Deposition rate and seasonal variations in precipitation of cosmogenic 10Be

The measurement of 10 Be using nuclear accelerators promises to widen the applications of this cosmogenic isotope considerably 1–3 . A parameter of fundamental importance in such applications is the production rate of this nuclide in the atmosphere. This production rate has previously been estimated by two methods: (1) by measuring the concentration of 10 Be in marine sediments having known accumulation rates; (2) by using model calculations of cosmic ray interaction rates, combined with estimated cross-sections for production of 10 Be. These two methods have led to an estimated global average 10 Be production rate of 0.015–0.018 atoms cm −2 s −1 (refs 4,5 and F. Guichard, unpublished work). The increased sensitivity available with the accelerator technique now makes it feasible to measure directly 10 Be deposition rates at the Earth's surface. We report here the results of such a measurement, which lead to an estimated global average production rate more than double the previous estimates. We also give some initial results on the seasonal variation of 10 Be concentration in precipitation, and comment on the possibility that such variations might permit the determination of ancient accumulation rates of polar ice.