Distribution Of Calcium Carbonate Research Articles

Coupled effect of PP fiber, PVA fiber and bacteria on self-healing efficiency of early-age cracks in concrete

Both bacteria and fiber can promote self-healing of cracks in concrete by accelerating calcium carbonate precipitation. Calcium carbonate in bacterial concrete grows from section surfaces of cracks, which might be altered after incorporating fibers. Therefore, this paper investigated coupled effect of PP fiber, PVA fiber and bacteria on self-healing efficiency of concrete. Optical density of bacteria cultivated in medium containing fiber was measured by using multifunction microplate reader, results showed that PP fiber and PVA fiber resulted in decrease of bacteria concentration. In addition, calcium carbonate induced by bacteria was synthesized in solution with fiber and characterized by using X-ray Diffraction, FTIR and particle size analyzer. Results revealed that the polymorphs of calcium carbonates were all calcite, while calcite generated in solution with PVA fiber showed lager particle size. In bacterial fiber reinforced concrete, crack width of 300–500 μm was obtained and autogenous healing performance was evaluated. The results showed that although repair ratio of crack area for specimens with bacteria and fiber was slightly lower than that with bacteria only, water tightness and flexural strength regain ratio were improved evidently. By measuring the amount of calcium ions in repair medium and observing calcium carbonate distribution in the cracks, it could be concluded that PP fiber and PVA fiber were conductive to calcium leaching and calcium ions utilization. Deposition was attached on surfaces of fibers and can even be observed on PVA fibers inside of cracks, which was due to effect of polarity groups and cell structure of polyvinyl alcohol fiber on calcium carbonate nucleation. Therefore, the study suggests that coupled effect of PP fiber, PVA fiber and bacteria has potential to enable excellent self-healing performance in concrete.

Elemental concentration and potential ecological risk assessment of reef associated surface sediments of Appa Island, Gulf of Mannar Biosphere Reserve, Southeast coast of India

Thirty three surface sediments were collected for the present study to assess the elemental concentration and its associated ecological risk in the reef associated surface sediments, Appa Island, Gulf of Mannar Biosphere Reserve, South east coast of India. The distribution of calcium carbonate in the reef sediments is controlled by coral debris and shell fragments whereas the Organic matter (OM) content are chiefly derived from mangroves and sea grasses. The circulation of trace elements and Fe, Mn are controlled by the fluvial process and re-suspended sediments. The concentration of Pb was primarily controlled by migration of pollutants through long shore sediment transport process. The main source of Pb in the study area is from coal incinerating power plants and coal handling operations from harbors.

Distribution of calcium carbonate in the process of concrete self-healing

The complete deposition distribution process of calcium carbonate is summarized in three directions of cracks. Distribution of calcium carbonate in the self-healing process of microbial concrete is studied in detail, with the help of a variety of analytical techniques. The results show that carbonate deposits along the x-axis direction of the cracks. The farther from the crack surfaces of concrete matrix in x-axis direction, the more the content of the substrate, the less content of calcium carbonate. Gradual accumulation of calcium carbonate along the y-axis direction is like building a house with bricks. Different repair points are gradually connected, and ultimately the whole of cracks are completely filled. In the z-axis direction, calcium deposits on the surface of fracture direction, when the crack is filled on the surface, because the internal crack hypoxia in the depths of cracks hardly produces calcium carbonate.

Features of the content of carbonates in the ordinary chernozem improved by forest under plantings of false acacia (Robinia pseudoacacia L.)

