A history of δ13C in atmospheric CH4 from the Cape Grim Air Archive and Antarctic firn air
A history of δ13C in atmospheric CH4 from the Cape Grim Air Archive and Antarctic firn air
复制标题
格里姆角空气档案馆和南极冷空气中大气 CH4 中 δ13C 的历史
DOI：
10.1029/1999jd900357
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发表时间：
1999
影响因子：
--
通讯作者：
L. Steele
中科院分区：
文献类型：
--
作者：
R. Francey;M. Manning;C. Allison;S. A. Coram;D. Etheridge;R. Langenfelds;D. Lowe;L. Steele
来自格里姆角(41°S)的海洋(基线)空气，在高压金属容器中收集和存档，提供了1978年以来大气甲烷中δ13C的历史。在对冰雪的扩散和重力沉降效应进行校正后，从南极洲罗德姆的不同积雪层抽出的空气也得到了类似的历史。这些档案记录与1992年以来使用格里姆角5-L玻璃瓶进行的测量相关联，并与1989年以来新西兰巴灵黑德的可比地点的数据进行了比较。18年来，温带南半球大气甲烷的δ13C增加了∼0.6ppb，甲烷混合比增加了200ppb。δ13C增长率在18年期间有所下降，但相对小于混合比增长率的同时降幅。δ13C的总体增长明显小于之前的估计，最近的放缓与之前的估计相冲突[史蒂文斯和恩格尔克迈尔，1989年]。δ13C的长期趋势和混合比趋势的不同形态与1982年以来全球恒定的甲烷源和汇一致。与混合比相比，观察到的δ13C的平衡速度较慢，这是谭恩斯最近指出的一个效应的例子。这里提供的数据限制了同位素重源和轻源的相对组合的变化很小，并表明在1978年至1995年期间，人为来源与自然来源的比率几乎没有变化。
Marine (baseline) air from Cape Grim (41°S), collected and archived in high-pressure metal containers, provides a history of δ13C in atmospheric methane from 1978. A similar history is obtained from air pumped from different layers of the firn at Law Dome, Antarctica, after correction for diffusion and gravitational settling effects in the firn. The archive records are linked to measurements since 1992 using 5-L glass flasks filled at Cape Grim, and compared to data since 1989 from a comparable site at Baring Head, New Zealand. Over 18 years the δ13C of atmospheric methane in the extratropical Southern Hemisphere has increased by ∼0.6‰ while the methane mixing ratio increased by ∼200 ppb. The δ13C growth rate decreases over the 18-year period, but by relatively less than the simultaneous decrease in mixing ratio growth rate. The overall increase in δ13C is significantly smaller than, and the recent slowing is in conflict with, previous estimates [Stevens and Engelkemeir, 1989]. The long-term trend in δ13C, and the different shape to the trend in mixing ratio, are shown to be consistent with constant global methane sources and sinks since 1982. The slower equilibration of observed δ13C, compared to that of the mixing ratio, is an example of an effect pointed out recently by Tans [1997]. The data presented here constrain changes in the relative mix of isotopically heavy and light sources to be small and suggest that there was little change in the ratio of anthropogenic to natural sources in the 1978 to 1995 period.