Alkenone-derived estimates of Cretaceous pCO2

Geology Pub Date : 2024-04-23 DOI:10.1130/g51939.1
Weimin Si, Joseph B. Novak, Nora Richter, P. Polissar, Ruigang Ma, Ewerton Santos, Jared Nirenberg, Timothy D. Herbert, Marie-Pierre Aubry
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Abstract

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.
白垩纪 pCO2 的烯酮估计值
烯酮类化合物是由浮游植物异绿藻纲产生的长链酮类化合物。由于它们在新生代海洋中无处不在,因此被广泛用于重建过去的海表温度。烯酮类与溶解无机碳之间的碳同位素分馏(εp)也可作为过去大气中pCO2的代用指标,并提供了可追溯到约45 Ma的连续pCO2估算值。在此,我们报告了烯酮类化合物在大约 130 Ma 时的长期存在。我们描述了这些中生代烯酮的分子结构和分布特征,并评估了它们与新生代烯酮的潜在系统发育关系。利用 C37 甲基烯酮(C37:2Me)的 δ13C 值,首次得出了中生代基于烯酮的 pCO2 估算值。这些估算结果表明,在早白垩世的超温室气候期间,pCO2 升高,范围为 548-4090ppm(中位数为 908ppm),与基于植烷的 pCO2 重建结果一致。最后,我们还对可能合成烯酮的白垩纪嗜球藻的身份提出了见解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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