Precipitation isotope (δ18O) gradients depict modern atmospheric circulation over the conterminous United States

Water isotopes can provide important information about water transport by the modern atmosphere and past atmospheric circulation patterns. Here we present the first analysis of precipitation isotope (δ18O) spatial gradients from 63 sites across the conterminous United States in the context of meteorological and air mass dynamics. The results demonstrate that the spatial derivative of isotopic composition is an indicator of the time-averaged position of air mass boundaries in the atmospheric circulation. In the summer, a strong gradient in the isotope field exist in a north-south band along the Rocky Mountain front, approximately corresponding to the boundary between Pacific and Gulf of Mexico air masses. During winter, the zone of strong isotope gradients forms a trough enclosing the Rocky Mountains and northern Great Plain, reflecting the influence of the polar front and presence of blocking high-pressure systems across this region. These results suggest new opportunities for interpretation of precipitation, vapor and paleoclimate water isotope data in the context of regional climate dynamics through spatial analysis.