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dc.contributor.authorWynn, Peter M.en_NZ
dc.contributor.authorFairchild, Ian J.en_NZ
dc.contributor.authorBorsato, Andreaen_NZ
dc.contributor.authorSpoetl, Christophen_NZ
dc.contributor.authorHartland, Adamen_NZ
dc.contributor.authorBaker, Andyen_NZ
dc.contributor.authorFrisia, Silviaen_NZ
dc.contributor.authorBaldini, James U.L.en_NZ
dc.date.accessioned2018-05-22T02:11:34Z
dc.date.available2018-04-01en_NZ
dc.date.available2018-05-22T02:11:34Z
dc.date.issued2018en_NZ
dc.identifier.citationWynn, P. M., Fairchild, I. J., Borsato, A., Spoetl, C., Hartland, A., Baker, A., … Baldini, J. U. L. (2018). Sulphate partitioning into calcite: Experimental verification of pH control and application to seasonality in speleothems. Geochimica Et Cosmochimica Acta, 226, 69–83. https://doi.org/10.1016/j.gca.2018.01.020en
dc.identifier.issn0016-7037en_NZ
dc.identifier.urihttps://hdl.handle.net/10289/11853
dc.description.abstractCarbonate-associated sulphate (CAS) is a useful carrier of palaeoenvironmental information throughout the geologic record, particularly through its stable isotope composition. However, a paucity of experimental data restricts quantitative understanding of sulphate incorporation into carbonates, and consequently CAS concentrations and their diagenetic modifications are rarely interpreted. However, in the case of calcite speleothems, the remarkably high-resolution CAS records which are obtainable via modern microanalytical techniques represent a potentially invaluable source of palaeoenvironmental information. Here, we describe the results of controlled experiments of sulphate co-precipitation with calcite in freshwater solutions where pH, saturation state, and sulphate concentration were varied independently of each other. Solution pH is confirmed as the principal control on sulphate incorporation into calcite. The relative efficiency of incorporation was calculated as a partition coefficient Dₛₒ₄=(mSO₄/mCO₃)solid/(mSO₄/mCO₃)solution. High crystal growth rates (driven by either pH or saturation state) encouraged higher values of Dₛₒ₄ because of an increasing concentration of defect sites on crystal surfaces. At low growth rates, Dₛₒ₄ was reduced due to an inferred competition between sulphate and bicarbonate at the calcite surface. These experimental results are applied to understand the incorporation of sulphate into speleothem calcite. The experimentally determined pH-dependence suggests that strong seasonal variations in cave air PCO₂ could account for annual cycles in sulphate concentration observed in stalagmites. Our new experimentally determined values of Dₛₒ₄ were compared with Dₛₒ₄ values calculated from speleothem-drip water monitoring from two caves within the Austrian and Italian Alps. At Obir cave, Austria, Dₛₒ₄ (×10⁵) varies between 11.1 (winter) and 9.0 (summer) and the corresponding figures for Ernesto cave, Italy, are 15.4 (winter) and 14.9 (summer). These values approximate predicted Dₛₒ₄ values based on our chamber experiments containing both low (2 ppm) and high (20 ppm) sulphate concentrations. Our experimental values of Dₛₒ₄ obtained at crystal growth rates typical of stalagmites, closely match those observed in other cave sites from around the world. This validates the universality of the controls behind Dₛₒ₄ and will enhance the use of speleothem CAS as a palaeoenvironmental proxy.
dc.format.mimetypeapplication/pdf
dc.language.isoenen_NZ
dc.publisherElsevieren_NZ
dc.rights© 2018 The Authors. Published by Elsevier Ltd.This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
dc.subjectScience & Technologyen_NZ
dc.subjectPhysical Sciencesen_NZ
dc.subjectGeochemistry & Geophysicsen_NZ
dc.subjectCarbonate Associated Sulphateen_NZ
dc.subjectSpeleothemen_NZ
dc.subjectPartition Coefficienten_NZ
dc.subjectSulphateen_NZ
dc.subjectpHen_NZ
dc.subjectCAVE DRIPWATER CHEMISTRYen_NZ
dc.subjectGROTTA DI ERNESTOen_NZ
dc.subjectGROWTH-RATEen_NZ
dc.subjectSTALAGMITE GROWTHen_NZ
dc.subjectPALEOCLIMATE RECORDSen_NZ
dc.subjectSOUTHEASTERN ETHIOPIAen_NZ
dc.subjectHYDROLOGICAL CONTROLSen_NZ
dc.subjectCLIMATE CHANGESen_NZ
dc.subjectKARSTen_NZ
dc.subjectRECONSTRUCTIONen_NZ
dc.titleSulphate partitioning into calcite: Experimental verification of pH control and application to seasonality in speleothemsen_NZ
dc.typeJournal Article
dc.identifier.doi10.1016/j.gca.2018.01.020en_NZ
dc.relation.isPartOfGeochimica et Cosmochimica Actaen_NZ
pubs.begin-page69
pubs.elements-id219440
pubs.end-page83
pubs.publication-statusPublisheden_NZ
pubs.volume226en_NZ
dc.identifier.eissn1872-9533en_NZ


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