of moisture saturations and pressure heads. Corresponding fluid-residence times in the profiles ranged from 10 to 44 years. Total SiO2 losses, based on chemical and volumetric changes in the respective profiles, ranged from 19 to 110 kmoles SiO2 m-2 of land surface as a result of 0.2-0.4 Ma of chemical weathering. Extrapolation of contemporary solute fluxes to comparable time periods reproduced these SiO2 losses to about an order of magnitude. Despite the large range and non-linearity of measured hydraulic conductivities, solute transport rates in weathering regoliths can be estimated from characterization of hydrologic conditions at sufficiently large depths. The agreement suggests that current weathering rates are representative of long-term average weathering rates in the regoliths.SiO2 fluxes associated with contemporary solute transport in three deeply weathered granitoid profiles are compared to bulk SiO2 losses during regolith development. Due to shallow impeding alluvial layers at two of the profiles, and seasonally uniform

  3. Silicate volcanism on Io

    NASA Technical Reports Server (NTRS)

    Carr, M. H.

    1986-01-01

    This paper is mainly concerned with the nature of volcanic eruptions on Io, taking into account questions regarding the presence of silicates or sulfur as principal component. Attention is given to the generation of silicate magma, the viscous dissipation in the melt zone, thermal anomalies at eruption sites, and Ionian volcanism. According to the information available about Io, it appears that its volcanism and hence its surface materials are dominantly silicic. Several percent of volatile materials such as sulfur, but also including sodium- and potassium-rich materials, may also be present. The volatile materials at the surface are continually vaporized and melted as a result of the high rates of silicate volcanism.

  4. Effect of natural fiber types and sodium silicate coated on natural fiber mat/PLA composites: Tensile properties and rate of fire propagation

    NASA Astrophysics Data System (ADS)

    Thongpin, C.; Srimuk, J.; hipkam, N.; Wachirapong, P.

    2015-07-01

    In this study, 3 types of natural fibres, i.e. jute, sisal and abaca, were plain weaved to fibre mat. Before weaving, the fibres were treated with 5% NaOH to remove hemi cellulose and lignin. The weaving was performed by hand using square wooden block fit with nails for weaving using one and two types of natural fibres as weft and warp fibre to produce natural fibre mat. The fibre mat was also impregnated in sodium silicate solution extracted from rich husk ash. The pH of the solution was adjusted to pH 7 using H2SO4 before impregnation. After predetermined time, sodium silicate was gelled and deposited on the mat. The fabric mat and sodium silicate coated mat were then impregnated with PLA solution to produce prepreg. Dried pepreg was laminated with PLA sheet using compressing moulding machine to obtain natural fibre mat/PLA composite. The composite containing abaca aligned in longitudinal direction with respect to tension force enhanced Young's modulus more than 300%. Fibre mat composites with abaca aligned in longitudinal direction also showed tensile strength enhancement nearly 400% higher than neat PLA. After coating with sodium silicate, the tensile modulus of the composites was found slightly increased. The silicate coating was disadvantage on tensile strength of the composite due to the effect of sodium hydroxide solution that was used as solvent for silicate extraction from rice husk ash. However, sodium silicate could retard rate of fire propagation about 50%compare to neat PLA and about 10% reduction compared to fibre mat composites without sodium silicate coated fibre mat.

  5. Elemental weathering fluxes and saprolite production rate in a Central African lateritic terrain (Nsimi, South Cameroon)

    NASA Astrophysics Data System (ADS)

    Braun, Jean-Jacques; Marechal, Jean-Christophe; Riotte, Jean; Boeglin, Jean-Loup; Bedimo Bedimo, Jean-Pierre; Ndam Ngoupayou, Jules Remy; Nyeck, Brunot; Robain, Henri; Sekhar, M.; Audry, Stéphane; Viers, Jérôme

    2012-12-01

    The comparison between contemporary and long-term weathering has been carried out in the Small Experimental Watershed (SEW) of Nsimi, South Cameroon in order to quantify the export fluxes of major and trace elements and the residence time of the lateritic weathering cover. We focus on the hillside system composed of a thick lateritic weathering cover topped by a soil layer. This study is built on the recent improvements of the hillside hydrological functioning and on the analyses of major and trace elements. The mass balance calculation at the weathering horizon scale performed with the parent rock as reference indicates (i) strong depletion profiles for alkalis (Na, K, Rb) and alkaline earths (Mg, Ca, Sr, Ba), (ii) moderate depletion profiles for Si, P, Cd, Cu, Zn, Ni and Co, (iii) depletion/enrichment profiles for Al, Ga, Ge, Sn, Pb, LREE, HREE, Y, U, Fe, V, Cr, Mn. It is noteworthy that (i) Mn and Ce are not significantly redistributed according to oxidative processes as it is the case for Fe, V and Cr, and (ii) Ge is fractionated compared to silica with enrichment in Fe-rich horizons. The calculations performed for the topsoil with iron crust as parent material reference reveal that the degradation of the iron crust is accompanied by the loss of most of the constituting elements, among which are those specifically accumulated as the redox sensitive elements (Fe, V, Cr) and iron oxide related elements like Th. The overall current elemental fluxes from the hillside system at the springs and the seepage zones are extremely low due to the inert lateritic mineralogy. Ninety-four percent of the whole Na flux generated from the hillside corrected from atmospheric deposits (77 mol/ha/yr) represents the current weathering rates of plagioclase (oligoclase) in the system, the other remaining 6% may be attributed to the dissolution of hornblende. The silica hillside flux is 300 mol/ha/yr and can be mostly attributed to the plagioclase and kaolinite dissolution. Al and Ga

  6. Putting weathering into a landscape context: Variations in exhumation rates across the Colorado Front Range

    NASA Astrophysics Data System (ADS)

    Anderson, Suzanne P.; Foster, Melissa A.; Anderson, Scott W.; Dühnforth, Miriam; Anderson, Robert S.

    2015-04-01

    Erosion rates are expected vary with lithology, climate, and topographic slope, yet assembling these variations for an entire landscape is rarely done. The Front Range of the southern Rocky Mountains in Colorado, USA, exhibits contrasts in all three parameters. The range comprises ~2300 m in relief from the Plains to the crags of the Continental Divide. Its abrupt mountain front coincides closely with the boundary between marine sedimentary rocks to the east and Proterozoic crystalline rocks (primarily granodiorite and gneiss) to the west. Mean annual temperature declines and mean annual precipitation increases with elevation, from ~11° C/490 mm at the western edge of the Plains to -3.7° C/930 mm on Niwot Ridge near the range crest. The range contains regions of low relief with rolling topography, in which slopes rarely exceed 20° , as well as deeply incised glacial valleys and fluvial canyons lined by steep slopes (>25° ). Cosmogenic 10Be based erosion rates vary by a factor of ~5 within crystalline rock across the range. The lowest rates (5-10 mm/ka) are found on low relief summit tors in the alpine, where temperatures are low and precipitation is high. Slightly higher erosion rates (20-30 mm/ka) are found in low relief crystalline rock areas with montane forest cover. Taken together, these rates suggest that on low slopes, rock-weathering rates (which place a fundamental limit on erosion rates) are lower in cold alpine settings. Over the 40-150 ka averaging time of 10Be erosion rates, lower rates are found where periglacial/tundra conditions have prevailed, while moderate rates occur where conditions have varied from periglacial/tundra in the past to frigid regime/montane forest in the Holocene. Higher basin-averaged erosion rates of 40-60 mm/ka are reported for 'canyon edge' basins (Dethier et al., 2014, Geology), which are small, steep basins responding to fluvial bedrock incision that formed the canyons in the late Cenozoic. Are higher erosion rates in

  7. First report on Cretaceous paleoweathering rates in western Panthalassa: Evidence of global enhancement of continental weathering during OAE 2

    NASA Astrophysics Data System (ADS)

    Ohta, T.

    2013-12-01

    Mid-Cretaceous is characterized by intensified oceanic anoxia (Oceanic Anoxic Events: OAEs) that raised global deposition of organic black shales. Several models have been proposed to explain the cause of the OAEs in conjunction with Cretaceous global warmth, active volcanism, sea-level changes and others. For example, Weissert et al. (1998) proposed a mechanism called 'weathering hypothesis'. In this model, the cause of the OAEs is explained in a following chain reaction, (1) global warmth and increase in atmospheric CO2 enhanced weathering of continental crust, (2) enhanced land weathering led excessive influx of nutrients from continents to oceans, (3) eutrophication enhanced primary productivity, (4) the excessive primary producers consumed dissolved oceanic oxygen that finally led to the OAEs. Several studies, in fact, revealed a causal relation between enhanced weathering and OAEs in northern Tethys region. However, it is necessary to collect worldwide information to unravel the global response of weathering hypothesis as a cause of OAEs. For such reason, the present contribution conducted measurements of the degree of hinterland paleoweathering during OAEs in northern Japan, for the purpose to provide a first report on the relation between continental weathering and OAEs in open ocean, the western Panthalassa Ocean. Aptian to Campanian forearc basin mudstones (Yezo Group) were analyzed by XRF and the degree of hinterland weathering was evaluated by geochemical weathering index (W index; Ohta and Arai, 2007). The W values obtained for the Yezo Group are 30~50, which is equivalent to the W values of recent soils developed in temperate mid-latitude climate. The W values show a fluctuation pattern that is concordant with the Cretaceous paleotemperature changes. This match indicates that the change in paleotemperature governed the weathering rates of East Asian continental crust. In addition, hinterland weathering rates show instantaneous increase during the OAE

  8. Quantifying rind formation and chemical weathering rates in weathering clasts with uranium-series isotopes: a case study from Basse-Terre Island, Guadeloupe

    NASA Astrophysics Data System (ADS)

    Ma, L.; Chabaux, F. J.; Pelt, E.; Granet, M.; Sak, P. B.; Gaillardet, J.; Lebedeva, M.; Brantley, S. L.

    2011-12-01

    Weathering of tropical volcanic islands is rapid because of the reactive nature of the volcanic rock and the hot humid climate. In the tropics, rock fragments in the regolith zone commonly form alteration rinds. Weathering rinds are excellent samples to understand key chemical weathering processes. To quantify rock weathering rates in a tropical climate and to understand the environmental factors that control these rates, we combined a novel U-series isotopic technique with chemical and electron microprobe analyses to study weathering rinds formed at Basse-Terre Island, Guadeloupe. U-series isotopes and element concentrations were analyzed in a basaltic/andesitic weathering rind collected from the Bras David watershed on Basse-Terre Island. From the clast, core and rind samples were obtained by drilling along two linear profiles. Elemental profiles reveal that elemental loss varies in the order of Ca, Na, Sr > K, Mg, Rb > Mn > Si > Ba > Al > Fe, and Ti =0 across the core-rind interface, consistent with relative reactivity of phases in the clast from plagioclase ≈ pyroxene ≈ glass matrix > apatite > ilmenite. Elemental profiles also reveal conservative behavior of Th and external addition of U into the rind during clast weathering. Measured (234U/238U) activity ratios of the rind samples (1.001 to 1.031) are mostly higher than the core samples (average at ~1.003). Measured (238U/232Th) and (230Th/232Th) activity ratios of the core and rind samples range from 0.973 to 1.817, and 0.971 to 1.375, respectively. Most importantly, both (238U/232Th) and (230Th/232Th) activity ratios increase systematically from the core into the weathering rind for the two profiles. The elemental profiles and electronic microprobe observations suggest that weathering reactions include dissolution of pyroxene, plagioclase, and glass matrix, and formation of Fe oxyhydroxides, gibbsite and minor kaolinite. The dissolution of plagioclase leads to significant porosity growth within the rind

  9. Permian Minimum and the Following Major Rise in Seawater 87Sr/86Sr Linked to the Glaciation/Deglaciation and Resultant Change in Weathering Rate

    NASA Astrophysics Data System (ADS)

    Kani, T.; Isozaki, Y.

    2014-12-01

    We report a detailed secular change of the middle Middle to early Late Permian seawater 87Sr/86Sr ratio for and Akasaka and Kamura carbonates (Japan) deposited on mid-Pansalassan seamounts and for Shizipo carbonates (South China) deposited on the shallow marine shelf. In these coeval sections, extremely low values (<0.7069; the lowest values of the Phanerozoic) continued from upper Wordian (middle Middle Permian) to the topmost Capitanian (upper Middle Permian) barren interval immediately below the Middle-Late Permian boundary characterized by the major crisis of large-tested fusulines and rugose corals. Immediately after ca. 5 m.y.-long minimum interval, the major rise in 87Sr/86Sr was started and the rate of the rise (0.00007/m.y.) continued in period of time containing 21 m.y. until early Triassic (~239 Ma), that is faster than the Cenozoic major rise (0.00003/m.y.). The most significant shift through Phanerozoic in Sr isotope trend can be explained by the remarkable changes in continental erosion/weathering rate; in particular, by the onset of glaciation and the following deglaciation, that is supported by global sea level change, in addition to the initial doming/rifting of Pangea. After the Capitanian cooling, the long-term climatic regime shifted to a warmer one during which inland ice sheet was removed to expose old crustal silicates for to erosion/weathering. A mantle plume impingiment might lead a domal uplift that accelerate weathering. Highly radiogenic continental Sr could enter the ocean along the new drainage systems developed with the rifting.

  10. Redetermination of the Space Weathering Rate Using Spectra of Iannini Asteroid Family Members

    NASA Astrophysics Data System (ADS)

    Willman, Mark; Jedicke, R.; Nesvorny, D.; Moskovitz, N.; Ivezic, Z.; Fevig, R.

    2007-12-01

    We have obtained moderate S/N ( 85) spectra at a realized resolution of R 100 for 11 members of the Iannini family, until recently the youngest known family at under 5 million years of age. The spectra were acquired using ESI in its low-resolution prism mode on the Keck II telescope. The family members belong to the S class of asteroids with perhaps some K class members. The Iannini family members's average spectral slope, the slope of the best-fit line constrained to pivot about 1 at 550 nm, is (0.30±0.04)/μm, matching that previously reported using SDSS color photometry. Using our spectra for this family as well as new observations of Karin family members and new classifications of some older families we revised the space weathering rate of S class asteroids. We parameterize the space weathering rate of the principal component color of the spectrum (PC1), which is correlated with the spectral slope, as PC1(t) = PC1(0) + Δ PC1[1 - \\exp^{-(t/κ)α}]. Our revised rate suggests that the characteristic time scale for space weathering is τ = 570 ± 220 Myr and that new S class clusters will have an initial color of PC1(0) = 0.31 ± 0.04. This rate is in better agreement with lab measurements, supporting the use of space weathering as a dating method. Under the assumption that all the spectra should be identical, since the members all derive from the same parent body and are presumably covered with similar regolith, we combined them to obtain a high-S/N composite spectrum for the family. While the combined spectrum is clearly within the S/K class we note the appearance of a 'green feature' near 550 nm that has not previously been identified in asteroid spectra. We tentatively identify it as a feature in the pyroxene spectra as observed in the lab.

  11. Apparent I-Xe Cooling Rates of Chondrules Compared with Silicates from the Colomera Iron Meteorite

    NASA Technical Reports Server (NTRS)

    Hohenberg, C. M.; Meshik, A. P.; Pravdivseva, O. V.

    2004-01-01

    In I-Xe dating, a regular pattern of increasing Xe-129/128Xe-128 ratio with increasing extraction temperature is often observed. If one makes the crude assumption that the temperatures at which the Xe is extracted in the laboratory is approximately the same as the temperature at which those sites closed 4.6 Ga ago, a (zeroth order) model cooling rate can be found. In order to test and refine this model we can apply the cooling theory of Dodson to those extraction steps approaching the I-Xe isochrons. Using an Arrhenius plot for these temperature fractions, and assuming that an only single phase is involved, the effective diffusion parameters can be estimated (frequency factor and activation energy). From the apparent (zeroth order) cooling rate, the closure temperature can be estimated from the Dodson equation. This model closure temperature can then be compared with the actual laboratory temperature at which the isochron begins. The ratio of the closure temperature and the temperature corresponding to the start of the isochron provides the ratio of the two temperature scales, incorporation and extraction. The actual cooling rate is then given by the apparent (zeroth order) cooling rate times the temperature scale factor. Figure 1 shows Arrhenius plots for I-Xe data

  12. The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

    SciTech Connect

    Maher, K.; Steefel, C. I.; White, A.F.; Stonestrom, D.A.

    2009-02-25

    In order to explore the reasons for the apparent discrepancy between laboratory and field weathering rates and to determine the extent to which weathering rates are controlled by the approach to thermodynamic equilibrium, secondary mineral precipitation and flow rates, a multicomponent reactive transport model (CrunchFlow) was used to interpret soil profile development and mineral precipitation and dissolution rates at the 226 ka marine terrace chronosequence near Santa Cruz, CA. Aqueous compositions, fluid chemistry, transport, and mineral abundances are well characterized (White et al., 2008, GCA) and were used to constrain the reaction rates for the weathering and precipitating minerals in the reactive transport modeling. When primary mineral weathering rates are calculated with either of two experimentally determined rate constants, the nonlinear, parallel rate law formulation of Hellmann and Tisser and [2006] or the aluminum inhibition model proposed by Oelkers et al. [1994], modeling results are consistent with field-scale observations when independently constrained clay precipitation rates are accounted for. Experimental and field rates, therefore, can be reconciled at the Santa Cruz site. Observed maximum clay abundances in the argillic horizons occur at the depth and time where the reaction fronts of the primary minerals overlap. The modeling indicates that the argillic horizon at Santa Cruz can be explained almost entirely by weathering of primary minerals and in situ clay precipitation accompanied by undersaturation of kaolinite at the top of the profile. The rate constant for kaolinite precipitation was also determined based on model simulations of mineral abundances and dissolved Al, SiO{sub 2}(aq) and pH in pore waters. Changes in the rate of kaolinite precipitation or the flow rate do not affect the gradient of the primary mineral weathering profiles, but instead control the rate of propagation of the primary mineral weathering fronts and thus total

  13. Hydrochemistry and weathering rates on Corumbataí River basin, São Paulo State, Brazil

    NASA Astrophysics Data System (ADS)

    Bonotto, Daniel Marcos; Lima, Jorge Luis Nepomuceno de

    2010-03-01

    SummaryThis work was held at the Corumbataí River basin that is inserted within the giant Paraná sedimentary basin (Paleozoic-Cenozoic) in South America. The Corumbataí River is the major river draining the area and its water is extensively used by water supply systems in the basin. Its surface waters were collected at two sampling points, upstream and downstream from Rio Claro city, the principal municipality within the basin. We report chemical and radionuclides ( 222Rn and 210Po) analyses for rainwater and river water samples in order to estimate chemical weathering fluxes. All major chemical data indicated poorer conditions of the water quality in Corumbataí River after reaching Rio Claro city. However, one very important finding was that the weighted mean of the 210Po activity concentration is the same (0.21 dpm/L) upstream and downstream from Rio Claro city, indicating that 210Po is a conservative nuclide. The net output flux in Corumbataí River basin estimated from the difference between the total discharge flux and the input flux based on wet precipitation yielded a negative value for polonium as it is a very particle-reactive radionuclide, tending to accumulate into fluvial sediments. The chemical weathering rate (removed material quantity) corresponded to 76.5 t/km 2 yr when Po data in sediments and rocks were utilized in the calculations. This rate is compatible with others determined elsewhere, indicating the usefulness of Po in studies of weathering processes, even in areas characterized by anthropogenic inputs.

  14. The role of basalt weathering on climate: the Siberian traps

    NASA Astrophysics Data System (ADS)

    Grard, A.; François, L.; Dessert, C.; Dupré, B.; Goddéris, Y.

    2003-04-01

    The Siberian traps represent one of the most important flood basalt provinces on Earth. Their onset coincides with a profound faunal mass extinction at the Permo-Trias boundary (250 my ago). The volcanic eruption has also environmental and climatic effects through aerosols and gases injection into the atmosphere. Chemical weathering processes play a major role in biogeochemical cycles and climate evolution. In particular, the weathering of silicate rocks represents an important sink of atmospheric CO_2. At the million-year timescale, the volcanic release of CO_2 into the atmosphere-ocean system is balanced by its consumption during silicate weathering followed by carbonate deposition on the seafloor. Recent data have shown that chemical weathering of basalt is five to ten times more efficient than weathering of acidic silicate rocks such as granite or gneiss (Dessert et al., EPSL, 188 : 459-474, 2001). Thus the weathering of basaltic rocks consumes more atmospheric CO_2 than other silicate rocks. In the case of subaerial basaltic volcanism, an eruption not only releases CO_2 to the atmosphere, but also produces basaltic rocks which weather rapidly, enhancing CO_2 consumption rates. Currently, the Siberian basaltic traps are located in a cold and dry region. The weathering rates of this province are low, and the climatic impact is thus currently low. But in the past, the latitudinal temperature gradient was smaller. During the Permian, the climate was significantly warmer than today. Thus the chemical weathering of the Siberian traps was enhanced at that time, and this process led to a long-term impact on the Triassic climate and on the carbon cycle. The used model calculates the traps impact on the long-term carbon cycle and climate evolution. This model has been refined and adapted to high latitudes environments. We quantify the cooling caused by traps weathering.

  15. Integrating topography, hydrology and rock structure in weathering rate models of spring watersheds

    NASA Astrophysics Data System (ADS)

    Pacheco, Fernando A. L.; Van der Weijden, Cornelis H.

    2012-03-01

    SummaryWeathering rate models designed for watersheds combine chemical data of discharging waters with morphologic and hydrologic parameters of the catchments. At the spring watershed scale, evaluation of morphologic parameters is subjective due to difficulties in conceiving the catchment geometry. Besides, when springs emerge from crystalline massifs, rock structure must be accounted in formulas describing the area of minerals exposed to the percolating fluids, for a realistic evaluation of the rates. These particular features are not included in the available approaches and for that reason a new model was developed, coined THROW model. This is a lumped approach that integrates (T)opography, (H)ydrology, (RO)ck structure and (W)eathering in a single algorithm. The study area comprises several stream watersheds and spring sites of the Vouga River basin (northern Portugal), shaped on granites. Firstly, the THROW model couples a terrain modeling analysis with hydrologic models based on discharge rates, to determine hydraulic conductivities (K), effective porosities (ne) and annual recharges (Vr) at the stream watershed scale. Subsequently, these parameters are used in a water balance model to estimate concomitant groundwater travel times (t). The mean K [(4.7 ± 3.2) × 10-7 m s-1] and ne [(2.0 ± 1.3) × 10-2] values are adopted as proxies for the spring watersheds and a firm regression equation is defined between time and stream watershed area (A). Secondly, two more runs of terrain modeling analysis are executed to extrapolate morphologic parameters for the spring watersheds. The first run hinges on scaling properties of the drainage networks, known as Horton laws, and is used to scale watershed areas across stream orders (i). The scaling function is described by another regression equation. The second run evaluates the order of a spring watershed, defined as equivalent order (ieq) and equated to the mean order of the surrounding stream watersheds. Having

  16. Experimental correlation of melt structures, nucleation rates, and thermal histories of silicate melts

    NASA Technical Reports Server (NTRS)

    Boynton, W. V.; DRAKE; HILDEBRAND; JONES; LEWIS; TREIMAN; WARK

    1987-01-01

    The theory and measurement of the structure of liquids is an important aspect of modern metallurgy and igneous petrology. Liquid structure exerts strong controls on both the types of crystals that may precipitate from melts and on the chemical composition of those crystals. An interesting aspect of melt structure studies is the problem of melt memories; that is, a melt can retain a memory of previous thermal history. This memory can influence both nucleation behavior and crystal composition. This melt memory may be characterized quantitatively with techniques such as Raman, infrared and NMR spectroscopy to provide information on short-range structure. Melt structure studies at high temperature will take advantage of the microgravity conditions of the Space Station to perform containerless experiments. Melt structure determinations at high temperature (experiments that are greatly facilitated by containerless technology) will provide invaluable information for materials science, glass technology, and geochemistry. In conjunction with studies of nucleation behavior and nucleation rates, information relevant to nucleation in magma chambers in terrestrial planets will be acquired.

