III.  Oceanic and atmospheric radiocarbon variability in the distant past

The ratio of ¹⁴C to ¹²C varies markedly in the natural environment because the decay of cosmogenically-produced ¹⁴C occurs faster than the isotopic equilibration time for the global carbon cycle. Large surface-to-deep gradients in the radiocarbon concentration of the ocean reflect radiocarbon's atmospheric source in addition to the long-term removal of deep-water from atmospheric exchange processes. Radiocarbon variability can occur via changes in the production rate of 14C, which is controlled by solar and geomagnetic parameters, or by changes in the global carbon cycle