Temporal changes in stable isotope composition of spring waters: Implications for recent changes in climate and atmospheric circulation

Abstract

Stable isotope values of shallow groundwater emerging from springs in a high-elevation basin in the central Sierra Nevada of California decrease with increasing geochemical groundwater ages. From water recharged in 1960 to water recharged in 1990, a 1.2‰ and 11‰ increase occurs in δ 18 O and δD, respectively. Historic temperature records from surrounding areas show a 1.3 °C increase in mean annual air temperature over the same time period. This temperature change alone is not great enough to explain the observed increase in δ 18 O. We suggest that changes in atmospheric circulation patterns, which have been documented in this region, account for the remaining increase in δ 18 O. The time scale of these climatic changes, recorded in both the historical and the hydrological records, is extremely short (decadal scale) and suggests that the δ 18 O of groundwater can be a useful tool for studying climatic and atmospheric circulation changes over very short time intervals. It also suggests that circulation changes must be considered along with temperature when interpreting paleoclimate data.