  17. Snowfall Rate Retrieval Using Passive Microwave Measurements and Its Applications in Weather Forecast and Hydrology

    NASA Technical Reports Server (NTRS)

    Meng, Huan; Ferraro, Ralph; Kongoli, Cezar; Yan, Banghua; Zavodsky, Bradley; Zhao, Limin; Dong, Jun; Wang, Nai-Yu

    2015-01-01

    (AMSU), Microwave Humidity Sounder (MHS) and Advance Technology Microwave Sounder (ATMS). ATMS is the follow-on sensor to AMSU and MHS. Currently, an AMSU and MHS based land snowfall rate (SFR) product is running operationally at NOAA/NESDIS. Based on the AMSU/MHS SFR, an ATMS SFR algorithm has also been developed. The algorithm performs retrieval in three steps: snowfall detection, retrieval of cloud properties, and estimation of snow particle terminal velocity and snowfall rate. The snowfall detection component utilizes principal component analysis and a logistic regression model. It employs a combination of temperature and water vapor sounding channels to detect the scattering signal from falling snow and derives the probability of snowfall. Cloud properties are retrieved using an inversion method with an iteration algorithm and a two-stream radiative transfer model. A method adopted to calculate snow particle terminal velocity. Finally, snowfall rate is computed by numerically solving a complex integral. The SFR products are being used mainly in two communities: hydrology and weather forecast. Global blended precipitation products traditionally do not include snowfall derived from satellites because such products were not available operationally in the past. The ATMS and AMSU/MHS SFR now provide the winter precipitation information for these blended precipitation products. Weather forecasters mainly rely on radar and station observations for snowfall forecast. The SFR products can fill in gaps where no conventional snowfall data are available to forecasters. The products can also be used to confirm radar and gauge snowfall data and increase forecasters' confidence in their prediction.

  18. Fresh and weathered crude oil effects on potential denitrification rates of coastal marsh soil.

    PubMed

    Pietroski, Jason P; White, John R; DeLaune, Ronald D; Wang, Jim J; Dodla, Syam K

    2015-09-01

    On April 20, 2010, the Deepwater Horizon oil platform experienced an explosion which triggered the largest marine oil spill in US history, resulting in the release of ∼795 million L of crude oil into the Gulf of Mexico. Once oil reached the surface, changes in overall chemical composition occurred due to volatilization of the smaller carbon chain compounds as the oil was transported onshore by winds and currents. In this study, the toxic effects of both fresh and weathered crude oil on denitrification rates of coastal marsh soil were determined using soil samples collected from an unimpacted coastal marsh site proximal to areas that were oiled in Barataria Bay, LA. The 1:10 ratio of crude oil:field moist soil fully coated the soil surface mimicking a heavy oiling scenario. Potential denitrification rates at the 1:10 ratio, for weathered crude oil, were 46 ± 18.4% of the control immediately after exposure and 62 ± 8.0% of the control following a two week incubation period, suggesting some adaptation of the denitrifying microbial consortium over time. Denitrification rates of soil exposed to fresh crude oil were 51.5 ± 5.3% of the control after immediate exposure and significantly lower at 10.9 ± 1.1% after a 2 week exposure period. Results suggest that fresh crude oil has the potential to more severely impact the important marsh soil process of denitrification following longer term exposure. Future studies should focus on longer-term denitrification as well as changes in the microbial consortia in response to oil exposure. PMID:25929872

  19. Role of hydraulic diffusivity in the decrease of weathering rates over time

    NASA Astrophysics Data System (ADS)

    Pacheco, Fernando A. L.; Van der Weijden, Cornelis H.

    2014-05-01

    Springs emerging within massifs of crystalline rocks were monitored for discharge rate (Q), and the Q values combined with geomorphic and hydrographic parameters in a hydrologic model to calculate hydraulic conductivity (K) and effective porosity (ne) of the spring watersheds. The spring waters, several borehole waters and rain water were analyzed for major dissolved compounds, strontium and isotopes (δ18O, δ2H, δ13C and 87Sr/86Sr). With a shift to less negative values, δ18O and δ2H were fitted by a line approximately parallel to the GMWL, but no significant dependence on altitude was found. The δ18O and δ2H values correlate better with those of precipitation amount. The 87Sr/86Sr ratios in drilled well waters correlate positively with the depth of water circulation reported in the borehole logs. The corresponding regression equations were used to extrapolate the depth of hydraulic circuits within the spring watersheds. The previous data, together with groundwater travel times calculated by a water balance model, and with reactions of granite/metassediment plagioclase and biotite precipitating halloysite, gibbsite and vermiculite, were assembled in a mass balance model to calculate solute-flux weathering rates of plagioclase (WPl). The WPl's were described as a function of √{D}∝√{K/n}, where D is the hydraulic diffusivity. The discrepancies between the WPl values and solid-state rates, based on the differences between elemental, isotopic and mineral compositions measured in present-day regoliths and in the assumed protolith, were assigned to a decrease in D over time, from values in the protolith to values in the weathered aquifer.

  20. All-weather ultraviolet solar spectra retrieved at a 0.5-Hz sampling rate.

    PubMed

    Thorseth, T M; Kjeldstad, B

    1999-10-20

    A measurement scheme and an algorithm have been developed to retrieve global irradiance ultraviolet solar spectra (290-400 nm) at a sampling rate of 0.5 Hz. The algorithm combines spectral irradiance measurements performed with a slow (a few minutes) scanning spectroradiometer (Optronic Model OL752) and a moderate bandwidth multichannel radiometer (Biospherical ground-based ultraviolet radiometer Model 541). The filter radiometer instrument allows for continuous observations of global UV radiation at five channels (approximately 10-nm bandwidth), performed simultaneously with spectral measurements. Information about changing cloud conditions during a spectral scan was retrieved from filter measurements and applied to spectral data, hence estimated spectra without cloud variations could be constructed. The quality of the estimated spectra depends on data quality from both instruments. The method works well in all kinds of weather conditions, as long as the Sun is above the horizon and none of the instruments are hampered by measurement errors. PMID:18324148

  1. The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

    NASA Astrophysics Data System (ADS)

    Maher, Kate; Steefel, Carl I.; White, Art F.; Stonestrom, Dave A.

    2009-05-01

    In order to explore the reasons for the apparent discrepancy between laboratory and field weathering rates and to determine the extent to which weathering rates are controlled by the approach to thermodynamic equilibrium, secondary mineral precipitation, and flow rates, a multicomponent reactive transport model (CrunchFlow) was used to interpret soil profile development and mineral precipitation and dissolution rates at the 226 ka Marine Terrace Chronosequence near Santa Cruz, CA. Aqueous compositions, fluid chemistry, transport, and mineral abundances are well characterized [White A. F., Schulz M. S., Vivit D. V., Blum A., Stonestrom D. A. and Anderson S. P. (2008) Chemical weathering of a Marine Terrace Chronosequence, Santa Cruz, California. I: interpreting the long-term controls on chemical weathering based on spatial and temporal element and mineral distributions. Geochim. Cosmochim. Acta72 (1), 36-68] and were used to constrain the reaction rates for the weathering and precipitating minerals in the reactive transport modeling. When primary mineral weathering rates are calculated with either of two experimentally determined rate constants, the nonlinear, parallel rate law formulation of Hellmann and Tisserand [Hellmann R. and Tisserand D. (2006) Dissolution kinetics as a function of the Gibbs free energy of reaction: An experimental study based on albite feldspar. Geochim. Cosmochim. Acta70 (2), 364-383] or the aluminum inhibition model proposed by Oelkers et al. [Oelkers E. H., Schott J. and Devidal J. L. (1994) The effect of aluminum, pH, and chemical affinity on the rates of aluminosilicate dissolution reactions. Geochim. Cosmochim. Acta58 (9), 2011-2024], modeling results are consistent with field-scale observations when independently constrained clay precipitation rates are accounted for. Experimental and field rates, therefore, can be reconciled at the Santa Cruz site. Additionally, observed maximum clay abundances in the argillic horizons occur at the

  2. The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

    USGS Publications Warehouse

    Maher, K.; Steefel, Carl; White, A.F.; Stonestrom, D.A.

    2009-01-01

    In order to explore the reasons for the apparent discrepancy between laboratory and field weathering rates and to determine the extent to which weathering rates are controlled by the approach to thermodynamic equilibrium, secondary mineral precipitation, and flow rates, a multicomponent reactive transport model (CrunchFlow) was used to interpret soil profile development and mineral precipitation and dissolution rates at the 226 ka Marine Terrace Chronosequence near Santa Cruz, CA. Aqueous compositions, fluid chemistry, transport, and mineral abundances are well characterized [White A. F., Schulz M. S., Vivit D. V., Blum A., Stonestrom D. A. and Anderson S. P. (2008) Chemical weathering of a Marine Terrace Chronosequence, Santa Cruz, California. I: interpreting the long-term controls on chemical weathering based on spatial and temporal element and mineral distributions. Geochim. Cosmochim. Acta 72 (1), 36-68] and were used to constrain the reaction rates for the weathering and precipitating minerals in the reactive transport modeling. When primary mineral weathering rates are calculated with either of two experimentally determined rate constants, the nonlinear, parallel rate law formulation of Hellmann and Tisserand [Hellmann R. and Tisserand D. (2006) Dissolution kinetics as a function of the Gibbs free energy of reaction: An experimental study based on albite feldspar. Geochim. Cosmochim. Acta 70 (2), 364-383] or the aluminum inhibition model proposed by Oelkers et al. [Oelkers E. H., Schott J. and Devidal J. L. (1994) The effect of aluminum, pH, and chemical affinity on the rates of aluminosilicate dissolution reactions. Geochim. Cosmochim. Acta 58 (9), 2011-2024], modeling results are consistent with field-scale observations when independently constrained clay precipitation rates are accounted for. Experimental and field rates, therefore, can be reconciled at the Santa Cruz site. Additionally, observed maximum clay abundances in the argillic horizons occur at

  3. Redetermination of the space weathering rate using spectra of Iannini asteroid family members

    NASA Astrophysics Data System (ADS)

    Willman, Mark; Jedicke, Robert; Nesvorný, David; Moskovitz, Nicholas; Ivezić, Željko; Fevig, Ronald

    2008-06-01

    We have obtained moderate S/N (˜85) spectra at a realized resolution of R˜100 for 11 members of the Iannini family, until recently the youngest known family at under 5 million years of age [Nesvorný, D., Bottke, W.F., Levison, H.F., Dones, L., 2003. Astrophys. J. 591, 486-497, 720-771]. The spectra were acquired using the Echellette Spectrograph and Imager in its low-resolution prism mode on the Keck II telescope. The family members belong to the S-complex of asteroids with perhaps some K class members. The Iannini family members' average spectral slope, defined as the slope of the best-fit line constrained to pivot about 1 at 550 nm, is (0.30±0.04)/μm, matching the (0.26±0.03)/μm reported by Jedicke et al. [Jedicke, R., Nesvorný, D., Whiteley, R.J., Ivezić, Ž., Jurić, M., 2004. Nature 429, 275-277] using SDSS [Ivezić, Ž., Jurić, M., Lupton, R.H., Tabachnik, S., Quinn, T., 2002. In: Tyson, J.A., Wolff, S. (Eds.), Survey and Other Telescope Technologies and Discoveries. In: Proc. SPIE, vol. 4836. SPIE, Bellingham, pp. 98-103] color photometry. Using our spectra for this family as well as new observations of Karin family members [Vernazza, P., Birlan, M., Rossi, A., Dotto, E., Nesvorný, D., Brunetto, R., Fornasier, S., Fulchignoni, M., Renner, S., 2006. Astron. Astrophys. 460, 945-951] and new classifications of some older families we have revised the space weathering rate of S-complex asteroids originally determined by Jedicke et al. [Jedicke, R., Nesvorný, D., Whiteley, R.J., Ivezić, Ž., Jurić, M., 2004. Nature 429, 275-277]. Following Jedicke et al. [Jedicke, R., Nesvorný, D., Whiteley, R.J., Ivezić, Ž., Jurić, M., 2004. Nature 429, 275-277] we parameterize the space weathering rate of the principal component color of the spectrum ( PC), which is correlated with the spectral slope, as PC(t)=PC(0)+ΔPC[1-exp]. Our revised rate suggests that the characteristic time scale for space weathering is τ=570±220 Myr and that new S-complex clusters

  4. Chemical weathering of a marine terrace chronosequence, Santa Cruz, California. Part II: Solute profiles, gradients and the comparisons of contemporary and long-term weathering rates

    USGS Publications Warehouse

    White, A.F.; Schulz, M.S.; Stonestrom, D.A.; Vivit, D.V.; Fitzpatrick, J.; Bullen, T.D.; Maher, K.; Blum, A.E.

    2009-01-01

    The spatial and temporal changes in hydrology and pore water elemental and 87Sr/86Sr compositions are used to determine contemporary weathering rates in a 65- to 226-kyr-old soil chronosequence formed from granitic sediments deposited on marine terraces along coastal California. Soil moisture, tension and saturation exhibit large seasonal variations in shallow soils in response to a Mediterranean climate. These climate effects are dampened in underlying argillic horizons that progressively developed in older soils, and reached steady-state conditions in unsaturated horizons extending to depths in excess of 15 m. Hydraulic fluxes (qh), based on Cl mass balances, vary from 0.06 to 0.22 m yr-1, resulting in fluid residence times in the terraces of 10-24 yrs. As expected for a coastal environment, the order of cation abundances in soil pore waters is comparable to sea water, i.e., Na > Mg > Ca > K > Sr, while the anion sequence Cl > NO3 > HCO3 > SO4 reflects modifying effects of nutrient cycling in the grassland vegetation. Net Cl-corrected solute Na, K and Si increase with depth, denoting inputs from feldspar weathering. Solute 87Sr/86Sr ratios exhibit progressive mixing of sea water-dominated precipitation with inputs from less radiogenic plagioclase. While net Sr and Ca concentrations are anomalously high in shallow soils due to biological cycling, they decline with depth to low and/or negative net concentrations. Ca/Mg, Sr/Mg and 87Sr/86Sr solute and exchange ratios are similar in all the terraces, denoting active exchange equilibration with selectivities close to unity for both detrital smectite and secondary kaolinite. Large differences in the magnitudes of the pore waters and exchange reservoirs result in short-term buffering of the solute Ca, Sr, and Mg. Such buffering over geologic time scales can not be sustained due to declining inputs from residual plagioclase and smectite, implying periodic resetting of the exchange reservoir such as by past vegetational

  5. Chemical weathering of a marine terrace chronosequence, Santa Cruz, California. Part II: Solute profiles, gradients and the comparisons of contemporary and long-term weathering rates

    NASA Astrophysics Data System (ADS)

    White, Art F.; Schulz, Marjorie S.; Stonestrom, David A.; Vivit, Davison V.; Fitzpatrick, John; Bullen, Tom D.; Maher, Kate; Blum, Alex E.

    2009-05-01

    The spatial and temporal changes in hydrology and pore water elemental and 87Sr/ 86Sr compositions are used to determine contemporary weathering rates in a 65- to 226-kyr-old soil chronosequence formed from granitic sediments deposited on marine terraces along coastal California. Soil moisture, tension and saturation exhibit large seasonal variations in shallow soils in response to a Mediterranean climate. These climate effects are dampened in underlying argillic horizons that progressively developed in older soils, and reached steady-state conditions in unsaturated horizons extending to depths in excess of 15 m. Hydraulic fluxes ( q h), based on Cl mass balances, vary from 0.06 to 0.22 m yr -1, resulting in fluid residence times in the terraces of 10-24 yrs. As expected for a coastal environment, the order of cation abundances in soil pore waters is comparable to sea water, i.e., Na > Mg > Ca > K > Sr, while the anion sequence Cl > NO 3 > HCO 3 > SO 4 reflects modifying effects of nutrient cycling in the grassland vegetation. Net Cl-corrected solute Na, K and Si increase with depth, denoting inputs from feldspar weathering. Solute 87Sr/ 86Sr ratios exhibit progressive mixing of sea water-dominated precipitation with inputs from less radiogenic plagioclase. While net Sr and Ca concentrations are anomalously high in shallow soils due to biological cycling, they decline with depth to low and/or negative net concentrations. Ca/Mg, Sr/Mg and 87Sr/ 86Sr solute and exchange ratios are similar in all the terraces, denoting active exchange equilibration with selectivities close to unity for both detrital smectite and secondary kaolinite. Large differences in the magnitudes of the pore waters and exchange reservoirs result in short-term buffering of the solute Ca, Sr, and Mg. Such buffering over geologic time scales can not be sustained due to declining inputs from residual plagioclase and smectite, implying periodic resetting of the exchange reservoir such as by past

  6. Forest soil respiration rate and delta13C is regulated by recent above ground weather conditions.

    PubMed

    Ekblad, Alf; Boström, Björn; Holm, Anders; Comstedt, Daniel

    2005-03-01

    Soil respiration, a key component of the global carbon cycle, is a major source of uncertainty when estimating terrestrial carbon budgets at ecosystem and higher levels. Rates of soil and root respiration are assumed to be dependent on soil temperature and soil moisture yet these factors often barely explain half the seasonal variation in soil respiration. We here found that soil moisture (range 16.5-27.6% of dry weight) and soil temperature (range 8-17.5 degrees C) together explained 55% of the variance (cross-validated explained variance; Q2) in soil respiration rate (range 1.0-3.4 micromol C m(-2) s(-1)) in a Norway spruce (Picea abies) forest. We hypothesised that this was due to that the two components of soil respiration, root respiration and decomposition, are governed by different factors. We therefore applied PLS (partial least squares regression) multivariate modelling in which we, together with below ground temperature and soil moisture, used the recent above ground air temperature and air humidity (vapour pressure deficit, VPD) conditions as x-variables. We found that air temperature and VPD data collected 1-4 days before respiration measurements explained 86% of the seasonal variation in the rate of soil respiration. The addition of soil moisture and soil temperature to the PLS-models increased the Q2 to 93%. delta13C analysis of soil respiration supported the hypotheses that there was a fast flux of photosynthates to root respiration and a dependence on recent above ground weather conditions. Taken together, our results suggest that shoot activities the preceding 1-6 days influence, to a large degree, the rate of root and soil respiration. We propose this above ground influence on soil respiration to be proportionally largest in the middle of the growing season and in situations when there is large day-to-day shifts in the above ground weather conditions. During such conditions soil temperature may not exert the major control on root respiration. PMID

  7. Chemical weathering in response to tectonic uplift and denudation rate in a semi-arid environment, southeast Spain

    NASA Astrophysics Data System (ADS)

    Ameijeiras-Mariño, Yolanda; Opfergelt, Sophie; Schoonejans, Jérôme; Vanacker, Veerle; Sonnet, Philippe; Delmelle, Pierre

    2014-05-01

    Soil thickness reflects the balance between soil production and denudation by chemical weathering and physical erosion. At topographic steady state, the soil weathering intensity is expected to be higher at low denudation rate (transport-limited) than at high denudation rate (weathering-limited). We tested this hypothesis for the first time in a semi-arid environment where chemical weathering processes are generally slow. The study site is the Internal Zone of the Betic Cordillera in Southeast Spain, Almeria province. The lithology is mainly mica-schist and quartzite with local presence of phyllite. Three catchments (EST, FIL, CAB) were selected upstream local faults along a gradient of increasing uplift rates (10-170 mm/kyr) and increasing denudation rates (20-250 mm/kyr), following the sequence ESTweathering intensity. Three independent indices were used to compare soil weathering intensity across the EST, FIL and CAB catchments: the Total Reserve in Bases (TRB = [Ca2+] + [Na+] + [K+] + [Mg2+]); the soil Fed/Fet ratio that reflects the formation of secondary Fe-oxides, and the Cation Exchange Capacity (CEC) that varies with the amount of secondary clay minerals and organic matter. The difference in TRB between the soil and the bedrock (ΔTRB = TRB soil - TRB bedrock) should be more negative as weathering increases, whereas the Fed/Fet ratio is expected to augment with the intensity of weathering. Since these soils have low organic carbon content, the CEC should increase with weathering degree. Our results indicate that the ΔTRB (cmolc.kg-1) is -8±14 (n=8), -79±2 (n=8) and -51±38 (n=9) for CAB, FIL and EST, respectively. The Fed/Fet ratio for CAB, FIL and EST is 0.20±0.05 (n=8), 0.20±0.03 (n=8) and 0.29±0.05 (n=9), respectively. The CEC (cmolc.kg-1) increases from 3.3

  8. The rate of chemical weathering of pyrite on the surface of Venus

    NASA Technical Reports Server (NTRS)

    Fegley, B., Jr.; Lodders, K.

    1993-01-01

    This abstract reports results of an experimental study of the chemical weathering of pyrite (FeS2) under Venus-like conditions. This work, which extends the earlier study by Fegley and Treiman, is part of a long range research program to experimentally measure the rates of thermochemical gas-solid reactions important in the atmospheric-lithospheric sulfur cycle on Venus. The objectives of this research are (1) to measure the kinetics of thermochemical gas-solid reactions responsible for both the production (e.g., anhydrite formation) and destruction (e.g., pyrrhotite oxidation) of sulfur-bearing minerals on the surface of Venus and (2) to incorporate these and other constraints into holistic models of the chemical interactions between the atmosphere and surface of Venus. Experiments were done with single crystal cubes of natural pyrite (Navajun, Logrono, Spain) that were cut and polished into slices of known weight and surface area. The slices were isothermally heated at atmospheric pressure in 99.99 percent CO2 (Coleman Instrument Grade) at either 412 C (685 K) or 465 C (738 K) for time periods up to 10 days. These two isotherms correspond to temperatures at about 6 km and 0 km altitude, respectively, on Venus. The reaction rate was determined by measuring the weight loss of the reacted slices after removal from the furnace. The reaction products were characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy on the SEM.

  9. Weathering and denudation rates determined by the combined analysis of Uranium series nuclides and in situ Beryllium in a weathering profile (Vosges massif, Strengbach catchment, France)

    NASA Astrophysics Data System (ADS)

    Ackerer, Julien; Chabaux, François; Van der Woerd, Jerome; Pelt, Eric; Kali, Elise; Pierret, Marie Claire; Viville, Daniel; Wyns, Robert; Negrel, Philippe

    2015-04-01

    The determination of soil sustainability is a major issue for societies. It is crucial to estimate the soil formation and denudation rates to evaluate the landscapes stability and their response to natural or anthropological forcings. In this work, we propose to combine the analysis of Uranium-Thorium-Radium isotopes with the cosmogenic in situ Beryllium in a weathering profile located in the Strengbach catchment to estimate both production rate of regolith and denudation rate of soil and to establish a soil mass balance at millennial timescales. The weathering profile is located on the summit of the watershed and extending from the top soil to the granitic fractured bedrock at 2 m depth. Whole rock data shows different trends of variation of major and trace element concentrations and also of U-Th-Ra disequilibria in the upper part of the regolith (0-80 cm) and the deeper part of the fractured saprolith and/or bedrock (100cm-200cm). Modeling of the U-Th-Ra data in this deeper part of the profile, using a particle swarm optimization model dedicated to isotopic ratios leads to a regolith production rate at the summit of the watershed of 35 ± 9 T/km²/year. In addition, a numerical optimization for nonlinear inverse problem has been performed to estimate the regolith residence time and the mean denudation rate at the summit from the Beryllium data. The results show that the regolith residence time is about 14 000 years and the mean denudation rate is 32 ± 8 T/km²/year. The consistency between the regolith production rate and the soil denudation rate suggests therefore that in such a temperate context, the long-term mass balance of soil developed on granitic bedrock would be close to a steady state. The data also highlights that the determination of a weathering production rate from analysis of Uranium series nuclides in whole rock samples cannot be easily obtained by analyzing only surficial soil samples, and requires the analysis of the deeper fractured saprolith

  10. Seafloor Weathering As a Long-Term Climate Regulation Mechanism

    NASA Astrophysics Data System (ADS)

    Farahat, N. X.; Abbot, D. S.; Archer, D. E.