Carbonate neoplasms are the characteristic feature of the black soil profile. The study of morphological and micromorphological characteristics and chemical composition gives an idea of the black soil genesis and serves as the diagnostic feature of classification units of them. The study of migration carbonate in the chernozem are of great scientific and practical interest (Afanasyeva, 1996). Nowadays the issues of migration carbonates, as well as the extent of the manifestation of this process in the soil profile need further researching, which is important as carbonates has one of the main role in basic soil processes, in particular, they affect the concentration and activity of calcium ions in the soil solution, the composition of the soil absorbing complex and pH in the soil solution. Carbonate neoplasms contribute to the formation of strong coagulation structures, which increases soil fertility and harvest agricultural crops, provides resistance against the wind, prevents reduction of the upper fertile soil layer, increases mobility of some chemical elements and improves such physical characteristics of soil as density, permeability and porosity (Goncharova, 1983). The aim of our work was to study the content of calcium carbonate in the soil profile of the test section 201–L under of the acacia plantations crops of forest ecosystems and to determine of their distribution in the soil genetic horizons. According to the aim of our work of we has the following tasks: to give a general characterization of carbonates of calcium in Chernozem usual, to perform sampling of the genetic horizons of the soil profile of test section 201–L, to determine the content of carbonates by conventional gravimetric methods; to study the features of the content of carbonates in soil profiles of test section 201–L; to conduct statistical processing of the obtained data; to formulate conclusions of the performed research. Soil samples were selected according to the standard technique in genetic horizons of the soil profile on three times (Fedorets, 2009). Determination of the percentage content of carbonates in the soil was performed by the gravimetric method, which is based on weight loss of soil due to discharge of CO2 during the destruction of carbonates with acid. It should be noted that the method can be applied in the case of the carbonates content up to 70 % (Travleev et al., 2009). The average coefficient of variation of carbonates of calcium content in genetic horizons of the soil profile is 77.5 %. This is quite a high rate, so as General it is considered that if the value of the coefficient of variation is less than 33 %, the result is considered homogeneous if more than 33 %, it is inhomogeneous. Based on this observation, we conclude that carbonate calcium has inhomogeneous redistribution of genetic horizons of test section 201–L. Regarding the reliability of the obtained data, we can see that the standard error calculations for each of the horizons does not exceed 0,34, which in turn confirms the accuracy of the our data. According to our calculations the lowest content of calcium carbonate is 1.47 % in the first horizon, and biggest – 16,07 % in the genetic horizon Ph (70–90 cm). These results are extending the current understanding of the processes of formation and distribution of calcium carbonate in the genetic horizons of the soil profile of the Chernozem ordinary. The data of percentage of calcium carbonate may be used in the solution of the question of the genesis, evolution and classification of soils, the obtained data can serve as the basis of the research the conditions of pedogenesis under the influence of natural climatic fluctuations and anthropogenic factors.

Modelling the abundance of soil calcium carbonate across Australia using geochemical survey data and environmental predictors

Soil calcium carbonate is a key component of the regolith, particularly in arid and semi-arid regions. It influences soil properties, is an important terrestrial carbon store, and is used in mineral exploration. Previous national overviews of soil carbonate distribution have been compiled from regional soil, regolith or geological maps with varying degrees of confidence and consistency. Here we develop a decision tree approach based on a piecewise linear regression model to map soil calcium carbonate abundance at the continental scale. The model is based on relationships established from 1311 field sites sampled across Australia at two depths (0–10 and ~60–80cm) and 49 national environmental predictor datasets reflecting fundamental soil formation processes (e.g., climate, parent material, relief).The resulting map of soil calcium carbonate distribution is based on the median results of twenty model runs generated by randomly selecting 90% training and 10% validation splits of the input data. Results present an average coefficient of determination (R2) of 0.5 on the validation dataset. The predictors used in the modelling are consistent with our understanding of the controls on the sources (inputs), formation, and preservation of soil calcium carbonate across Australian landscapes. The model produces a continuous, internally consistent, quantitative prediction of soil calcium carbonate abundance in surficial regolith at a resolution of 90m with associated uncertainty estimates. This type of analysis provides a framework for better understanding environmental controls on regolith processes and has the potential to also be used to predict other soil geochemical properties. Furthermore, the methodology has utility globally where geochemical survey data are available.

