The volcanic effect has a limited distance however. (1980) found that at 200 m away from the source, plants yielded an age in agreement with that expected.
They suggested that the influence of depleted CO2 declined rapidly with increasing distance from the source.
A shellfish alive today in a lake within a limestone catchment, for instance, will yield a radiocarbon date which is excessively old.
The reason for this anomaly is that the limestone, which is weathered and dissolved into bicarbonate, has no radioactive carbon.
In the northern hemisphere the amount of artificial carbon in the atmosphere reached a peak in 1963 (in the southern hemisphere around 1965) at about 100% above normal levels.
Ellen Druffel has called this the silver lining in thermonuclear bomb testing.Hans Suess (1955) discovered the industrial effect (also called after him) in the 1950's.A number of researchers found that the activity they expected from material growing since 1890 AD was lower.In order to ascertain the ages of samples which were formed in equilibrium with different reservoirs to these materials, it is necessary to provide an age correction.Implicit in the Conventional Radiocarbon Age BP is the fact that it is not adjusted for this correction.Thus, it dilutes the activity of the lake meaning that the radioactivity is depleted in comparison to 14C activity elsewhere.