Short-Term Fluctuations of Carbon Isotope Levels in Atmospheric Carbon Dioxide

Farmer, John G (1972) Short-Term Fluctuations of Carbon Isotope Levels in Atmospheric Carbon Dioxide. PhD thesis, University of Glasgow.

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Natural 14C fluctuations are known to have occurred over periods of 50 to thousands of years during the last 10 millennia. As the fluctuations represent deviations from the basic assumptions of the radiocarbon dating method, major research programmes have concentrated on the establishment of the main trends of secular 14C variations. Recent work has questioned the assumed constancy of natural C levels over shorter time periods of 10 years and has thus implied the reduced effectiveness of present calibration curves to the age-correction of shortlived dating samples. In this research, annual atmospheric 14C concentrations in the northern hemisphere have been studied through analyses of 19th Century single tree rings. Natural C fluctuations of 2% over the 11-year sunspot cycle appear to have occurred in correlation with solar activity. Consequently, an additional error of at least +/-80 years is inevitable in the radiocarbon age determination of dating samples of lifetime 1 year. In addition, the selection of dating samples which incorporate the products of 10-11 years' growth (or a multiple of this) is urged by the apparent relationship between annual C levels and the 11-year sunspot cycle. It is suggested that the origin of this relationship lies in changes in 14C production and in internal atmospheric mixing through the modulation of incident radiation by variations in solar activity. Annual atmospheric C concentrations in the southern hemisphere during this century have also been studied through analyses of tree rings, wines, seeds and wool. No correlation between southern hemisphere 14C activity and the 11-year sunspot cycle has been observed. It is believed that the greater surface area of the southern oceans may be responsible for observed 14C differences between hemispheres through enhanced uptake and exchange of atmospheric CO2. Variations of the stable carbon isotope composition of atmospheric CO2 during the 20th Century have been detected by mass-spectrometric measurements of the 13C/12C ratios of single tree rings. A decrease of 0.2% has been observed in the atmospheric 13C/12C ratio as a result of the input of isotopically lighter CO2 from fossil fuel combustion. The temporal trend of the 13C/12C variations suggests that industrial CO2 has been removed from the atmosphere at an increased rate during the past few decades. Generally, the study implies non-uniform CO2 transfer rates across the atmosphere/biosphere/ocean interface during this century.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Atmospheric sciences, Atmospheric chemistry
Date of Award: 1972
Depositing User: Enlighten Team
Unique ID: glathesis:1972-78590
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:09
Last Modified: 30 Jan 2020 15:09

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