Shipboard determinations of 13C in atmospheric methane in the Pacific
Shipboard determinations of 13C in atmospheric methane in the Pacific
复制标题
太平洋大气甲烷中 13C 的船载测定
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
M. Maata
中科院分区：
文献类型：
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作者：
D. Lowe;A. Bromley;W. Allan;G. Brailssford;M. Manning;D. Ferretti;A. Gomez;R. Knobben;R. Martin;Z. Mei;R. Moss;K. Koshy;M. Maata
1996年和1997年，在新西兰和美国西海岸之间的太平洋上进行了四次航行，每隔2.5°至5°纬度采集一次大型清洁空气样本，报告了甲烷混合比和δ13C （δ13CH4）的测量结果。结果表明，δ13CH4半球间梯度随季节变化较大，1996年11月δ13CH4半球间梯度为0.5‰，年平均值为0.2 ~ 0.3‰。δ13CH4的季节循环呈现出三个不同的纬度带。南半球温带地区的峰值出现在1 - 2月，热带地区的峰值出现在9 - 10月，北半球温带地区的峰值出现在6 - 7月。将这些数据与三维输运和大气化学模型的结果进行了比较，该模型较好地模拟了观测到的δ13CH4或甲烷混合比的纬度结构，但不能同时模拟两者。甲烷源汇预算与这两种数据相一致的要求显然比单独使用混合比或同位素数据施加了更严格的限制。本文利用南半球温带地区的季节δ13CH4数据估算了CH4汇的净分馏值为12-15‰，这比目前实验室测量的OH + CH4反应和土壤汇过程的动力学同位素效应所能解释的值要大。讨论了这种差异是由海洋边界层中活性氯与甲烷的竞争反应引起的假设。
Measurements of the mixing ratio and δ13C in methane (δ13CH4) are reported from large, clean air samples collected every 2.5° to 5° of latitude on four voyages across the Pacific between New Zealand and the West Coast of the United States in 1996 and 1997. The data show that the interhemispheric gradient for δ13CH4 was highly dependent on season and varied from 0.5‰ in November 1996 with an estimated annual mean of 0.2–0.3‰. The seasonal cycles in δ13CH4 reveal three distinct latitude bands differentiated by phase. Maxima occur in January-February for the extratropical Southern Hemisphere, in September-October for the tropics, and in June-July for the extratropical Northern Hemisphere. The data are compared with results from a three-dimensional transport and atmospheric chemistry model that simulates the observed latitudinal structure of either δ13CH4 or the methane mixing ratio well, but not both simultaneously. The requirement that a methane source-sink budget be consistent with both types of data clearly imposes stricter constraints than arise from either mixing ratio or isotopic data alone. The seasonal δ13CH4 data in the extratropical Southern Hemisphere are used to estimate a value for the net fractionation in the CH4 sink of 12–15‰, which is larger than can be explained by current laboratory measurements of a kinetic isotope effect for the OH + CH4 reaction and soil sink processes. The hypothesis that the discrepancy is caused by competitive reaction of active chlorine with methane in the marine boundary layer is discussed.