Ba/Ca of stylasterid coral skeletons records dissolved seawater barium concentrations
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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.
Kershaw , J , Stewart , J A , Strawson , I , de Carvalho Ferreira , M L , Robinson , L F , Hendry , K R , Samperiz , A , Burke , A , Rae , J W B , Day , R D , Etnoyer , P J , Williams , B & Häussermann , V 2023 , ' Ba/Ca of stylasterid coral skeletons records dissolved seawater barium concentrations ' , Chemical Geology , vol. 622 , 121355 . https://doi.org/10.1016/j.chemgeo.2023.121355
Copyright © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
DescriptionFunding: Funding for this work was provided by a NERC GW4+ Doctoral Training Partnership studentship (NE/S007504/1) awarded to J.K., an Antarctic Bursary awarded to J.A.S, and NERC grants awarded to L.F.R. (NE/S001743/1; NE/R005117/1; NE/N003861/1). Cruise DY081 was funded by European Research Council starting grant ICY-LAB (Grant Agreement 678371).
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