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The isotopic composition of atmospheric oxygen

机译：大气氧的同位素组成

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Atmospheric O_2 is almost 24‰ more enriched in ~(18)O than seawater, and this enrichment is known as the Dole effect. For a long time it has been accepted that there is no oxygen isotope fractionation in photosynthesis, and thus the Dole effect should be the result of preferential terrestrial and marine respiratory consumption of ~(16)O over ~(18)O, and also several permil enrichment of leaf water from which terrestrial photosynthesis produces ~(18)O enriched O_2. This concept has led to the understanding that the record of past Dole effect variations was strongly affected by changes in the ratio of photosynthetic production between land and sea. However, recent studies in our lab have led to two major new observations: (1) O_2 produced by certain marine phytoplankton, representing important groups of primary producers, is significantly enriched (up to 6‰) in ~(18)O with respect to the substrate seawater and (2) effective oxygen isotope fractionation in soil respiration is considerably smaller than the intrinsic respiratory fractionation. Here we take these two observations into account and show that the magnitudes of the terrestrial and marine components of the Dole effect are close, and both are close to the measured Dole effect. As a result, the magnitude of the global Dole effect should not be sensitive to past changes in the ratio of land-to-sea photosynthetic rates. Instead of the land-sea control, variations in low-latitude hydrology, and possibly changes of fractionations in the marine biosphere, are more important in regulating the magnitude of the Dole effect and its past variations.
机译：大气中的O_2比海水中的（18）O富集了将近24‰，这种富集称为Dole效应。长期以来，人们一直认为光合作用中不存在氧同位素分级分离，因此，多尔效应应是陆地和海洋呼吸优先消耗〜（16）O而不是〜（18）O的结果。陆地水的Permil富集，陆地光合作用产生〜（18）O富集的O_2。这一概念使人们认识到，过去的Dole效应变化的记录受到陆地和海洋之间光合产量比率变化的强烈影响。但是，我们实验室的最新研究得出了两个主要的新发现：（1）某些海洋浮游植物所产生的O_2代表了重要的初级生产者群，相对于（18）O而言，O_2的含量显着丰富（高达6‰）。底物海水和（2）土壤呼吸中的有效氧同位素分馏比固有的呼吸分馏要小得多。在这里，我们考虑到这两个观察结果，并表明，都尔效应的陆地和海洋成分的幅度接近，并且都与实测的都尔效应接近。结果，全球Dole效应的强度不应对过去海陆光合速率比率的变化敏感。在控制都尔效应的幅度及其过去的变化中，低纬度水文学的变化以及海洋生物圈中各个部分的变化可能会比陆地-海洋控制更为重要。

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