3D spatial distribution of the calcium carbonate caused by carbonation of cement paste

Carbonation of cement-based materials is one area of concern for the durability of concrete structures. The calcium carbonate caused by carbonation is an important indicator of carbonation degrees. The present paper, using 3D tomography data, proposes a nondestructive method to characterize the 3D spatial distributions of calcium carbonate. It allows monitoring of 3D carbonation evolutions. The evolution of the calcium carbonate distributions in a specimen of cement paste with different carbonation degrees is given using the current method. The results are compared with the average quantity of calcium carbonate determined by thermal analysis. From the sharp edge of the calcium carbonate distribution, we conclude that the accelerated carbonation in this experimental condition is a diffusion controlling process.

Crystallization and mechanical properties of isotactic polypropylene/calcium carbonate nanocomposites with a stratified distribution of calcium carbonate

ABSTRACTIsotactic polypropylene (iPP)/calcium carbonate (CaCO3) nanocomposites with a stratified distribution of CaCO3 were prepared by two‐step molding. The iPP and CaCO3 nanoparticles were first mixed by a batch mixer and then compressed into thin layers. Thin iPP/CaCO3 layers alternating with thin neat iPP layers were finally compressed together to form the stratified samples. The transcrystals were observed in the stratified samples by polarized optical microscopy and scanning electron microscopy. The transcrystals grew from the surfaces of the filled layers and occupied most of the space in the neat iPP layers. The β‐form crystals were found in the stratified samples with thick transcrystalline layers, whereas the thickness of the transcrystalline layer was dependent on the content of CaCO3 nanoparticles and the cooling rate of the processing. The relative crystallinity index of the conventional samples first increased and then decreased with the content of CaCO3 nanoparticles. However, the relative crystallinity index of the stratified samples deceased slightly with the content of CaCO3 nanoparticles because of the stratified distribution of the CaCO3 nanoparticles. The stratified samples, except for the samples with high β‐form contents, became more brittle than the conventional samples because of the transcrystal formation in the iPP layers. The stratified samples with high β‐form contents showed much better mechanical properties than the conventional samples. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39632.

Spatial distribution of calcite and amorphous calcium carbonate in the cuticle of the terrestrial crustaceans Porcellio scaber and Armadillidium vulgare

The crustacean cuticle is an interesting model to study the properties of mineralized bio-composites. The cuticle consists of an organic matrix composed of chitin-protein fibres associated with various amounts of crystalline and amorphous calcium carbonate. It is thought that in isopods the relative amounts of these mineral polymorphs depend on its function and the habitat of the animal. In addition to the composition, the distribution of the various components should affect the properties of the cuticle. However, the spatial distribution of calcium carbonate polymorphs within the crustacean cuticle is unknown. Therefore, we analyzed the mineralized cuticles of the terrestrial isopods Armadillidium vulgare and Porcellio scaber using scanning electron-microscopy, electron probe microanalysis and confocal mu-Raman spectroscopic imaging. We show for the first time that the mineral phases are arranged in distinct layers. Calcite is restricted to the outer layer of the cuticle that corresponds to the exocuticle. Amorphous calcium carbonate is located within the endocuticle that lies below the exocuticle. Within both layers mineral is arranged in rows of granules with diameters of about 20 nm. The results suggest functional implications of mineral distribution that accord to the moulting and escape behaviour of the animals.

Granule fraction inhomogeneity of calcium carbonate/sorbitol in roller compacted granules

The granule fraction inhomogeneity of roller compacted granules was examined on mixtures of three different morphologic forms of calcium carbonate and three particle sizes of sorbitol. The granule fraction inhomogeneity was determined by the distribution of the calcium carbonate in each of the 10 size fractions between 0 and 2000 μm and by calculating the demixing potential. Significant inhomogeneous occurrence of calcium carbonate in the size fractions was demonstrated, depending mostly on the particles sizes of sorbitol but also on the morphological forms of calcium carbonate. The heterogeneous distribution of calcium carbonate was related to the decrease in compactibility of roller compacted granules in comparison to the ungranulated materials. This phenomenon was explained by a mechanism where fracturing of the ribbon during granulation occurred at the weakest interparticulate bonds (the calcium carbonate: calcium carbonate bonds) and consequently exposed the weakest areas of bond formation on the surface of the granules. Accordingly, the non-uniform allocation of the interparticulate attractive forces in a tablet would cause a lowering of the compactibility. Furthermore, the ability of the powder to agglomerate in the roller compactor was demonstrated to be related to the ability of the powder to be compacted into a tablet, thus the most compactable calcium carbonate and the smallest sized sorbitol improved the homogeneity by decreasing the demixing potential.

