This proposal requests funds to earn out the following investigations: (1) to measure the concentrations of cosmogenic radionuclide 26Al (half-life = 0.7 my) in several composite Arctic and Antarctic Holocene and glacial period ice samples, along with the concentrations of the two other cosmogenic nuclides 10Be (half-life = 1.5 my) and 36Cl (half-life = 0.3 my), and (2) to develop coupled cosmic ray-atmospheric circulation and aerosol scavenging models which can adequately' predict the tropospheric fallout of these nuclides. The proposed work is intended to show that (i) measurements of 26Al, which require large ice samples can be made using the available Arctic and Antarctic ice samples, by combining several sections, covering' tine periods of 500-1000 years. and that (ii) these measurements would be extremely valuable for understanding the nature of fallout of cosmogenic nuclides. The modeling effort will develop the coupled models taking into account all available data on the cosmic ray source function and its expected variability, seasonal variations in the last 30 years bused on the re-analysis global climatological data, and data' on the fallout of the three cosmogenic nuclides.
