Atmospheric Oxygen Abundance, Marine Nutrient Availability, and Organic Carbon Fluxes to the Seafloor
Atmospheric Oxygen Abundance, Marine Nutrient Availability, and Organic Carbon Fluxes to the Seafloor
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DOI：
10.1029/2021gb007052
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发表时间：
2021-04
影响因子：
5.2
通讯作者：
D. Cole;K. Ozaki;C. Reinhard
中科院分区：
文献类型：
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作者：
D. Cole;K. Ozaki;C. Reinhard
地球表面的全球规模氧化是地球历史上最基本的化学转变之一。有实证和理论证据表明，地球表面氧化至少存在两种截然不同且稳定的状态——一种是以普遍缺氧的深海海水为特征的“低氧世界”，以及一种以我们现代地表环境为代表的、深海海水主要富氧的“高氧世界”。众多生物地球化学过程和反馈控制着海洋系统的氧化还原状态，尤其是在全球范围和地质时间尺度上考虑时。因此，要对使深海氧化所需的大气氧含量（以及由此产生的生产力、营养物质可利用性和还原剂消耗）进行定量且内部一致的估算已被证明具有挑战性。在此，我们利用一个追踪碳、氮、氧、磷和硫循环的地球系统生物地球化学模型，对这种关系提供新的定量约束。我们探究了在从当前大气水平（PAL）的0.01%到100%的广泛大气氧含量范围内的海洋生物地球化学以及还原碳向海底的通量，并采用一种随机方法对我们的结果提供不确定性的正式估算。我们发现，在pO₂水平达到约40% PAL之前，深海海水大体上仍然缺氧，并且海洋生产力相对于现代海洋生物圈仍然显著较低。这些结果对于新元古代晚期和古生代期间大气pO₂水平的定量约束具有重要意义，无论是就早期动物的环境宜居性而言，还是就底栖群落生长和多样化的潜在能量约束而言。
The global‐scale oxygenation of Earth's surface represents one of the most fundamental chemical transformations in our planet's history. There is empirical and theoretical evidence for at least two distinct and stable regimes of Earth surface oxygenation—a “low‐O2 world” characterized by pervasively anoxic deep ocean waters, and a “high‐O2 world” with dominantly well‐oxygenated deep ocean waters represented by our modern surface environment. Numerous biogeochemical processes and feedbacks control the redox state of the marine system, particularly when considered globally and on geologic timescales. It has therefore proven challenging to provide quantitative and internally consistent estimates of the atmospheric oxygen levels (and thereby, productivity, nutrient availability, and reductant consumption) necessary to oxygenate the deep seas. Here, we leverage an Earth‐system biogeochemical model that tracks the carbon, nitrogen, oxygen, phosphorus, and sulfur cycles to provide new quantitative constraints on this relationship. We explore ocean biogeochemistry and fluxes of reduced carbon to the seafloor across a wide range of atmospheric oxygen levels from 0.01% to 100% of the present atmospheric level (PAL), and implement a stochastic approach to provide formal estimates of uncertainty on our results. We find that deep ocean waters remain largely anoxic, and ocean productivity remains significantly muted relative to the modern marine biosphere, until pO2 levels reach ∼40% PAL. These results have major implications for quantitative constraints on atmospheric pO2 levels during the latest Proterozoic and Paleozoic, both in terms of environmental habitability for early animals and with respect to potential energetic constraints on growing and diversifying benthic communities.