Partitioning of Mg, Sr, Ba and U into a subaqueous calcite speleothem

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dc.contributor.authorDrysdale, RNen_AU
dc.contributor.authorZanchetta, Gen_AU
dc.contributor.authorBaneschi, Ien_AU
dc.contributor.authorGuidi, Men_AU
dc.contributor.authorIsola, Ien_AU
dc.contributor.authorCouchoud, Ien_AU
dc.contributor.authorPiccini, Len_AU
dc.contributor.authorGreig, Aen_AU
dc.contributor.authorWong, HKYen_AU
dc.contributor.authorWoodhead, JDen_AU
dc.contributor.authorRegattieri, Een_AU
dc.contributor.authorCorrick, Een_AU
dc.contributor.authorPaul, Ben_AU
dc.contributor.authorSpötl, Cen_AU
dc.contributor.authorDenson, Een_AU
dc.contributor.authorGordon, Jen_AU
dc.contributor.authorJaillet, Sen_AU
dc.contributor.authorDux, Fen_AU
dc.contributor.authorHellstrom, JCen_AU
dc.date.accessioned2022-09-02T03:41:04Zen_AU
dc.date.available2022-09-02T03:41:04Zen_AU
dc.date.issued2019-11-01en_AU
dc.date.statistics2022-08-30en_AU
dc.descriptionThe pre-print version of the manuscript is made available under the Elsevier user license.en_AU
dc.description.abstractThe trace-element geochemistry of speleothems is becoming increasingly used for reconstructing palaeoclimate, with a particular emphasis on elements whose concentrations vary according to hydrological conditions at the cave site (e.g. Mg, Sr, Ba and U). An important step in interpreting trace-element abundances is understanding the underlying processes of their incorporation. This includes quantifying the fractionation between the solution and speleothem carbonate via partition coefficients (where the partitioning (D) of element X (DX) is the molar ratio [X/Ca] in the calcite divided by the molar ratio [X/Ca] in the parent water) and evaluating the degree of spatial variability across time-constant speleothem layers. Previous studies of how these elements are incorporated into speleothems have focused primarily on stalagmites and their source waters in natural cave settings, or have used synthetic solutions under cave-analogue laboratory conditions to produce similar dripstones. However, dripstones are not the only speleothem types capable of yielding useful palaeoclimate information. In this study, we investigate the incorporation of Mg, Sr, Ba and U into a subaqueous calcite speleothem (CD3) growing in a natural cave pool in Italy. Pool-water measurements extending back 15 years reveal a remarkably stable geochemical environment owing to the deep cave setting, enabling the calculation of precise solution [X/Ca]. We determine the trace element variability of ‘modern’ subaqueous calcite from a drill core taken through CD3 to derive DMg, DSr, DBa and DU then compare these with published cave, cave-analogue and seawater-analogue studies. The DMg for CD3 is anomalously high (0.042 ± 0.002) compared to previous estimates at similar temperatures (∼8 °C). The DSr (0.100 ± 0.007) is similar to previously reported values, but data from this study as well as those from Tremaine and Froelich (2013) and Day and Henderson (2013) suggest that [Na/Sr] might play an important role in Sr incorporation through the potential for Na to outcompete Sr for calcite non-lattice sites. DBa in CD3 (0.086 ± 0.008) is similar to values derived by Day and Henderson (2013) under cave-analogue conditions, whilst DU (0.013 ± 0.002) is almost an order of magnitude lower, possibly due to the unusually slow speleothem growth rates (<1 μm a−1), which could expose the crystal surfaces to leaching of uranyl carbonate. Finally, laser-ablation ICP-MS analysis of the upper 7 μm of CD3, regarded as ‘modern’ for the purposes of this study, reveals considerable heterogeneity, particularly for Sr, Ba and U, which is potentially indicative of compositional zoning. This reinforces the need to conduct 2D mapping and/or multiple laser passes to capture the range of time-equivalent elemental variations prior to palaeoclimate interpretation. © 2019 Elsevier Ltden_AU
dc.description.sponsorshipThis research was supported by funding from the Australian Research Council (Discovery Project number DP160102969, awarded to RD, GZ, ER and JW; Laureate Fellowship FL160100028 awarded to JW; and Future Fellowship FT130100801 awarded to JH.en_AU
dc.identifier.citationDrysdale, R. N., Zanchetta, G., Baneschi, I., Guidi, M., Isola, I., Couchoud, I., Piccini, L., Greig, A., Wong, H., Woodhead, J. D., Regattieri, E., Corrick, E., Paul, B., Spötl, C., Denson, E., Gordon, J., Jaillet, S., Dux, F., & Hellstrom, J. C. (2019). Partitioning of Mg, Sr, Ba and U into a subaqueous calcite speleothem. Geochimica et Cosmochimica Acta, 264, 67-91. doi:10.1016/j.gca.2019.08.001en_AU
dc.identifier.issn0016-7037en_AU
dc.identifier.journaltitleGeochimica et Cosmochimica Actaen_AU
dc.identifier.pagination67-91en_AU
dc.identifier.urihttps://doi.org/10.1016/j.gca.2019.08.001en_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/13717en_AU
dc.identifier.volume264en_AU
dc.language.isoenen_AU
dc.publisherElsevieren_AU
dc.subjectMagnesiumen_AU
dc.subjectStrontiumen_AU
dc.subjectBariumen_AU
dc.subjectUraniumen_AU
dc.subjectCalciteen_AU
dc.subjectPaleoclimatologyen_AU
dc.subjectGeochemistryen_AU
dc.subjectCavesen_AU
dc.subjectTrace amountsen_AU
dc.titlePartitioning of Mg, Sr, Ba and U into a subaqueous calcite speleothemen_AU
dc.typeJournal Articleen_AU
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