    2014-12-01

    The global carbon cycle determines the distribution of carbon between the atmosphere, ocean, and solid earth. Carbon from the mantle enters the Earth's surficial environment as CO2 by volcanic outgassing, and carbon is buried in the oceanic crust as carbonate rocks during silicate rock weathering. The subduction of carbonate-rich oceanic plates returns carbon to the mantle, closing the cycle. Subtle adjustments in continental silicate weathering, widely held to consume atmospheric CO2 at a rate controlled by climate, are believed to have maintained habitable conditions throughout Earth's history. This long term climate regulation mechanism is known as a climate-weathering feedback. Seafloor weathering, low-temperature basalt alteration and carbonate precipitation in the permeable upper oceanic crust, has been proposed as a climate-weathering feedback as well, but the link to climate is presently poorly understood. Such a climate regulation mechanism would be particularly important on waterworld planets where continental silicate weathering cannot regulate climate. It has so far not been possible to determine whether changes in seafloor weathering could contribute to climate regulation on Earth or in a waterworld scenario because the necessary modeling framework has not yet been developed. However, advances in porous media flow modeling and reactive transport modeling, as well as the availability of inexpensive computational power, allow the seafloor weathering problem to be looked at in greater detail. We have developed a spatially resolved two-dimmensional (2D) numerical model of seafloor weathering in the permeable upper oceanic crust. This model simulates 2D off-axis hydrothermal flow coupled to geochemical alteration of seafloor basalt by modeling reactive transport of chemical species in seawater-derived hydrothermal fluids. The focus of this research is to use the model to determine the effect of geological and climatic factors on seafloor weathering, which

  11. Stable runoff and weathering fluxes into the oceans over Quaternary climate cycles

    NASA Astrophysics Data System (ADS)

    von Blanckenburg, Friedhelm; Bouchez, Julien; Ibarra Daniel, E.; Kate, Maher

    2016-04-01

    Throughout the Quaternary, erosion and biogeochemical cycles at the Earth surface responded to large oscillations in temperature and precipitation. Such changes are recorded in sedimentary archives and radiogenic isotope mass balances. In contrast, climate models combined with empirical relationships between measures of climate and weatheringindicate minimal change in global weathering rates. Here we resolve the extent to which the supply of dissolved elements to oceans was altered by glacial-interglacial oscillations with a new weathering proxy. We estimate relative weathering fluxes from the ratio of cosmogenic beryllium-10, produced in the atmosphere, to the stable isotope beryllium-9, introduced into the oceans by the riverine silicate weathering flux [1]. Using sedimentary Be records,we show over multiple glacial-interglacial cycles, and over the last 2 Myr, shifts in global silicate weathering inputs are not detectable [2]. Combining climate model simulations of the Last Glacial Maximum with a new model for silicate weathering, we show how large regional variability in runoff between glacial and interglacial periods was insufficient to shift global weathering fluxes. The observed and modeled stability explains why removal of atmospheric CO2 by silicate weathering has been balanced to within 2% of net CO2 degassing over the last 600 kyr. Because over >104 yr time scales weathering and erosion are also coupled, our study provides additional evidence that global erosion rates did not shift along any long-term trend over the Quaternary [3]. [1] von Blanckenburg, F. and Bouchez, J. (2014). "River fluxes to the sea from the oceans 10Be/9Be ratio." Earth and Planetary Science Letters 387: 34-43. [2] von Blanckenburg, F., Bouchez. J. Ibarra, D.E., Maher, K. (2015). "Stable runoff and weathering fluxes into the oceans over Quaternary climate cycles." Nature Geosciences 10.1038/ngeo2452. [3] Willenbring, J. K. and von Blanckenburg, F. (2010). "Long-term stability of

  12. Chemical weathering rate, denudation rate, and atmospheric and soil CO2 consumption of Paraná flood basalts in São Paulo State, Brazil

    NASA Astrophysics Data System (ADS)

    da Conceição, Fabiano Tomazini; dos Santos, Carolina Mathias; de Souza Sardinha, Diego; Navarro, Guillermo Rafael Beltran; Godoy, Letícia Hirata

    2015-03-01

    The chemical weathering rate and atmospheric/soil CO2 consumption of Paraná flood basalts in the Preto Stream basin, São Paulo State, Brazil, were evaluated using major elements as natural tracers. Surface and rain water samples were collected in 2006, and analyses were performed to assess pH, temperature, dissolved oxygen (DO), electrical conductivity (EC) and total dissolved solids (TDS), including SO42-, NO3-, PO43 -, HCO3-, Cl-, SiO2, Ca2 +, Mg2 +, Na+ and K+. Fresh rocks and C horizon samples were also collected, taking into account their geological context, abundance and spatial distribution, to analyze major elements and mineralogy. The Preto Stream, downstream from the city of Ribeirão Preto, receives several elements/compounds as a result of anthropogenic activities, with only sulfate yielding negative flux values. The negative flux of SO42 - can be attributed to atmospheric loading that is mainly related to anthropogenic inputs. After corrections were made for atmospheric inputs, the riverine transport of dissolved material was found to be 30 t km- 2 y- 1, with the majority of the dissolved material transported during the summer (wet) months. The chemical weathering rate and atmospheric/soil CO2 consumption were 6 m/Ma and 0.4 · 106 mol km- 2 y- 1, respectively. The chemical weathering rate falls within the lower range of Paraná flood basalt denudation rates between 135 and 35 Ma previously inferred from chronological studies. This comparison suggests that rates of basalt weathering in Brazil's present-day tropical climate differ by at most one order of magnitude from those prevalent at the time of hothouse Earth. The main weathering process is the monosiallitization of anorthoclase, augite, anorthite and microcline. Magnetite is not weathered and thus remains in the soil profile.

  13. Seafloor weathering buffering climate: numerical experiments

    NASA Astrophysics Data System (ADS)

    Farahat, N. X.; Archer, D. E.; Abbot, D. S.

    2013-12-01

    Continental silicate weathering is widely held to consume atmospheric CO2 at a rate controlled in part by temperature, resulting in a climate-weathering feedback [Walker et al., 1981]. It has been suggested that weathering of oceanic crust of warm mid-ocean ridge flanks also has a CO2 uptake rate that is controlled by climate [Sleep and Zahnle, 2001; Brady and Gislason, 1997]. Although this effect might not be significant on present-day Earth [Caldeira, 1995], seafloor weathering may be more pronounced during snowball states [Le Hir et al., 2008], during the Archean when seafloor spreading rates were faster [Sleep and Zahnle, 2001], and on waterworld planets [Abbot et al., 2012]. Previous studies of seafloor weathering have made significant contributions using qualitative, generally one-box, models, and the logical next step is to extend this work using a spatially resolved model. For example, experiments demonstrate that seafloor weathering reactions are temperature dependent, but it is not clear whether the deep ocean temperature affects the temperature at which the reactions occur, or if instead this temperature is set only by geothermal processes. Our goal is to develop a 2-D numerical model that can simulate hydrothermal circulation and resulting alteration of oceanic basalts, and can therefore address such questions. A model of diffusive and convective heat transfer in fluid-saturated porous media simulates hydrothermal circulation through porous oceanic basalt. Unsteady natural convection is solved for using a Darcy model of porous media flow that has been extensively benchmarked. Background hydrothermal circulation is coupled to mineral reaction kinetics of basaltic alteration and hydrothermal mineral precipitation. In order to quantify seafloor weathering as a climate-weathering feedback process, this model focuses on hydrothermal reactions that influence carbon uptake as well as ocean alkalinity: silicate rock dissolution, calcium and magnesium leaching

  14. The effects of lichen cover upon the rate of solutional weathering of limestone

    NASA Astrophysics Data System (ADS)

    McIlroy de la Rosa, J. P.; Warke, P. A.; Smith, B. J.

    2014-09-01

    The contribution of lichens to the biomodification of limestone surfaces is an area of conflict within bioweathering studies, with some researchers suggesting a protective effect induced by lichen coverage and others a deteriorative effect induced by the same organisms. Data are reported demonstrating the potential role of endolithic lichen, in particular of Bagliettoa baldensis, in the active protection of Carboniferous limestone surfaces from rainfall-induced solutional weathering. During a 12-month microcatchment exposure period in the west of Northern Ireland, average dissolutional losses of calcium are greater from a lichen-free limestone surface compared with a predominantly endolithic lichen-covered surface by just under 1.25 times. During colder winter months, the lichen-free surface experiences calcium loss almost 1.5 times greater than the lichen-covered surface. Using extrapolation to upscale from the micro-catchment sample scale, for the year of sample exposure, the rate of calcium loss is 1.001 g m- 2 a- 1 from lichen-covered limestone surfaces and 1.228 g m- 2 a- 1 from lichen-free bare limestone surfaces. This research has implications for our understanding of karst environments, the contribution of lichens to karren development and the conservation of lichen-colonised dimension stone within a cultural setting.

  15. Carbon dioxide efficiency of terrestrial enhanced weathering.

    PubMed

    Moosdorf, Nils; Renforth, Phil; Hartmann, Jens

    2014-05-01

    Terrestrial enhanced weathering, the spreading of ultramafic silicate rock flour to enhance natural weathering rates, has been suggested as part of a strategy to reduce global atmospheric CO2 levels. We budget potential CO2 sequestration against associated CO2 emissions to assess the net CO2 removal of terrestrial enhanced weathering. We combine global spatial data sets of potential source rocks, transport networks, and application areas with associated CO2 emissions in optimistic and pessimistic scenarios. The results show that the choice of source rocks and material comminution technique dominate the CO2 efficiency of enhanced weathering. CO2 emissions from transport amount to on average 0.5-3% of potentially sequestered CO2. The emissions of material mining and application are negligible. After accounting for all emissions, 0.5-1.0 t CO2 can be sequestered on average per tonne of rock, translating into a unit cost from 1.6 to 9.9 GJ per tonne CO2 sequestered by enhanced weathering. However, to control or reduce atmospheric CO2 concentrations substantially with enhanced weathering would require very large amounts of rock. Before enhanced weathering could be applied on large scales, more research is needed to assess weathering rates, potential side effects, social acceptability, and mechanisms of governance. PMID:24597739

  16. The Cretaceous Okhotsk-Chukotka Volcanic Belt (NE Russia): Geology, geochronology, magma output rates, and implications on the genesis of silicic LIPs

    NASA Astrophysics Data System (ADS)

    Tikhomirov, P. L.; Kalinina, E. A.; Moriguti, T.; Makishima, A.; Kobayashi, K.; Cherepanova, I. Yu.; Nakamura, E.

    2012-04-01

    The Cretaceous Okhotsk-Chukotka volcanic belt (OCVB) is a prominent subduction-related magmatic province, having the remarkably high proportion of silicic rocks (ca. 53% of the present-day crop area, and presumably over 70% of the total volcanic volume). Its estimated total extrusive volume ranges between 5.5 × 105 km3 (the most conservative estimate) and over 106 km3. This article presents a brief outline of the geology of OCVB, yet poorly described in international scientific literature, and results of a geochronological study on the northern part of the volcanic belt. On the base of new and published U-Pb and 40Ar/39Ar age determinations, a new chronological model is proposed. Our study indicates that the activity of the volcanic belt was highly discontinuous and comprised at least five main episodes at 106-98 Ma, 94-91 Ma, 89-87 Ma, 85.5-84 Ma, and 82-79 Ma. The new data allow a semi-quantitative estimate of the volcanic output rate for the observed part of the OCVB (area and volume approximately 105 km2 and 2.5 × 105 km3, respectively). The average extrusion rate for the entire lifetime of the volcanic belt ranges between 1.6 and 3.6 × 10- 5 km3yr- 1 km- 1, depending on the assumed average thickness of the volcanic pile; the optimal value is 2.6 × 10- 5 km3yr- 1 km- 1. Despite imprecise, such estimates infer the time-averaged volcanic productivity of the OCVB is similar to that of silicic LIPs and most active recent subduction-related volcanic areas of the Earth. However, the most extensive volcanic flare-ups at 89-87 and 85.5-84 Ma had higher rates of over 9.0 × 10- 5 km3yr- 1 km- 1. The main volumetric, temporal and compositional parameters of the OCVB are similar to those of silicic LIPs. This gives ground for discussion about the geodynamic setting of the latters, because the widely accepted definition of a LIP implies a strictly intraplate environment. Considering the genesis of the OCVB and other large provinces of silicic volcanism, we propose that

  17. Carbon Dioxide Sequestration, Weathering Approaches to

    NASA Astrophysics Data System (ADS)

    Schuiling, R. D.

    The aim of enhanced weathering is to capture CO2 by the carbonation of silicates, or by dissolution of these silicates during which the greenhouse gas CO2 is converted to bicarbonate in solution. Research in this field is still focused on increasing the rate of reaction, but the required additional technologies add considerably to the cost of the process. In this entry, the focus is on the optimization of the weathering conditions, by selecting the most reactive abundantly available minerals, grinding them, and spreading the grains over land. Thereafter nature takes its course. Since its formulation in the late 1990s, more and more people realize that this simple and natural approach may well turn out to be one of the most promising and environmentally friendliest ways to counteract climate change and ocean acidification

  18. Characterizing the process and quantifying the rate of subaerial rock weathering on desert surfaces using roughness analysis

    NASA Astrophysics Data System (ADS)

    Mushkin, Amit; Sagy, Amir; Trabelci, Eran

    2013-04-01

    Subaerial weathering of rocks is a common process observed on desert surfaces on Earth and other planetary terrestrial surfaces such as on Mars. On Earth, this weathering process has been previously identified as one of the key erosion agent driving geomorphic surface evolution and the development of desert pavements. And yet, fundamental aspects of the process, such as the relative contribution of the different weathering modes that drive it (e.g., mechanical breakdown of rocks, chemical weathering, aeolian abrasion and exfoliation) as well as the rate by which this weathering process occurs have not been systematically examined. Here, we present a new approach for quantitatively addressing these fundamental aspects of process geomorphology on desert surfaces. We focus here on co-genetic desert alluvial surfaces of different ages, i.e. alluvial chronosequences, which provide excellent recorders for the evolution of boulder-strewn surfaces into smooth desert pavements through in-situ subaerial weathering of rocks. Our approach combines independent measures of two different surface attributes: High resolution (mm-scale) 3D ground-based laser scanning (LiDAR) of surface micro-topography, and numerical dating of surface age. Roughness analysis of the LiDAR data in power spectral density (PSD) space allows us to characterize the geometric manifestation of rock weathering on the surface and to distinguish between the different weathering modes. Numerical age constraints provide independent estimates for the time elapsed since the process began. Accordingly, we are able to constrain surface roughness evolution on alluvial fan desert chronosequences through time, and present PSD analysis of surface roughness as a new quantitative tool to examine the process of subaerial rock weathering in desert environments. In this study we present results from two late Quaternary alluvial chronosequences along the Dead Sea Transform in the hyper-arid Negev desert of southern Israel. Li

  19. The null hypothesis: steady rates of erosion, weathering and sediment accumulation during Late Cenozoic mountain uplift and glaciation

    NASA Astrophysics Data System (ADS)

    Willenbring, J. K.; Jerolmack, D. J.

    2015-12-01

    At the largest time and space scales, the pace of erosion and chemical weathering is determined by tectonic uplift rates. Deviations from this equilibrium condition arise from the transient response of landscape denudation to climatic and tectonic perturbations, and may be long lived. We posit that the constraint of mass balance, however, makes it unlikely that such disequilibrium persists at the global scale over millions of years, as has been proposed for late Cenozoic erosion. To support this contention, we synthesize existing data for weathering fluxes, global sedimentation rates, sediment yields and tectonic motions. The records show a remarkable constancy in the pace of Earth-surface evolution over the last 10 million years. These findings provide strong support for the null hypothesis; that global rates of landscape change have remained constant over the last ten million years, despite global climate change and massive mountain building events. Two important implications are: (1) global climate change may not change global denudation rates, because the nature and sign of landscape responses are varied; and (2) tectonic and climatic perturbations are accommodated in the long term by changes in landscape form. This work undermines the hypothesis that increased weathering due to late Cenozoic mountain building or climate change was the primary agent for a decrease in global temperatures.

  20. Tectonic uplift and denudation rate influence soil chemical weathering intensity in a semi-arid environment, southeast Spain: physico-chemical and mineralogical evidence

    NASA Astrophysics Data System (ADS)

    Ameijeiras-Mariño, Yolanda; Opfergelt, Sophie; Schoonejans, Jérôme; Vanacker, Veerle; Sonnet, Philippe; Delmelle, Pierre

    2015-04-01

    Tectonic uplift is known to influence denudation rates. Denudation, including chemical weathering and physical erosion, affects soil production rates and weathering intensities. At topographic steady state, weathering can be transport- or weathering-limited. In the transport-limited regime, low denudation rates should lead to comparatively high weathering intensities, while in the weathering-limited case high denudation rates are associated with lower weathering intensities. Here, we test if this relationship applies to semi-arid environments where chemical weathering is generally slow. Three catchments (EST, FIL and CAB) were studied in the Internal Zone of the Betic Cordillera in southeast Spain, spanning a range of increasing uplift rates (10-170 mm/kyr) and increasing denudation rates (20-250 mm/kyr) from EST to CAB. In each catchment, two ridgetop soil profiles were sampled down to the bedrock. The three catchments have similar vegetation and climatic conditions, with precipitation of 250- 315 mm/yr and mean annual temperature of 15-17 °C. The mineralogy of the bedrock, as determined by XRD, is similar across the three catchments and is characterized by the presence of quartz, muscovite, clinochlore, biotite and plagioclase. This primary mineral assemblage is also found in the catchment soils, indicating that the soils studied derive from the same parent material. The soil clay-size fraction is dominated by kaolinite, vermiculite and illite. However, the proportions of the soil primary and secondary minerals vary between the catchment sites. The abundance of biotite decreases from CAB (14%) to EST (4%), whereas the quartz and clay contents show an opposite tendency (from 30 to 69% and 9.9 to 14.3%, respectively). Further, the abundance of vermiculite increases from CAB to EST. The results are interpreted in terms of increasing weathering intensity from CAB to EST by weathering of biotite into vermiculite and enrichment of soils on more weathering resistant

  1. Basalt weathering rates on Earth and the duration of liquid water on the plains of Gusev Crater, Mars

    SciTech Connect

    Steefel, Carl; Hausrath, E.M.; Navarre-Sitchler, A.K.; Sak, P.B.; Steefel, C.; Brantley, S.L.

    2008-03-15

    Where Martian rocks have been exposed to liquid water, chemistry versus depth profiles could elucidate both Martian climate history and potential for life. The persistence of primary minerals in weathered profiles constrains the exposure time to liquid water: on Earth, mineral persistence times range from {approx}10 ka (olivine) to {approx}250 ka (glass) to {approx}1Ma (pyroxene) to {approx}5Ma (plagioclase). Such persistence times suggest mineral persistence minima on Mars. However, Martian solutions may have been more acidic than on Earth. Relative mineral weathering rates observed for basalt in Svalbard (Norway) and Costa Rica demonstrate that laboratory pH trends can be used to estimate exposure to liquid water both qualitatively (mineral absence or presence) and quantitatively (using reactive transport models). Qualitatively, if the Martian solution pH > {approx}2, glass should persist longer than olivine; therefore, persistence of glass may be a pH-indicator. With evidence for the pH of weathering, the reactive transport code CrunchFlow can quantitatively calculate the minimum duration of exposure to liquid water consistent with a chemical profile. For the profile measured on the surface of Humphrey in Gusev Crater, the minimum exposure time is 22 ka. If correct, this estimate is consistent with short-term, episodic alteration accompanied by ongoing surface erosion. More of these depth profiles should be measured to illuminate the weathering history of Mars.

  2. Rates and mechanisms of chemical weathering in an organic environment at Panolo Mountain, Georgia

    NASA Astrophysics Data System (ADS)

    Nixon, R. A., III

    Chemical weathering consists of alteration of micas and feldspars to halloysite through intermediate gibbsite and allophane. Gibbsite is the first mineral produced from chemical weathering. Allophane results from the reaction of gibbsite with dissolved silica. Analyses of more than 600 published water analyses were used to calculate a free energy of formation for allophane of -896.79 kcal/mole based on the kaolin formula and disregarding the effects of structural water. A trend surface plot of the data using least squares gave a surface which represents equilibrium, and has a minimum solubility of aluminum at pH 6.7. The Gibbs free energy of formation for the ion Al(OH)2(+) is calculated to be -216.8 kcal/mole.

  3. Age and weathering rate of sediments in small catchments: The role of hillslope erosion

    NASA Astrophysics Data System (ADS)

    Dosseto, Anthony; Buss, Heather L.; Chabaux, François

    2014-05-01

    Uranium-series (U-series) isotopes in river material can be used to determine quantitative time constraints on the transfer of erosion products from source to sink. In this study, we investigate the U-series isotope composition of river-borne material in small catchments of Puerto Rico and southeastern Australia in order to improve our understanding of (i) the controls on the U-series isotope composition of river-borne material and (ii) how erosion products acquire their geochemical characteristics. In both regions, thorium isotopes track the origin of sediment and dissolved loads. Stream solutes are mainly derived from the deepest part of the weathering profile, whereas stream sediments originate from much shallower horizons, even in landslide-dominated Puerto Rican catchments. This suggests that in environments where thick weathering profiles have developed, solutes and sediments have distinct origins.

  4. Dual-polarization C-band weather radar algorithms for rain rate estimation and hydrometeor classification in an alpine region

    NASA Astrophysics Data System (ADS)

    Paulitsch, H.; Teschl, F.; Randeu, W. L.

    2009-03-01

    Dual polarization is becoming the standard for new weather radar systems. In contrast to conventional weather radars, where the reflectivity is measured in one polarization plane only, a dual polarization radar provides transmission in either horizontal, vertical, or both polarizations while receiving both the horizontal and vertical channels simultaneously. Since hydrometeors are often far from being spherical, the backscatter and propagation are different for horizontal and vertical polarization. Comparing the reflected horizontal and vertical power returns and their ratio and correlation, information on size, shape, and material density of cloud and precipitation particles can be obtained. The use of polarimetric radar variables can therefore increase the accuracy of the rain rate estimation compared to standard Z-R relationships of non-polarimetric radars. It is also possible to derive the type of precipitation from dual polarization parameters, although this is not an easy task, since there is no clear discrimination between the different values. Fuzzy logic approaches have been shown to work well with overlapping conditions and imprecisely defined class output. In this paper the implementation of different polarization algorithms for the new Austrian weather radar on Mt. Valluga is described, and first results from operational use are presented. This study also presents first observations of rain events in August 2007 during the test run of the radar. Further, the designated rain rate estimation and hydrometeor classification algorithms are explained.

  5. Dissolution rate of borosilicate glass SON68: A method of quantification based upon interferometry and implications for experimental and natural weathering rates of glass

    NASA Astrophysics Data System (ADS)

    Icenhower, Jonathan P.; Steefel, Carl I.

