Over geological timescales, variations in atmospheric O2 are typically attributed to the imbalance between the weathering of organic carbon (OC) and reduced sulfur on land, the major sink terms for atmospheric O2, and the burial of OC and reduced sulfur in marine sediments, the major source terms of O2 to the atmosphere. But the Fe cycle matters too. Using a compilation of C, Fe, S and H fluxes between the Earth's exosphere, continents, and mantle reservoirs, I demonstrate that hydrothermal weathering of the oceanic lithosphere and volcanic degassing of SO2 have acted as net sinks of O2, amounting to ca. 2.7 ± 1.1 Tmol O2/y, over the Cenozoic. Near constancy of atmospheric oxygen concentrations over the same interval of time suggests that this igneous sink is compensated by the sedimentary cycles of C, S and Fe. The net subduction and accretion of OC likely made the dominant contribution and, therefore, operated as a net source of atmospheric O2 over the last 50-60 Myr. This result implies that redox steady-state in the Cenozoic is dynamically maintained by a net input of solar (photosynthetic) energy, ∼ 0.8 to 2 EJ/y, into the lithospheric cycles of C, S and Fe.

中文翻译：

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氧化还原对有机碳循环新生代失衡的限制

在地质时间尺度上，大气 O2 的变化通常归因于有机碳 (OC) 的风化和陆地上还原硫、大气 O2 的主要汇项以及海洋沉积物中 OC 和还原硫的掩埋之间的不平衡，大气中 O2 的主要来源。但铁循环也很重要。使用地球外逸层、大陆和地幔储层之间的 C、Fe、S 和 H 通量的汇编，我证明了海洋岩石圈的热液风化和 SO2 的火山脱气作为 O2 的净汇，总计约 2.7 ± 1.1 Tmol O2/y，在新生代。在相同的时间间隔内，大气氧浓度接近恒定表明这个火成岩汇被 C、S 和 Fe 的沉积循环所补偿。OC 的净俯冲和吸积可能做出了主要贡献，因此在过去的 50-60 Myr 中作为大气 O2 的净来源运行。这一结果意味着新生代的氧化还原稳态是通过向 C、S 和 Fe 的岩石圈循环中净输入太阳能（光合）能量，约 0.8 至 2 EJ/y 来动态维持的。