Th-230 / U-234 / U-238 age dating of corals by alpha counting or mass spectrometry has been instrumental in our understanding of sea level, radiocarbon calibration, ocean and climate change rates, and El Nino timing, among other applications . The age of corals by mass spectrometry is remarkably accurate. but many samples that have been exposed to freshwater give imprecise ages. The first indication of the age of Th-230 / U-234 / U-238 in the open system is increased U-234 / U-238 (initial) values, very common in samples older than 100,000 years. Age validation is required for samples that are less than 100,000 years old and have U-234 / (238) (initial) values in the vicinity of seawater. Redundant Th-230 / U-234 / U-238 and Pa-231 / U-235 ages in a single fossil coral fragment are possible through Multi-Collector Magnetic Sector Inductively Coupled Plasma Mass Spectrometry (MC-MS-ICPMS) and standard anion Exchange column chemistry modified to allow the separation of uranium. Thorium and protactinium isotopes from a single solution. A highly efficient nebulizer for sample application enables the determination of the age of both Th-230 / U-234 / U-238 and Pa-231 / U-235 in fragments as small as Th-230 / U-234 / U-238 500 mg. We obtained an excellent match between ages Th-230 / U-234 / U-238 and Pa-231 / U-235 in Barbados corals (30 ka) and suggest that the methods described in this paper can be used to get the Th-230 / U-234 / U-238 age accuracy.
Remarks:892WITimes Cited: 11 References Cited Number: 40
URL: ://000226680300011 DOI: DOI 10.1016/j.gca.2004.06.033
