Earth surface evaporative process: A case study from the Great Lakes region of the United States based on deuterium excess in precipitation

Abstract

The “deuterium excess” parameter in rain, defined as d = δD − 8 δ 18O, is a powerful geophysical tool which can be used to estimate secondary processes that influence atmospheric vapor content in the evaporation-condensation cycle in nature. The d-excess has been calculated, based on the systematic analysis of the stable oxygen and hydrogen isotope ratios, in precipitation samples from Kalamazoo, southwest Michigan. The results show that moisture derived from the evaporation of Lake Michigan contributes between 9–16% during the summer months to the atmospheric vapor load in the region. Admittedly, this estimate is an upper value since in our model we have assumed that transpiration from leaf surfaces is minimal compared to the evaporation from Lake Michigan. It is therefore obvious that large freshwater systems need to be regarded as a potentially significant source of atmospheric vapor load. Isotopic investigations such as this will enable to attain quantitative estimates of this important aspect, a knowledge of which, will enhance the usefulness of or perhaps even be essential in calculations based on many atmospheric circulation models.