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

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Monnin, Christophe, Cividini, Damien
• Other Authors: Laboratoire des Mécanismes et Transfert en Géologie (LMTG), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Hydrologie et de Géochimie de Strasbourg (LHyGeS), Ecole et Observatoire des Sciences de la Terre (EOST), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Nationale du Génie de l'Eau et de l'Environnement de Strasbourg (ENGEES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2006
• Subjects: [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; Southern Ocean; Pacific
• Online Access: https://hal.science/hal-00662992; https://hal.science/hal-00662992/document; https://hal.science/hal-00662992/file/1-s2.0-S0016703706001682-main.pdf; https://doi.org/10.1016/J.GCA.2006.04.002

International audience Barite 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 ...