This project is a study of the processes that are active in determining the characteristics of aerosols that are removed from the arctic atmosphere and deposited in the Greenland ice sheet. These processes involve the dynamics of tropospheric and stratospheric mass exchange, the efficiency with which aerosols and associated chemical species are removed from the lower atmosphere, the relative importance of wet and dry deposition, and the early post-depositional chemical and concentration changes in the snow. Knowledge of these processes is crucial to the reconstruction of paleoatmospheres from the record that is preserved in the ice sheet. Air sample filters and snow and ice samples collected in a year-long effort at Dye-3 in southern Greenland will be analyzed for radionuclides, including Beryllium-7, Beryllium-10, Chlorine-36, and Lead-210. Beryllium-7 is a cosmogenic radionuclide that is useful as a tracer of intrusions of stratospheric air, while Lead-210 results from the decay of radon emitted from the Earth's surface and is a tracer for continental air masses. While Chlorine-36 is an important modulator in ozone chemistry, its ratio to Beryllium-10 may possibly become a method for dating ice cores older than 50,000 years. Results to date have been mixed because the ratio can fluctuate greatly over small depth intervals. This project however will obtain data on time scales short enough to determine whether short term differences in the transport mechanism or seasonal variations in the efficiency of the removal process cause the observed fluctuations.
