LONG-TERM ENVIRONMENTAL MONITORING OF C-14 LEVELS IN THE OTTAWA REGION

Ambient levels of C-14 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 C-14 in the mid-1960s and its exponential decline to the present. This bio-generated data set indicates that the half-life of bomb-generated C-14 is 12 y as a result of dilution with prebomb C-14 from the decay of organic matter and exchange with the oceanic reservoir, and, of course, a dilution from fossil fuel combustion. Atmospheric C-14 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 C-14 are approached.