Start Atomic bomb radiocarbon dating

Atomic bomb radiocarbon dating

Since radiocarbon is incorporated into all living things, this pulse is an isotopic chronometer of the past half-century.

Using an annual average of the carbon intake over a growing season can account for much food chain lag and produce a usable curve (Figure 1).

Caution must be exercised when dating an elevated sample since the pulse is double valued.

[A Conventional Radiocarbon Age or CRA, does not take into account specific differences between the activity of different carbon reservoirs.

A CRA is derived using an age calculation based upon the decay corrected activity of the absolute radiocarbon standard (1890 AD wood) which is in equilibrium with atmospheric radiocarbon levels (as mentioned previously, 1890 wood is no longer used as the primary radiocarbon standard, instead Oxalic Acid standards I and II were correlated with the activity of the original standard).

The atmospheric concentration of C becomes the fingerprint of this radioisotope in a given year's food supply.

Herbivores lag the atmosphere slightly because their primary carbon source is on the order of months old.

Plants which grow in the vicinity of active volcanic fumeroles will yield a radiocarbon age which is too old. (1980) measured the radioactivity of modern plants growing near hot springs heated by volcanic rocks in western Germany and demonstrated a deficiency in radiocarbon of up to 1500 years through comparison with modern atmospheric radiocarbon levels.

Similarly, this effect has been noted for plants in the bay of Palaea Kameni near the prehistoric site of Akrotiri, which was buried by the eruption of the Thera volcano over 3500 years ago (see Weninger, 1989).

One of the most commonly referenced reservoir effects concerns the ocean.

The average difference between a radiocarbon date of a terrestrial sample such as a tree, and a shell from the marine environment is about 400 radiocarbon years (see Stuiver and Braziunas, 1993).

Omnivores and carnivores lag the atmosphere further because their carbon sources are another step removed.