Effect of pCO2 and temperature on the boron isotopic composition of the zooxanthellate coral Acropora sp.
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Culture experiments were carried out with Acropora sp. (a branching scleractinian coral) in seawater at two pCO2 conditions (438 and 725 µatm) and two temperatures (25 and 28 °C) in order to establish the pH and temperature dependence of the boron isotopic composition of the skeleton. A clear pCO2 effect, but no temperature effect, on the coral boron isotope composition is seen. For corals cultured at “normal pCO2” (438 µatm), the δ11B of the skeleton was 24.0±0.2‰ at 25 °C, and 23.9±0.3‰ at 28 °C. The values of δ11B measured for corals cultured at higher pCO2 (725 µatm) were lower: 22.5±0.1‰, and 22.8±0.1‰ at 25 and 28 °C, respectively. The δ11B of corals cultivated at both high and normal pCO2 conditions are consistent with a dominant pH control, and are very close to that calculated from theoretical considerations. Thus, the corals do not seem to significantly alter ambient seawater for calcification with respect to pH. Co-variation between boron and carbon isotope values is explored.
KeywordsCorals Skeleton δ11B Boron Culture Temperature pCO2
Thanks are due to H. Spero for the δ13C seawater analysis, to P. Joannot, T. Corrège, and G. Cabioch for providing an Acropora colony from New Caledonia. We are grateful to N. Leclercq for his help in coral culture, to N. Lebec for her help with mass spectrometry, and to B. Hönisch for valuable discussions. Thanks are also due to four anonymous referees and to A. Grottoli for their constructive comments. Partial support for this research was provided by the National Science Foundation grant #OCE 00-83061.
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