• 14C Variations During the Upper Pleistocene

      Vogel, J. C. (American Journal of Science, 1983-01-01)
      Parallel determinations of 14C and ionium dates on a stalagmite from the Cango Caves provide evidence of variations in the 14C content of the atmosphere beyond the range of the California tree-ring sequence. During the Holocene growth period the 230Th dates are compatible with the tree-ring calibrated 14C dates. At 18,000 BP and between 30,000 and 40,000 BP the 14C ages are markedly younger than the 230Th ages, suggesting that the 14C level of the atmosphere was considerably higher at these times. Between the 230Th ages of 35,000 and 29,000 BP the 14C ages remain nearly constant at 29,500 BP, indicating that 14C production must have been drastically reduced during this period. The 14C fluctuation is greater than that predicted by Barbetti (1980) but it may be explained by postulating a substantial increase in the geomagnetic dipole field, for which there is mounting evidence.
    • Calibrated 14C Dates in Central Europe - Same as Elsewhere?

      Freundlich, J. C.; Schmidt, Burghart (American Journal of Science, 1983-01-01)
      14C dating results derived from an absolutely-dated 471-year tree-ring sequence from central European oak show a trend towards somewhat older dates than those for bristlecone pine tree rings of the same age, but similar to those for Egyptian historical samples. Differences visible between these trend lines are not relevant considering the standard errors proposed by Clark (1975).