CONSTRUCTING A LOCAL METEORIC WATER LINE FOR GUNNISON COLORADO—SEVEN YEARS OF PRECIPITATION STABLE ISOTOPE DATA

The stable isotope ratios of hydrogen and oxygen in meteoric waters have been extensively used to study atmospheric dynamics, regional climatology and surface and groundwater hydrology as well as a host of other interesting applications in archeology, ecology, forensic science and paleoclimatology. Although isotopic ratios in precipitation can be modeled fairly accurately for any spot on Earth more empirical datasets of isotopic ratios, especially from extreme or unique environments, are needed to test these models and capture the full range of isotopic values that exist. Since late 2007 we have collected meteoric waters from a site in Gunnison Colorado, USA and presently have δD and δ¹⁸O values for more than 175 separate precipitation samples. Gunnison is located at 38.54° N and 106.92° W and sits in a high elevation valley (2350 m) surrounded by considerably higher mountain ranges with peak elevations exceeding 4200 m. The climate of Gunnison is classified as frigid (MAT 0-8 °C) and semiarid (MAP 250-500 mm). Annual precipitation in Gunnison is moderately bimodal; with significant winter snowfall and strong convective summer thunderstorms associated with the North American southwestern monsoon. Stable isotope values of precipitation for Gunnison span an incredible range, with summer rains as high as δD = +15‰ and δ¹⁸O = +4.7‰ (SMOW standard) and winter snowfall having values as low as δD = -286‰ and δ¹⁸O = -36.7‰. These data define a local meteoric water line for Gunnison of δD = 7.2 δ¹⁸O – 6.5.