    2015-05-01

    Rates of glass dissolution from laboratory and field studies are often considered to be irreconcilable, although potential causes for the difference, such as solution saturation state and increasing surface area from progressive weathering, have not been explored in depth. The dissolution rate of SON68 glass, the non-radioactive analog of the French R7T7 composition, was determined in a single-pass flow-through (SPFT) system at 90 °C and pH 9 over a silica-saturation interval. Dissolution rates were determined on both powdered and monolithic specimens by assaying the concentration of elements released from glass to effluent solution. In addition, rates of 12 monolithic specimens were quantified using a Vertical Scanning Interferometry (VSI) method. The method entails measuring the difference in height between a reference and reaction surface. The height difference is proportional to the dissolution rate. By adjusting the relative position of the reacted surface to average surface roughness, the effects of surface area on the dissolution rate can be minimized. Values of the dissolution rate, based upon chemical assay of the effluent solution on the one hand, and VSI methods on the other, were compared. In general, rates determined by the two methods are within a factor of 2×. The difference in rates may be due to the presence of a reaction layer that develops on the glass surface, resulting in an underestimation of the height difference measurement. The dissolution rates of SON68 glass in silica-saturated solutions were then compared to rates previously determined on basalt glass in natural weathering environments (Gordon and Brady, 2002, Chem. Geol. 190, 113-122). When adjusted for differences in temperature and pH, the ranges of borosilicate and basalt glass dissolution rates overlap, indicating that laboratory and field rates can be reconciled and that the principal control on glass dissolution is solution saturation with respect to amorphous silica.

  6. Chemical weathering of a marine terrace chronosequence, Santa Cruz, California I: Interpreting rates and controls based on soil concentration-depth profiles

    USGS Publications Warehouse

    White, A.F.; Schulz, M.S.; Vivit, D.V.; Blum, A.E.; Stonestrom, D.A.; Anderson, S.P.

    2008-01-01

    The spatial and temporal changes in element and mineral concentrations in regolith profiles in a chronosequence developed on marine terraces along coastal California are interpreted in terms of chemical weathering rates and processes. In regoliths up to 15 m deep and 226 kyrs old, quartz-normalized mass transfer coefficients indicate non-stoichiometric preferential release of Sr > Ca > Na from plagioclase along with lesser amounts of K, Rb and Ba derived from K-feldspar. Smectite weathering results in the loss of Mg and concurrent incorporation of Al and Fe into secondary kaolinite and Fe-oxides in shallow argillic horizons. Elemental losses from weathering of the Santa Cruz terraces fall within the range of those for other marine terraces along the Pacific Coast of North America. Residual amounts of plagioclase and K-feldspar decrease with terrace depth and increasing age. The gradient of the weathering profile bs is defined by the ratio of the weathering rate, R to the velocity at which the profile penetrates into the protolith. A spreadsheet calculator further refines profile geometries, demonstrating that the non-linear regions at low residual feldspar concentrations at shallow depth are dominated by exponential changes in mineral surface-to-volume ratios and at high residual feldspar concentrations, at greater depth, by the approach to thermodynamic saturation. These parameters are of secondary importance to the fluid flux qh, which in thermodynamically saturated pore water, controls the weathering velocity and mineral losses from the profiles. Long-term fluid fluxes required to reproduce the feldspar weathering profiles are in agreement with contemporary values based on solute Cl balances (qh = 0.025-0.17 m yr-1). During saturation-controlled and solute-limited weathering, the greater loss of plagioclase relative to K-feldspar is dependent on the large difference in their respective solubilities instead of the small difference between their respective

  7. Silicate, borosilicate, and borate bioactive glass scaffolds with controllable degradation rate for bone tissue engineering applications. I. Preparation and in vitro degradation.

    PubMed

    Fu, Qiang; Rahaman, Mohamed N; Fu, Hailuo; Liu, Xin

    2010-10-01

    Bioactive glass scaffolds with a microstructure similar to that of dry human trabecular bone but with three different compositions were evaluated for potential applications in bone repair. The preparation of the scaffolds and the effect of the glass composition on the degradation and conversion of the scaffolds to a hydroxyapatite (HA)-type material in a simulated body fluid (SBF) are reported here (Part I). The in vitro response of osteogenic cells to the scaffolds and the in vivo evaluation of the scaffolds in a rat subcutaneous implantation model are described in Part II. Scaffolds (porosity = 78-82%; pore size = 100-500 microm) were prepared using a polymer foam replication technique. The glasses consisted of a silicate (13-93) composition, a borosilicate composition (designated 13-93B1), and a borate composition (13-93B3), in which one-third or all of the SiO2 content of 13-93 was replaced by B2O3, respectively. The conversion rate of the scaffolds to HA in the SBF increased markedly with the B2O3 content of the glass. Concurrently, the pH of the SBF also increased with the B2O3 content of the scaffolds. The compressive strengths of the as-prepared scaffolds (5-11 MPa) were in the upper range of values reported for trabecular bone, but they decreased markedly with immersion time in the SBF and with increasing B2O3 content of the glass. The results show that scaffolds with a wide range of bioactivity and degradation rate can be achieved by replacing varying amounts of SiO(2) in silicate bioactive glass with B2O3. PMID:20544804

  8. Weathering profiles in granitoid rocks of the Sila Massif uplands, Calabria, southern Italy: New insights into their formation processes and rates

    NASA Astrophysics Data System (ADS)

    Scarciglia, Fabio; Critelli, Salvatore; Borrelli, Luigi; Coniglio, Sabrina; Muto, Francesco; Perri, Francesco

    2016-05-01

    soil formation rates was achieved for different depths of corresponding weathering profile zones. Soil formation rates ranged from 0.01-0.07 mm a- 1 for A and Bw horizons (weathering class VI) to 0.04-0.36 mm a- 1 for the underlying saprolite (C and Cr layers; class V). By comparing these results with the corresponding erosion rates available in the literature for the study area, that range from < 0.01-0.05 to 0.10-0.21 mm a- 1, we suggest that the upland landscape of the Sila Massif is close to steady-state conditions between weathering and erosive processes.

  9. Weather in Your Life.

    ERIC Educational Resources Information Center

    Kannegieter, Sandy; Wirkler, Linda

    Facts and activities related to weather and meteorology are presented in this unit. Separate sections cover the following topics: (1) the water cycle; (2) clouds; (3) the Beaufort Scale for rating the speed and force of wind; (4) the barometer; (5) weather prediction; (6) fall weather in Iowa (sleet, frost, and fog); (7) winter weather in Iowa…

  10. Chemical weathering and CO₂ consumption in the Lower Mekong River.

    PubMed

    Li, Siyue; Lu, X X; Bush, Richard T

    2014-02-15

    Data on river water quality from 42 monitoring stations in the Lower Mekong Basin obtained during the period 1972-1996 was used to relate solute fluxes with controlling factors such as chemical weathering processes. The total dissolved solid (TDS) concentration of the Lower Mekong varied from 53 mg/L to 198 mg/L, and the median (114 mg/L) was compared to the world spatial median value (127 mg/L). Total cationic exchange capacity (Tz(+)) ranged from 729 to 2,607 μmolc/L, and the mean (1,572 μmolc/L) was 1.4 times higher than the world discharge-weighted average. Calcium and bicarbonate dominated the annual ionic composition, accounting for ~70% of the solute load that equalled 41.2×10(9)kg/y. TDS and major elements varied seasonally and in a predictable way with river runoff. The chemical weathering rate of 37.7t/(km(2)y), with respective carbonate and silicate weathering rates of 27.5t/(km(2) y) (13.8mm/ky) and 10.2t/(km(2) y) (3.8mm/ky), was 1.5 times higher than the global average. The CO2 consumption rate was estimated at 191×10(3)molCO2/(km(2)y) for silicate weathering, and 286×10(3)molCO2/(km(2)y) by carbonate weathering. In total, the Mekong basin consumed 228×10(9)molCO2/y and 152×10(9)molCO2/y by the combined weathering of carbonate and silicate, constituting 1.85% of the global CO2 consumption by carbonate weathering and 1.75% by silicates. This is marginally higher than its contribution to global water discharge ~1.3% and much higher than (more than three-fold) its contribution to world land surface area. Remarkable CO2 consumed by chemical weathering (380×10(9)mol/y) was similar in magnitude to dissolved inorganic carbon as HCO3(-) (370×10(9)mol/y) exported by the Mekong to the South China Sea. In this landscape, atmospheric CO2 consumption by rock chemical weathering represents an important carbon sink with runoff and physical erosion controlling chemical erosion. PMID:24291559

  11. River geochemistry, chemical weathering, and atmospheric CO2 consumption rates in the Virunga Volcanic Province (East Africa)

    NASA Astrophysics Data System (ADS)

    Balagizi, Charles M.; Darchambeau, François; Bouillon, Steven; Yalire, Mathieu M.; Lambert, Thibault; Borges, Alberto V.

    2015-09-01

    We report a water chemistry data set from 13 rivers of the Virunga Volcanic Province (VVP) (Democratic Republic of Congo), sampled between December 2010 and February 2013. Most parameters showed no pronounced seasonal variation, whereas their spatial variation suggests a strong control by lithology, soil type, slope, and vegetation. High total suspended matter (289-1467 mg L-1) was recorded in rivers in the Lake Kivu catchment, indicating high soil erodibility, partly as a consequence of deforestation and farming activities. Dissolved and particulate organic carbon (DOC and POC) were lower in rivers from lava fields, and higher in nonvolcanic subcatchments. Stable carbon isotope signatures (δ13C) of POC and DOC mean δ13C of -22.5‰ and -23.5‰, respectively, are the first data to be reported for the highland of the Congo River basin and showed a much higher C4 contribution than in lowland areas. Rivers of the VVP were net sources of CH4 to the atmosphere (4-5052 nmol L-1). Most rivers show N2O concentrations close to equilibrium, but some rivers showed high N2O concentrations related to denitrification in groundwaters. δ13C signatures of dissolved inorganic carbon suggested magmatic CO2 inputs to aquifers/soil, which could have contributed to increase basalt weathering rates. This magmatic CO2-mediated basalt weathering strongly contributed to the high major cation concentrations and total alkalinity. Thus, chemical weathering (39.0-2779.9 t km-2 yr-1) and atmospheric CO2 consumption (0.4-37.0 × 106 mol km-2 yr-1) rates were higher than previously reported in the literature for basaltic terrains.

  12. Global CO2-consumption by chemical weathering: What is the contribution of highly active weathering regions?

    NASA Astrophysics Data System (ADS)

    Hartmann, Jens; Jansen, Nils; Dürr, Hans H.; Kempe, Stephan; Köhler, Peter

    2010-05-01

    CO2-consumption by chemical weathering of silicates and resulting silicate/carbonate weathering ratios influences the terrestrial lateral inorganic carbon flux to the ocean and long-term climate changes. However, little is known of the spatial extension of highly active weathering regions and their proportion of global CO2-consumption. As those regions may be of significant importance for global climate change, global CO2-consumption is calculated here at high resolution, to adequately represent them. In previous studies global CO2-consumption is estimated using two different approaches: i) a reverse approach based on hydrochemical fluxes from large rivers and ii) a forward approach applying spatially explicit a function for CO2-consumption. The first approach results in an estimate without providing a spatial resolution for highly active regions and the second approach applied six lithological classes while including three sediment classes (shale, sandstone and carbonate rock) based at a 1° or 2° grid resolution. It remained uncertain, if the applied lithological classification schemes represent adequately CO2-consumption from sediments on a global scale (as well as liberation of other elements like phosphorus or silicon by chemical weatheirng). This is due to the large variability of sediment properties, their diagenetic history and the contribution from carbonates apparent in silicate dominated lithological classes. To address these issues, a CO2-consumption model, trained at high-resolution data, is applied here to a global vector based lithological map with 15 lithological classes. The calibration data were obtained from areas representing a wide range of weathering rates. Resulting global CO2-consumption by chemical weathering is similar to earlier estimates (237 Mt C a-1) but the proportion of silicate weathering is 63%, and thus larger than previous estimates (49 to 60%). The application of the enhanced lithological classification scheme reveals that it

  13. Artificial weathering as a function of CO2 injection in Pahang Sandstone Malaysia: investigation of dissolution rate in surficial condition.

    PubMed

    Jalilavi, Madjid; Zoveidavianpoor, Mansoor; Attarhamed, Farshid; Junin, Radzuan; Mohsin, Rahmat

    2014-01-01

    Formation of carbonate minerals by CO2 sequestration is a potential means to reduce atmospheric CO2 emissions. Vast amount of alkaline and alkali earth metals exist in silicate minerals that may be carbonated. Laboratory experiments carried out to study the dissolution rate in Pahang Sandstone, Malaysia, by CO2 injection at different flow rate in surficial condition. X-ray Powder Diffraction (XRD), Scanning Electron Microscope (SEM) with Energy Dispersive X-ray Spectroscopy (EDX), Atomic Absorption Spectroscopy (AAS) and weight losses measurement were performed to analyze the solid and liquid phase before and after the reaction process. The weight changes and mineral dissolution caused by CO2 injection for two hours CO2 bubbling and one week' aging were 0.28% and 18.74%, respectively. The average variation of concentrations of alkaline earth metals in solution varied from 22.62% for Ca(2+) to 17.42% for Mg(2+), with in between 16.18% observed for the alkali earth metal, potassium. Analysis of variance (ANOVA) test is performed to determine significant differences of the element concentration, including Ca, Mg, and K, before and after the reaction experiment. Such changes show that the deposition of alkali and alkaline earth metals and the dissolution of required elements in sandstone samples are enhanced by CO2 injection. PMID:24413195

  14. Artificial Weathering as a Function of CO2 Injection in Pahang Sandstone Malaysia: Investigation of Dissolution Rate in Surficial Condition

    NASA Astrophysics Data System (ADS)

    Jalilavi, Madjid; Zoveidavianpoor, Mansoor; Attarhamed, Farshid; Junin, Radzuan; Mohsin, Rahmat

    2014-01-01

    Formation of carbonate minerals by CO2 sequestration is a potential means to reduce atmospheric CO2 emissions. Vast amount of alkaline and alkali earth metals exist in silicate minerals that may be carbonated. Laboratory experiments carried out to study the dissolution rate in Pahang Sandstone, Malaysia, by CO2 injection at different flow rate in surficial condition. X-ray Powder Diffraction (XRD), Scanning Electron Microscope (SEM) with Energy Dispersive X-ray Spectroscopy (EDX), Atomic Absorption Spectroscopy (AAS) and weight losses measurement were performed to analyze the solid and liquid phase before and after the reaction process. The weight changes and mineral dissolution caused by CO2 injection for two hours CO2 bubbling and one week' aging were 0.28% and 18.74%, respectively. The average variation of concentrations of alkaline earth metals in solution varied from 22.62% for Ca2+ to 17.42% for Mg2+, with in between 16.18% observed for the alkali earth metal, potassium. Analysis of variance (ANOVA) test is performed to determine significant differences of the element concentration, including Ca, Mg, and K, before and after the reaction experiment. Such changes show that the deposition of alkali and alkaline earth metals and the dissolution of required elements in sandstone samples are enhanced by CO2 injection.

  15. Artificial Weathering as a Function of CO2 Injection in Pahang Sandstone Malaysia: Investigation of Dissolution Rate in Surficial Condition

    PubMed Central

    Jalilavi, Madjid; Zoveidavianpoor, Mansoor; Attarhamed, Farshid; Junin, Radzuan; Mohsin, Rahmat

    2014-01-01

    Formation of carbonate minerals by CO2 sequestration is a potential means to reduce atmospheric CO2 emissions. Vast amount of alkaline and alkali earth metals exist in silicate minerals that may be carbonated. Laboratory experiments carried out to study the dissolution rate in Pahang Sandstone, Malaysia, by CO2 injection at different flow rate in surficial condition. X-ray Powder Diffraction (XRD), Scanning Electron Microscope (SEM) with Energy Dispersive X-ray Spectroscopy (EDX), Atomic Absorption Spectroscopy (AAS) and weight losses measurement were performed to analyze the solid and liquid phase before and after the reaction process. The weight changes and mineral dissolution caused by CO2 injection for two hours CO2 bubbling and one week' aging were 0.28% and 18.74%, respectively. The average variation of concentrations of alkaline earth metals in solution varied from 22.62% for Ca2+ to 17.42% for Mg2+, with in between 16.18% observed for the alkali earth metal, potassium. Analysis of variance (ANOVA) test is performed to determine significant differences of the element concentration, including Ca, Mg, and K, before and after the reaction experiment. Such changes show that the deposition of alkali and alkaline earth metals and the dissolution of required elements in sandstone samples are enhanced by CO2 injection. PMID:24413195

  16. Proterozoic oxygen rise linked to shifting balance between seafloor and terrestrial weathering.

    PubMed

    Mills, Benjamin; Lenton, Timothy M; Watson, Andrew J

    2014-06-24

    A shift toward higher atmospheric oxygen concentration during the late Proterozoic has been inferred from multiple indirect proxies and is seen by many as a prerequisite for the emergence of complex animal life. However, the mechanisms controlling the level of oxygen throughout the Proterozoic and its eventual rise remain uncertain. Here we use a simple biogeochemical model to show that the balance between long-term carbon removal fluxes via terrestrial silicate weathering and ocean crust alteration plays a key role in determining atmospheric oxygen concentration. This balance may be shifted by changes in terrestrial weatherability or in the generation rate of oceanic crust. As a result, the terrestrial chemical weathering flux may be permanently altered--contrasting with the conventional view that the global silicate weathering flux must adjust to equal the volcanic CO2 degassing flux. Changes in chemical weathering flux in turn alter the long-term supply of phosphorus to the ocean, and therefore the flux of organic carbon burial, which is the long-term source of atmospheric oxygen. Hence we propose that increasing solar luminosity and a decrease in seafloor spreading rate over 1,500-500 Ma drove a gradual shift from seafloor weathering to terrestrial weathering, and a corresponding steady rise in atmospheric oxygen. Furthermore, increased terrestrial weatherability during the late Neoproterozoic may explain low temperature, increases in ocean phosphate, ocean sulfate, and atmospheric oxygen concentration at this time. PMID:24927553

  17. Proterozoic oxygen rise linked to shifting balance between seafloor and terrestrial weathering

    PubMed Central

    Mills, Benjamin; Lenton, Timothy M.; Watson, Andrew J.

    2014-01-01

    A shift toward higher atmospheric oxygen concentration during the late Proterozoic has been inferred from multiple indirect proxies and is seen by many as a prerequisite for the emergence of complex animal life. However, the mechanisms controlling the level of oxygen throughout the Proterozoic and its eventual rise remain uncertain. Here we use a simple biogeochemical model to show that the balance between long-term carbon removal fluxes via terrestrial silicate weathering and ocean crust alteration plays a key role in determining atmospheric oxygen concentration. This balance may be shifted by changes in terrestrial weatherability or in the generation rate of oceanic crust. As a result, the terrestrial chemical weathering flux may be permanently altered—contrasting with the conventional view that the global silicate weathering flux must adjust to equal the volcanic CO2 degassing flux. Changes in chemical weathering flux in turn alter the long-term supply of phosphorus to the ocean, and therefore the flux of organic carbon burial, which is the long-term source of atmospheric oxygen. Hence we propose that increasing solar luminosity and a decrease in seafloor spreading rate over 1,500–500 Ma drove a gradual shift from seafloor weathering to terrestrial weathering, and a corresponding steady rise in atmospheric oxygen. Furthermore, increased terrestrial weatherability during the late Neoproterozoic may explain low temperature, increases in ocean phosphate, ocean sulfate, and atmospheric oxygen concentration at this time. PMID:24927553

  18. Suicide and Homicide Rates: Their Relationship to Latitude and Longitude and to the Weather.

    ERIC Educational Resources Information Center

    Lester, David

    1986-01-01

    Explored variation of suicide and homicide rates in the major standard metropolitan statistical areas of the United States to see whether regional variations in temperature and precipitation could account for some of the variation. Only the correlation between precipitation and homicide rates survived controls for latitude and longitude.…

  19. FTIR Spectra of Possible End Products of Martian Surface Weathering

    NASA Astrophysics Data System (ADS)

    Maxe, L. P.

    2008-03-01

    Comparative analysis of IR spectra shows that martian weathering can lead to separating destruction of surface rocks. The semi-cosmic martian weathering results in amorphous silica dust and open unique ferry aluminum/ferry silicate martian rocks.

  20. Weathering and Secondary Minerals in the Martian Meteorite Shergotty

    NASA Technical Reports Server (NTRS)

    Wentworth, Susan J.; Thomas-Keprta, Kathie L.; McKay, David S.

    2000-01-01

    The Shergotty martian meteorite contains weathering features and secondary minerals much like those in Nakhla, including secondary silicates, NaCl, and Ca-sulfate. It is likely that the weathering occurred on Mars.

  1. Space weathering on Mercury: Simulation of plagioclase weathering

    NASA Astrophysics Data System (ADS)

    Sasaki, Sho; Hiroi, Takahiro; Helbert, Jorn; Arai, Tomoko

    The optical property of the surfaces of airless silicate bodies such as the Moon, Mercury and asteroids should change in time. Typical characteristics of the change, "space weathering", are darkening, spectral reddening, and attenuation of absorption bands in reflectance spectra. The space weathering is caused by the formation of nanophase metallic iron particles in amorphous surface coatings from the deposition of ferrous silicate vapor, which was formed by high velocity dust impacts as well as irradiation of the solar wind ions. Nanophase iron particles have been confirmed in the lunar soil coating [1]. Moreover, experimental studies using pulse laser showed the formation of nanophase ion particles on the surface should control the spectral darkening and reddening [2]. Mariner 10 and MESSENGER spacecraft showed that Mercury has more impact craters asso-ciated with bright rays than the Moon. The space weathering rate on Mercury's surface might be slower than that of the lunar surface, although dust flux and solar wind flux causing the weathering should be one order of magnitude of greater on Mercury than on the Moon [3]. The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on board MES-SENGER measured reflectance spectra from Mercury's surface during the two flybys in 2008 [4] with the wavelength range between 0.2 and 1.3 microns. MASCS spectra show variation in the slope, which can be explained by lunar-like maturity trend due to the difference of space weathering degree. Spectral absorption in the UV range shows that the ferrous oxide (Fe2+) content in average surface/subsurface material is as low as a few weight percent. This could explain apparent low weathering rate on Mercury. Growth of size of nanophase iron could also have lowered the weathering degree. Size of nanophase iron particles should increase by Ostwald ripening under high temperature of several 100C [5] . And repeated irradiation by high velocity dust impacts as well as solar wind

  2. Physical and chemical weathering. [of Martian surface and rocks

    NASA Technical Reports Server (NTRS)

    Gooding, James L.; Arvidson, Raymond E.; Zolotov, Mikhail IU.

    1992-01-01

    Physical and chemical weathering processes that might be important on Mars are reviewed, and the limited observations, including relevant Viking results and laboratory simulations, are summarized. Physical weathering may have included rock splitting through growth of ice, salt or secondary silicate crystals in voids. Chemical weathering probably involved reactions of minerals with water, oxygen, and carbon dioxide, although predicted products vary sensitively with the abundance and physical form postulated for the water. On the basis of kinetics data for hydration of rock glass on earth, the fate of weathering-rind formation on glass-bearing Martian volcanic rocks is tentatively estimated to have been on the order of 0.1 to 4.5 cm/Gyr; lower rates would be expected for crystalline rocks.

