Seawater temperature proxies based on DSr, DMg, and DU from culture experiments using the branching coral Porites cylindrica

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 degrees 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) x T (degrees C) (r(2) = 0.59, p < 0.05); Mg/Ca (mmol/mol) = 1.973(+/- 0.302) + 0.1002 (+/- 0.0118) x T (degrees C) (r(2) = 0.67, p < 0.05); and U/Ca (mu mol/mol) = 1.488(+/- 0.0484) - 0.0212(+/- 0.00189) x T (degrees C) (r(2) = 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 D-U calibration. The calibration sensitivity of D-Sr, D-Mg, and D-U to seawater temperature change during the experiment was 0.64%/degrees C, 1.93%/degrees C, and 1.97%/degrees 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. (C) 2011 Elsevier Ltd. All rights reserved.