The saturation state of the world's ocean with respect to (Ba,Sr)SO4 solid solutions

International audienceBarite is commonly found in suspended matter in ocean waters and in marine sediments. The calculation of the barite saturation index of the world's ocean waters has shown that the vast majority of the oceans are undersaturated with respect to pure barium sulfate, equilibrium being reached at a few locations like the Southern Ocean surface waters, deep waters of the Bay of Bengal or intermediate waters of the Pacific [Monnin, C., Jeandel, C., Cattaldo, T., Dehairs, F., 1999. The marine barite saturation state of the world's oceans. Mar. Chem.65 (3-4), 253 261.]. It is thus paradoxical to commonly find barite in a globally undersaturated ocean. Strontium is the most common impurity in natural barite. It is often suggested that the Ba content of ocean waters is controlled by equilibrium with Sr-substituted barite, and not with pure BaSO4. In order to address this problem, we have used the GEOSECS data (49 stations, 1404 data points) to calculate the saturation index of substituted barite in the world's ocean using Lippmann's description of thermodynamic equilibrium between a solid solution and an aqueous solution for the (Ba,Sr)SO4 system. Recent studies indicate that the (Ba,Sr)SO4 solid solution is most likely regular and continuous. The calculated saturation indices of the regular solid solution (with the interaction parameter A0 equal to 1.6) are closer to those of pure barite than those calculated for the ideal solid solution. Conclusions previously reached for the pure barite case are not changed: the saturation state of ocean waters with respect to a regular solid solution is very close to that of pure barite. Sr-substitution for Ba in barium sulfate does not bring barite at equilibrium. When equilibrium is reached, the degree of Sr substitution of Ba amounts to only a few mole percent of Sr. Equilibrium values of the Sr content of the solid solutions in the intermediate (0.2 0.8) range are found for ocean surface waters where the Ba/Sr ratio is low, but as these waters are undersaturated, such solids are not stable in the water column. This provides another reason for the bimodal distribution of (Ba,Sr)SO4 solid solutions in nature, on top of that induced by the large ratio of the end member solubility products. Equilibrium is found for cold waters (i.e. for temperatures below 5 °C) having a Ba content greater than about 70 nmol/kg. The distribution coefficient of Sr in barite can be calculated from the Ba and Sr concentrations of these samples and from the equilibrium Sr mole fraction of the solid solution obtained from Lippmann's diagram. It was found independent of pressure and it varies only slightly with the temperature of the sample. For the regular solid solution (with A0 = 1.6), it is: 10DBaSOBa(regular)=10mmxx=0.227t+3.753. This expression (which has been established for temperatures below 5 °C) can be used to directly calculate the composition of solid solutions at equilibrium with a given seawater sample, or conversely to know the Ba content of seawater at equilibrium with a given (Ba,Sr)SO4 solid solution

Temporal variability of lagoon–sea water exchange and seawater circulation through a Mediterranean barrier beach

The subterranean flow of water through sand barriers between coastal lagoons and the sea, driven by a positive hydraulic gradient, is a net new pathway for solute transfer to the sea. On the sea side of sand barriers, seawater circulation in the swash-zone generates a flux of recycled and new solutes. The significance and temporal variability of these vectors to the French Mediterranean Sea is unknown, despite lagoons constituting ~ 50% of the coastline. A one-dimensional 224Raex/223Ra reactive-transport model was used to quantify water flow between a coastal lagoon (La Palme) and the sea over a 6-month period. Horizontal flow between the lagoon and sea decreased from ~ 85 cm d−1 during May 2017 (0.3 m3 d−1 m−1 of shoreline) to ~ 20 cm d−1 in July and was negligible in the summer months thereafter due to a decreasing hydraulic gradient. Seawater circulation in the swash-zone varied from 10 to 52 cm d−1 (0.4–2.1 m3 d−1 m−1), driven by short-term changes in the prevailing wind and wave regimes. Both flow paths supply minor dissolved silica fluxes on the order of ~ 3–10 mmol Si d−1 m−1. Lagoon–sea water exchange supplies a net dissolved inorganic carbon (DIC) flux (320–1100 mmol C d−1 m−1) two orders of magnitude greater than seawater circulation and may impact coastal ocean acidification. The subterranean flow of water through sand barriers represents a significant source of new DIC, and potentially other solutes, to the Mediterranean Sea during high lagoon water-level periods and should be considered in seasonal element budgets

Analysis reuse exploiting taxonomical information and belief assignment in industrial problem solving

To take into account the experience feedback on solving complex problems in business is deemed as a way to improve the quality of products and processes. Only a few academic works, however, are concerned with the representation and the instrumentation of experience feedback systems. We propose, in this paper, a model of experiences and mechanisms to use these experiences. More specifically, we wish to encourage the reuse of already performed expert analysis to propose a priori analysis in the solving of a new problem. The proposal is based on a representation in the context of the experience of using a conceptual marker and an explicit representation of the analysis incorporating expert opinions and the fusion of these opinions. The experience feedback models and inference mechanisms are integrated in a commercial support tool for problem solving methodologies. The results obtained to this point have already led to the definition of the role of ‘‘Rex Manager’’ with principles of sustainable management for continuous improvement of industrial processes in companies

