Browsing Radiocarbon, Volume 31, Number 3 (1989) by Authors
Accelerator-Measured 14C Activity in Tree Rings from the Vicinity of the First Atomic Bomb TestLeavitt, S. W.; Long, Austin (Department of Geosciences, The University of Arizona, 1989-01-01)Detonation of the first fission bomb at White Sands, New Mexico, on July 16, 1945, produced a tremendous neutron flux capable of creating tritium and radiocarbon byproducts. We sampled a 115-year-old pinyon (Pinus edulis) 10km east of the Trinity test site to determine 14C evidence of this event. The most likely mechanism for this enrichment in the 1945 tree ring would be fixation of 14CO2 produced at the blast site and carried with the fallout cloud over the pinyon site. Analysis of cellulose of the 1944 and 1945 rings shows delta-13C values of -19.9 and -19.5 per mil, respectively, and 14C activity (fraction of modern uncorrected for delta-13C) as 0.991 +/- .005 and 0.991 +/- .006, respectively. It is likely that the duration and/or concentration of the 14CO2 exposure was not sufficient to increase 14C activity expected for that year.
The Atmospheric delta-13C Record as Derived from 56 Pinyon Trees at 14 Sites in the Southwestern United StatesLeavitt, S. W.; Long, Austin (Department of Geosciences, The University of Arizona, 1989-01-01)We have developed a master delta-13C chronology from 14 pinyon pine sites in 6 states of the southwestern U S. Two of the individual isotopic chronologies, reported here for the first time, and 10 of those previously reported (Leavitt & Long, 1986; 1988) are from sites where cores from 4 trees were pooled prior to analysis, and the other 2 are merged from groups of 4 single-tree chronologies (sites) developed in an earlier phase of research (Leavitt & Long, 1985). Regressions of first differences of ring-width indices and delta-13C values from each site were used to "correct" individual delta-13C chronologies for climate effects which appear primarily related to high-frequency delta-13C fluctuations, many of which are common among sites. These climate-corrected chronologies were normalized as deviations from their respective 1800-1849 delta-13C means, and these normalized chronologies were averaged into the master. The overall 6130 drop from 1600 to the present is ca 1.2-1.4 per mil, consistent with recent ice-core data showing a drop of 1.14 +/- 0.15 per mil from 1740 to present (Friedli et al, 1986). However, the delta-13C decline in the late 19th and early 20th centuries is greater in the pinyon chronology than that of the ice cores, thus supporting a greater biospheric CO2 input to the atmosphere than that indicated in the ice-core data.
Variation of Concentration, 14C Activity and 13C/12C Ratios of CO2 in Air Samples from Kitt Peak, ArizonaLeavitt, S. W.; Long, Austin (Department of Geosciences, The University of Arizona, 1989-01-01)Air was sampled with 5L flasks at Kitt Peak (2100m elev) from 1983 through 1984 at approximately monthly intervals, occasionally supplemented with air samples from urban Tucson ca 75km away (760m elev). The Kitt Peak CO2 concentrations, represented by a yield measurement, fluctuated ca 25% over the monitoring period. The delta-13C values (uncorrected for N20) varied from ca -7.6 to -9.0%, with high values (and low CO2 yields) in the late summer consistent with hemispheric seasonal biosphere effects. Tucson air has lower delta-13C values and possibly greater CO2 yield suggesting a local fossil-fuel effect. 14C activity of four Kitt Peak samples range from 1.158 +/- .007 to 1.223 +/- .008 as uncorrected fraction of modern, below free air activity of ca 1.250 for 1984 even after correcting for fractionation. The slightly low 14C activity and delta-13C values suggest the Kitt Peak air is not quite 100% clean and there may be a local/regional fossil-fuel contribution, but CO2 concentrations are similar to background atmospheric values.