Distribution of calcium carbonate and silicone elastomer in a flame retardant system based on ethylene–acrylate copolymer, chalk and silicone elastomer and its effect on flame retardant properties

AbstractA combination of microscopy studies (SEM, ESEM/EDX, and TEM/EDX) is proven to be useful in locating chalk particles and silicone elastomer in a flame retardant system based on ethylene–acrylate copolymer, chalk, and silicone elastomer. The dispersion of the two additives was also obtained. The chalk particles were visually observed (at a certain degree of magnification), and the silicone elastomer was detected using characteristic X‐ray mapping and line scans. The analysis provided a good contrast between chalk particles and silicone elastomer in the surrounding polymer matrix. It is shown that dispersion of the additives depends on the mixing conditions, where tougher mixing conditions improve dispersion. A discussion is given on how dispersion correlates with the flame retardant properties of this system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2085–2095, 2006

Evaluation of the self-absorption of 14C beta-rays in gel-suspension samples by Monte Carlo simulation

In order to investigate the self-absorption of the β-rays from 14C in a gel-suspension sample, the Monte Carlo code, simulating the sequence of stages occurring in the sample, has been developed. The trajectory of the electron was calculated by the continuous slowing down approximation and the multiple Coulomb scattering theory. The effects of the self-absorption, strong quenching and particle size distribution of calcium carbonate on the output counting efficiency and the shape of the energy spectrum were evaluated.

Reinforcement of natural rubber latex film by ultrafine calcium carbonate

AbstractUsing ultrafine calcium carbonate to reinforce natural rubber latex film, the effect of its content on latex properties such as surface tension, viscosity, mechanical stability, and heat stability and the physical properties of latex film before and after aging such as tear strength, modulus, and tensile strength were investigated. The results showed that the surface tension of natural rubber latex reinforced by ultrafine calcium carbonate only changed slightly; when the content of calcium carbonate was less than 20%, the change of viscosity was not obvious, but when the content was greater than 20%, the viscosity significantly lowered. Ultrafine calcium carbonate could effectively improve the tear strength, tensile strength, and modulus of the natural rubber latex film. The modulus increased with the increment of the calcium carbonate. When the content of calcium carbonate was less than 15%, the tear strength and tensile strength increased with the increments of calcium carbonate, but when the content was greater than 15%, the above‐mentioned properties decreased with the increment of calcium carbonate. By comprehensive consideration, the best reinforcing effect was obtained at a content of 15% ultrafine calcium carbonate. The particle diameters of calcium carbonate and their distribution in the calcium carbonate emulsion and in the rubber film were analyzed with SEM and a laser particle size tester, which showed that the distribution of calcium carbonate in the latex film was even and that it could effectively reinforce natural rubber latex film. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 982–985, 2003

Significance of pteropods in deciphering the late Quaternary sea-level history along the southwestern Indian shelf

