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Atmospheric Chemistry and Physics


In this study, precipitation isotopic variations at Barrow, AK, USA, are linked to conditions at the moisture source region, along the transport path, and at the precipita- tion site. Seventy precipitation events between January 2009 and March 2013 were analyzed for δ2H and deuterium ex- cess. For each precipitation event, vapor source regions were identified with the hybrid single-particle Lagrangian inte- grated trajectory (HYSPLIT) air parcel tracking program in back-cast mode. The results show that the vapor source re- gion migrated annually, with the most distal (proximal) and southerly (northerly) vapor source regions occurring during the winter (summer). This may be related to equatorial ex- pansion and poleward contraction of the polar circulation cell and the extent of Arctic sea ice cover. Annual cycles of vapor source region latitude and δ2H in precipitation were in phase; depleted (enriched) δ2H values were associated with winter (summer) and distal (proximal) vapor source regions. Precipitation δ2H responded to variation in vapor source region as reflected by significant correlations betweenδ2H with the following three parameters: (1) total cooling between lifted condensation level (LCL) and precipitating cloud at Barrow, 􏰀T cool , (2) meteorological conditions at the evaporation site quantified by 2 m dew point, T d, and (3) whether the vapor transport path crossed the Brooks and/or Alaskan ranges, expressed as a Boolean variable, mt n. These three variables explained 54 % of the variance (p<0.001) in precipitation δ2H with a sensitivity of −3.51 ± 0.55 ‰ ◦C−1(p<0.001) to 􏰀T cool, 3.23 ± 0.83 ‰ ◦C−1 (p<0.001) to Td, and −32.11 ± 11.04 ‰ (p = 0.0049) depletion when mt n is true.