  3. Saprolite Formation Rates using U-series Isotopes in a Granodiorite Weathering Profile from Boulder Creek CZO (Colorado, USA)

    NASA Astrophysics Data System (ADS)

    Pelt, Eric; Chabaux, Francois; Mills, T. Joseph; Anderson, Suzanne P.; Foster, Melissa A.

    2015-04-01

    Timescales of weathering profile formation and evolution are important kinetic parameters linked to erosion, climatic, and biological processes within the critical zone. In order to understand the complex kinetics of landscape evolution, water and soil resources, along with climate change, these parameters have to be estimated for many different contexts. The Betasso catchment, within the Boulder Creek Critical Zone Observatory (BC-CZO) in Colorado, is a mountain catchment in Proterozoic granodiorite uplifted in the Laramide Orogeny ca. 50 Ma. In an exposure near the catchment divide, an approximately 1.5 m deep profile through soil and saprolite was sampled and analysed for bulk U-series disequilibria (238U-234U-230Th-226Ra) to estimate the profile weathering rate. The (234U/238U), (230Th/234U) and (226Ra/230Th) disequilibria through the entire profile are small but vary systematically with depth. In the deepest samples, values are close to equilibrium. Above this, values are progressively further from equilibrium with height in the profile, suggesting a continuous leaching of U and Ra compared to Th. The (234U/238U) disequilibria remain < 1 along the profile, suggesting no significant U addition from pore waters. Only the shallowest sample (~20 cm depth) highlights a 226Ra excess, likely resulting from vegetation cycling. In contrast, variations of Th content and (230Th/232Th) - (238U/232Th) activity ratios in the isochron diagram are huge, dividing the profile into distinct zones above and below 80 cm depth. Below 80 cm, the Th content gradually increases upward from 1.5 to 3.5 ppm suggesting a relative accumulation linked to chemical weathering. Above 80 cm, the Th content jumps to ~15 ppm with a similar increase of Th/Ti or Th/Zr ratios that clearly excludes the same process of relative accumulation. This strong shift is also observed in LREE concentrations, such as La, Ce and Nd, and in Sr isotopic composition, which suggests an external input of radiogenic

  4. Major ion chemistry in the headwaters of the Yamuna river system:. Chemical weathering, its temperature dependence and CO 2 consumption in the Himalaya

    NASA Astrophysics Data System (ADS)

    Dalai, T. K.; Krishnaswami, S.; Sarin, M. M.

    2002-10-01

    The Yamuna river and its tributaries in the Himalaya constitute the Yamuna River System (YRS). The YRS basin has a drainage area and discharge comparable in magnitude to those of the Bhagirathi and the Alaknanda rivers, which merge to form the Ganga at the foothills of the Himalaya. A detailed geochemical study of the YRS was carried out to determine: (i) the relative significance of silicate, carbonate and evaporite weathering in contributing to its major ion composition; (ii) CO 2 consumption via silicate weathering; and (iii) the factors regulating chemical weathering of silicates in the basin. The results show that the YRS waters are mildly alkaline, with a wide range of TDS, ˜32 to ˜620 mg l-1. In these waters, the abundances of Ca, Mg and alkalinity, which account for most of TDS, are derived mainly from carbonates. Many of the tributaries in the lower reaches of the Yamuna basin are supersaturated with calcite. In addition to carbonic acid, sulphuric acid generated by oxidation of pyrites also seems to be supplying protons for chemical weathering. Silicate weathering in YRS basin contributes, on average, ˜25% (molar basis) of total cations on a basin wide scale. Silicate weathering, however, does not seem to be intense in the basin as evident from low Si/(Na*+K) in the waters, ˜1.2 and low values of chemical index of alteration (CIA) in bed sediments, ˜60. CO 2 drawdown resulting from silicate weathering in the YRS basin in the Himalaya during monsoon ranges between (4 to 7) × 10 5 moles km -2 y -1. This is higher than that estimated for the Ganga at Rishikesh for the same season. The CO 2 consumption rates in the Yamuna and the Ganga basins in the Himalaya are higher than the global average value, suggesting enhanced CO 2 drawdown in the southern slopes of the Himalaya. The impact of this enhanced drawdown on the global CO 2 budget may not be pronounced, as the drainage area of the YRS and the Ganga in the Himalaya is small. The CO 2 drawdown by

  5. Atmospheric CO2 Removal by Enhancing Weathering

    NASA Astrophysics Data System (ADS)

    Koster van Groos, A. F.; Schuiling, R. D.

    2014-12-01

    The increase of the CO2 content in the atmosphere by the release of anthropogenic CO2 may be addressed by the enhancement of weathering at the surface of the earth. The average emission of mantle-derived CO2 through volcanism is ~0.3 Gt/year (109 ton/year). Considering the ~3.000 Gt of CO2 present in the atmosphere, the residence time of CO2 in the earth's atmosphere is ~10,000 years. Because the vast proportion of carbon in biomass is recycled through the atmosphere, CO2 is continuously removed by a series of weathering reactions of silicate minerals and stored in calcium and magnesium carbonates. The addition of anthropogenic CO2 from fossil fuel and cement production, which currently exceeds 35 Gt/year and dwarfs the natural production 100-fold, cannot be compensated by current rates of weathering, and atmospheric CO2 levels are rising rapidly. To address this increase in CO2 levels, weathering rates would have to be accelerated on a commensurate scale. Olivine ((Mg,Fe)2SiO4) is the most reactive silicate mineral in the weathering process. This mineral is the major constituent in relatively common ultramafic rocks such as dunites (olivine content > 90%). To consume the current total annual anthropogenic release of CO2, using a simplified weathering reaction (Mg2SiO4 + 4CO2 + 4H2O --> 2 Mg2+ + 4HCO3- + H4SiO4) would require ~30 Gt/year or ~8-9 km3/year of dunite. This is a large volume; it is about double the total amount of ore and gravel currently mined (~ 17 Gt/year). To mine and crush these rocks to <100 μm costs ~ 8/ton. The transport and distribution over the earth's surface involves additional costs, that may reach 2-5/ton. Thus, the cost of remediation for the release of anthropogenic CO2 is 300-400 billion/year. This compares to a 2014 global GDP of ~80 trillion. Because weathering reactions require the presence of water and proceed more rapidly at higher temperatures, the preferred environments to enhance weathering are the wet tropics. From a socio

  6. Water geochemistry of the Qiantangjiang River, East China: Chemical weathering and CO2 consumption in a basin affected by severe acid deposition

    NASA Astrophysics Data System (ADS)

    Liu, Wenjing; Shi, Chao; Xu, Zhifang; Zhao, Tong; Jiang, Hao; Liang, Chongshan; Zhang, Xuan; Zhou, Li; Yu, Chong

    2016-09-01

    The chemical composition of the Qiantangjiang River, the largest river in Zhejiang province in eastern China, was measured to understand the chemical weathering of rocks and the associated CO2 consumption and anthropogenic influences within a silicate-dominated river basin. The average total dissolved solids (TDS, 113 mg l-1) and total cation concentration (TZ+, 1357 μeq l-1) of the river waters are comparable with those of global major rivers. Ca2+ and HCO3- followed by Na2+ and SO42-, dominate the ionic composition of the river water. There are four major reservoirs (carbonates, silicates, atmospheric and anthropogenic inputs) contributing to the total dissolved load of the investigated rivers. The dissolved loads of the rivers are dominated by both carbonate and silicate weathering, which together account for about 76.3% of the total cationic load origin. The cationic chemical weathering rates of silicate and carbonate for the Qiantangjiang basin are estimated to be approximately 4.9 ton km-2 a-1 and 13.9 ton km-2 a-1, respectively. The calculated CO2 consumption rates with the assumption that all the protons involved in the weathering reaction are provided by carbonic acid are 369 × 103 mol km-2 a-1 and 273 × 103 mol km-2 a-1 by carbonate and silicate weathering, respectively. As one of the most severe impacted area by acid rain in China, H2SO4 from acid precipitation is also an important proton donor in weathering reactions. When H2SO4 is considered, the CO2 consumption rates for the river basin are estimated at 286 × 103 mol km-2 a-1 for carbonate weathering and 211 × 103 mol km-2 a-1 for silicate weathering, respectively. The results highlight that the drawdown effect of CO2 consumption by carbonate and silicate weathering can be largely overestimated if the role of sulfuric acid is ignored, especially in the area heavily impacted by acid deposition like Qiantangjiang basin. The actual CO2 consumption rates (after sulfuric acid weathering effect

  7. Weathering, Soil Production, and Erosion Across Climatic and Tectonic Gradients

    NASA Astrophysics Data System (ADS)

    Norton, K. P.; Larsen, I. J.

    2014-12-01

    Weathering is one of the fundamental processes that sustain life on our planet. Physical weathering breaks down rock for soil production and chemical weathering is thought to operate as the ultimate long-term negative feedback on atmospheric CO2 concentrations. There remains, however, uncertainty as to the relationship between chemical and physical weathering at very fast rates. If chemical weathering becomes kinetically limited at rapid erosion rates, as has been shown in a number of locations around the globe, then the fastest erosion rates will be associated with reduced chemical weathering. This has led to a debate as to whether tectonically active mountain ranges or rolling plains are the main source of CO2 drawdown through silicate weathering. At the heart of this debate is the dearth of chemical weathering data at fast erosion rates. New cosmogenic nuclide-derived denudation rates from the West Coast of the New Zealand Southern Alps are among the fastest in the world and are linearly correlated with chemical weathering rates. The associated soil production rates reach an order of magnitude faster than previous estimates and far exceed the suggested maximum soil production rate. This suggests that very fast weathering and soil production is possible in such active landscapes and extreme climates. We investigate the controls on these rapid rates with a climate-driven soil production model. At the most basic level, soil production requires chemical weathering of primary minerals to secondary minerals. We apply soil production models with both exponential and hump-shaped dependencies on soil thickness. Mean annual temperature and precipitation are incorporated in the form of a modified Arrhenius equation that controls the maximum soil production rate. When applied to the Southern Alps, the model predicts very rapid soil production that matches the magnitude of the cosmogenic nuclide-derived rates. High annual precipitation in the Southern Alps supports rapid

  8. Effects of climate on chemical weathering in watersheds

    USGS Publications Warehouse

    White, A.F.; Blum, A.E.

    1995-01-01

    Climatic effects on chemical weathering are evaluated by correlating variations in solute concentrations and fluxes with temperature, precipitation, runoff, and evapotranspiration (ET) for a worldwide distribution of sixty-eight watersheds underlain by granitoid rock types. Stream solute concentrations are strongly correlated with proportional ET loss, and evaporative concentration makes stream solute concentrations an inapprorpiate surrogate for chemical weathering. Chemical fluxes are unaffected by ET, and SiO2 and Na weathering fluxes exhibit systematic increases with precipitation, runoff, and temperature. However, warm and wet watersheds produce anomalously rapid weathering rates. A proposed model that provides an improved prediction of weathering rates over climatic extremes is the product of linear precipitation and Arrhenius temperature functions. The resulting apparent activation energies based on SiO2 and Na fluxes are 59.4 and 62.5 kJ.mol-1, respectively. The coupling between temperature and precipitation emphasizes the importance of tropical regions in global silicate weathering fluxes, and suggests it is not representative to use continental averages for temperature and precipitation in the weathering rate functions of global carbon cycling and climatic change models. Fluxes of K, Ca, and Mg exhibit no climatic correlation, implying that other processes, such as ion exchange, nutrient cycling, and variations in lithology, obscure any climatic signal. -from Authors

  9. Slow advance of the weathering front during deep, supply-limited saprolite formation in the tropical Highlands of Sri Lanka

    NASA Astrophysics Data System (ADS)

    Hewawasam, Tilak; von Blanckenburg, Friedhelm; Bouchez, Julien; Dixon, Jean L.; Schuessler, Jan A.; Maekeler, Ricarda

    2013-10-01

    Silicate weathering - initiated by major mineralogical transformations at the base of ten meters of clay-rich saprolite - generates the exceptionally low weathering flux found in streams draining the crystalline rocks of the mountainous and humid tropical Highlands of Sri Lanka. This conclusion is reached from a thorough investigation of the mineralogical, chemical, and Sr isotope compositions of samples within a regolith profile extending >10 m from surface soil through the weathering front in charnockite bedrock (a high-grade metamorphic rock), corestones formed at the weathering front, as well as from the chemical composition of the dissolved loads in nearby streams. Weatherable minerals and soluble elements are fully depleted at the top of the profile, showing that the system is supply-limited, such that weathering fluxes are controlled directly by the supply of fresh minerals. We determine the weathering rates using two independent means: (1) in situ-produced cosmogenic nuclides in surface soil and creek sediments in the close vicinity of the regolith combined with immobile element mass balance across the regolith and (2) river dissolved loads. Silicate weathering rates determined from both approaches range from 16 to 36 t km-2 y-1, corresponding to a weathering front advance rate of 6-14 mm ky-1. These rates agree across the 101 to 104 y time scales over which our rate metrics integrate, suggesting that the weathering system operates at steady state. Within error these rates are furthermore compatible with those obtained by modeling the advance rate of the weathering front from chemical gradients and mineral dissolution rates. The silicate weathering flux out of the weathering profile, measured on small creeks, amounts to 84% of the profile’s export flux; the remaining 16% is contributed by non-silicate, atmospheric-derived input. The silicate weathering flux, as measured by dissolved loads in large catchments, amounts to ca. 50% of the total dissolved flux

  10. Range profiling of the rain rate by an airborne weather radar

    NASA Technical Reports Server (NTRS)

    Meneghini, Robert; Nakamura, Kenji

    1990-01-01

    A class of methods based on a measure of path attenuation that is used to constrain the Hitschfeld-Bordan solution is investigated. Such methods are investigated for lidar, radar, and combined radar-radiometer applications. Their function is to allocate the attenuation in proportion to the strength of the measured reflectivity. A description is provided of four estimates of rain rate that have been tested using data from a dual-wavelength airborne radar at 10 GHz and 35 GHz. It is concluded, that when attenuation is significant, the estimates are generally more accurate than those without attenuation correction. Thus, such methodologies can be utilized to extend the effective dynamic range of the radar to higher rain rates.

  11. TEM Analyses of Itokawa Regolith Grains and Lunar Soil Grains to Directly Determine Space Weathering Rates on Airless Bodies

    NASA Technical Reports Server (NTRS)

    Berger, Eve L.; Keller, Lindsay P.; Christoffersen, Roy

    2016-01-01

    Samples returned from the moon and Asteroid Itokawa by NASA's Apollo Missions and JAXA's Hayabusa Mission, respectively, provide a unique record of their interaction with the space environment. Space weathering effects result from micrometeorite impact activity and interactions with the solar wind. While the effects of solar wind interactions, ion implantation and solar flare particle track accumulation, have been studied extensively, the rate at which these effects accumulate in samples on airless bodies has not been conclusively determined. Results of numerical modeling and experimental simulations do not converge with observations from natural samples. We measured track densities and rim thicknesses of three olivine grains from Itokawa and multiple olivine and anorthite grains from lunar soils of varying exposure ages. Samples were prepared for analysis using a Leica EM UC6 ultramicrotome and an FEI Quanta 3D dual beam focused ion beam scanning electron microscope (FIB-SEM). Transmission electron microscope (TEM) analyses were performed on the JEOL 2500SE 200kV field emission STEM. The solar wind damaged rims on lunar anorthite grains are amorphous, lack inclusions, and are compositionally similar to the host grain. The rim width increases as a smooth function of exposure age until it levels off at approximately 180 nm after approximately 20 My (Fig. 1). While solar wind ion damage can only accumulate while the grain is in a direct line of sight to the Sun, solar flare particles can penetrate to mm-depths. To assess whether the track density accurately predicts surface exposure, we measured the rim width and track density in olivine and anorthite from the surface of rock 64455, which was never buried and has a surface exposure age of 2 My based on isotopic measurements. The rim width from 64455 (60-70nm) plots within error of the well-defined trend for solar wind amorphized rims in Fig. 1. Measured solar flare track densities are accurately reflecting the

  12. Emergent relation between surface vapor conductance and relative humidity profiles yields evaporation rates from weather data

    PubMed Central

    Salvucci, Guido D.; Gentine, Pierre

    2013-01-01

    The ability to predict terrestrial evapotranspiration (E) is limited by the complexity of rate-limiting pathways as water moves through the soil, vegetation (roots, xylem, stomata), canopy air space, and the atmospheric boundary layer. The impossibility of specifying the numerous parameters required to model this process in full spatial detail has necessitated spatially upscaled models that depend on effective parameters such as the surface vapor conductance (Csurf). Csurf accounts for the biophysical and hydrological effects on diffusion through the soil and vegetation substrate. This approach, however, requires either site-specific calibration of Csurf to measured E, or further parameterization based on metrics such as leaf area, senescence state, stomatal conductance, soil texture, soil moisture, and water table depth. Here, we show that this key, rate-limiting, parameter can be estimated from an emergent relationship between the diurnal cycle of the relative humidity profile and E. The relation is that the vertical variance of the relative humidity profile is less than would occur for increased or decreased evaporation rates, suggesting that land–atmosphere feedback processes minimize this variance. It is found to hold over a wide range of climate conditions (arid–humid) and limiting factors (soil moisture, leaf area, energy). With this relation, estimates of E and Csurf can be obtained globally from widely available meteorological measurements, many of which have been archived since the early 1900s. In conjunction with precipitation and stream flow, long-term E estimates provide insights and empirical constraints on projected accelerations of the hydrologic cycle. PMID:23576717

  13. Silicate production and availability for mineral carbonation.

    PubMed

    Renforth, P; Washbourne, C-L; Taylder, J; Manning, D A C

    2011-03-15

    Atmospheric carbon dioxide sequestered as carbonates through the accelerated weathering of silicate minerals is proposed as a climate change mitigation technology with the potential to capture billions of tonnes of carbon per year. Although these materials can be mined expressly for carbonation, they are also produced by human activities (cement, iron and steel making, coal combustion, etc.). Despite their potential, there is poor global accounting of silicates produced in this way. This paper presents production estimates (by proxy) of various silicate materials including aggregate and mine waste, cement kiln dust, construction and demolition waste, iron and steel slag, and fuel ash. Approximately 7-17 billion tonnes are produced globally each year with an approximate annual sequestration potential of 190-332 million tonnes C. These estimates provide justification for additional research to accurately quantify the contemporary production of silicate minerals and to determine the location and carbon capture potential of historic material accumulations. PMID:21332128

  14. Quasi-real time estimation of intense rainfall rates from weather radar

    NASA Astrophysics Data System (ADS)

    Libertino, Andrea; Allamano, Paola; Claps, Pierluigi; Cremonini, Roberto; Laio, Francesco

    2015-04-01

    Rainfall intensity estimation from radar is known to be prone to different sources of uncertainty, both in the detection and in the processing phase. These sources of uncertainty are especially relevant when severe rainfall rates are considered, thus calling for the adoption of advanced methods for the estimation of the rainfall rate from radar observations. We introduce a quasi-real time procedure for the adaptive estimation of the coefficients of the Z-R relation that links radar reflectivity to rainfall rate. The proposed quasi-real time calibration can grant Z-R relationships consistent with the evolution of the event while the use of a spatially adaptive approach makes the technique amenable to be applied in large areas with complex orography. The aim is to define a simple and operative methodology suitable for a systematic and possibly unsupervised application, capable to reconstruct the whole spectrum of intensities occurred during an intense rainfall event. We propose to readjust the power-law equation commonly used to transform reflectivity to rainfall intensity at each time step, calibrating its parameters by means of Z-R pairs collected in the time proximity of the considered instant. Z-R data are filtered with a reflectivity threshold, which varies in time, in order to discriminate between the presence and absence of rainfall. For every location, the spatial calibration domain is limited to the rain gauges belonging to a neighbourhood. Z-R coefficients are estimated for each location and each time step by minimizing the standard deviation between observed and estimated rainfall, through a non-linear procedure. The case study includes a set of 16 severe rainfall events occurred in the north-west of Italy. The technique outperforms the classical estimation methods for most of the analysed events and shows significant potential for operational uses. The determination coefficient undergoes up to 30% improvements and the BIAS values are reduced, for

  15. The Weather-Beaten Dorsal Hand Clinical Rating, Shadow Casting Optical Profilometry, and Skin Capacitance Mapping

    PubMed Central

    Delvenne, Marie; Piérard-Franchimont, Claudine; Seidel, Laurence; Albert, Adelin; Piérard, Gérald E.

    2013-01-01

    Laypeople commonly perceive some skin xerosis and withering (roughness) changes during winter on some parts of the body, particularly on the dorsal hands. The aim of the study was to assess the withered skin surface changes occurring during the four seasons. A total of 47 menopausal women completed the study. A group of 31 volunteers were on hormone replacement therapy (HRT) and 16 were out of HRT. Skin xerosis and scaliness were rated clinically. In addition, skin whitening was assessed by computerized shadow casting optical profilometry and by skin capacitance mapping. The volunteers were not using topical creams and over-the-counter products on their hands. Marked changes, recorded over the successive seasons, corresponded to patchy heterogeneous stratum corneum hydration and heterogeneous skin surface roughness changing over seasons; they likely resulted from changes in the environmental temperature and atmosphere moisture. The severity of the changes revealed by clinical inspection was not supported by similar directions of fluctuations in the instrumental assessments. This seemingly contradiction was in fact due to different levels of scale observation. The clinical centimetric scale and the instrumental inframillimetric scale possibly provide distinct aspects of a given biological impact. PMID:24222921

  16. Direct measurement of the combined effects of lichen, rainfall, and temperature onsilicate weathering

    USGS Publications Warehouse

    Brady, P.V.; Dorn, R.I.; Brazel, A.J.; Clark, J.; Moore, R.B.; Glidewell, T.

    1999-01-01

    A key uncertainty in models of the global carbonate-silicate cycle and long-term climate is the way that silicates weather under different climatologic conditions, and in the presence or absence of organic activity. Digital imaging of basalts in Hawaii resolves the coupling between temperature, rainfall, and weathering in the presence and absence of lichens. Activation energies for abiotic dissolution of plagioclase (23.1 ?? 2.5 kcal/mol) and olivine (21.3 ?? 2.7 kcal/mol) are similar to those measured in the laboratory, and are roughly double those measured from samples taken underneath lichen. Abiotic weathering rates appear to be proportional to rainfall. Dissolution of plagioclase and olivine underneath lichen is far more sensitive to rainfall.

  17. Evaluating the Contribution of Eolian Dust to the Weathering Flux From Mountain Soils

    NASA Astrophysics Data System (ADS)

    Lawrence, C. R.; Neff, J. C.; Farmer, G. L.

    2008-12-01

    The weathering of silicate minerals is an important control on the global carbon cycle over geologic timescales. In order to accurately characterize the influence of silicate weathering on the carbon cycle, it is important to quantify the mechanisms that may influence weathering. Tectonics, erosion, climate, and rock chemistry are all important factors in the weathering process. There is also evidence that eolian dust deposition may influence weathering fluxes in some settings. The transport of fine sediments from arid regions, with relatively slow rates of chemical weathering, to regions more favorable to weathering may act to accelerate global weathering rates. Detailed studies of dust deposition and soil evolution are required to better quantify the role that dust plays in the weathering process. The San Juan Mountains of southern Colorado are situated downwind from large dust producing regions of the Colorado Plateau and the Mojave Dessert. A recent study suggests the transport of dust from these semi-arid environments to the downwind mountain ecosystems has increased by 500% over the past century, likely as a result of human land-use changes. At present, the San Juan Mountains receive between 5-15 g/m2 of fine textured dust deposition each year. Over many years, dust accretion may have altered the geochemical characteristics of soils and could be an important factor for the chemical weathering flux from these soils. We combine soil geochemical mass balance calculations with quantitative mineralogy and strontium isotope measurements of sequential soil leaches to better constrain the input of dust to soils and to estimate the contribution of dust to the long- term chemical weathering flux.

