Abstract
summary This study investigates the factors that control the oxygen isotopic composition of precipitation and cave drip waters in central Texas. Precipitation samples collected in Austin, Texas at monthly to bimonthly intervals between 1999 and 2007 have d 18 O values between 12.6‰ and 1.1‰ VSMOW and a weighted average value of 4.1‰. This weighted average value likely reflects the isotopic composition of precipitation generated predominantly by moisture masses that originate from the Gulf of Mexico. Samples with the lowest d 18 O values (12.6 ± 0.1‰) are associated with precipitation from moisture masses related to Pacific tropical cyclones. Precipitation amount appears to be an important control on the oxygen isotope composition of rainfall during summertime periods with the warmest weather, but does not account for the variability of the precipitation isotopic data for colder months. Drip-water samples collected at monthly to quarterly intervals from multiple drip sites in three regionally distributed central Texas caves between 1998 and 2007 have d 18 O values between 5.5‰ and 0.6‰ with individual drip sites generally
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