As one of the most important greenhouse gases, CO is considered a major controlling factor of Earth's climate over geological timescales. However, the origins of quasi-periodic fluctuations in CO on a million-year timescale remain unclear. Here, we used published datasets of atmospheric CO, oxygen isotopes of benthic foraminifera (δO) and global mean sea-level (GMSL) from 23 Ma to the present to explore the pacing of CO changes and concomitant climatic effects using multiple time series analysis approaches. Our results indicate that the evolution of late Cenozoic CO and climate was paced by the grand orbital cycles, in particular the ∼4.5 Myr and ∼2.4 Myr eccentricity cycles, and ∼1.3 Myr obliquity cycle. Periodic occurrence of cold conditions was associated with low climate seasonality during the minima of ∼4.5 Myr and ∼2.4 Myr eccentricity cycles. We suggest that cooler conditions are associated with decreased atmospheric CO as a result of higher organic carbon burial due to lower metabolic rate of heterotrophic bacteria and more organic carbon export to the deep ocean. Furthermore, the buildup of glaciers during the minima of grand eccentricity cycles might lower CO via increased ice cover and enhanced dust fluxes. In contrast, high seasonal climate may lead to an opposite effect on atmospheric CO during the maxima of the grand eccentricity cycles. Moreover, we found a distinct shift in the dominant signal from eccentricity to obliquity cycles recorded in the CO, δO and GMSL datasets at ∼13 Ma, a time when perennial sea ice occurred in the Arctic and significant ice growth shown in Antarctica. We suggest that the change in the type and distribution of the ice sheets would shift glacial response to orbital forcing and hence mediated global climate and CO. Our analysis reveals a clear synchrony among atmospheric CO, climate change, and the grand orbital cycles in the late Cenozoic.

中文翻译：

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新生代晚期 pCO2 和气候的变化受大轨道周期的影响


作为最重要的温室气体之一，二氧化碳被认为是地质时间尺度上地球气候的主要控制因素。然而，百万年时间尺度上二氧化碳准周期波动的起源仍不清楚。在这里，我们使用已发布的 23 Ma 至今的大气 CO、底栖有孔虫氧同位素 (δ18O) 和全球平均海平面 (GMSL) 数据集，利用多种时间序列分析方法探索 CO 变化的节奏和随之而来的气候影响。我们的结果表明，晚新生代二氧化碳和气候的演化是由大轨道周期决定的，特别是~4.5 Myr和~2.4 Myr偏心率周期，以及~1.3 Myr倾角周期。寒冷条件的周期性出现与 4.5 Myr 和 2.4 Myr 偏心率周期最小值期间的低气候季节性有关。我们认为，较冷的条件与大气中二氧化碳的减少有关，这是由于异养细菌的代谢率较低和更多的有机碳输出到深海而导致的有机碳埋藏较高。此外，在大偏心率周期的最小值期间冰川的堆积可能会通过增加冰盖和增强尘埃通量来降低二氧化碳。相反，在大偏心率周期的最大值期间，高季节性气候可能会对大气二氧化碳产生相反的影响。此外，我们发现 CO、δ18O 和 GMSL 数据集中记录的主导信号在约 13 Ma 时发生了从偏心率到倾斜周期的明显转变，此时北极出现常年海冰，南极洲出现显着的冰生长。我们认为冰盖类型和分布的变化将改变冰川对轨道强迫的反应，从而调节全球气候和二氧化碳。 我们的分析揭示了大气二氧化碳、气候变化和新生代晚期大轨道循环之间明显的同步性。