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Sr/Ca and Mg/Ca vital effects correlated with skeletal architecture in a scleractinian deep-sea coral and the role of Rayleigh fractionation

Gagnon, Alexander C. and Adkins, Jess F. and Fernandez, Diego P. and Robinson, Laura F. (2007) Sr/Ca and Mg/Ca vital effects correlated with skeletal architecture in a scleractinian deep-sea coral and the role of Rayleigh fractionation. Earth and Planetary Science Letters, 261 (1-2). pp. 280-295. ISSN 0012-821X.

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Deep-sea corals are a new tool in paleoceanography with the potential to provide century long records of deep ocean change at sub-decadal resolution. Complicating the reconstruction of past deep-sea temperatures, Mg/Ca and Sr/Ca paleothermometers in corals are also influenced by non-environmental factors, termed vital effects. To determine the magnitude, pattern and mechanism of vital effects we measure detailed collocated Sr/Ca and Mg/Ca ratios, using a combination of micromilling and isotope-dilution ICP-MS across skeletal features in recent samples of Desmophyllum dianthus, a scleractinian coral that grows in the near constant environment of the deep-sea. Sr/Ca variability across skeletal features is less than 5% (2σ relative standard deviation) and variability of Sr/Ca within the optically dense central band, composed of small and irregular aragonite crystals, is significantly less than the surrounding skeleton. The mean Sr/Ca of the central band, 10.6 ± 0.1 mmol/mol (2σ standard error), and that of the surrounding skeleton, 10.58±0.09 mmol/mol, are statistically similar, and agree well with the inorganic aragonite Sr/Ca-temperature relationship at the temperature of coral growth. In the central band, Mg/Ca is greater than 3 mmol/mol, more than twice that of the surrounding skeleton, a general result observed in the relative Mg/Ca ratios of D. dianthus collected from separate oceanographic locations. This large vital effect corresponds to a ∼ 10 °C signal, when calibrated via surface coral Mg/Ca-temperature relationships, and has the potential to complicate paleoreconstructions. Outside the central band, Mg/Ca ratios increase with decreasing Sr/Ca. We explain the correlated behavior of Mg/Ca and Sr/Ca outside the central band by Rayleigh fractionation from a closed pool, an explanation that has been proposed elsewhere, but which is tested in this study by a simple and general relationship. We constrain the initial solution and effective partition coefficients for a Rayleigh process consistent with our accurate Metal/Ca measurements. A process other than Rayleigh fractionation influences Mg in the central band and our data constrain a number of possible mechanisms for the precipitation of this aragonite. Understanding the process affecting tracer behavior during coral biomineralization can help us better interpret paleoproxies in biogenic carbonates and lead to an improved deep-sea paleothermometer.

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Adkins, Jess F.0000-0002-3174-5190
Additional Information:© 2007 Elsevier B.V. Received 29 November 2006; received in revised form 15 May 2007; accepted 3 July 2007. Available online 17 July 2007. Editor: H. Elderfield. Special thanks to Dr. Stephen Cairns and The Smithsonian Institution National Museum of Natural History for allowing the analysis of the deep-sea coral specimens in this study. A.C.G. would like to thank D. Rees of the California Institute of Technology for continued scientific advice and guidance. Comments by Glen Gaetani and Anne Cohen as well as two anonymous reviewers contributed to improving this manuscript.
Subject Keywords:biomineralization; paleo-oceanography; deep-sea coral; Mg/Ca; Sr/Ca; thermometry
Issue or Number:1-2
Record Number:CaltechAUTHORS:20120828-091252247
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Official Citation:Alexander C. Gagnon, Jess F. Adkins, Diego P. Fernandez, Laura F. Robinson, Sr/Ca and Mg/Ca vital effects correlated with skeletal architecture in a scleractinian deep-sea coral and the role of Rayleigh fractionation, Earth and Planetary Science Letters, Volume 261, Issues 1–2, 15 September 2007, Pages 280-295, ISSN 0012-821X, 10.1016/j.epsl.2007.07.013. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33595
Deposited By: Ruth Sustaita
Deposited On:28 Aug 2012 17:11
Last Modified:24 Feb 2020 10:30

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