TEMPORAL VARIATION OF STABLE HYDROGEN AND OXYGEN ISOTOPES FOR PRECIPITATION IN STILLWATER, OKLAHOMA

Stable isotopes of hydrogen (δ²H) and oxygen (δ¹⁸O) can be used to explore the relationships between the local climate and hydrological cycle. The δ2H and δ18O in precipitation forms the foundations from which to assess local hydrologic cycles. We collected precipitation from 2006-2008 in Stillwater (36^oN05”17.4”, 97^o08’48.0”W), north-central Oklahoma and analyzed them for δ²H and δ¹⁸O. Our objectives were to document the temporal variations in the δ²H and δ¹⁸O and to develop a local meteoric water line (LMWL) and to assess the processes that control the δ²H and δ¹⁸O composition over seasonal cycles. The results showed that the temporal δ²H and δ¹⁸O isotopic composition were more depleted in the fall and winter and more enriched in the spring and summer. The lower δ²H and δ¹⁸O isotopic composition in the fall and winter were due to precipitation under colder conditions and the more enriched values in the spring and summer are due to warmer temperatures. The δ¹⁸O and δ²H define an LMWL of 7.6753x+11.0192 (R²=0.9167), which has a slightly lower slope than that of the Global Meteoric Water Line (GMWL). The lower slope may be due to evaporation of rain during precipitation within this semi-arid environment or from a mixture of evaporated water from the terrestrial environment with precipitating air mass in Oklahoma. The LMWL for Stillwater will serve as a useful tool for future surface and groundwater studies conducted in north-central Oklahoma. Such studies, which involve the use of stable isotopes of hydrogen and oxygen, will help geologists and other scientists to couple geochemical processes with the hydrologic cycle.