  18. Weathering and dissolution rates among Pb shot pellets of differing elemental compositions exposed to various aqueous and soil conditions.

    PubMed

    Takamatsu, Takejiro; Murata, Tomoyoshi; Koshikawa, Masami K; Watanabe, Mirai

    2010-07-01

    The present study was performed to investigate the weathering and dissolution rates of Pb shot pellets differing in elemental composition (Pb, Sb, and As) exposed under various aqueous and soil conditions using five commercial shot pellet preparations. Upon immersion in distilled water, the dissolution rates of shot pellets, calculated from the difference in weight before versus after immersion, decreased with increasing Sb + As contents and the dominant precipitate was hydrocerussite. These subsidiary ingredients may be related to the difficulty of metallic Pb oxidation (transformation to PbO). Weight losses standardized by the amount of rainfall upon exposure to rainfall on open grassland and under canopies of Japanese cedar (Cryptomeria japonica) and bamboo-leafed oak (Quercus myrsinaefolia) were 1.11, 1.07, and 7.35 mg g pellets(-1) year(-1) L(-1), respectively, and was also related to Sb + As contents in shot pellets. However, annual dissolution rates of Pb standardized by the amount of rainfall as the soluble fraction at the same sites were 0.72, 0.33, and 0.40 mg Pb g pellets(-1) year(-1) L(-1) in the same order. These trends seemed to be related to the rainfall pH, which induces precipitation of Pb dissolved as PbCO(3) under conditions of higher pH at the Q. myrsinaefolia site or organic matter released from leaves, etc., which can form metal complexes. Dissolution rates of shot pellets buried in soils (Cambisol, Fluvisol, Regosol, Andosol) also seemed to be related to the soil pH and dissolved organic matter contents but were about sixfold faster than those with exposure to rainfall. PMID:20039167

  19. Nonlinear dynamics and instability of aqueous dissolution of silicate glasses and minerals

    PubMed Central

    Wang, Yifeng; Jove-Colon, Carlos F.; Kuhlman, Kristopher L.

    2016-01-01

    Aqueous dissolution of silicate glasses and minerals plays a critical role in global biogeochemical cycles and climate evolution. The reactivity of these materials is also important to numerous engineering applications including nuclear waste disposal. The dissolution process has long been considered to be controlled by a leached surface layer in which cations in the silicate framework are gradually leached out and replaced by protons from the solution. This view has recently been challenged by observations of extremely sharp corrosion fronts and oscillatory zonings in altered rims of the materials, suggesting that corrosion of these materials may proceed directly through congruent dissolution followed by secondary mineral precipitation. Here we show that complex silicate material dissolution behaviors can emerge from a simple positive feedback between dissolution-induced cation release and cation-enhanced dissolution kinetics. This self-accelerating mechanism enables a systematic prediction of the occurrence of sharp dissolution fronts (vs. leached surface layers), oscillatory dissolution behaviors and multiple stages of glass dissolution (in particular the alteration resumption at a late stage of a corrosion process). Our work provides a new perspective for predicting long-term silicate weathering rates in actual geochemical systems and developing durable silicate materials for various engineering applications. PMID:27443508

  20. Nonlinear dynamics and instability of aqueous dissolution of silicate glasses and minerals

    NASA Astrophysics Data System (ADS)

    Wang, Yifeng; Jove-Colon, Carlos F.; Kuhlman, Kristopher L.

    2016-07-01

    Aqueous dissolution of silicate glasses and minerals plays a critical role in global biogeochemical cycles and climate evolution. The reactivity of these materials is also important to numerous engineering applications including nuclear waste disposal. The dissolution process has long been considered to be controlled by a leached surface layer in which cations in the silicate framework are gradually leached out and replaced by protons from the solution. This view has recently been challenged by observations of extremely sharp corrosion fronts and oscillatory zonings in altered rims of the materials, suggesting that corrosion of these materials may proceed directly through congruent dissolution followed by secondary mineral precipitation. Here we show that complex silicate material dissolution behaviors can emerge from a simple positive feedback between dissolution-induced cation release and cation-enhanced dissolution kinetics. This self-accelerating mechanism enables a systematic prediction of the occurrence of sharp dissolution fronts (vs. leached surface layers), oscillatory dissolution behaviors and multiple stages of glass dissolution (in particular the alteration resumption at a late stage of a corrosion process). Our work provides a new perspective for predicting long-term silicate weathering rates in actual geochemical systems and developing durable silicate materials for various engineering applications.

  1. Nonlinear dynamics and instability of aqueous dissolution of silicate glasses and minerals

    DOE PAGESBeta

    Wang, Yifeng; Jove-Colon, Carlos F.; Kuhlman, Kristopher L.

    2016-07-22

    Aqueous dissolution of silicate glasses and minerals plays a critical role in global biogeochemical cycles and climate evolution. The reactivity of these materials is also important to numerous engineering applications including nuclear waste disposal. The dissolution process has long been considered to be controlled by a leached surface layer in which cations in the silicate framework are gradually leached out and replaced by protons from the solution. This view has recently been challenged by observations of extremely sharp corrosion fronts and oscillatory zonings in altered rims of the materials, suggesting that corrosion of these materials may proceed directly through congruentmore » dissolution followed by secondary mineral precipitation. Here we show that complex silicate material dissolution behaviors can emerge from a simple positive feedback between dissolution-induced cation release and cation-enhanced dissolution kinetics. This self-accelerating mechanism enables a systematic prediction of the occurrence of sharp dissolution fronts (vs. leached surface layers), oscillatory dissolution behaviors and multiple stages of glass dissolution (in particular the alteration resumption at a late stage of a corrosion process). In conclusion, our work provides a new perspective for predicting long-term silicate weathering rates in actual geochemical systems and developing durable silicate materials for various engineering applications.« less

  2. Nonlinear dynamics and instability of aqueous dissolution of silicate glasses and minerals.

    PubMed

    Wang, Yifeng; Jove-Colon, Carlos F; Kuhlman, Kristopher L

    2016-01-01

    Aqueous dissolution of silicate glasses and minerals plays a critical role in global biogeochemical cycles and climate evolution. The reactivity of these materials is also important to numerous engineering applications including nuclear waste disposal. The dissolution process has long been considered to be controlled by a leached surface layer in which cations in the silicate framework are gradually leached out and replaced by protons from the solution. This view has recently been challenged by observations of extremely sharp corrosion fronts and oscillatory zonings in altered rims of the materials, suggesting that corrosion of these materials may proceed directly through congruent dissolution followed by secondary mineral precipitation. Here we show that complex silicate material dissolution behaviors can emerge from a simple positive feedback between dissolution-induced cation release and cation-enhanced dissolution kinetics. This self-accelerating mechanism enables a systematic prediction of the occurrence of sharp dissolution fronts (vs. leached surface layers), oscillatory dissolution behaviors and multiple stages of glass dissolution (in particular the alteration resumption at a late stage of a corrosion process). Our work provides a new perspective for predicting long-term silicate weathering rates in actual geochemical systems and developing durable silicate materials for various engineering applications. PMID:27443508

  3. Soil weathering and accumulation rates of oxalate-extractable phases derived from alpine chronosequences of up to 1 Ma in age

    NASA Astrophysics Data System (ADS)

    Dahms, Dennis; Favilli, Filippo; Krebs, Rolf; Egli, Markus

    2012-05-01

    In this study we compare newly-developed chemical weathering data with previously published data from soils developed along two chronosequences of glacial deposits in the European Alps and the Rocky Mountains (Wind River Range, USA). By combining these chronosequences, we are able to present a comprehensive dataset that represents a time period of > 1 Ma. We describe weathering trends of important elements using a number of weathering indices (e.g., K + Ca/Ti ratio, the weathering 'index B' of Kronberg and Nesbitt (1981) and the open mass transport function). Further, we describe the accumulation of Al, Fe, Si and Mn oxyhydroxides (including partially organic phases) as a function of time, and derive the corresponding accumulation rates. We calculated pedogenetically formed oxyhydroxides using an approach based on immobile elements. Our study represents one of only a few studies that describe rates of soil chemical weathering over a period as long as ~ 1 Ma. Results show that rates of chemical weathering clearly decrease along the chronosequences with increasing age of the soils. We find weathering rates are nearly four orders of magnitude lower in the 1 Ma-old soils than in the young soils. Our results suggest that the older soils may be reaching a steady state for these chemical properties in their present environments. A power function best explains the measured time-trends of the 'index B' and (K + Ca)/Ti) ratios in the soils. The best time-trend model for pedogenic weakly- to poorly crystalline phases and the relative losses/gains (based on the open-system mass transport function) were obtained with an exponential decay model function. In terms of the soil system, the decreases in the accumulation rate of the oxyhydroxides appears to be influenced not only by the factor of time but by climate as well (increased precipitation at higher altitudes slows the decrease in weathering rate over time). Thus, our ~ 1 Ma chronosequences also become pedogenic gradients

  4. Isotopic exchange in mineral-fluid systems. 4. The crystal chemical controls on oxygen isotope exchange rates in carbonate-H{sub 2}O and layer silicate-H{sub 2}O systems

    SciTech Connect

    Cole, D.R.

    2000-03-01

    Oxygen isotope exchange between minerals and water in systems far from chemical equilibrium is controlled largely by surface reactions such as dissolution-precipitation. In many cases, this behavior can be modeled adequately by a simple pseudo-first order rate model that accounts for changes in surface area of the solid. Previous modeling of high temperature isotope exchange data for carbonates, sulfates, and silicates indicated that within a given mineral group there appears to be a systematic relationship between rate and mineral chemistry. The author tested this idea by conducting oxygen isotope exchange experiments in the systems, carbonate-H{sub 2}O and layer silicate-H{sub 2}O at 300 and 350 C, respectively. Witherite (BaCO{sub 3}), strontianite (SrCO{sub 3}) and calcite (CaCO{sub 3}) were reacted with pure H{sub 2}O for different lengths of time (271--1,390 H) at 300 C and 100 bars. The layer silicates, chlorite, biotite and muscovite were reacted with H{sub 2}O for durations ranging from 132 to 3,282 h at 350 C and 250 bars. A detailed survey of grain sizes and grain habits using scanning electron microscopy (SEM) indicated that grain regrowth occurred in all experiments to varying extents. The isotopic rates (ln r) for the carbonate-H{sub 2}O system are {minus}20.75 {+-} 0.44, {minus}18.95 {+-} 0.62 and {minus}18.51 {+-} 0.48 mol O/m{sup 2} s for calcite, strontianite and witherite, respectively. The oxygen isotope exchange rates for layer silicate-H{sub 2}O systems are {minus}23.99 {+-} 0.89, {minus}23.14 {+-} 0.74 and {minus}22.40 {+-} 0.66 mol O/m{sup 2} s for muscovite, biotite and chlorite, respectively.

  5. Steady- and non-steady-state carbonate-silicate controls on atmospheric CO2

    USGS Publications Warehouse

    Sundquist, E.T.

    1991-01-01

    Two contrasting hypotheses have recently been proposed for the past long-term relation between atmospheric CO2 and the carbonate-silicate geochemical cycle. One approach (Berner, 1990) suggests that CO2 levels have varied in a manner that has maintained chemical weathering and carbonate sedimentation at a steady state with respect to tectonically controlled decarbonation reactions. A second approach (Raymo et al., 1988), applied specificlly to the late Cenozoic, suggests a decrease in CO2 caused by an uplift-induced increase in chemical weathering, without regard to the rate of decarbonation. According to the steady-state (first) hypothesis, increased weathering and carbonate sedimentation are generally associated with increasing atmospheric CO2, whereas the uplift (second) hypothesis implies decreasing CO2 under the same conditions. An ocean-atmosphere-sediment model has been used to assess the response of atmospheric CO2 and carbonate sedimentation to global perturbations in chemical weathering and decarbonation reactions. Although this assessment is theoretical and cannot yet be related to the geologic record, the model simulations compare steady-state and non-steady-state carbonate-silicate cycle response. The e-fold response time of the 'CO2-weathering' feedback mechanism is between 300 and 400 ka. The response of carbonate sedimentation is much more rapid. These response times provide a measure of the strength of steady-state assumptions, and imply that certain systematic relations are sustained throughout steady-state and non-steady-state scenarios for the carbonate-silicate cycle. The simulations suggest that feedbacks can maintain the system near a steady state, but that non-steady-state effects may contribute to long-term trends. The steady-state and uplift hypotheses are not necessarily incompatible over time scales of a few million years. ?? 1991.

  6. Sr isotopic characteristics in two small watersheds draining typical silicate and carbonate rocks: implication for the studies on seawater Sr isotopic evolution

    NASA Astrophysics Data System (ADS)

    Wu, W. H.; Zheng, H. B.; Yang, J. D.

    2013-06-01

    We systematically investigated Sr isotopic characteristics of small silicate watershed - the tributary Xishui River of the Yangtze River, and small carbonate watershed - the tributary Guijiang River of the Pearl River. The results show that the Xishui River has relatively high Sr concentrations (0.468-1.70 μmol L-1 in summer and 1.30-3.17 μmol L-1 in winter, respectively) and low 87Sr/86Sr ratios (0.708686-0.709148 in summer and 0.708515-0.709305 in winter), which is similar to the characteristics of carbonate weathering. The Guijiang River has low Sr concentrations (0.124-1.098 μmol L-1) and high 87Sr/86Sr ratios (0.710558-0.724605), being characterized by silicate weathering. In the Xishui River catchment, chemical weathering rates in summer are far higher than those in winter, indicating significant influence of climate regime. However, slight differences of 87Sr/86Sr ratios between summer and winter show that influence of climate on Sr isotope is uncertainty owing to very similar Sr isotope values in silicate and carbonate bedrocks. As 87Sr/86Sr ratios in the Xishui River are lower than those in seawater, they will decrease 87Sr/86Sr ratio of seawater after transported into oceans. Previous studies also showed that some basaltic watersheds with extremely high chemical weathering rates reduced the seawater Sr isotope ratios. In other words, river catchments with high silicate weathering rates do not certainly transport highly radiogenic Sr into oceans. Therefore, it may be questionable that using the variations of seawater 87Sr/86Sr ratio to indicate the continental silicate weathering intensity. In the Guijiang River catchment, 87Sr/86Sr ratios of carbonate rocks and other sources (rainwater, domestic and industrial waste water, and agricultural fertilizer) are lower than 0.71. In comparison, some non-carbonate components, such as, sand rocks, mud rocks, shales, have relatively high Sr isotopic compositions. Moreover, granites accounted for only 5% of the

  7. Regolith production rates calculated with Uranium-series isotopes at Shale Hills Critical Zone Observatory: implications on chemical weathering and landscape evolution

    NASA Astrophysics Data System (ADS)

    Ma, L.; Chabaux, F. J.; Pelt, E.; Blaes, E.; Jin, L.; Brantley, S. L.

    2009-12-01

    It is essential to understand the rates and mechanisms of regolith formation as it contributes to important Critical Zone processes such as nutrient cycling, carbon sequestration, erosion, and acid rain mitigation. Over the long term, the rates of weathering and erosion also combine to control the evolution of landscapes. Uranium-series isotopes offer a powerful tool to investigate regolith production rates and residence times within a weathering system because of their well-documented fractionation behavior during chemical weathering and transport by water. Here, we present a study of U-series isotopes (238U, 234U and 230Th) in soils developed on shale bedrock at the Shale Hills catchment in central Pennsylvania. (234U/238U) and (230Th/238U) activity ratios in samples collected from soil profiles along a planar hillslope in the catchment range from 0.934 to 1.072 and from 0.920 to 1.096, respectively. These values show significant U-series disequilibrium and are explained by a dual process of U-series isotopes during weathering: a loss of 234U, 238U, and 230Th during water-rock interactions and a gain of 234U and 238U as U precipitated from circulating soil water. Regolith production rates calculated with U-series isotopes for these soil profiles range from ~15 to 45 m/Myr and decrease systematically with increasing distance from the ridge top to the middle slope and to the valley floor. Soil residence times within these profiles increase from the ridge to the valley floor. The regolith production rates at Shale Hills vary as an exponential function of soil thickness, similar to the soil production functions derived from many other studies. With the local soil production function at Shale Hills, a hillslope soil transport model is used to predict the landscape evolution and change of soil thickness along the planar transect. The simulation results suggest that both the landscape and soil thickness along the planar hillscope at Shale Hills are currently at a

  8. Biogeochemical weathering under ice: Size matters

    NASA Astrophysics Data System (ADS)

    Wadham, J. L.; Tranter, M.; Skidmore, M.; Hodson, A. J.; Priscu, J.; Lyons, W. B.; Sharp, M.; Wynn, P.; Jackson, M.

    2010-09-01

    The basal regions of continental ice sheets are gaps in our current understanding of the Earth's biosphere and biogeochemical cycles. We draw on existing and new chemical data sets for subglacial meltwaters to provide the first comprehensive assessment of sub-ice sheet biogeochemical weathering. We show that size of the ice mass is a critical control on the balance of chemical weathering processes and that microbial activity is ubiquitous in driving dissolution. Carbonate dissolution fueled by sulfide oxidation and microbial CO2 dominate beneath small valley glaciers. Prolonged meltwater residence times and greater isolation characteristic of ice sheets lead to the development of anoxia and enhanced silicate dissolution due to calcite saturation. We show that sub-ice sheet environments are highly geochemically reactive and should be considered in regional and global solute budgets. For example, calculated solute fluxes from Antarctica (72-130 t yr-1) are the same order of magnitude as those from some of the world's largest rivers and rates of chemical weathering (10-17 t km-2 yr-1) are high for the annual specific discharge (2.3-4.1 × 10-3 m). Our model of chemical weathering dynamics provides important information on subglacial biodiversity and global biogeochemical cycles and may be used to design strategies for the first sampling of Antarctic Subglacial Lakes and other sub-ice sheet environments for the next decade.

  9. Enhanced weathering strategies for stabilizing climate and averting ocean acidification

    NASA Astrophysics Data System (ADS)

    Taylor, Lyla L.; Quirk, Joe; Thorley, Rachel M. S.; Kharecha, Pushker A.; Hansen, James; Ridgwell, Andy; Lomas, Mark R.; Banwart, Steve A.; Beerling, David J.

    2016-04-01

    Chemical breakdown of rocks, weathering, is an important but very slow part of the carbon cycle that ultimately leads to CO2 being locked up in carbonates on the ocean floor. Artificial acceleration of this carbon sink via distribution of pulverized silicate rocks across terrestrial landscapes may help offset anthropogenic CO2 emissions. We show that idealized enhanced weathering scenarios over less than a third of tropical land could cause significant drawdown of atmospheric CO2 and ameliorate ocean acidification by 2100. Global carbon cycle modelling driven by ensemble Representative Concentration Pathway (RCP) projections of twenty-first-century climate change (RCP8.5, business-as-usual; RCP4.5, medium-level mitigation) indicates that enhanced weathering could lower atmospheric CO2 by 30-300 ppm by 2100, depending mainly on silicate rock application rate (1 kg or 5 kg m-2 yr-1) and composition. At the higher application rate, end-of-century ocean acidification is reversed under RCP4.5 and reduced by about two-thirds under RCP8.5. Additionally, surface ocean aragonite saturation state, a key control on coral calcification rates, is maintained above 3.5 throughout the low latitudes, thereby helping maintain the viability of tropical coral reef ecosystems. However, we highlight major issues of cost, social acceptability, and potential unanticipated consequences that will limit utilization and emphasize the need for urgent efforts to phase down fossil fuel emissions.

  10. Enhanced Weathering Strategies for Stabilizing Climate and Averting Ocean Acidification

    NASA Technical Reports Server (NTRS)

    Taylor, Lyla L.; Quirk, Joe; Thorley, Rachel M. S.; Kharecha, Pushker A.; Hansen, James; Ridgwell, Andy; Lomas, Mark R.; Banwart, Steve A.; Beerling, David J.

    2015-01-01

    Chemical breakdown of rocks, weathering, is an important but very slow part of the carbon cycle that ultimately leads to CO2 being locked up in carbonates on the ocean floor. Artificial acceleration of this carbon sink via distribution of pulverized silicate rocks across terrestrial landscapes may help offset anthropogenic CO2 emissions. We show that idealized enhanced weathering scenarios over less than a third of tropical land could cause significant drawdown of atmospheric CO2 and ameliorate ocean acidification by 2100. Global carbon cycle modelling driven by ensemble Representative Concentration Pathway (RCP) projections of twenty-first-century climate change (RCP8.5, business-as-usual; RCP4.5, medium-level mitigation) indicates that enhanced weathering could lower atmospheric CO2 by 30-300 ppm by 2100, depending mainly on silicate rock application rate (1 kg or 5 kg m(exp -2) yr (exp -1)) and composition. At the higher application rate, end-of-century ocean acidification is reversed under RCP4.5 and reduced by about two-thirds under RCP8.5. Additionally, surface ocean aragonite saturation state, a key control on coral calcification rates, is maintained above 3.5 throughout the low latitudes, thereby helping maintain the viability of tropical coral reef ecosystems. However, we highlight major issues of cost, social acceptability, and potential unanticipated consequences that will limit utilization and emphasize the need for urgent efforts to phase down fossil fuel emissions.

  11. Denudation rates of tropical mountain regions : What is the proportion of chemical weathering vs. mechanical denudation in a tectonically active settings?

    NASA Astrophysics Data System (ADS)

    Roelandt, C.; Vanacker, V.; Goddéris, Y.; Kaplan, J. O.

    2009-04-01

    Denudation rates of tropical mountain regions in tectonically active settings, such as the northern Andes, are known to be high. Rivers draining the northern Andes are important sources of sediment and nutrients to the low-lying basins and oceans. The largest part of the total denudation rates in these environments is often considered to be mechanical denudation, given their steep topography, young geology and humid and warm climate. In this study, we try to better understand the linkage between physical denudation and chemical weathering for degraded catchments with shallow, eroded soils. We selected a limited number of case-studies from the Ecuadorian Andes being characterized by humid climate, steep topography, and intensive land use. For these catchments, the total denudation rates are derived from cosmogenic isotope concentrations in riverborne quartz (Vanacker et al, 2007, Geology). The B-WITCH model (Roelandt et al. submitted, GBC) is used to quantify chemical weathering rates. The results of this study will allow us to get a better insight in the linkage between chemical and physical denudation rates for an active tectonic setting. Besides, the data will give the opportunity to explore the effect of land use change on chemical weathering rates.

  12. Weather Watch

    ERIC Educational Resources Information Center

    Bratt, Herschell Marvin

    1973-01-01

    Suggests a number of ways in which Federal Aviation Agency weather report printouts can be used in teaching the weather section of meteorology. These weather sequence reports can be obtained free of charge at most major airports. (JR)

  13. A test of the cosmogenic 10Be(meteoric)/9Be proxy for simultaneously determining basin-wide erosion rates, denudation rates, and the degree of weathering in the Amazon basin

    NASA Astrophysics Data System (ADS)

    Wittmann, H.; Blanckenburg, F.; Dannhaus, N.; Bouchez, J.; Gaillardet, J.; Guyot, J. L.; Maurice, L.; Roig, H.; Filizola, N.; Christl, M.

