Abstract
Fossil coral Acropora sp. samples with ages of between 1570 and 3780 yBP collected from Miyako Island, Okinawa, were analyzed for their boron content and boron isotopic composition. The boron content was 37.7 ppm-51.5 ppm, nearly falling within the range of boron content previously reported. The boron isotopic composition expressed as σ11B was+22.26%-+28.34%. These values lay within the range expected from the theoretical equilibrium constant (=1.0194) of the boron isotope exchange reaction between boric acid and borate anion in seawater. These results supported the claim that boron is mainly absorbed by corals in the form of borate anion.
