Carbon-isotopic compositions of geoporphyrins have been measured from marine sediments of Mesozoic and Cenozoic age in order to elucidate the timing and extent of depletion of 13C in marine primary producers. These results indicate that the difference in isotopic composition of coeval marine carbonates and marine primary photosynthate was approximately 5 to 7 permil greater during the Mesozoic and early Cenozoic than at present. In contrast to the isotopic record of marine primary producers, isotopic compositions of terrestrial organic materials have remained approximately constant for this same interval of time. This difference in the isotopic records of marine and terrestrial organic matter is considered in terms of the mechanisms controlling the isotopic fractionation associated with photosynthetic fixation of carbon. We show that the decreased isotopic fractionation between marine carbonates and organic matter from the Early to mid-Cenozoic may record variations in the abundance of atmospheric CO2.

中文翻译：

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后古生代海洋原生有机质中 13 C 消耗的年代学和机制

已从中生代和新生代海洋沉积物中测量了地卟啉的碳同位素组成，以阐明海洋初级生产者中 13C 消耗的时间和程度。这些结果表明，在中生代和新生代早期，同时期海洋碳酸盐和海洋初级光合产物的同位素组成差异比现在大约 5 至 7 permil。与海洋初级生产者的同位素记录相反，陆地有机材料的同位素组成在相同的时间间隔内保持大致恒定。海洋和陆地有机质同位素记录的这种差异被认为是控制与碳光合作用固定相关的同位素分馏的机制。