• Fine and Hyperfine Structure in the Spectrum of Secular Variations of Atmospheric 14C

      Damon, Paul E.; Cheng, Songlin; Linick, Timothy W. (Department of Geosciences, The University of Arizona, 1989-01-01)
      The coarse structure of the 14C spectrum consists of a secular trend curve that may be closely fit by a sinusoidal curve with period ca 11,000 yr and half amplitude +/- 51 per mil. This long-term trend is the result of changes in the earth's geomagnetic dipole moment. Consequently, it modulates solar components of the 14C spectrum but does not appear to modulate a component of the spectrum of ca 2300-yr period. The ca 2300-yr period is of uncertain origin but may be due to changes in climate because it also appears in the delta-18O spectrum of ice cores. This component strongly modulates the well-known ca 200-yr period of the spectrum's fine structure. The hyperfine structure consists of two components that fluctuate with the 11-yr solar cycle. One component results from solar-wind modulation of the galactic cosmic rays and has a half-amplitude of ca +/- 1.5%. The other component is the result of 14C production by solar cosmic rays that arrive more randomly but rise and fall with the 11-yr cycle and appear to dominate the fluctuation of the galactic cosmic-ray-produced component by a factor of two.
    • Global Production and Decay of Radiocarbon

      Damon, Paul E.; Sternberg, Robert E. (Department of Geosciences, The University of Arizona, 1989-01-01)
      The production rate of 14C during the Holocene averaged 2.4 +/- 0.2 atoms 14C/cme sec. Neutrons produced by galactic cosmic rays account for 90% of the 14C production with the remainin 10% resulting from neutrons produced by protons from solar flares. Production and decay of 4C can be reconciled by including 14C permanently or temporarily stored in sediments. Sedimentary reservoirs contain ca 30% of all terrestrial 14C. The lagoons, bays, marshes and deltas of the coastal wetlands alone account for 12% of the 14C inventory. The capacity of the coastal wetlands to store carbon has become the subject of renewed interest.