Date of Award

8-1997

Degree Name

Doctor of Philosophy

Department

Geosciences

First Advisor

Dr. R. V. Krishnamurthy

Second Advisor

Dr. Elen Cutrim

Third Advisor

Dr. Alan Kehew

Abstract

Precipitation samples were collected at Kalamazoo from June 1992 to March 1995. The samples were analyzed for their 8D and 8lgO values. The 5D - 5I80 relationship is comparable to that of Meteoric Water Line (MWL). The monthly mean isotopic values in precipitation exhibited strong seasonality, being higher in summer and lower in winter months. This behavior is apparently a direct consequence of the temperature effect on isotope fractionation.

The summer precipitation at Kalamazoo is derived predominantly from the water vapor originated in the Gulf of Mexico. A box model calculation showed that a Rayleigh type distillation with Gulf moisture as the source would explain the bulk of the observed isotopic ratios in summer precipitation. Additional factors such as Gulf vapor divergence, Atlantic moisture and convective precipitation appear to account for the rest of the isotope data. The summer precipitation is characterized by a higher ^/-excess than that of the precipitation defined by the MWL. This is probably due to the contribution of evaporated moisture from Lake Michigan. The contribution of lake-evaporated moisture to summer precipitation was estimated by using the Craig - Gordon model. When compared over a three year period, the percent contribution of lake-evaporated moisture to summer precipitation is positively correlated to mean summer temperatures.

The isotopic ratios in winter precipitation reflect multiple moisture sources with significant ‘Lake Effect’ component The isotopic signature of lake effect precipitation was shown to be the result o f thermodynamically controlled condensation from a cloud super saturated with respect to ice. Precipitation samples collected separately from January to December 1994 were analyzed for 7Be and 210Pb concentrations in addition to the stable isotopes. The concentrations of these nuclides in precipitation are strongly correlated.

The precipitation during wanner months is characterized by higher 7Be and lower 210Pb concentrations. Based on meteorological and stable isotope data it was shown that 2l0Pb concentrations are controlled mainly by the nature of precipitation whereas the concentrations of 7Be are influenced by the vertical mixing in troposphere and tropopause folding.

Access Setting

Dissertation-Open Access

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