Alkenones are long-chain ketones produced by phytoplankton of the order Isochrysidales. They are widely used in reconstructing past sea surface temperatures, benefiting from their ubiquitous occurrence in the Cenozoic ocean. Carbon isotope fractionation (εp) between alkenones and dissolved inorganic carbon may also be used as a proxy for past atmospheric pCO2 and has provided continuous pCO2 estimates back to ca. 45 Ma. Here, an extended occurrence of alkenones from ca. 130 Ma is reported. We characterize the molecular structure and distribution of these Mesozoic alkenones and evaluate their potential phylogenetic relationship with Cenozoic alkenones. Using δ13C values of the C37 methyl alkenone (C37:2Me), the first alkenone-based pCO2 estimates for the Mesozoic are derived. These estimates suggest elevated pCO2 with a range of 548–4090 ppm (908 ppm median) during the super-greenhouse climate of the Early Cretaceous, in agreement with phytane-based pCO2 reconstructions. Finally, insights into the identity of the Cretaceous coccolithophores that possibly synthesized alkenones are also offered.

中文翻译：

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白垩纪 pCO2 的烯酮估算值


烯酮是由等鞭藻目浮游植物产生的长链酮。得益于它们在新生代海洋中的普遍存在，它们被广泛用于重建过去的海面温度。烯酮和溶解的无机碳之间的碳同位素分馏 (εp) 也可用作过去大气 pCO2 的代理，并提供了连续的 pCO2 估计值，可追溯到大约 100 年前。 45马。在这里，来自大约的烯酮的广泛出现。据报告为 130 Ma。我们表征了这些中生代烯酮的分子结构和分布，并评估了它们与新生代烯酮的潜在系统发育关系。使用 C37 甲基烯酮 (C37:2Me) 的 δ13C 值，得出第一个基于烯酮的中生代 pCO2 估计值。这些估计表明，在白垩纪早期的超级温室气候期间，pCO2 升高了 548-4090 ppm（中值 908 ppm），这与基于植烷的 pCO2 重建一致。最后，还提供了对可能合成烯酮的白垩纪球石藻身份的见解。