Effect Of pCO2 and temperature on the boron isotopic composition of the zooxanthellate coral Acropora sp.

Culture experiments were carried out with Acropora sp. (a branching scleractinian coral) in seawater at two PCO2 conditions (438 and 725 muatm) and two temperatures (25 and 28 degreesC) 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 muatm), the delta(11)B of the skeleton was 24.0 +/-0.2parts per thousand at 25 degreesC, and 23.9 0.3parts per thousand at 28 degreesC. The values of delta(11)B measured for corals cultured at higher PCO2 (725 muatm) were lower: 22.5 +/- 0.1parts per thousand, and 22.8 +/- 0.1parts per thousand at 25 and 28 degreesC, respectively. The delta(11)B 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.