We have measured cosmogenic 10Be, 26Al and 36Cl, and the indigenous concentrations of the stable elements, Be, Al and Cl in 120 - 200 kyr old corals from Barbados and Puerto Rico. Cosmogenic nuclide concentrations lie in the range 104 to 108 atoms/g. A comparison of the measured nuclide concentrations with those expected to be produced in the corals by nuclear interactions of energetic cosmic radiation shows that (i) the radionuclides, 26Al and 36Cl are derived from in-situ cosmic ray interactions in the corals after their formation, but that (ii) the radionuclide, 10Be owes its provenance in the coralline lattice primarily due to incorporation of dissolved beryllium in sea-water in the lattice structure of the corals.
We discuss production rates and potential uses of cosmogenic radionuclides in corals, and the implications of the measurements reported here on the concentration of the cosmogenic radionuclides, 10Be, 26Al and 36Cl. We show that the latter 2 radionuclides serve as gauges of coral terrace erosion rates, whereas the cosmogenic 10Be is suitable for determining the ages of old corals, of ages exceeding a few million years, up to ~ 10 my. The erosion rates of the corals range from 0.7 to 5 x 10-3 cm/year, corresponding to an appreciable surface loss after aerial exposure: 1-3 m since the last interglacial and ~ 8 m since the penultimate interglacial.
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