Short-term Variability of Stable Isotope Ratios of AIRMoN Precipitation Samples:
The Influence of Precipitation Source on Isotopic Composition

Derek Sjostrom
Dept. of Geological Sciences, University of Alaska Anchorage,
3211 Providence Dr., Anchorage, AK 99508

Jeff Welker
Environmental and Natural Resources Institute, University of Alaska Anchorage
707 A St., Anchorage, AK 99501


The Atmospheric Integrated Research Monitoring Network (AIRMoN) program consists of a subset of NADP precipitation collection stations located throughout the eastern and central United States. At these locations, frequent sample collection has resulted in an extensive archive of precipitation that allows for analysis on the scale of individual precipitation events. Approximately 500 of these samples collected during 1996-2000 from Florida, Illinois, Ohio, Tennessee, Vermont, and West Virginia have been analyzed for dD and delta d18O in order to assess the short-term variability of the isotopic composition of precipitation. The isotopic composition of samples among precipitation events from all locations is highly variable. For example, delta values range by as much as approximately 100‰ for hydrogen and approximately 12‰ for oxygen for precipitation events separated by only a few days regardless of geographic location and time of year. There is a weak correlation between temperature at the time of the precipitation event and isotopic value of precipitation at all locations. In general, the long-established trends in isotopic values at different geographic locations are evident in this dataset. In order to assess how much of an influence precipitation source (storm track) has on the isotopic ratios for each storm event, storm backtrajectories were calculated for many data points using NOAA's HYSPLIT model. In general, where isotope value is similar among several storms, the modeled storm trajectories are fairly similar at most sites, with some exceptions. However, the results from Florida suggest that storm track is not the major control of isotopic ratios in precipitation; the amount effect and ambient temperature appear to be the dominant controls. Previous predictive models of isotopic ratios of precipitation have not included a storm track component. The addition of a precipitation source component to these models, which is the ultimate goal of this project, should help to refine and improve these models.