The paper evaluates the usefulness of pteropods in palaeobathymetric synthesis along the southwestern continental shelf of India. Core samples collected from the shelf off north Kerala (SW coast of India) were studied for faunal assemblages (pteropods and foraminifers), calcium carbonate contents and lithological characteristics. A fundamental precept for considering any organism as a bathometer is that it should be highly sensitive to changing water depths. To ascertain this, the bathymetric distribution patterns of modern pteropods as well as planktonic and benthic foraminifers were recorded in core-top samples. The results reveal that certain pteropod species (Limacina inflata, Creseis acicula, Creseis virgula, and Creseis chierchiae) are highly depth sensitive. The response of these species to depth changes was assessed in terms of the L. inflata and Creseis spp. abundance ratio. A model for the relationship between water depths and the L. inflata/Creseis spp. ratio is proposed for the southwestern shelf of India. Variations of benthic/planktonic foraminifers (BF/PF) and pteropods/planktonic foraminifers (Pt/PF) in the modern sediments were also found to be depth controlled. Two sediment cores, representing the last 36,000 and 23,000 years, were collected to investigate past sea-level changes. These cores comprised two distinct lithological units, the upper unit corresponding to the Holocene, and the lower unit to the last glacial period. The L. inflata/Creseis spp. model was successfully applied to the fossil record for reconstructing the palaeobathymetry of the shelf study locations. Down-core variations in the BF/PF and Pt/PF ratios support these inferred sea-level changes. Major periods of sea-level oscillations were also found to have a strong influence on the calcium carbonate distribution. For both core sites, the palaeobathymetric curves reflect consistency in terms of changing sea level. The results suggest that the sea level stood around 100 m below the present mean sea level during the last glacial maximum. A rapid rise in sea level was documented between 15 and 10 ka B.P. The sea-level rise has been slower since 7 ka B.P.

Bulk calcite size fraction distribution and Sr/Ca composition for deep-sea sediments at selected age horizons

Strontium/calcium (Sr/Ca) ratios in bulk and foraminiferal calcite have been used to constrain the history of Sr/Ca in the oceans and to evaluate calcite diagenetic alteration. However bulk Sr/Ca records also may be influenced by differences in Sr uptake and/or in the diagenetic susceptibility of different calcium carbonate sedimentary components. We present data on the sediment size fraction and calcium carbonate distribution in bulk samples, Sr/Ca in a range of sedimentary size components, and Sr/Ca in bulk sediments. Ocean Drilling Program samples from sites on Ontong Java Plateau and Ceara Rise (in the western equatorial Pacific and Atlantic, respectively) and from sites in the eastern equatorial Pacific were selected to represent progressive stages in the diagenetic pathway from the sea floor through a range of burial depths equivalent to sediment ages of ∼5.6, ∼9.4, and ∼37.1 Ma. Samples were subdivided by size to produce a unique data set of size-specific Sr/Ca ratios. Fine fraction (<45 μm) Sr/Ca ratios are higher than those of all corresponding coarse fractions, indicating that fine nannofossil-dominated calcite has a Sr partition coefficient 1.3–1.5 times greater than that of coarse foraminifera-dominated calcite. Thus, absolute values of bulk Sr/Ca in contemporaneous samples reflect, in part, the ratio of fine to coarse calcite sedimentary components. Sr/Ca values in fine and coarse components also behave differently in their response to pre-burial dissolution and to recrystallization at depth. Coarse size components are sensitive to bottom water carbonate ion undersaturation, and they lose original Sr/Ca differences among contemporary samples over ∼10 my. In contrast, fine components recrystallize faster in more deeply buried samples. Interpretation of the historical Sr/Ca record is complicated by post-depositional diagenetic artifacts, and thus our data do not provide clear evidence of specific temporal changes in oceanic Sr/Ca ratios over the past 10 million years. This paper represents the first systematic attempt to examine trends in calcite Sr/Ca as a function of sediment size fraction and age.

Segmented, curved faults: the example of the Balduini Thrust Zone, Northern Apennines, Italy

Meso- and micro-structural studies of the well-exposed Balduini Thrust (Northern Apennines, Italy) indicate that the structure formed during a single folding event, contemporaneous with diagenesis, and is a zone comprising curved, en-échelon fault segments. The geometry of each segment is arcuate with pure compression at one end and right-lateral displacement along the other. The thrust developed during the Tortonian within a single mud-rich formation, the Upper Eocene–Upper Oligocene Scaglia Cinerea, but rheological variations within the unit led to differences in deformation style; zones of scaly fabric are discontinuous and calcite veins vary in abundance. The mesoscopic morphology of the veins and the distribution of calcium carbonate along the formation indicate variations in the distribution of fluids at the time of deformation, which affected both diagenesis and the structural response of the material. Systematic variations of mechanical properties within the thickness of the Scaglia Cinerea Formation account for the curvature of the propagating thrust. Together with the heterogeneity of the stress field, the confinement of the arcing thrust to this single, weak unit lead to repeated initiation of new fractures and hence segmentation of the propagating thrust. Geometric analysis of the calcite veins and their microscopic characters suggests that hydrofracturing was involved, with the Scaglia Cinerea Formation experiencing high fluid pressure followed by rapid water expulsion. The Balduini Thrust is therefore an example of a fluid-driven, refracted compound shear zone. The analysis presented here provides insights into the three-dimensional arrangement of fault zones and fluid-migration patterns during regional faulting.

