| Abstrakt: |
Radiochemical, mineralogie, and minor element analyses of three Pavona clavussamples spanning 350 years from Urvina Bay, Isabela Island, Galapagos, are presented here. The 210Pb results, the first reported from corals treated with all the precautions developed for obtaining reliable stable lead measurements, indicate the importance of these procedures for measuring coral 210Pb activities which can be directly related to surface water activities. Sr/Ca and Mg/Ca ratios, mineralogy, uranium concentration and isotopic ratio data, and activities < 0.2 dpm/100 g for 230Th (in the two youngest samples) and 232Th indicate no significant post-depositional alteration or contamination. Calculated initial 210Pb activities in the two youngest samples are ~6 to 9 dpm/100 g, lower than observed for other Galapagos corals and consistent with surface water conditions inferred from other trace element data on these corals. Initial 226Ra activities are typically ~4.4 dpm/100 g. Further investigation is required to document fully the effects of cleaning procedures on coral radionuclide measurements and the relationship of variability in coral radionuclides with water column events. |
