Global cooling with the onset of Antarctic glaciation ca. 34 Ma across the Eocene-Oligocene transition (EOT) terminated the early Cenozoic greenhouse climate state and marked the beginning of icehouse conditions. Although a pCO2 decline is considered to have been a major cause of this climate shift, the associated carbon-sequestration mechanism remains unclear. Here, we assessed ocean production and circulation changes across the EOT using numerical simulations combined with a novel proxy, namely, bacterial magnetofossils, the abundance and morphology of which are sensitive to sedimentary organic matter accumulation and oxygenation. We detected production and oxygenation declines in the equatorial Pacific Ocean coeval with increased biological production in the Southern Ocean after the EOT. Corroborated by simulation results and evidence from the Subantarctic region, we interpret this counterintuitive combination as a result of enhanced bottom-water formation and biological pump efficiency in the Southern Ocean due to Antarctic glacial buildup across the EOT. These results provide key evidence for deep Pacific Ocean deoxygenation and increased respired carbon concentrations, which amplified CO2 decline across the EOT.

中文翻译：

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南极冰川形成过程中太平洋呼吸碳储存增强的细菌磁化石证据


随着南极冰川作用的开始，全球变冷。 34Ma始新世-渐新世过渡期（EOT）结束了新生代早期的温室气候状态，并标志着冰室条件的开始。尽管 pCO2 下降被认为是这种气候变化的主要原因，但相关的碳封存机制仍不清楚。在这里，我们使用数值模拟结合一种新的替代物（即细菌磁化石）来评估整个 EOT 的海洋生产和环流变化，细菌磁化石的丰度和形态对沉积有机质的积累和氧化很敏感。我们发现，在EOT之后，赤道太平洋的生物产量和氧合作用下降，而南大洋的生物产量增加。通过模拟结果和来自亚南极地区的证据的证实，我们将这种违反直觉的组合解释为由于南极冰川在EOT上的堆积而导致南大洋底水形成和生物泵效率增强的结果。这些结果为深太平洋脱氧和呼吸碳浓度增加提供了关键证据，从而放大了整个EOT中二氧化碳的下降。