Annual variation in event-scale precipitation δ 2 H at Barrow, AK, reflects vapor source region

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 precipitation site. Seventy precipitation events between January 2009 and March 2013 were analyzed for δ 2 H and deuterium excess. For each precipitation event, vapor source regions were identified with the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) air parcel tracking program in back-cast mode. The results show that the vapor source region migrated annually, with the most distal (proximal) and southerly (northerly) vapor source regions occurring during the winter (summer). This may be related to equatorial expansion and poleward contraction of the polar circulation cell and the extent of Arctic sea ice cover. Annual cycles of vapor source region latitude and δ 2 H in precipitation were in phase; depleted (enriched) δ 2 H values were associated with winter (summer) and distal (proximal) vapor source regions. Precipitation δ 2 H responded to variation in vapor source region as reflected by significant correlations between δ 2 H with the following three parameters: (1) total cooling between lifted condensation level (LCL) and precipitating cloud at Barrow, Δ 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, m t n . These three variables explained 54 % of the variance ( p 0. 001) in precipitation δ 2 H with a sensitivity of −3.51 ± 0.55 ‰ °C −1 ( p 0. 001) to Δ T cool , 3.23 ± 0.83 ‰ °C −1 ( p 0. 001) to T d , and −32.11 ± 11.04 ‰ ( p  = 0. 0049) depletion when m t n is true. The magnitude of each effect on isotopic composition also varied with vapor source region proximity. For storms with proximal vapor source regions (where Δ T cool T cool explained 3 % of the variance in δ 2 H, T d alone accounted for 43 %, while m t n explained 2 %. For storms with distal vapor sources (Δ T cool  > 7°C), Δ T cool explained 22 %, T d explained only 1 %, and m t n explained 18 %. The deuterium excess annual cycle lagged by 2–3 months during the δ 2 H cycle, so the direct correlation between the two variables is weak. Vapor source region relative humidity with respect to the sea surface temperature, h ss , explained 34 % of variance in deuterium excess, (−0.395 ± 0.067 ‰ % −1 , p 0. 001). The patterns in our data suggest that on an annual scale, isotopic ratios of precipitation at Barrow may respond to changes in the southerly extent of the polar circulation cell, a relationship that may be applicable to interpretation of long-term climate change records like ice cores.