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dc.contributor.authorBlättler, Clara L.
dc.contributor.authorHong, Wei-Li
dc.contributor.authorKirsimae, Kalle
dc.contributor.authorHiggins, John A.
dc.contributor.authorLepland, Aivo
dc.date.accessioned2021-04-20T09:04:07Z
dc.date.available2021-04-20T09:04:07Z
dc.date.issued2021-04-01
dc.description.abstractNatural calcium carbonate minerals express a range of calcium isotope fractionations, with the precipitated mineral typically enriched in the lighter isotopes of calcium relative to source fluids. Experimental and theoretical evidence shows a strong dependence on precipitation rate, although this relationship has not been well quantified over the range of precipitation rates observed in natural settings. Endmember cases show that average marine carbonate precipitation expresses a large fractionation ( values lower than seawater by approximately 1‰), while diagenetic carbonate phases assumed to have precipitated or recrystallized at very slow rates show negligible fractionation. The limited examples of quantified precipitation rates in natural settings with measurable, non-zero fractionation represents a barrier for applying mechanistic models of calcium isotope fractionation to geological applications. This study examines a methane seep system in the northern Barents Sea south of Svalbard where authigenic carbonate minerals are precipitating, driven by anaerobic oxidation of methane, and where the apparent calcium isotope fractionation factor and precipitation rate can be constrained by measuring properties of the pore fluids. Pore fluid profiles are analyzed in two shallow cores, and authigenic carbonate nodules are analyzed in one of these cores. The pore fluid profiles point to a transitional, non-steady state which approximates a closed system, where the elevation of pore fluid calcium isotope ratios through carbonate precipitation can be modeled as a Rayleigh distillation system. The apparent fractionation factors for 44Ca/40Ca ratios at these sites are  = 0.99985 and 0.9996, although the carbonate nodules suggest a different calcium isotope fractionation factor may have been expressed under past conditions. Precipitation rates at the two sites are estimated to be 1.4 and 3.5 μmol/m2/h, intermediate between those of typical laboratory experiments and the much slower rates of marine diagenesis. Trace element analyses of the nodules (Mg/Ca and Sr/Ca ratios) suggest that both precipitation rate and mineralogy affect nodule composition. These results provide new constraints for the relationship between precipitation rate and calcium isotope fractionation and can inform modeling efforts leading towards mechanistic understanding of calcium isotope fractionation and trace element distributions in carbonate minerals.en_US
dc.identifier.citationBlättler, Hong H, Kirsimae K, Higgins, Lepland A. Small calcium isotope fractionation at slow precipitation rates in methane seep authigenic carbonates. Geochimica et Cosmochimica Acta. 2021en_US
dc.identifier.cristinIDFRIDAID 1895817
dc.identifier.doi10.1016/j.gca.2021.01.001
dc.identifier.issn0016-7037
dc.identifier.issn1872-9533
dc.identifier.urihttps://hdl.handle.net/10037/20942
dc.language.isoengen_US
dc.publisherElsevieren_US
dc.relation.journalGeochimica et Cosmochimica Acta
dc.relation.projectIDinfo:eu-repo/grantAgreement/RCN/SFF/223259/Norway/Centre for Arctic Gas Hydrate, Environment and Climate/CAGE/en_US
dc.relation.projectIDinfo:eu-repo/grantAgreement/RCN/PETROMAKS2/255150/Norway/Norwegian margin fluid systems and methane- derived carbonate crusts - Recent scientific advances in service of petroleum exploration//en_US
dc.rights.accessRightsopenAccessen_US
dc.rights.holderCopyright 2021 The Author(s)en_US
dc.subjectVDP::Mathematics and natural science: 400::Chemistry: 440::Environmental chemistry, natural environmental chemistry: 446en_US
dc.subjectVDP::Matematikk og Naturvitenskap: 400::Kjemi: 440::Miljøkjemi, naturmiljøkjemi: 446en_US
dc.subjectVDP::Mathematics and natural science: 400::Geosciences: 450::Mineralogy, petrology, geochemistry: 462en_US
dc.subjectVDP::Matematikk og Naturvitenskap: 400::Geofag: 450::Mineralogi, petrologi, geokjemi: 462en_US
dc.titleSmall calcium isotope fractionation at slow precipitation rates in methane seep authigenic carbonatesen_US
dc.type.versionacceptedVersionen_US
dc.typeJournal articleen_US
dc.typeTidsskriftartikkelen_US
dc.typePeer revieweden_US


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