David Knies, Purdue University

Ph.D. Thesis, Purdue University

A combination of three-hundred and fifty event and sub-event (greater than 3 mm resolution) ground level precipitation samples were collected near West Lafayette, IN. They included most of the significant precipitation events occurring between April 18, 1992 and August 31, 1993. The cosmogenic radionuclide (7Be (t1/2 = 53 d), 10Be (t1/2 = 1.5 MY), and 36Cl (t1/2 = 0.3 My)), anion (Cl^-, NO3, SO4^-2), and cation (NA^+, K^+, Mg^2+) concentrations were measured in selected samples. Acclerator mass spectrometry was used to determine the 10Be and 36Cl content. We used these data along with other standard meteorological data bases to investigate relationships between the cosmogenic radionuclides in mid-latitude wet deposition and storm type, air mass history, and season. Understanding the circumstances that lead to local variations in the ratio of 10Be to 36cl should aid other investigators in unlocking information stored in form of this ratio in the ice sheets, and thereby gain a better understanding of paleoclimates. In addition, the source functions for these radionuclides and how they vary with differing meteorological conditions are needed for ground water (36Cl) and erosion rate (10Be) studies. A departure from the 10Be/36Cl ratio of 40 predicted by La et al. 1967 is seen. Using a new semiempirical cross section formula, we estimated the production ratio to be greater than 9. Our mean 10Be/36Cl ratio is 11.4 and typically varies from 4 to 40. We see a higher mean 10Be/36Cl ratio in stratiform precipitation (14), and a lower mean ratio in convective precipitation (9.7). The estimated 10Be flux from re-suspended soil is 10% of the total 10Be flux.