Deposition rate and seasonal variations in precipitation of cosmogenic Be-10

Nuclear accelerator measurements of the rate of Be-10 deposition at the surface of the earth are reported and initial data on the seasonal variation of Be-10 content in precipitation are presented. Be-10 deposition was determined from the Be-10/Be-9 ratio of a pool of water to which a known amount of Be-9 had been added prior to exposure to the sky for a year. An average deposition rate of 0.055 plus or minus 0.008 atoms/sq cm per sec is obtained, which is used to estimate an average global rate of 0.042 atoms/sq cm per sec according to yearly average rainfall distributions and latitude distributions of cosmic rays. The value obtained is noted to be significantly greater than previous estimates based on marine sediments and cosmic ray interaction rates. Analysis of a 10-year series of monthly precipitation samples reveals a sharp increase in Be-10 deposition during the spring, corresponding to the transfer of stratospheric air into the troposphere, which may be useful in determining accumulation rates in polar ice cores.