Recent Fluctuations of Atmospheric Carbon-14 Concentrations

Baxter, Murdoch S (1969) Recent Fluctuations of Atmospheric Carbon-14 Concentrations. PhD thesis, University of Glasgow.

Abstract

Natural fluctuations of atmospheric C-14 concentrations over time periods from several hundred to several thousand years are known to have occurred during the last 6 millenia. The fluctuations represent deviations from the basic assumption of the radiocarbon dating method and, although their origin is not fully understood, probably stem from the variation of one or more of the geophysical parameters which control carbon circulation. The scope of past studies was limited by the availability of complete series of samples of precisely known origin. Consequently it has not been possible to establish whether natural atmospheric C-14 concentrations are constant over shorter time periods of several years. In this research annual variations of atmospheric C-14 concentrations over the past century have been studied through analyses of plant seeds, wines and spirits. Using exchange rate data obtained from recent investigations of the transport of artificial "bomb" C-14, the magnitude of the "Suess effect" during the past century has been assessed theoretically and compared with the experimental results. Predictions of the "Suess effect" to 2,025 A.D. suggest a marked increase in atmospheric CO2 concentrations to levels about 50% above natural. It is concluded that the enhanced infrared absorption in the atmosphere implied by such an increase may be sufficient to raise world temperatures by several degrees. Correction of observed atmospheric C-14 activities for "Suess effect" dilution revealed that between 1890 and 1950 natural fluctuations appear to have occurred over the 11-year sunspot cycle in inverse correlation with solar activity. It is suggested that the origin of this correlation lies in the variable mixing rates of stratospheric and tropospheric air masses caused by modulation of the incident U.V. and corpuscular radiation over each solar cycle. A general decrease in atmospheric C-14 concentrations was also observed and is attributed to a reduction in the mean C-14 production rate through increased solar activity. The results therefore support theories of solar-sensitive atmospheric circulation. In addition they imply the probability of increased errors in radiocarbon age determinations and endorse the universal use of the N.B.S. modern standard in C-14 assay.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Atmospheric sciences, Atmospheric chemistry
• Date of Award: 1969
• Depositing User: Enlighten Team
• Unique ID: glathesis:1969-78501
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 30 Jan 2020 15:14
• Last Modified: 30 Jan 2020 15:14
• URI: https://theses.gla.ac.uk/id/eprint/78501