Global Change: Geologic Records Inferred from Cosmic Ray Produced Neon at the Surface of the Earth

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In the last few years, several cosmic-ray-produced radionuclides (10Be, 14C, 26Al, 36Cl), as well as stable 3He, 21Ne and 22Ne have been discovered in terrestrial surface materials. Some of these nuclides are already employed as tracers in studies of geophysical and geological phenomena and open up a new field of study and are expected to provide essential data on rates of change in global change research. Such studies require an accurate knowledge of of the production rates, present and past, which are not currently available. We are using a direct method for the determination of some of present production rates, by exposing relevant targets at mountain altitudes. Production rates averaged over the last solar cycles can be obtained by comparing production rates with neutron monitor data. We are currently evaluating the relevant production ratio P21/P26 of the cosmic-ray-produced nuclides 21Ne and 26Al by isotopic measurements of Ne in quartz samples. Our preliminary experimental data do not agree well with theoretical predictions. Average production rates over 104-105years can be obtained from measurements of samples of known age. Measurements of the 3He/21Ne ratio show that 3He is often incompletely retained in quartzites. Therefore, 21Ne production rates and 21Ne/10Be and 21Ne/26Al ratios provide essential information, which is required to evaluate erosion rates and to define geological processes (uplift, variations in ice cover etc).