    2015-12-01

    We present an extensive investigation of a new erosion and weathering proxy derived from the 10Be(meteoric)/9Be(stable) ratio in the Amazon River basin. This new proxy combines a radioactive atmospheric flux tracer, meteoric cosmogenic 10Be, with 9Be, a trace metal released by weathering. Results show that meteoric 10Be concentrations ([10Be]) and 10Be/9Be ratios increase by >30% from the Andes to the lowlands. We can calculate floodplain transfer times of 2-30 kyr from this increase. Intriguingly however, the riverine exported flux of meteoric 10Be shows a deficit with respect to the atmospheric depositional 10Be flux. Most likely, the actual area from which the 10Be flux is being delivered into the mainstream is smaller than the basin-wide one. Despite this imbalance, denudation rates calculated from 10Be/9Be ratios from bed load, suspended sediment, and water samples from Amazon Rivers agree within a factor of 2 with published in situ 10Be denudation rates. Erosion rates calculated from meteoric [10Be], measured from depth-integrated suspended sediment samples, agree with denudation rates, suggesting that grain size-induced variations in [10Be] are minimized when using such sampling material instead of bed load. In addition, the agreement between erosion and denudation rates implies minor chemical weathering intensity in most Amazon tributaries. Indeed, the Be-specific weathering intensity, calculated from mobilized 9Be comprising reactive and dissolved fractions that are released during weathering, is constant at approximately 40% of the total denudation from the Andes across the lowlands to the Amazon mouth. Therefore, weathering in the Amazon floodplain is not detected.

  14. Quantifying regolith production rates with Uranium-series isotopes at Shale Hills Critical Zone Observatory: implications for chemical weathering and landscape evolution

    NASA Astrophysics Data System (ADS)

    Ma, Lin; Chabaux, Francois; Pelt, Eric; Blaes, Estelle; Jin, Lixin; Brantley, Susan

    2010-05-01

    Quantifying regolith production rates is essential in understanding many important Earth's surface processes such as nutrient cycling, carbon sequestration, erosion, and acid rain mitigation. Over the long term, the rates of weathering and erosion also combine to control the evolution of surface landscapes. Uranium-series isotopes offer a powerful tool to investigate regolith production rates and weathering timescales within a weathering system because of their well-documented fractionation behavior during chemical weathering and transport by water. To quantify regolith formation rates on shale lithology, we measured U-series isotopes (238U, 234U, and 230Th) in three weathering soil profiles along a planar north-facing hillslope at the Susquehanna Shale Hills Observatory (SSHO) in central Pennsylvania. All regolith samples show significant U-series disequilibrium: (234U/238U) and (230Th/238U) activity ratios range from 0.934 to 1.072 and from 0.903 to 1.096, respectively. These values display depth trends that are consistent with fractionation of U-series isotopes during chemical weathering, i.e., the relative mobility decreases in the order 234U > 238U >> 230Th. The activity ratios observed in the soils are explained by i) loss of U-series isotopes during water-rock interactions and ii) re-precipitation of 234U and 238U downslope. Regolith production rates calculated with U-series isotopes for these soil profiles decrease systematically with increasing distance from the ridge: from ~45 m/Myr at the ridge top, the highest point along the hillslope, to ~26 m/Myr at the middle slope site, and to ~15 m/Myr at the valley floor. Soil weathering timescales within these profiles range from 7 kyr to 45 kyr, increasing from the ridge to the valley floor. Given that the SSHO experienced peri-glacial climate ~15 ky ago, we conclude that the hillslope retains regolith formed before that glacial period and that the hillslope is not at geomorphological steady state. The regolith

  15. Caura River basin: Weathering rates, CO2 consumption, and chemistry of major and trace elements in an Orinoco River tributary coming from the Precambrian Guayana Shield, Venezuela

    NASA Astrophysics Data System (ADS)

    Mora, Abrahan; Alfonso, Juan A.; Baquero, Juan Carlos; Balza, Laura; Pisapia, Daniel

    2010-11-01

    This study describes the geochemistry of dissolved elements in the Caura River and gives information about weathering rates and associated CO2 consumption in an Orinoco River subbasin. Physicochemical variables (pH, conductivity, HCO3-, dissolved O2, and temperature), dissolved elements (Na, K, Ca, Mg, Si, Al, Fe, Cu, Mn, Zn, and Cr), total suspended sediments (TSS), and dissolved organic carbon (DOC) concentrations were measured monthly from June 2007 to August 2008 in the Caura River. Major element concentrations (Na, Ca, Mg, and Si) showed an inverse correlation with discharge, whereas K showed high concentration values during the rising waters, probably due to biogenic sources. All these elements are provided mainly from weathering of plagioclases and K feldspars. The weathering rate (riverine flux of dissolved major cations and SiO2 derived from weathering per unit area) and the CO2 consumption rate in the Caura basin (15.4 tons km-2 yr-1 and 1.1 × 105 mol km-2 yr-1, respectively) were higher than those reported for the Orinoco basin and other black water river basins. This fact can be due to several factors such as lithology (volcanic rocks), high runoff, and the presence of organic acids, which can enhance the chemical weathering. The variability of the trace elements showed a different behavior than major elements. Fe and Al concentrations were correlated with DOC. Dissolved Mn content was correlated with pH, whereas the low concentrations of Cu and Cr are possibly associated with the low content of small size organic colloids. The high values of Zn observed during the decreasing stage suggest biogenic input of Zn to river waters.

  16. Reconnaissance of Field Sites for the Study of Chemical Weathering on the Guayana Shield, South America

    SciTech Connect

    Steefell, C I

    2003-02-01

    Despite the fact that chemical weathering of silicate rocks plays an important role in the draw-down of CO{sub 2} over geologic time scales (Berner and Berner, 1996), the overall controls on the rate of chemical weathering are still not completely understood. Lacking a mechanistic understanding of these controls, it remains difficult to evaluate a hypothesis such as that presented by Raymo and Ruddiman (1992), who suggested that enhanced weathering and CO{sub 2} draw-down resulting from the uplift of the Himalayas contributed to global cooling during the Cenozoic. At an even more fundamental level, the three to four order of magnitude discrepancy between laboratory and field weathering rates is still unresolved (White et al., 1996). There is as yet no comprehensive, mechanistic model for silicate chemical weathering that considers the coupled effects of precipitation, vadose zone flow, and chemical reactions. The absence of robust process models for silicate weathering and the failure to resolve some of these important questions may in fact be related-the controls on the overall rates of weathering cannot be understood without considering the weathering environment as one in which multiple, time-dependent chemical and physical processes are coupled (Malmstrom, 2000). Once chemical weathering is understood at a mechanistic process level, the important controls on chemical weathering (physical erosion, temperature, precipitation) can be folded into larger scale models tracking the global carbon cycle. Our goal in this study was to carry out the preliminary work needed to establish a field research site for chemical weathering om the Cuayana Shield in South America. The Guayana Shield is a Precambrian province greater than 1.5 billion years old covering portions of Venezuela, Guyana (the country), Surinam, French Guiana, and Brazil (Figure 1). More important than the age of the rocks themselves, however, is the age of the erosion surface developed on the Shield, with

  17. Hit Rate of Space Weather Forecasts of the Japanese Forecast Center and Analysis of Problematic Events on the Forecasts between June 2014 and March 2015

    NASA Astrophysics Data System (ADS)

    Watari, S.; Kato, H.; Yamamoto, K.

    2015-12-01

    The hit rate of space weather forecasts issued by the Japanese forecast center in the National Institute of Information and Communications Technology (NICT) between June 2014 and March 2015 are compared with that by the persistence method. It is shown that the hit rate of the forecasts by the Japanese center is better than that by the persistence method. Several problematic events on the space weather forecasts during the same period are analyzed. Those events are (1) geomagnetic storms associated with coronal mass ejections (CMEs) on 9 September 2014 and on 15 March 2015 with different durations of southward interplanetary magnetic field (IMF), (2) a large active region, AR 12192 without CMEs, solar energetic particle events, and geomagnetic storms, (3) a geomagnetic storm on 7 January 2015 caused by a faint CME, and (4) disagreement between the in-situ observation at 1 AU and the prediction of the Potential Field Source Surface (PFSS) model on timing of sector crossing in January 2015.

  18. Severe Weather

    ERIC Educational Resources Information Center

    Forde, Evan B.

    2004-01-01

    Educating the public about safety issues related to severe weather is part of the National Oceanic and Atmospheric Administration's (NOAA) mission. This article deals with a poster entitled, "Severe Weather," that has been created by NOAA to help educate the public about hazardous weather conditions. The four types of severe weather highlighted in…

  19. Severe Weather

    ERIC Educational Resources Information Center

    Forde, Evan B.

    2004-01-01

    Educating the public about safety issues related to severe weather is part of the National Oceanic and Atmospheric Administration's (NOAA) mission. This month's insert, Severe Weather, has been created by NOAA to help educate the public about hazardous weather conditions. The four types of severe weather highlighted in this poster are hurricanes,…

  20. Modeling weather and stocking rate threshold effects on forage and steer production in northern mixed-grass prairie

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Model evaluations of forage production and yearling steer weight gain (SWG) responses to stocking density (SD) and seasonal weather patterns are presented for semi-arid northern mixed-grass prairie. We used the improved Great Plains Framework for Agricultural Resource Management-Range (GPFARM-Range)...

  1. Continental weathering response to climate change: a modelling study (Invited)

    NASA Astrophysics Data System (ADS)

    Godderis, Y.; Williams, J. Z.; Schott, J.; Pollard, D.; Brantley, S. L.

    2009-12-01

    Chemical weathering is dependent on the climatic conditions, including air temperature and rainfall. Although obvious at the geological scale, this dependence has been recently evidenced at millenia to decadal timescales. In the present contribution, we explore the link between climate and weathering at these shorter timescales through numerical modelling. The rates of mineral weathering in loess deposited 23 ky ago in the Mississippi valley and experiencing soil formation for 10 ky are estimated using the WITCH model for weathering and the GENESIS model for climate simulation. The initial mineralogical composition of the loess is uniform along the Mississippi valley and mixes dolomite and alumino-silicates. Over the 10 kyr of the simulation, temperature at the soil surface is rising by up to 4°C, while the increase in the drainage of the loess section ranges from 10 to 40 % depending on the latitude of the simulated site. The calculated mineralogical evolution of the loess section is impacted, the main feature being the fast deepening of the dolomite weathering front by about 4 meters and the formation of a shallow plagioclase weathering front. The time evolution of the dissolved species production (hence the CO2 consumption) is calculated over the simulations. The exported dissolved silica output may rise by up to 25 %, but depends heavily on the latitude of the site. This coupled climatic-weathering study is then extended 200 years in the future to estimate the impact of the anthropogenic climate change on a weathering profile and on the CO2 consumption by weathering.

  2. Developing approaches to hindcast and earthcast climate controls on solute fluxes during shale weathering in the Critical Zone

    NASA Astrophysics Data System (ADS)

    Sullivan, P. L.; Godderis, Y.; Shi, Y.; Schott, J.; Duffy, C.; Brantley, S. L.

    2013-12-01

    To quantify the anthropogenic and climatic controls on regolith formation and global weathering fluxes, it is critical to understand the evolution of weathering profiles and the consumption of CO2 associated with weathering. Using a cascade of global circulation, biota, and weathering models, Goddéris et al. (2010) hindcasted the evolution of weathering profiles over the last 10k years along a loess transect in the Mississippi Valley. After using the weathering code, WITCH, in this way to investigate the dissolution and precipitation of silicate and carbonate minerals in loess along the climosequence, Godderis et al. (2013) then used a similar cascade of models to project the response of weathering of the transect through 2100 - we call this forward projection an 'earthcast'. The effect of projected climate change on the weathering profile was largely dictated by increasing temperature (which slows the rate of advance of the dolomite reaction front but increases silicate weathering) and changes in drainage (variable along the transect). To a lesser extent, changes in soil CO2 affected weathering. The response of the dolomite reaction front acts like a terrestrial lysocline as it responds to changing CO2 and climate. Here, we embark on a similar study of shale weathering. Like the loess formations, shale has high surface area of silicates per unit volume, and can contain carbonate minerals. Shale also comprises 25% of the continental landmass. Specifically, to explore how climate evolution controls shale weathering we are beginning to compare soils along a shale climosequence transect that spans from Wales to Puerto Rico (Dere et al. in press)--i.e., like the loess north-south transect, a climosequence of pedons. For the shales, we will also explore the effects of climate variables by comparing soils on the north- and south-facing hillslopes of the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO). The eventual goal is to utilize our understanding of the

  3. Using U-series isotopes to quantify regolith formation and chemical weathering rates along a climosequence associated with the Susquehanna Shale Hills Critical Zone Observatory

    NASA Astrophysics Data System (ADS)

    Ma, L.; Chabaux, F. J.; Dere, A. L.; White, T.; Jin, L.; Brantley, S. L.

    2012-12-01

    Regolith formation and chemical weathering are important Critical Zone processes and are responsible for soil development. Despite their fundamental importance, we still lack effective tools to quantify these processes. U-series isotopes offer a powerful geochronometer to quantify regolith production rates and weathering duration. This is largely due to improvements in analytical methods and mathematical approaches made over the last decade in measuring U-series isotopes and interpreting their fractionation during chemical weathering. Here, we present a systematic study of U-series isotopes (238U, 234U and 230Th) in shale-derived soils from five small watersheds in the eastern USA to understand the rates of regolith formation as a function of climate. The selected watersheds in Pennsylvania, Virginia, Tennessee, Alabama, and Puerto Rico are part of the shale transect established as part of the Susquehanna Shale Hills Critical Zone Observatory. We first measured U-series isotopes in six regolith profiles from two planar hill-slopes (north vs. south) within the Shale Hills CZO in central PA to evaluate the role of aspect on regolith formation in the small watershed. All regolith samples display significant U-series disequilibrium. These U-series disequilibrium values are explained by two processes acting on U-series isotopes during weathering: a loss of 234U, 238U, and 230Th during water-rock interactions and a gain from circulating soil water and/or downslope particle transport. Regolith production rates and weathering durations were calculated with a U-series isotope mass balance model. On the southern (shaded) slope, regolith production rates decrease systematically with increasing soil thickness and distance from the ridge: from ~44.5 m/Myr at the ridge top to ~15.0 m/Myr at the valley floor. Durations of chemical weathering within these profiles range from 6.7 kyr to 44.7 kyr, increasing from the ridge to the valley floor. The regolith profiles on the northern

  4. Biotic enhancement of weathering, atmospheric oxygen and carbon dioxide in the Neoproterozoic

    NASA Astrophysics Data System (ADS)

    Lenton, Timothy M.; Watson, Andrew J.

    2004-03-01

    It has been suggested that biological colonization of the land surface began in the Neoproterozoic 1000-544 million years ago (Ma). We hypothesize that this colonization involved selective weathering of P from rocks, as well as an amplification of overall weathering rates. We show that two recent models, despite differences in the feedback mechanisms represented, predict that an increase in the weathering flux of P to the ocean would have caused a rise in atmospheric O2 in the Neoproterozoic. This in turn may have provided a necessary condition for the evolution of animals with hard skeletons seen in the 'Cambrian explosion'. Increased weathering of silicate rocks would also have caused a decline in atmospheric CO2, which could have been a causal factor in the Neoproterozoic glaciations.

  5. Weather & Weather Maps. Teacher's Manual.

    ERIC Educational Resources Information Center

    Metro, Peter M.; Green, Rachel E.

    This guide is intended to provide an opportunity for students to work with weather symbols used for reporting weather. Also included are exercises in location of United States cities by latitude and longitude, measurement of distances in miles and kilometers, and prediction of weather associated with various types of weather fronts. (RE)

  6. Chemical weathering and the role of sulfuric and nitric acids in carbonate weathering: Isotopes (13C, 15N, 34S, and 18O) and chemical constraints

    NASA Astrophysics Data System (ADS)

    Li, Cai; Ji, Hongbing

    2016-05-01

    Multiple isotopes (13C-DIC, 34S and 18O-SO42-, 15N and 18O-NO3-) and water chemistry were used to evaluate weathering rates and associated CO2 consumption by carbonic acid and strong acids (H2SO4 and HNO3) in a typical karst watershed (Wujiang River, Southwest China). The dual sulfate isotopes indicate that sulfate is mainly derived from sulfide oxidation in coal stratum and sulfide-containing minerals, and dual nitrate isotopes indicate that nitrate is mainly derived from soil N and nitrification. The correlation between isotopic compositions and water chemistry suggests that sulfuric and nitric acids, in addition to carbonic acid, are involved in carbonate weathering. The silicate and carbonate weathering rates are 7.2 t km-2 yr-1 and 76 t km-2 yr-1, respectively. In comparison with carbonate weathering rates (43 t km-2 yr-1) by carbonic acid alone, the subsequent increase in rates indicates significant enhancement of weathering when combined with sulfuric and nitric acids. Therefore, the role of sulfuric and nitric acids in the rock weathering should be considered in the global carbon cycle.

  7. The acid and alkalinity budgets of weathering in the Andes-Amazon system: Insights into the erosional control of global biogeochemical cycles

    NASA Astrophysics Data System (ADS)

    Torres, Mark A.; West, A. Joshua; Clark, Kathryn E.; Paris, Guillaume; Bouchez, Julien; Ponton, Camilo; Feakins, Sarah J.; Galy, Valier; Adkins, Jess F.

    2016-09-01

    The correlation between chemical weathering fluxes and denudation rates suggests that tectonic activity can force variations in atmospheric pCO2 by modulating weathering fluxes. However, the effect of weathering on pCO2 is not solely determined by the total mass flux. Instead, the effect of weathering on pCO2 also depends upon the balance between 1) alkalinity generation by carbonate and silicate mineral dissolution and 2) sulfuric acid generation by the oxidation of sulfide minerals. In this study, we explore how the balance between acid and alkalinity generation varies with tectonic uplift to better understand the links between tectonics and the long-term carbon cycle. To trace weathering reactions across the transition from the Peruvian Andes to the Amazonian foreland basin, we measured a suite of elemental concentrations (Na, K, Ca, Mg, Sr, Si, Li, SO4, and Cl) and isotopic ratios (87Sr/86Sr and δ34S) on both dissolved and solid phase samples. Using an inverse model, we quantitatively link systematic changes in solute geochemistry with elevation to downstream declines in sulfuric acid weathering as well as the proportion of cations sourced from silicates. With a new carbonate-system framework, we show that weathering in the Andes Mountains is a CO2 source whereas foreland weathering is a CO2 sink. These results are consistent with the theoretical expectation that the ratio of sulfide oxidation to silicate weathering increases with increasing erosion. Altogether, our results suggest that the effect of tectonically-enhanced weathering on atmospheric pCO2 is strongly modulated by sulfide mineral oxidation.

  8. Demographic effects of extreme weather events: snow storms, breeding success, and population growth rate in a long-lived Antarctic seabird.

    PubMed

    Descamps, Sébastien; Tarroux, Arnaud; Varpe, Øystein; Yoccoz, Nigel G; Tveraa, Torkild; Lorentsen, Svein-Håkon

    2015-01-01

    Weather extremes are one important element of ongoing climate change, but their impacts are poorly understood because they are, by definition, rare events. If the frequency and severity of extreme weather events increase, there is an urgent need to understand and predict the ecological consequences of such events. In this study, we aimed to quantify the effects of snow storms on nest survival in Antarctic petrels and assess whether snow storms are an important driver of annual breeding success and population growth rate. We used detailed data on daily individual nest survival in a year with frequent and heavy snow storms, and long term data on petrel productivity (i.e., number of chicks produced) at the colony level. Our results indicated that snow storms are an important determinant of nest survival and overall productivity. Snow storm events explained 30% of the daily nest survival within the 2011/2012 season and nearly 30% of the interannual variation in colony productivity in period 1985-2014. Snow storms are a key driver of Antarctic petrel breeding success, and potentially population dynamics. We also found state-dependent effects of snow storms and chicks in poor condition were more likely to die during a snow storm than chicks in good condition. This stresses the importance of considering interactions between individual heterogeneity and extreme weather events to understand both individual and population responses to climate change. PMID:25691959

  9. Demographic effects of extreme weather events: snow storms, breeding success, and population growth rate in a long-lived Antarctic seabird

    PubMed Central

    Descamps, Sébastien; Tarroux, Arnaud; Varpe, Øystein; Yoccoz, Nigel G; Tveraa, Torkild; Lorentsen, Svein-Håkon

    2015-01-01

    Weather extremes are one important element of ongoing climate change, but their impacts are poorly understood because they are, by definition, rare events. If the frequency and severity of extreme weather events increase, there is an urgent need to understand and predict the ecological consequences of such events. In this study, we aimed to quantify the effects of snow storms on nest survival in Antarctic petrels and assess whether snow storms are an important driver of annual breeding success and population growth rate. We used detailed data on daily individual nest survival in a year with frequent and heavy snow storms, and long term data on petrel productivity (i.e., number of chicks produced) at the colony level. Our results indicated that snow storms are an important determinant of nest survival and overall productivity. Snow storm events explained 30% of the daily nest survival within the 2011/2012 season and nearly 30% of the interannual variation in colony productivity in period 1985–2014. Snow storms are a key driver of Antarctic petrel breeding success, and potentially population dynamics. We also found state-dependent effects of snow storms and chicks in poor condition were more likely to die during a snow storm than chicks in good condition. This stresses the importance of considering interactions between individual heterogeneity and extreme weather events to understand both individual and population responses to climate change. PMID:25691959

  10. The Climate and its Impacts on deterioration and weathering rate of EI-Nadura Temple in El- Kharga Oasis, Western Desert of Egypt.

    NASA Astrophysics Data System (ADS)

    Ismael, Hossam

    2015-04-01

    Undoubtedly, El-Kharga Oasis monumental sites are considered an important part of our world's cultural heritage in the South Western Desert of Egypt. These sites are scattered on the floor of the oasis representing ancient civilizations. The Roman stone monuments in Kharga represent cultural heritage of an outstanding universal value. Such those monuments have suffered weathering deterioration. There are various elements which affect the weathering process of stone monuments: climate conditions, shapes of cultural heritages, exposed time periods, terrains, and vegetation around them, etc. Among these, climate conditions are the most significant factor affecting the deterioration of Archeological sites in Egypt. El- Kharga Oasis belongs administratively to the New Valley Governorate. It is located in the southern part of the western desert of Egypt, lies between latitudes 22°30'14" and 26°00'00" N, and between 30°27'00" and 30°47'00" E. The area of El Kharga Oasis covers about 7500 square kilometers. Pilot studies were carried out on the EI-Nadura Temple, composed of sandstones originating from the great sand sea. The major objective of this study is to monitor and measure the weathering features and the weathering rate affecting the building stones forming El-Nadora Roman building rocks in cubic cm. To achieve these aims, the present study used analysis of climatic data such as annual and seasonal solar radiation, Monthly average number of hours of sunshine, maximum and minimum air temperatures, wind speed, which have obtained from actual field measurements and data Meteorological Authority of El-Kharga station for the period 1977 to 2010 (33 years), and from the period 1941-2050 (110 years) as a long term of temperature data. Several samples were collected and examined by polarizing microscopy (PLM), X-ray diffraction analysis (XRD) and scanning electron microscopy equipped with an energy dispersive X-ray analysis system (SEM-EDX). The results were in

  11. Soil Organic Carbon Loss: An Overlooked Factor in the Carbon Sequestration Potential of Enhanced Mineral Weathering

    NASA Astrophysics Data System (ADS)

    Dietzen, Christiana; Harrison, Robert

    2016-04-01

    Weathering of silicate minerals regulates the global carbon cycle on geologic timescales. Several authors have proposed that applying finely ground silicate minerals to soils, where organic acids would enhance the rate of weathering, could increase carbon uptake and mitigate anthropogenic CO2 emissions. Silicate minerals such as olivine could replace lime, which is commonly used to remediate soil acidification, thereby sequestering CO2 while achieving the same increase in soil pH. However, the effect of adding this material on soil organic matter, the largest terrestrial pool of carbon, has yet to be considered. Microbial biomass and respiration have been observed to increase with decreasing acidity, but it is unclear how long the effect lasts. If the addition of silicate minerals promotes the loss of soil organic carbon through decomposition, it could significantly reduce the efficiency of this process or even create a net carbon source. However, it is possible that this initial flush of microbial activity may be compensated for by additional organic matter inputs to soil pools due to increases in plant productivity under less acidic conditions. This study aimed to examine the effects of olivine amendments on soil CO2 flux. A liming treatment representative of typical agricultural practices was also included for comparison. Samples from two highly acidic soils were split into groups amended with olivine or lime and a control group. These samples were incubated at 22°C and constant soil moisture in jars with airtight septa lids. Gas samples were extracted periodically over the course of 2 months and change in headspace CO2 concentration was determined. The effects of enhanced mineral weathering on soil organic matter have yet to be addressed by those promoting this method of carbon sequestration. This project provides the first data on the potential effects of enhanced mineral weathering in the soil environment on soil organic carbon pools.

