Stable carbon isotope record of terrestrial organic materials for the last 450 Ma yr

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• 作者：Lee Nordt^a ; ; Jack Tubbs^b ; Steven Dworkin^a
• 关键词：Stable carbon isotope ; Terrestrial plants ; Phanerozoic ; pCO2 ; Atmospheric δ13C ; Marine δ13C
• 刊名：Earth Science Reviews
• 出版年：2016
• 出版时间：August 2016
• 年：2016
• 卷：159
• 期：Complete
• 页码：103-117
• 全文大小：1453 K

文摘

The timing and magnitude of carbon isotope excursions is essential for understanding the global transfer of carbon among the oceansland, and atmosphere. Numerous studies have focused on data collection of stable carbon isotopes (δ¹³C) from marine sediments, and by extension to the atmosphere, but many fewer systematic studies have been conducted on land plants over long time intervals. We pursued three approaches to determining stable carbon isotope trends for the past 450 Ma yr from C₃ plants (δ¹³Cp) in 5 Ma yr time steps. First, a compilation of 6888 δ¹³Cp values from ten carbon sources from the literature average − 24.6 ± 1.7‰ (ISOORG data base). The second approach assumes the δ¹³Cp is controlled primarily by the δ¹³C of atmospheric CO₂ (δ¹³Ca) and subsequent isotopic fractionation from diffusion and carboxylation during photosynthesis (MOD1). The third approach assumes changes in atmospheric CO₂ concentration (pCO₂) causes physiological-driven isotopic fractionation during photosynthesis when pCO₂ is greater than average Holocene conditions (MOD2). Compared to ISOORG and MOD1, MOD2 reveals lower δ¹³Cp by up to 6‰ during periods when pCO₂ is elevated. As secular governors of δ¹³Cp, the δ¹³Ca and pCO₂ are most influential when they are directional and amplify the isotopic signal. Despite potential influences from local and regional environmental conditions, and averaging the δ¹³Cp of multiple plant sources in many of the 5 Ma yr age bins, ten positive carbon isotopic excursions (PCIEs) are identified in ISOORG of this study. Most of the excursions occurred during cool to glacial conditions or ocean anoxic events. One prominent negative isotopic excursion ensued from 260 to 240 Ma yr, which may have been a response to oxidation of light C, methane outbursts, volcanic eruptions, or bolide impact.