Carbon 14 Calibration, Production and Reservoir Changes Over the Past 50,000 Years

Columbia University, New York NY

Investigators

Abstract

This award will measure paired uranium and thorium isotopes and radiocarbon measurements on 300 coral specimens dated from between 12,000 and 50,000 years before present. These data will extend the tree ring carbon isotope-based time series to the technical limits of radiocarbon determinations using pristine coral samples. Combining such results with records generated by others, the researchers expect to contribute to a precise and accurate International Radiocarbon Calibration program that will broadly impact those fields of science that utilize radiocarbon data as a measure of time. The primary justification of the research is that initial results from the analyses of corals demonstrate that the radiocarbon time scale is more than 5,000 years offset from time scales based on uranium and thorium methods, for the last glacial period. Changes in the Earth's magnetic field, the Sun's convection, and supernova events from outer space all affect the cosmic ray production of radiocarbon in the atmosphere. The carbon exchange rate between the atmosphere, oceans, and biosphere, and its decay, regulate the concentration of carbon isotopes in the atmosphere. This history over the past 11,500 years is recorded in a variety of natural archives such as annually banded tree rings, varved-sediments, speleothems, and corals. Radiocarbon ages provide a critical radiometric chronometer for many fields of science such as archeology, anthropology, climate, paleoceanograhy, tracer oceanography, palynology, lake studies, and antiquities dating. When combined with other geophysical data, it is possible to interpret the radiocarbon time series as a monitor or measure of the Earth's magnetic field, solar variability, magnetic excursions, and climate related changes.