Ba/Ca of stylasterid coral skeletons records dissolved seawater barium concentrations

Kershaw, James, Stewart, Joseph A., Strawson, Ivo, de Carvalho Ferreira, Maria Luiza, Robinson, Laura F., Hendry, Katharine R., Samperiz Vizcaino, Ana ORCID: https://orcid.org/0000-0002-9553-1124, Burke, Andrea, Rae, James W.B., Day, Russell D., Etnoyer, Peter J., Williams, Branwen and Häussermann, Vreni 2023. Ba/Ca of stylasterid coral skeletons records dissolved seawater barium concentrations. Chemical Geology 622 , 121355. 10.1016/j.chemgeo.2023.121355

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Abstract

The concentration of dissolved barium in seawater ([Ba]SW) is influenced by both primary productivity and ocean circulation patterns. Reconstructing past subsurface [Ba]SW can therefore provide important information on processes which regulate global climate. Previous Ba/Ca measurements of scleractinian and bamboo deep-sea coral skeletons exhibit linear relationships with [Ba]SW, acting as archives for past Ba cycling. However, skeletal Ba/Ca ratios of the Stylasteridae – a group of widely distributed, azooxanthellate, hydrozoan coral – have not been previously studied. Here, we present Ba/Ca ratios of modern stylasterid (aragonitic, calcitic and mixed mineralogy) and azooxanthellate scleractinian skeletons, paired with published proximal hydrographic data. We find that [Ba]SW and sample mineralogy are the primary controls on stylasterid Ba/Ca, while seawater temperature exerts a weak secondary control. [Ba]SW also exerts a strong control on azooxanthellate scleractinian Ba/Ca. However, Ba-incorporation into scleractinian skeletons varies between locations and across depth gradients, and we find a more sensitive relationship between scleractinian Ba/Ca and [Ba]SW than previously reported. Paired Sr/Ca measurements suggest that this variability in scleractinian Ba/Ca may result from the influence of varying degrees of Rayleigh fractionation during calcification. We find that these processes exert a smaller influence on Ba-incorporation into stylasterid coral skeletons, a result consistent with other aspects of their skeletal geochemistry. Stylasterid Ba/Ca ratios are therefore a powerful, novel archive of past changes in [Ba]SW, particularly when measured in combination with temperature sensitive tracers such as Li/Mg or Sr/Ca. Indeed, with robust [Ba]SW and temperature proxies now established, stylasterids have the potential to be an important new archive for palaeoceanographic studies.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Publisher:	Elsevier
ISSN:	0009-2541
Date of First Compliant Deposit:	15 February 2023
Date of Acceptance:	29 January 2023
Last Modified:	05 May 2023 17:21
URI:	https://orca.cardiff.ac.uk/id/eprint/157045

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