The 1950s atmospheric bomb- 14 C peak

Comparison of cellulose 14 C of the growth rings 1962–1965 of Norwegian Scots pine with Norwegian atmospheric 14 CO 2 over these bomb spike years indicates that tree rings can provide a good proxy for atmospheric 14 CO 2 . The sub-seasonal cellulose 14 C values of five trees from 63° to 69° N reveal local atmospheric 14 CO 2 values for the growing seasons 1950–1965. The 1950s are of special importance because there exist few direct measurements of atmospheric 14 CO 2 during this period of active atmospheric nuclear testing. First indications of bomb 14 C are seen already in 1952. The temporary halt of atmospheric testing from November 1958 to September 1961 led to a temporary maximum in atmospheric 14 C concentrations in 1959, creating the 1950s atmospheric bomb- 14 C peak. Longer atmospheric travel of 14 C from low-latitude and Southern Hemisphere tests to Norway led to the highest tree 14 C values in 1959 and 1963/’64 after testing stopped, respectively, in 1958 and 1962. The Scots pine data demonstrate that local atmospheric 14 CO 2 records with sub-annual resolution can generally be obtained. Combination with the SIPRI data base of nuclear testing, allows a focus on the production of bomb 14 C and its transport through the atmosphere to the tree and promises a better understanding of the atmospheric mixing of CO 2 . Together with high-resolution local 14 CO 2 records this can better define the exchange between the atmosphere and the other reservoirs of the carbon cycle during the period of isotopic disequilibrium caused by atmospheric nuclear testing.