Seasonal variations in N and O isotopes of nitrate in snow at Summit, Greenland: Implications for the study of nitrate in snow and ice cores
Seasonal variations in N and O isotopes of nitrate in snow at Summit, Greenland: Implications for the study of nitrate in snow and ice cores
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DOI：
10.1029/2004jd004991
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发表时间：
2004-10
影响因子：
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通讯作者：
M. Hastings;E. Steig;D. Sigman
中科院分区：
文献类型：
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作者：
M. Hastings;E. Steig;D. Sigman
[1]在格陵兰萨米特的雪和积雪中测量了NO3-的氮和氧同位素。最近降雪中NO3-的15 N/14 N和18 O/16 O比值与地表雪相似。NO3−的15 N/14 N和可能的18 O/16 O存在日变化，表明NO3−在白天从雪中分离损失，随后在夜间恢复。一个更大的季节变化，观察到较高的15 N/14 N和较低的18 O/16 O的NO3-在夏季比冬季，这不能解释的沉积后分馏。格陵兰雪中NO3−的18 O/16 O通常较高（δ 18 O与VSMOW = 65.2至79.6‰），表明臭氧中的氧原子已被纳入NOx中，随后以HNO 3的形式沉积。夏季雪中NO3−的平均δ 18 O低于冬季（2000年夏季为68.9‰，2001年夏季为70.5‰，2000- 2001年冬季为77.5 ‰），这是由于夏季NO2与羟基自由基（OH）反应产生HNO 3的结果，这稀释了臭氧赋予NO2的高δ 18 O。春季雪中NO3−的平均15 N/14 N较高（2000年δ 15 N对空气N2 = +5.9‰，2001年为-1.4 ‰）和夏季（2000年为+0.1‰，2001年为-0.8 ‰）根据目前的知识，冬季（2000- 2001年为-10.0 ‰）和冬季（2000- 2001年为-9.2 ‰）更难以用季节性光化学来解释。季节性的15 N/14 N变化可以反映NOx来源，相对于NOx的其他输入，化石燃料排放的秋季和冬季贡献更大（即，生物源土壤排放、生物量燃烧和闪电）。
[1] Nitrogen and oxygen isotopes of NO3− have been measured in snow and firn from Summit, Greenland. The 15N/14N and 18O/16O ratios of NO3− in recently fallen snow are similar to those of surface snow. Diurnal variation is observed in 15N/14N of NO3−, and possibly 18O/16O, suggesting fractionating loss of NO3− from snow during the day, which is subsequently recovered at night. A larger seasonal variation is observed, with higher 15N/14N and lower 18O/16O of NO3− in summer than winter, which cannot be explained by postdepositional fractionation. The generally high 18O/16O of NO3− in Greenland snow (δ18O versus VSMOW = 65.2 to 79.6‰) indicates that oxygen atoms from ozone have been incorporated into NOx that was subsequently deposited as HNO3. The lower mean δ18O of NO3− in summer snow relative to winter (68.9‰ in summer 2000 and 70.5‰ in summer 2001 versus 77.5‰ in winter 2000–01) is a result of summertime HNO3 production via NO2 reaction with hydroxyl radical (OH), which dilutes the high δ18O imparted on NO2 from ozone. The higher mean 15N/14N of NO3− observed in snow from spring (δ15N versus air N2 = +5.9‰ in 2000 and −1.4‰ in 2001) and summer (+0.1‰ in 2000 and −0.8‰ in 2001) than fall (−9.2‰ in 2000) and winter (−10.0‰ in 2000–01) is more difficult to explain with seasonal photochemistry, given current knowledge. The seasonal 15N/14N change may reflect NOx sources, with a greater fall and wintertime contribution from fossil fuel emissions relative to other inputs of NOx (i.e., biogenic soil emissions, biomass burning, and lightning).