科研之友
微信
新浪微博
Facebook
分享链接
摘要
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 delta H-2 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 delta H-2 in precipitation were in phase; depleted (enriched) delta H-2 values were associated with winter (summer) and distal (proximal) vapor source regions. Precipitation delta H-2 responded to variation in vapor source region as reflected by significant correlations between delta H-2 with the following three parameters: (1) total cooling between lifted condensation level (LCL) and precipitating cloud at Barrow, Delta(T) over bar (cool), (2) meteorological conditions at the evaporation site quantified by 2m dew point, (T) over bar (d), and (3) whether the vapor transport path crossed the Brooks and/or Alaskan ranges, expressed as a Boolean variable, mtn. These three variables explained 54% of the variance (p < 0.001) in precipitation delta H-2 with a sensitivity of -3.51 +/- 0.55 parts per thousand degrees C-1 (p < 0.001) to Delta(T) over bar (cool), 3.23 +/- 0.83 parts per thousand degrees C-1 (p < 0.001) to T-d, and -32.11 +/- 11.04 parts per thousand (p = 0.0049) depletion when mtn 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 Delta<(T)over bar>(cool) <7 degrees C), Delta<(T)over bar>(cool) explained 3% of the variance in delta H-2, (T) over bar (d) alone accounted for 43 %, while mtn explained 2 %. For storms with distal vapor sources (Delta(T) over bar (cool) >7 degrees C), Delta(T) over bar (cool) cool explained 22 %, (T) over bar (d) explained only 1 %, and mtn explained 18 %. The deuterium excess annual cycle lagged by 2-3 months during the delta H-2 cycle, so the direct correlation between the two variables is weak. Vapor source region relative humidity with respect to the sea surface temperature, (h) over bar (ss), explained 34% of variance in deuterium excess, (-0.395 +/- 0.067 parts per thousand parts per thousand(-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.
- 出版日期2017-4-7
