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Seawater temperature proxies based on DSr, DMg, and DU from culture experiments using the branching coral Porites cylindrica |
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| Authors: | Alrum Armid Ryuji Asami Mohammed Ali Sheikh Tomihiko Higuchi Ryuichi Shinjo |
| Institution: | a Graduate School of Engineering and Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan b Trans-disciplinary Research Organization for Subtropical Island Studies (TRO-SIS), University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan c Department of Chemistry, Faculty of Science, University of Haluoleo, Anduonohu, Kendari 93-232, Indonesia d Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan e Aqua Culture Okinawa Co., Urasoe, Okinawa 901-2131, Japan f Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan |
| Abstract: | In order to investigate the incorporation of Sr, Mg, and U into coral skeletons and its temperature dependency, we performed a culture experiment in which specimens of the branching coral (Porites cylindrica) were grown for 1 month at three seawater temperatures (22, 26, and 30 °C). The results of this study showed that the linear extension rate of P. cylindrica has little effect on the skeletal Sr/Ca, Mg/Ca, and U/Ca ratios. The following temperature equations were derived: Sr/Ca (mmol/mol) = 10.214(±0.229) − 0.0642(±0.00897) × T (°C) (r2 = 0.59, p < 0.05); Mg/Ca (mmol/mol) = 1.973(±0.302) + 0.1002(±0.0118) × T (°C) (r2 = 0.67, p < 0.05); and U/Ca (μmol/mol) = 1.488(±0.0484) − 0.0212(±0.00189) × T (°C) (r2 = 0.78, p < 0.05). We calculated the distribution coefficient (D) of Sr, Mg, and U relative to seawater temperature and compared the results with previous data from massive Porites corals. The seawater temperature proxies based on D calibrations of P. cylindrica established in this study are generally similar to those for massive Porites corals, despite a difference in the slope of DU calibration. The calibration sensitivity of DSr, DMg, and DU to seawater temperature change during the experiment was 0.64%/°C, 1.93%/°C, and 1.97%/°C, respectively. These results suggest that the skeletal Sr/Ca ratio (and possibly the Mg/Ca and/or U/Ca ratio) of the branching coral P. cylindrica can be used as a potential paleothermometer. |
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