Long-term environmental monitoring of [sup 14]C levels in the Ottawa region

Ambient levels of [sup 14]C have been monitored near Ottawa, Canada by the Radiocarbon Dating Laboratory, Geological Survey of Canada, since 1961. The 32 y of data on maple leaves documents the rapid increase of bomb-generated [sup 14]C in the mid-1960s and its exponential decline to the present. This bio-generated data set indicates that the half-life of bomb-generated [sup 14]C is 12 y as a result of dilution with prebomb [sup 14]C from the decay of organic matter and exchange with the oceanic reservoir, and, of course, a dilution from fossil fuel combustion. Atmospheric [sup 14]C activity will approach 10% of prebomb levels by the turn of the century, but it will be another century before the prebomb levels of atmospheric [sup 14]C are approached. 4 refs., 3 figs., 1 tab.