Th-230/U-234/U-238 and Pa-231/U-235 ages from a single fossil coral fragment by multi-collector magnetic-sector inductively coupled plasma mass spectrometry

The Th-230/U-234/U-238 age dating of corals via alpha counting or mass spectrometry has significantly contributed to Our understanding of sea level, radiocarbon calibration, rates of ocean and climate change, and timing of El Nino, among many applications. Age dating of corals by mass spectrometry, is remarkably precise. but many samples exposed to freshwater yield inaccurate ages. The first indication of open-system Th-230/U-234/U-238 ages is elevated U-234/U-238(initial) values, very common in samples older than 100,000 yr. For samples younger than 100,000 yr that have U-234/(238)(initial) values close to seawater, there is a need for age validation. Redundant Th-230/U-234/U-238 and Pa-231/U-235 ages in a single fossil coral fragment are possible by Multi-Collector Magnetic Sector Inductively Coupled Plasma Mass Spectrometry (MC-MS-ICPMS) and standard anion exchange column chemistry, modified to permit the separation of uranium. thorium, and protactinium isotopes from a single solution. A high-efficiency nebulizer employed for sample introduction permits the determination of both Th-230/U-234/U-238 and Pa-231/U-235 ages in fragments as small as Th-230/U-234/U-238 500 mg. We have obtained excellent agreement between Th-230/U-234/U-238 and Pa-231/U-235 ages in Barbados corals (30 ka) and suggest that the methods described in this paper can be used to test the Th-230/U-234/U-238 age accuracy.