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首页> 外文期刊>Atmospheric chemistry and physics >Air–snow transfer of nitrate on the East Antarctic Plateau – Part 2: An isotopic model for the interpretation of deep ice-core records
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Air–snow transfer of nitrate on the East Antarctic Plateau – Part 2: An isotopic model for the interpretation of deep ice-core records

机译：东极南极高原上硝酸盐的气雪传递–第2部分：解释深冰芯记录的同位素模型

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Unraveling the modern budget of reactive nitrogen on the Antarctic Plateauis critical for the interpretation of ice-core records of nitrate. Thisrequires accounting for nitrate recycling processes occurring in near-surface snow and the overlying atmospheric boundary layer. Not onlyconcentration measurements but also isotopic ratios of nitrogen and oxygenin nitrate provide constraints on the processes at play. However, due tothe large number of intertwined chemical and physical phenomena involved,numerical modeling is required to test hypotheses in a quantitative manner.Here we introduce the model TRANSITS (TRansfer of Atmospheric Nitrate StableIsotopes To the Snow), a novel conceptual, multi-layer andone-dimensional model representing the impact of processes operating onnitrate at the air–snow interface on the East Antarctic Plateau, in terms ofconcentrations (mass fraction) and nitrogen (δ15N) and oxygenisotopic composition (17O excess, Δ17O) in nitrate. At theair–snow interface at Dome C (DC; 75° 06' S, 123° 19' E),the model reproduces well the values of δ15N in atmospheric andsurface snow (skin layer) nitrate as well as in the δ15Nprofile in DC snow, including the observed extraordinary high positive values(around +300 ‰) below 2 cm. The model also capturesthe observed variability in nitrate mass fraction in the snow. While oxygendata are qualitatively reproduced at the air–snow interface at DC and inEast Antarctica, the simulated Δ17O values underestimate theobserved Δ17O values by several per mill. This isexplained by the simplifications made in the description of the atmosphericcycling and oxidation of NO2 as well as by our lack of understanding ofthe NOx chemistry at Dome C. The model reproduces well the sensitivityof δ15N, Δ17O and the apparent fractionationconstants (15ϵapp, 17Eapp) to thesnow accumulation rate. Building on this development, we propose a frameworkfor the interpretation of nitrate records measured from ice cores.Measurement of nitrate mass fractions and δ15N in the nitratearchived in an ice core may be used to derive information about pastvariations in the total ozone column and/or the primary inputs of nitrateabove Antarctica as well as in nitrate trapping efficiency (defined as theratio between the archived nitrate flux and the primary nitrate input flux).The Δ17O of nitrate could then be corrected from the impact ofcage recombination effects associated with the photolysis of nitrate insnow. Past changes in the relative contributions of the Δ17O inthe primary inputs of nitrate and the Δ17O in the locallycycled NO2 and that inherited from the additional O atom in theoxidation of NO2 could then be determined. Therefore, information aboutthe past variations in the local and long-range processes operating onreactive nitrogen species could be obtained from ice cores collected in low-accumulation regions such as the Antarctic Plateau.
机译：揭示南极高原活性氮的现代预算对于解释硝酸盐冰芯记录至关重要。这需要考虑到发生在近地表雪和上覆大气边界层中的硝酸盐再循环过程。不仅浓度测量值而且硝酸盐中氮和氧的同位素比值也对进行中的过程提供了限制。然而，由于涉及大量相互交织的化学和物理现象，因此需要进行数值建模以定量地检验假设。在这里，我们引入了模型TRANSITS（大气硝酸盐稳定同位素向雪地的转移），这是一种新颖的概念性多层结构一维模型，表示浓度（质量分数）和氮（δ 15 N）和氧同位素组成（ 17 O过量，Δ 17 O）。在圆顶C（DC; 75°06'S，123°19'E）的风雪界面处，该模型很好地再现了大气和表层硝酸盐（皮层）硝酸盐中的δ 15 N值以及DC雪中的δ 15 N剖面，包括在2 cm以下观察到的非常高的正值（约+300‰）。该模型还捕获了观测到的雪中硝酸盐质量分数的变化。在DC和南极东部的风雪界面上定性地复制了氧气数据时，模拟的Δ 17 O值低估了每轧机观测到的Δ 17 O值。可以通过对NO 2 的大气循环和氧化的描述简化以及我们对NO x 化学的认识不足来解释这一点。该模型很好地再现了δ 15 N，Δ 17 O和表观分馏常数（ 15 ＆varepsilon; app ， 17 E app ）表示雪的累积速率。在此基础上，我们提出了一个解释从冰芯测得的硝酸盐记录的框架。测量冰芯中硝酸盐的硝酸盐质量分数和δ 15 N的方法可用于得出有关过去变化的信息在总臭氧柱和/或南极洲上方的硝酸盐的主要输入量以及硝酸盐的捕集效率（定义为已归档的硝酸盐通量和主要的硝酸盐输入通量之间的比值）。Δ 17 O然后可以从笼子重组效应的影响中纠正硝酸盐，其中笼子重组效应与硝酸盐雪片的光解有关。硝酸盐主要输入中的Δ 17 O和局部循环的NO 2 中的Δ 17 O的相对贡献的过去变化然后可以确定NO 2 氧化中其他O原子的含量。因此，可以从收集在低积聚地区（如南极高原）的冰芯中获得有关对反应性氮物种进行操作的本地和远程过程过去变化的信息。

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