High Precision Thorium-230 Ages of Corals and the Timing of Sea Level Fluctuations in the Late Quaternary

Mass spectrometric techniques for the measurement of ²³⁰Th and ²³⁴U have been developed. These techniques have made it possible to reduce the analytical errors in ²³⁰Th dating of corals using very small samples. Samples of 8 x 10⁷ atoms of ²³⁰Th can be measured to an accuracy of ±130% (2 sigma), 6 x 10⁸ atoms of ²³⁰Th can be measured to an accuracy of ±29%, and 3 x 10¹⁰ atoms of ²³⁰Th can be measured to an accuracy of ±2%. The time range over which useful data on corals can now be obtained ranges from 15 to 500,000 years. The error in age (based on analytical error) for a sample that is 18 years old ±3 years (2 sigma). The error is ±5 years at 180 years, ±44 years at 8294 years, and ±1 ky at 123.1 ky. For young corals, this approach may be preferable to ¹⁴C dating. Fluctuations in climate result in changes in sea level because the ice stored in continental glaciers is ultimately derived from the ocean. Certain species of coral grow close to the sea surface. Fossils of these species therefore record the former height of the sea surface. The precision with which the age of a coral can now be determined makes it possible to determine, with some precision, the timing of sea level fluctuations in the late Quaternary. This record will allow a critical test of the Milankovitch hypothesis, which predicts the timing of Pleistocene climate fluctuations from changes in the distribution of solar insolation that result from changes in the earth's orbital geometry. Analyses of a number of corals that grew during the last interglacial period yield ages of 122 to 130 ky. The ages coincide with or slightly postdate the summer solar insolation high at 65°N latitude, which occurred 128 ky ago. This supports the idea that changes in Pleistocene climate can be the result of orbital forcing. Apparent fluctuations in sea level recorded on tectonically active shorelines are the result of both sea level change and vertical tectonic movement. If the record of sea level chang