  12. Subarctic weathering of mineral wastes provides a sink for atmospheric CO(2).

    PubMed

    Wilson, Siobhan A; Dipple, Gregory M; Power, Ian M; Barker, Shaun L L; Fallon, Stewart J; Southam, Gordon

    2011-09-15

    The mineral waste from some mines has the capacity to trap and store CO(2) within secondary carbonate minerals via the process of silicate weathering. Nesquehonite [MgCO(3)·3H(2)O] forms by weathering of Mg-silicate minerals in kimberlitic mine tailings at the Diavik Diamond Mine, Northwest Territories, Canada. Less abundant Na- and Ca-carbonate minerals precipitate from sewage treatment effluent deposited in the tailings storage facility. Radiocarbon and stable carbon and oxygen isotopes are used to assess the ability of mine tailings to trap and store modern CO(2) within these minerals in the arid, subarctic climate at Diavik. Stable isotopic data cannot always uniquely identify the source of carbon stored within minerals in this setting; however, radiocarbon isotopic data provide a reliable quantitative estimate for sequestration of modern carbon. At least 89% of the carbon trapped within secondary carbonate minerals at Diavik is derived from a modern source, either by direct uptake of atmospheric CO(2) or indirect uptake though the biosphere. Silicate weathering at Diavik is trapping 102-114 g C/m(2)/y within nesquehonite, which corresponds to a 2 orders of magnitude increase over the background rate of CO(2) uptake predicted from arctic and subarctic river catchment data. PMID:21854037

  13. Chemical weathering fluxes from volcanic islands and the importance of groundwater: The Hawaiian example

    NASA Astrophysics Data System (ADS)

    Schopka, Herdis Helga; Derry, Louis A.

    2012-07-01

    We investigated the products and rates of chemical weathering on the Hawaiian Islands, sampling streams on Kaua'i and both streams and groundwater wells on the island of Hawai'i. Dissolved silica was used to investigate the flowpaths of water drained into streams. We found that flowpaths exert a major control on the observed chemical weathering rates. A strong link exists between the degree of landscape dissection and flowpaths of water through the landscape, with streams in undissected landscapes receiving water mainly from surface runoff and streams in highly dissected landscapes receiving a considerable fraction of their water from groundwater (springs and/or seepage). Total alkalinity in Hawaiian streams and groundwater is produced exclusively by silicate chemical weathering. We find that fluxes of total alkalinity (often called "CO2 consumption rate" in the geochemical literature), from the islands are lower than those observed in basaltic regions elsewhere. Groundwater is, overall, the major transport vector for products of chemical weathering from the Hawaiian Islands. On the youngest and largest island, submarine groundwater discharge (SGD) transports more than an order of magnitude more solutes to the ocean than surface water and on the youngest part of the youngest island, SGD is the only link between the terrestrial weathering system and the ocean. These results suggest that groundwater, and particularly SGD, needs to be included in geochemical weathering budgets of volcanic islands.

  14. Chemical weathering in a tropical watershed, Luquillo Mountains, Puerto Rico: I. Long-term versus short-term weathering fluxes

    USGS Publications Warehouse

    White, A.F.; Blum, A.E.; Schulz, M.S.; Vivit, D.V.; Stonestrom, D.A.; Larsen, M.; Murphy, S.F.; Eberl, D.

    1998-01-01

    The pristine Rio Icacos watershed in the Luquillo Mountains in eastern Puerto Rico has the fastest documented weathering rate of silicate rocks on the Earth's surface. A regolith propagation rate of 58 m Ma-1 calculated from iso-volumetric saprolite formation from quartz diorite, is comparable to the estimated denudation rate (25-50 Ma-1) but is an order of magnitude faster than the global average weathering rate (6 Ma-1). Weathering occurs in two distinct environments; plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith. These environments produce distinctly different water chemistries, with K, Mg, and Si increasing linearly with depth in saprolite porewaters and with stream waters dominated by Ca, Na, and Si. Such differences are atypical of less intense weathering in temperate watersheds. Porewater chemistry in the shallow regolith is controlled by closed-system recycling of inorganic nutrients such as K. Long-term elemental fluxes through the regolith (e.g., Si = 1.7 ?? 10-8 moles m-2 s-1) are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface (200 Ma). Mass losses attributed to solute fluxes are determined using a step-wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water. Pressure heads decrease with depth in the shallow regolith (-2.03 m H2O m-1), indicating that both increasing capillary tension and graviometric potential control porewater infiltration. Interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr-1 at average field moisture saturation which is comparable with LiBr tracer tests and with base discharge from the watershed. Short term weathering fluxes calculated from solute chemistries and infiltration rates (e.g., Si = 1.4 ?? 10-8 moles m-2 s-1) are compared to watershed

  15. Reply to the comments on [open quotes]Weathering, plants, and the long-term carbon cycle[close quotes

    SciTech Connect

    Cochran, M.F.; Berner, R.A. )

    1993-05-01

    Some lichens can and do promote the weathering of their substrates. The authors' sole interest for purposes of carbon-cycle modeling is the degree of that enhancement for calcium and magnesium silicates relative to both abiotic chemical weathering due to water-rock interaction and the weathering that occurs beneath higher plants. The work by Jackson and Keller (1970) had offered the most dramatic quantitative, empirical evidence for weathering-rate enhancement by a primitive terrestrial organism; thus, reassessment of their conclusions is of considerable importance. In analyzing their samples, the authors used the technique of back-scattered electron imaging. Their results showed that the ferrihydrite-rich gels created by Stereocaulon vulcani were formed from wind-supplied dust, volcanic ash, and detrital rock fragments, not the lichen's immediate substrate.

  16. Stream geochemistry, chemical weathering and CO 2 consumption potential of andesitic terrains, Dominica, Lesser Antilles

    NASA Astrophysics Data System (ADS)

    Goldsmith, Steven T.; Carey, Anne E.; Johnson, Brent M.; Welch, Susan A.; Lyons, W. Berry; McDowell, William H.; Pigott, Jeffrey S.

    2010-01-01

    Recent studies of chemical weathering of andesitic-dacitic material on high-standing islands (HSIs) have shown these terrains have some of the highest observed rates of chemical weathering and associated CO 2 consumption yet reported. However, the paucity of stream gauge data in many of these terrains has limited determination of chemical weathering product fluxes. In July 2006 and March 2008, stream water samples were collected and manual stream gauging was performed in watersheds throughout the volcanic island of Dominica in the Lesser Antilles. Distinct wet and dry season solute concentrations reveal the importance of seasonal variations on the weathering signal. A cluster analysis of the stream geochemical data shows the importance of parent material age on the overall delivery of solutes. Observed Ca:Na, HCO 3:Na and Mg:Na ratios suggest crystallinity of the parent material may also play an important role in determining weathering fluxes. From total dissolved solids concentrations and mean annual discharge calculations we calculate chemical weathering yields of (6-106 t km -2 a -1), which are similar to those previously determined for basalt terrains. Silicate fluxes (3.1-55.4 t km -2 a -1) and associated CO 2 consumption (190-1575 × 10 3 mol km -2 a -1) determined from our study are among the highest determined to date. The calculated chemical fluxes from our study confirm the weathering potential of andesitic-dacitic terrains and that additional studies of these terrains are warranted.

  17. Silicate Stardust in Meteorites

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2004-06-01

    One of the most exciting discoveries in cosmochemistry during the past 15 years is the presence of presolar grains in meteorites. They are identified by the unusual abundances of isotopes of oxygen, silicon, and other elements. Presolar grains, also called stardust, are exotic compounds such as diamond, graphite, aluminum oxide, and silicon carbide. Why are there no silicates? Spectroscopic observations of young stars show that silicates are abundant. This means that silicates are abundant in molecular clouds like the one in which the solar system formed. Cosmochemists wondered why do we not find silicates in the most primitive extraterrestrial materials: interplanetary dust particles (IDPs) and primitive chondrites. These materials are the least altered since they formed and if any preserved presolar silicate grains, IDPs and chondrites would. Were they all destroyed as the solar system formed? Or was it that we were looking for stardust in all the wrong places? As we reported previously [see PSRD article A New Type of Stardust], Scott Messenger and colleagues have found silicates in IDPs. Now, researchers report finding presolar silicate grains in primitive chondritic meteorites. Ann Nguyen and Ernst Zinner (Washington University in St. Louis) and Kazuhide Nagashima and Hisayoshi Yurimoto (Tokyo Institute of Technology), with Alexander Krot (University of Hawaii) used advanced instrumentation to image the isotopic compositions of small regions of the Acfer 094 carbonaceous chondrite and found several silicate grains with isotopically anomalous oxygen isotopes, a clear indicator of presolar origin. Nagashima and his colleagues also investigated the primitive CR2 carbonaceous chondrite Northwest Africa 530, finding presolar grains in it as well. The grains will shed (star)light on the histories of the stars in which they formed. The relative abundances of presolar silicates in different types of meteorites will help cosmochemists understand the processes of heating

  18. Continental flood basalt weathering as a trigger for Neoproterozoic Snowball Earth

    NASA Astrophysics Data System (ADS)

    Cox, Grant M.; Halverson, Galen P.; Stevenson, Ross K.; Vokaty, Michelle; Poirier, André; Kunzmann, Marcus; Li, Zheng-Xiang; Denyszyn, Steven W.; Strauss, Justin V.; Macdonald, Francis A.

    2016-07-01

    Atmospheric CO2 levels and global climate are regulated on geological timescales by the silicate weathering feedback. However, this thermostat has failed multiple times in Earth's history, most spectacularly during the Cryogenian (c. 720-635 Ma) Snowball Earth episodes. The unique middle Neoproterozoic paleogeography of a rifting, low-latitude, supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo. Under these primed conditions, the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation. Weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios (δ13 C) of Neoproterozoic seawater due to their elevated P contents. In order to test these hypotheses, we have compiled new and previously published Neoproterozoic Nd isotope data from mudstones in northern Rodinia (North America, Australia, Svalbard, and South China) and Sr isotope data from carbonate rocks. The Nd isotope data are used to model the mafic detrital input into sedimentary basins in northern Rodinia. The results reveal a dominant contribution from continental flood basalt weathering during the ca. 130 m.y. preceding the onset of Cryogenian glaciation, followed by a precipitous decline afterwards. These data are mirrored by the Sr isotope record, which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early-middle Neoproterozoic ocean, including a pulse of unradiogenic Sr input into the oceans just prior to the onset of Cyrogenian glaciation. Hence, our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average δ13 C of seawater in the Neoproterozoic and to the initiation of the first (Sturtian) Snowball Earth.

  19. Weather Instruments.

    ERIC Educational Resources Information Center

    Brantley, L. Reed, Sr.; Demanche, Edna L.; Klemm, E. Barbara; Kyselka, Will; Phillips, Edwin A.; Pottenger, Francis M.; Yamamoto, Karen N.; Young, Donald B.

    This booklet presents some activities to measure various weather phenomena. Directions for constructing a weather station are included. Instruments including rain gauges, thermometers, wind vanes, wind speed devices, humidity devices, barometers, atmospheric observations, a dustfall jar, sticky-tape can, detection of gases in the air, and pH of…

  20. Wacky Weather

    ERIC Educational Resources Information Center

    Sabarre, Amy; Gulino, Jacqueline

    2013-01-01

    What do a leaf blower, water hose, fan, and ice cubes have in common? Ask the students who participated in an integrative science, technology, engineering, and mathematics (I-STEM) education unit, "Wacky Weather," and they will tell say "fun and severe weather"--words one might not have expected! The purpose of the unit…

  1. Space Weather

    NASA Technical Reports Server (NTRS)

    Gallagher, Dennis L.

    2010-01-01

    This video provides a narrated exploration of the history and affects of space weather. It includes information the earth's magnetic field, solar radiation, magnetic storms, and how solar winds affect electronics on earth, with specific information on how space weather affects space exploration in the future.

  2. MSATT Workshop on Chemical Weathering on Mars

    NASA Technical Reports Server (NTRS)

    Burns, Roger (Editor); Banin, Amos (Editor)

    1992-01-01

    The topics covered with respect to chemical weathering on Mars include the following: Mars soil, mineralogy, spectroscopic analysis, clays, silicates, oxidation, iron oxides, water, chemical reactions, geochemistry, minerals, Mars atmosphere, atmospheric chemistry, salts, planetary evolution, volcanology, Mars volcanoes, regolith, surface reactions, Mars soil analogs, carbonates, meteorites, and reactivity.

  3. Enhanced Weathering Strategies for Stabilizing Climate and Averting Ocean Acidification - Supplementary Information

    NASA Technical Reports Server (NTRS)

    Taylor, Lyla L.; Quirk, Joe; Thorley, Rachel M. S.; Kharecha, Pushker A.; Hansen, James; Ridgwell, Andy; Lomas, Mark R.; Banwart, Steve A.; Beerling, David J.

    2015-01-01

    Chemical breakdown of rocks, weathering, is an important but very slow part of the carbon cycle that ultimately leads to CO2 being locked up in carbonates on the ocean floor. Artificial acceleration of this carbon sink via distribution of pulverized silicate rocks across terrestrial landscapes may help offset anthropogenic CO2 emissions. We show that idealized enhanced weathering scenarios over less than a third of tropical land could cause significant drawdown of atmospheric CO2 and ameliorate ocean acidification by 2100. Global carbon cycle modelling driven by ensemble Representative Concentration Pathway (RCP) projections of twenty-first-century climate change (RCP8.5, business-as-usual; RCP4.5, medium-level mitigation) indicates that enhanced weathering could lower atmospheric CO2 by 30-300 ppm by 2100, depending mainly on silicate rock application rate (1 kg or 5 kg m(exp. -2) yr (exp -1)) and composition. At the higher application rate, end-of-century ocean acidification is reversed under RCP4.5 and reduced by about two-thirds under RCP8.5. Additionally, surface ocean aragonite saturation state, a key control on coral calcification rates, is maintained above 3.5 throughout the low latitudes, thereby helping maintain the viability of tropical coral reef ecosystems. However, we highlight major issues of cost, social acceptability, and potential unanticipated consequences that will limit utilization and emphasize the need for urgent efforts to phase down fossil fuel emissions.

  4. Modelling 3D Chemical Weathering Evolution Using Dissolving and Moving Clasts in a Landscape Evolution Model

    NASA Astrophysics Data System (ADS)

    Carretier, S.; Martinez, J.; Martinod, P.; Reich, M.; Godderis, Y.

    2014-12-01

    During mountain uplift, fresh silicate rocks are exhumed and broken into small pieces, potentially increasing their chemical weathering rate and thus the consumption of atmospheric CO2. This process remains debated because although erosion provides fresh rocks, it may also decrease their residence time near Earth's surface where clasts weather. Several recent publications also emphasized the key role of forelands in the weathering of clasts exported from the mountains by erosion. Predicting the chemical outflux of mountains requires to account for the chemical evolution of these rocks from their source to outlet. Powerful chemical models based on diffusion-advection of species between rocks and water have been developed at pedon scale, and recently at hillslope scale. In order to track the weathered material, we have developed a different approach based on the introduction into a 3D landscape evolution model (CIDRE) of dissolving discrete spherical clasts that move downslope. In CIDRE, local erosion and deposition depend on slope and water discharge which adapt dynamically during the topographical evolution. On a cell, bedrock is converted to soil at a rate depending on soil thickness. Clasts are initially spread at specified depths. They have a specified initial size and mineralogical composition. Once they enter the soil, they begins to dissolve at a rate depending on their minerals, temperature and exposed area, which decreases the clast size. Clasts move downstream according to probabilities depending on the ratio between the calculated local deposition and erosion fluxes. Chemical outflux is calculated for each clast during its life. At pedon scale, the model predicts chemical depleted fractions close to that obtained with advection-diffusion models and in agreement with measurements. An integrated chemical flux is estimated for the whole landscape from the clast dissolution rates. This flux reaches a stable solution using a suitable number of initial clasts

  5. Erosion rates and weathering history of rock surfaces associated with Aboriginal rock art engravings (petroglyphs) on Burrup Peninsula, Western Australia, from cosmogenic nuclide measurements

    NASA Astrophysics Data System (ADS)

    Pillans, Brad; Fifield, L. Keith

    2013-06-01

    The Burrup Peninsula and surrounding Dampier Archipelago, in Western Australia, contain the world's largest known gallery of rock art engravings (petroglyphs), estimated to number up to 1 million images. The peninsula is also the site of major industrial development and there are concerns that industrial emissions may adversely affect the stability and longevity of the rock art. We have studied the natural processes and rates of weathering and erosion, including the effects of fire, that affect the stability of rock surfaces and hence the longevity of the rock art, using cosmogenic nuclides. The concentration of 10Be in quartz yields erosion rates in the range 0.15-0.48 mm/1000 years on horizontal rock surfaces and 0.34-2.30 mm/1000 years on vertical rock faces. The former, largely caused by mm-scale surface flaking, are amongst the lowest erosion rates measured by cosmogenic nuclides anywhere in the world. The latter are inferred to represent a combination of mm-scale flaking and very rare centimetre- to metre-scale block falls, controlled by failure along joint planes. Such low erosion rates result from a combination of resistant rocks, low relief and low rainfall, favouring long-term preservation of the petroglyphs - long enough to encompass the known period of human settlement in Australia.

  6. Calcium silicate insulation structure

    DOEpatents

    Kollie, Thomas G.; Lauf, Robert J.

    1995-01-01

    An insulative structure including a powder-filled evacuated casing utilizes a quantity of finely divided synthetic calcium silicate having a relatively high surface area. The resultant structure-provides superior thermal insulating characteristics over a broad temperature range and is particularly well-suited as a panel for a refrigerator or freezer or the insulative barrier for a cooler or a insulated bottle.

  7. Calibration and evaluation of the Canadian Forest Fire Weather Index (FWI) System for improved wildland fire danger rating in the United Kingdom

    NASA Astrophysics Data System (ADS)

    de Jong, Mark C.; Wooster, Martin J.; Kitchen, Karl; Manley, Cathy; Gazzard, Rob; McCall, Frank F.

    2016-05-01

    Wildfires in the United Kingdom (UK) pose a threat to people, infrastructure and the natural environment. During periods of particularly fire-prone weather, wildfires can occur simultaneously across large areas, placing considerable stress upon the resources of fire and rescue services. Fire danger rating systems (FDRSs) attempt to anticipate periods of heightened fire risk, primarily for early-warning and preparedness purposes. The UK FDRS, termed the Met Office Fire Severity Index (MOFSI), is based on the Fire Weather Index (FWI) component of the Canadian Forest FWI System. The MOFSI currently provides daily operational mapping of landscape fire danger across England and Wales using a simple thresholding of the final FWI component of the Canadian FWI System. However, it is known that the system has scope for improvement. Here we explore a climatology of the six FWI System components across the UK (i.e. extending to Scotland and Northern Ireland), calculated from daily 2km × 2km gridded numerical weather prediction data and supplemented by long-term meteorological station observations. We used this climatology to develop a percentile-based calibration of the FWI System, optimised for UK conditions. We find this approach to be well justified, as the values of the "raw" uncalibrated FWI components corresponding to a very "extreme" (99th percentile) fire danger situation vary by more than an order of magnitude across the country. Therefore, a simple thresholding of the uncalibrated component values (as is currently applied in the MOFSI) may incur large errors of omission and commission with respect to the identification of periods of significantly elevated fire danger. We evaluate our approach to enhancing UK fire danger rating using records of wildfire occurrence and find that the Fine Fuel Moisture Code (FFMC), Initial Spread Index (ISI) and FWI components of the FWI System

  8. Olivine Weathering in Soil, and Its Effects on Growth and Nutrient Uptake in Ryegrass (Lolium perenne L.): A Pot Experiment

    PubMed Central

    ten Berge, Hein F. M.; van der Meer, Hugo G.; Steenhuizen, Johan W.; Goedhart, Paul W.; Knops, Pol; Verhagen, Jan

    2012-01-01

    Mineral carbonation of basic silicate minerals regulates atmospheric CO2 on geological time scales by locking up carbon. Mining and spreading onto the earth's surface of fast-weathering silicates, such as olivine, has been proposed to speed up this natural CO2 sequestration (‘enhanced weathering’). While agriculture may offer an existing infrastructure, weathering rate and impacts on soil and plant are largely unknown. Our objectives were to assess weathering of olivine in soil, and its effects on plant growth and nutrient uptake. In a pot experiment with perennial ryegrass (Lolium perenne L.), weathering during 32 weeks was inferred from bioavailability of magnesium (Mg) in soil and plant. Olivine doses were equivalent to 1630 (OLIV1), 8150, 40700 and 204000 (OLIV4) kg ha−1. Alternatively, the soluble Mg salt kieserite was applied for reference. Olivine increased plant growth (+15.6%) and plant K concentration (+16.5%) in OLIV4. At all doses, olivine increased bioavailability of Mg and Ni in soil, as well as uptake of Mg, Si and Ni in plants. Olivine suppressed Ca uptake. Weathering estimated from a Mg balance was equivalent to 240 kg ha−1 (14.8% of dose, OLIV1) to 2240 kg ha−1 (1.1%, OLIV4). This corresponds to gross CO2 sequestration of 290 to 2690 kg ha−1 (29 103 to 269 103 kg km−2.) Alternatively, weathering estimated from similarity with kieserite treatments ranged from 13% to 58% for OLIV1. The Olsen model for olivine carbonation predicted 4.0% to 9.0% weathering for our case, independent of olivine dose. Our % values observed at high doses were smaller than this, suggesting negative feedbacks in soil. Yet, weathering appears fast enough to support the ‘enhanced weathering’ concept. In agriculture, olivine doses must remain within limits to avoid imbalances in plant nutrition, notably at low Ca availability; and to avoid Ni accumulation in soil and crop. PMID:22912685

  9. Weatherizing America

    ScienceCinema

    Stewart, Zachary; Bergeron, T.J.; Barth, Dale; Qualis, Xavier; Sewall, Travis; Fransen, Richard; Gill, Tony;

    2013-05-29

    As Recovery Act money arrives to expand home weatherization programs across the country, Zachary Stewart of Phoenix, Ariz., and others have found an exciting opportunity not only to start working again, but also to find a calling.

  10. Weatherizing America

    SciTech Connect

    Stewart, Zachary; Bergeron, T.J.; Barth, Dale; Qualis, Xavier; Sewall, Travis; Fransen, Richard; Gill, Tony

    2009-01-01

    As Recovery Act money arrives to expand home weatherization programs across the country, Zachary Stewart of Phoenix, Ariz., and others have found an exciting opportunity not only to start working again, but also to find a calling.