Barium and Carbon fluxes in the Canadian Arctic Archipelago

Seasonal and spatial variability of dissolved Barium (Ba) in Amundsen Gulf, southeastern Beaufort Sea, was monitored over a full year from September 2007 to September 2008. Dissolved Ba displays a nutrient-type behavior: the maximum water column concentration is located below the surface layer. Highest Ba concentrations are typically observed at river mouths, the lowest concentrations are found in water masses of Atlantic origin. Barium concentrations decrease eastward through the Canadian Arctic Archipelago. Barite (BaSO4) saturation is reached at the maximum concentrations of dissolved Ba in the subsurface layer, whereas the remaining water column is undersaturated. A three end-member mixing model comprising freshwater from sea-ice melt and rivers, as well as upper halocline water, was used to establish their relative contributions to the Ba concentrations in the upper water column of the Amundsen Gulf. Based on water column and riverine Ba contributions, we assess the depletion of dissolved Ba by formation and concomitant sinking of biologically bound Ba (bio-Ba), from which we derive an estimate of the carbon export production. In the upper 50 m of the water column of Amundsen Gulf, riverine Ba accounts for up to 15% of the available dissolved Ba inventory, of which up to 20% is depleted by bio-Ba formation and export. Since riverine inputs and Ba export occur concurrently, the seasonal variability of dissolved Ba in the upper water column is moderate. Assuming a fixed organic carbon to bio-Ba flux ratio, carbon export out of the surface layer is estimated at 1.8{plus minus}0.45 mol C m‑2 yr‑1. We propose a climatological carbon budget for the Amundsen Gulf

An ion interaction model for the volumetric properties of natural waters: Density of the solution and partial molal volumes of electrolytes to high concentrations at 25°C

International audienceLiterature density data for binary and common ion ternary solutions in the Na-K-Ca-Mg-Cl-SO 4 -HCO 3 -CO3-H 2 O system at 25°C have been analysed with Pitzer's ion interaction model, which provides an adequate representation of the experimental data for binary and common ion ternary solutions up to high concentration. This analysis yields Pitzer's interaction parameters for the apparent and partial molal volumes, which are the first derivatives with respect to pressure of the interaction parameters for the free energy. From this information, densities of natural waters as well as partial molal volumes of their solutes can be predicted with good accuracy, as shown by several comparisons of calculated and measured values. It is shown that , the excess partial molal volume of the salt MX , depends more on the type of salt than on the electrolyte itself and that it increases with the charges of the salt components. The influence of concentration and composition on the variation of activity coefficients with pressure and on the partial molal volumes of the salts is discussed, using as an example the partial molal volume of CaSO 4 (aq) in solutions of various compositions. The increase of , with ionic strength is very large but is not very different for a NaCl-dominated natural water like the Red Sea lower brine than for a simple NaCl solution. Although the variation of activity coefficients with pressure is usually ignored for moderate pressures, like those found in hydrothermal environments, the present example shows that it can be as large as 30% for a 2-2 salt for a pressure increase from 1 to 500 bars at high ionic strength

Thermodynamic properties of the Na-K-Ca-Ba-Cl-H2O system to 473.15K and solubility of barium chloride hydrates

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The influence of pressure on the activity coefficients of the solutes and on the solubility of minerals in the system Na-Ca-Cl-SO4-H2O to 200°C and 1 kbar

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Recherches sur les mécanismes du concrétionnement. Coefficients d'activité des ions, solubilité des sels et de la silice dans les pores de petite taille

Variation of salt or silica solubility as a function of water activity, capillarity pressure or pore size, is discussed as a probable origine of matter migration, concentration, and finally concretioning.La variation de la solubilité des sels et de la silice en fonction de l'activité de l'eau, de la pression capillaire ou de la taille des pores est considérée comme une cause probable de migration ou de concentration de matière. Le mécanisme du concrétionnement est discuté.Tardy Yves, Monnin Christophe. Recherches sur les mécanismes du concrétionnement. Coefficients d'activité des ions, solubilité des sels et de la silice dans les pores de petite taille. In: Bulletin de Minéralogie, volume 106, 3, 1983. pp. 321-328

The solubility of celestite and barite in electrolyte solutions and natural waters at 25°C

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Determination of the solubility products of sodium carbonate minerals and an application to trona deposition in Lake Magadi (Kenya)

International audienceThe ion-interaction model of PITZER (1973), is very effective in deriving stability relationships at high concentrations for the system Na - Cl - HCO 3 - CO 3 - OH - H 2 O . The solubility products of the main sodium carbonates have been calculated from solubility data between 5 and 50°C. The stability diagram in log p co2 -- temperature coordinates and the invariant points deduced from the newly determined data are in good agreement with the most recent measurements. These results are used to calculate the activities of the major dissolved species in Lake Magadi brines (Kenya). The thermodynamic treatment confirms the main conclusions reached earlier by Eugster (1970, 1980) mainly from field observations. Trona precipitation occurs at equilibrium while natron is likely to form when the temperature decreases below 25°C. After the salt deposition the CO 2 supply from the atmosphere is too slow to allow equilibrium between the atmosphere and the brines. In the next stages of evaporative concentration thermonatrite and halite precipitate. The deposition of the latter salts along with the observed HCO - 3 depletion suggest that fractional crystallization is likely to control trona deposition