CARBON-14 MEASUREMENTS 427 PERCENT ABOVE NORMAL 4c LEVEL AVERAGE GROUND—LEVEL '4c J 72 ~~. 70 O 4 8 12 16 20 APR. 9, 1964 4 30.10 / Pe 0 4 8 12 1420 RELATIVE WIND VELOCITY + 30.00 7-RELATIVE PRECIPITATION RATE 0 APR. 10, 1964 4 7 30.20 8 BAROMETER BAROMETRIC PRESSURE 29.90 APR. 11, 1964 Fig. 3—Specific “C content of samples of atmospheric CO, collected on Hurricane Ridge during the passage of successive storm fronts. Activities of 4C are expressed in percent above pre-1945 levels. Samples of atmospheric CO, collected on Hurricane Ridge at about 4hr intervals showed '‘C specific activities that fluctuate significantly above and below the nearly constant 4c specific activity measured at ground levels during the late winter and early spring. Particularly in- teresting are the two low values of the specific activity which were measured after most of the precipitation, snow, had fallen. Since the source of this moisture was marine air, the low specific activity probably represented an air mass from over the ocean which had undergone partial exchange and which had not yet mixed with the air masses of higher specific activity which were associated with the storm system. REFERENCES 1. G. J, Fergusson, Upper Tropospheric Carbon-14 Levels During Spring 1962, J. Geophys. Res., 68: 3933-3941 (1963), 2. H. E, Suess, Natural Radiocarbon and the Rate of Exchange of Carbon Dioxide Between the Atmosphere and the Sea, in Proceedings of Conference on Nu- clear Processes in Geologic Settings, pp. 52-56, National Academy of Sciences ~ National Research Council Publication, Washington, D. C., 1953. 3. H. Craig, The Natural Distribution of Radiocarbon and the Exchange Time of Carbon Dioxide Between Atmosphere and Sea, Tellus, 9: 1-17 (1957). 4, R. Revelle and H. E. Suess, Carbon Dioxide Exchange Between Atmosphere and Ocean and the Question of an Increase of Atmospheric CO, During the Past Decades, Tellus, 9: 18-27 (1957). 5. J, R, Arnold and E, C. Anderson, The Distribution of Carbon-14 in Nature, Tellus, 9: 28-32 (1957).