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Minor and trace element incorporation into branching coral Acropora nobilis skeleton |
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| Authors: | Kotaro Shirai Tatsunori Kawashima Tsuyoshi Watanabe Naoto Takahata Yuji Sano |
| Institution: | a International Coastal Research Center, Ocean Research Institute, The University of Tokyo, 2-106-1, Akahama, Otsuchi, Iwate 028-11-2, Japan b Department of Natural History Sciences, Graduate School of Science, Hokkaido University, Japan c Institute of Geology and Paleontology, Graduate School of Science, Tohoku University, Japan d Center for Advanced Marine Research, Ocean Research Institute, The University of Tokyo, Japan |
| Abstract: | Chemical and isotopic compositions of the Acropora nobilis skeleton were analyzed at various spatial resolutions to investigate the mechanism by which elements are incorporated into the skeleton. Chemical and isotopic profiles along growth axes of axial and radial corallites did not show seasonal variation, with the exception of the δ18O profile of the axial corallite. Detailed observations of the skeletal structure revealed that the skeletal density increased with distance from the tip because secondarily precipitated aragonite (here called the “infilling” skeleton) filled pore spaces in the “framework” skeleton. Microscale element analyses revealed that main part of the infilling skeleton had lower Mg/Ca and higher Sr/Ca and U/Ca than the framework skeleton. At microscale, Sr/Ca and U/Ca were positively correlated with each other, and negatively correlated with Mg/Ca but only weakly. The results showed that the infilling skeleton differed significantly from the adjacent framework skeleton in terms of not only formation chronology but also chemical composition, and that the bulk composition was influenced by the infilling/framework skeletal ratio. In order to use the Acropora skeleton as a paleoclimate archive, the relationship between environmental factors and the chemical composition of each skeletal component needs to be established. |
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