title: ENSO effects on δ18O, δ2H and d-excess values in precipitation across the U.S. using a high-density, long-term network (USNIP).
abstract: BACKGROUND
  Isotope (δ(18)O and δ(2)H values) ratios in precipitation have been central to understanding changes in Earth's climate as recorded in ice, coral, speleothems, lake varves and long-lived plants. Understanding how climate phases (i.e. ENSO) affect the spatial and temporal patterns of δ(18)O and δ(2)H values in precipitation has, however, been uncertain across the USA.
  
  
  METHODS
  A spatial precipitation isotope network (USNIP) has been established that aims to: (1) characterize the δ(18)O, δ(2)H and d-excess values in precipitation across the USA with the highest spatially dense network of measurements yet undertaken; (2) quantify the annual and seasonal patterns of precipitation δ(18)O and δ(2)H values that may be affected by ENSO climate phases; and (3) provide a new isotope database for scientific studies that can be incorporated into NEON, BASIN, GNIP, and IsoMAP.
  
  
  RESULTS
  On average, precipitation δ(18)O and δ(2)H values are very low in the northern Rocky Mountain region (~ -15‰ δ(18)O, and ~ -120‰ δ(2)H), and precipitation δ(18)O and δ(2)H values are relatively higher along the Gulf Coast (~ -5‰ δ(18)O and -10‰ δ(2)H) and in the Southeast. During El Niño periods the precipitation δ(18)O and δ(2)H values are lowest in northwest Montana, with precipitation that is depleted in (18)O and (2)H extending into northern Colorado, while moisture that is enriched in (18)O and (2)H continues to dominate the Gulf Coast. The annual average differences between the climate phases generally show especially depleted (18)O and (2)H in precipitation across the Rocky Mountain region during El Niño, compared with Neutral periods.
  
  
  CONCLUSIONS
  Detailed spatial and seasonal patterns of δ(18)O, δ(2)H and d-excess values provide fine-scale resolution not previously recognized. Climate phases of ENSO have major effects on the spatial patterns of δ(18)O, δ(2)H and d-excess values, being especially important on a seasonal basis in the Desert Southwest.
authors: Environment and Natural Resources Institute, Stable Isotope Laboratory and Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA. afjmw1@uaa.alaska.edu
authors: Jeffrey M
authors: JM
authors: Welker
mesh_terms: D003903:Deuterium / Q000032:analysis*; D059000:El Nino-Southern Oscillation; D013058:Mass Spectrometry; D010103:Oxygen Isotopes / Q000032:analysis*; D011891:Rain / Q000737:chemistry*; D014481:United States
chemical_list: D010103:Oxygen Isotopes; D003903:Deuterium