Interacting climate oscillations modulate the long-term spatiotemporal variability of precipitation isotopes (18O, 2H, d-excess) across the USA.

Temperature and precipitation patterns across globe are modulated by couplings between Climate Oscillations (COs) (ENSO, PDO, AO, NAO and PNA) and their phases (i.e., weak/strong, positive/negative) through zonal and meridional air-flow patterns. However, the degree to which COs interact to affect precipitation isotope (δ18O, δ2H, d-excess) patterns remains poorly constrained. Discerning these interactions is important as temperature, precipitation, and/or moisture source signatures are preserved in the precipitation isotopic composition and subsequently transferred to ice cores and other climate proxies. Therefore, understanding contemporary processes governing the variability of precipitation isotopes in response to COs can help define modern atmospheric patterns, unravel paleoclimates and improve process representation in climate models. This 25-year USNIP weekly precipitation isotope database from 77 sites across the contiguous USA provides the basis to delineate the role of individual COs and their interactions, as they control the spatiotemporal variability of precipitation isotopes at the continental scale, like never before. Wavelet multiple regression analysis reveals an intricate and nuanced association between the COs. The relationship between the individual CO indexes and the precipitation isotopes is spatially and temporally inconsistent with varying time periods of linear (positive/negative), non-linear, or no coherence. Fluctuating interactions between multiple COs cause reorganization of atmospheric circulation patterns leading to changes in moisture transport pathways/storm-tracks, which is supported by back-trajectory analysis and mirrored in spatial precipitation isotope anomalies. Our results provide a new framework in which to: 1) reflect on paleoclimate interpretations of an ice core from the Rocky Mountains, whereby, large shifts in the Beartooth ice core d-excess values can only be explained by variable contribution of moisture, sourced from oceanic regions with contrasting physical conditions; and 2) provide the basis on which to recalibrate Isotope Enabled Global Climate Models (iGCMs) to overcome significant discrepancies when comparing the observed precipitation isotopic composition to that modelled by six iGCMs.