Stable isotope studies of cave seepage water

D/H and 18O16O ratios for vadose seepage and precipitation were determined at three cave sites in the eastern U.S.A. Samples were collected over a period of ∼ 1 yr. between the summers of 1978 and 1979. In addition, isotopic determinations were made on a number of individual vadose seepage samples from a variety of caves predominantly located throughout North America. The results of the former portion of the study suggest that the isotopic composition of the recharge water is constant and approximately equal to that of the weighted mean annual precipitation in the locality. In the latter part of the study, the notion of the constancy of isotopic composition of vadose seepage was applied to a number of cave sites and the results agree with other precipitation data.Since it has been shown that caves record mean annual surface temperatures, the relationship between mean temperature and δ18O of precipitation can also be determined. There is good agreement between the relationship based on our data and that based on meteorological data and isotopic analyses by I.A.E.A.The study demonstrates that vadose seepage provides an effective means of assessing mean annual isotope ratios of precipitation in most continental regions.