Dynamics of Atlantic water advection to the Norwegian-Greenland Sea — a time-slice record of carbonate distribution in the last 300 ky

Short-term variability in volume and configuration of Atlantic water advection to the Norwegian-Greenland Sea (NGS) has recently been identified as a new and significant element for northern hemisphere glacial/interglacial climatic fluctuations. The amount of salt, heat and moisture transferred by Atlantic waters to the high Arctic effectively influences Northern Hemisphere climates and is critical for the overall oceanic turnover rate. In particular, determining the extent and duration of Atlantic Water intrusions in the NGS is essential because of: (1) its effect on the climate of the Nordic continents; and (2) its trigger function on the stability of the ice sheets with (a) weak inflows of Atlantic Water during glacials, promoting an increase in ice volume by moisture supply to polar areas; and (b) positive feed-back mechanisms of Atlantic water intrusions during ice sheet decay. In this study, the dynamics of surface water mass regimes in the NGS have been reconstructed for the past 300 ky by means of time-slice compilations of calcium carbonate distribution and micropaleontologic proxies. In addition, carbonate preservation records are used to quantify deep water ventilation and production rates. In contrast to the CLIMAP scenario, but in accordance with many recent publications, results of this study indicate that Atlantic water advection was also a common feature during most glacial periods but varied strongly in volume and configuration. Significant modes recognized are: (1) the full interglacial mode with a wide inflow of warm Atlantic waters covering a broad area in the eastern sector of the NGS and extending far north, combined with excellent carbonate preservation and very efficient deep water formation (stages 1 and 5.5.1); (2) the moderate interglacial mode with a rather small extension of Atlantic waters along a narrow corridor in the southeastern sector of the NGS but still very efficient deep water exchange (stages 9, isotopic events 7.5, 7.3–7.1, 5.3 and 5.1); (3) pronounced cool phases during interglacials with only a very narrow inflow of Atlantic waters into the southeastern NGS, while the coastal areas off Norway were still affected by iceberg drift (substages 7.4 and 5.2), carbonate preservation records indicate ongoing deep water formation in the NGS; (4) the normal glacial mode characterized by a variable but persistent inflow of cool-temperate Atlantic water (lower stage 8, repetitively during stages 6, 4, 3.1 and 2), carbonate preservation records indicate ongoing deep water formation in the NGS; (5) short glacial and deglacial periods characterized by episodic high inputs of IRD, evidenced by a wide coverage of diamicton deposition and strong carbonate dissolution (e.g. episodically within stages 10, 6 and 2, the 6 5 , 4 3 and 2 1 transitions). Some of these NGS diamicton layers correlate with Heinrich layers in the North Atlantic, but generally NGS diamicton layers occur more frequently than Heinrich layers. The role of Atlantic water influence during these events remains enigmatic but Atlantic water influence is frequently found just above and below these sections. A scenario with rapid ice sheet disintegration induced by Atlantic water advection (via increase of the thermal regime along the ice margin, possibly triggered by small-scale sea level rise) might be envisaged. More obviously, the short-term cessation of deep-water formation in the NGS, as evidenced by the dissolution spikes, may be correlated with contemporaneous ventilation minima in the North Atlantic.

Phisico-Chemical Investigation on a 32-Year-Old Concrete Marine Struture

A 32-year-old concrete marine structure was phisico-chemically investigated, in order toevaluate its durability.The influence of sulfate ion on concrete must be synthetically determined by ettringite, Friedel's salt and monosulfate. A great difference was found in the distribution of calcium carbonate and calcium hydroxide between concrete exposed to sea air and concrete exposed to sea water.

