Pacific–North American Teleconnection Controls on Precipitation Isotopes (δ18O) across the Contiguous United States and Adjacent Regions: A GCM-Based Analysis

Abstract

he Pacific?North American (PNA) teleconnection pattern has a strong influence on North America?s winter climate, but much less is known about how the PNA pattern controls precipitation isotopes (e.g., δ18O) across the United States. In this study, an isotopically equipped atmospheric general circulation model (isoGSM) is used to investigate how divergent phases of the PNA affect precipitation δ18O values across the United States. A simulation using observational climate and isotope data over the United States is evaluated first. The simulation explains 84% of the spatial variability of winter precipitation δ18O, with an overestimation in the northern Rocky Mountains and the Great Lakes. Temporally, the simulation explains 29%?81% of the interannual variability of winter precipitation δ18O, with typically a higher explained variance in the east than the west. The modeled winter precipitation δ18O exhibits a clear northwest?southeast (NW?SE) dipolelike pattern in response to shifts in the PNA pattern, with the center of positive polarity in the northwestern United States and the Canadian prairies and the center of negative polarity over the Ohio River valley. This dipolelike spatial pattern is a result of the difference in atmospheric circulation and moisture sources associated with the PNA pattern. These results highlight the importance of the PNA-associated circulation dynamics in governing precipitation isotope patterns across the United States. This understanding improves our ability to interpret paleoclimate records of water isotope/hydrologic change across the United States with a much greater appreciation of regional traits. The robust antiphase oscillation in precipitation isotopes in response to shifting the PNA pattern provides a promising opportunity to reconstruct the past variability in the PNA pattern that may be recorded in ice cores, tree rings, lake sediments, and speleothems.