Ultrastructural analysis of the integument during the moult cycle in Ligia italica (Crustacea, Isopoda).

The formation of the cuticle was investigated during moulting of the isopod crustacean Ligia italica. The intermoult cuticle is a four-layered lamellar structure composed of chitin-protein fibrils and mineralized in its upper half. The distribution of calcium carbonate in cuticle during moult cycle was determined by cytochemical methods and X-ray microanalysis, Epi-and exocuticle are secreted during premoult. Calcium is resorbed from the old cuticle and accumulates in the ecdysal gap as calcium granules. Endocuticle is secreted after moult when the mineralization of exocuticle starts. The shape and ultrastructure of epithelial cells change during cuticle secretion and mineralization. Mitochondria, bundles of filaments, calcium granules and large amounts of glycogen accumulate in the apical cytoplasm of cells in premoult animals.

An atlas of the distribution of calcium carbonate in sediments of the deep sea

Historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater CO3= concentration to reveal regional variations in the calcite lysocline. The most obvious mode of variability of the calcite lysocline is the thickness of the lysocline (defined here as the difference in overlying water carbonate saturation, ΔCO3=, between high and low calcite sediments) with a thicker lysocline in the Atlantic than in the Pacific. I attribute this variation to differences in the delivery rate of terriginous material. A recent model for the lower glacial atmospheric pCO2 proposed to change the relationship between the depth of the lysocline and the ΔCO3= of the water column by changing the rain rate ratio of organic carbon to calcite production (the “rain ratio model”: Archer and Maier‐Reimer, 1994). I search the data set for analogs to the proposed glacial world, by looking for a link between the regional climate at the sea surface and the depth of the lysocline below. The ΔCO3= at the carbonate compensation depth (CCD) in the tropics appears to be 10–20 μmol kg−1 ΔCO3= more undersaturated than in high latitudes, but this is smaller than the ∼40 μmol kg−1 shift required by the model. In addition, the general resemblance of the glacial lysocline to the present day requires that the proposed shift in ΔCO3= at the CCD be globally uniform rather than locally variable, as climate forcing would probably generate. I conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time, such as a change in ocean Si content, if it is to explain the entire pCO2 decrease observed in the glacial atmosphere. Finally, I grid the sedimentary data to estimate that the inventory CaCO3 which is available to neutralize fossil fuel CO2 is approximately 1600 Gt carbon, a quantity which may be exceeded by fossil fuel release in the next several centuries.

Long-term effects of irrigation and date-palm production on Torripsamments, Saudi Arabia

Specimens of soil profiles from four date-palm orchards under irrigation for periods ranging from 10 to 230 years, were compared with one another and with a profile from the nearly barren desert. Soil properties were recorded through field and laboratory observations. Distribution and mass of plant roots in each layer to a depth of 135 cm were also measured, as was the quality of the irrigation water used in each orchard. The data indicate changes in several characteristics of the soils after they were put under irrigation. Some differences were also observed among the profiles in the orchards in relation to their ages. Differences were found in the amounts and distribution of calcium carbonate, the levels of organic matter, the values of strength and bulk density, and possibly in the amounts and distribution of the clay fraction. Total amounts of carbonates are several times larger in profiles from the older orchards than in the one from the desert. Most of that difference is in carbonates of claysize. The largest amounts of carbonates occur in the same layers as where the greatest mass of plant roots is found. Levels of organic matter are two to three times as high in the profiles in the orchards as in that in the desert, with the biggest difference between the barren profile and that in the orchard of 10 years old. Amounts of the clay fraction are greater in the profiles under irrigation, with a tendency for the amounts to increase with time. Greater amounts of clay are attributed chiefly to precipitation of carbonates in that fraction. The profiles in the orchards developed increasing strengths and decreasing bulk densities over time. Differences among the profiles thus indicate not only that pathways of genesis have been altered under irrigation but that some effects become evident in a short space of time and are gradually enhanced over longer periods.