Rise of Earth's atmospheric oxygen controlled by efficient subduction of organic carbon
Rise of Earth's atmospheric oxygen controlled by efficient subduction of organic carbon
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DOI：
10.1038/ngeo2939
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发表时间：
2017-05-01
影响因子：
18.3
通讯作者：
Dasgupta, Rajdeep
中科院分区：
文献类型：
--
作者：
Duncan, Megan S.;Dasgupta, Rajdeep
地球内部和外部之间的碳净通量对氧化还原演化和行星可居住性至关重要，这在很大程度上取决于碳俯冲的程度。虽然对俯冲过程中碳酸盐的命运进行了研究，但对有机碳如何从地球表面转移到内部知之甚少，尽管有机碳封存与地表环境中的氧气来源有关。在这里，我们使用高压-温度实验来确定的能力，流纹质熔体进行碳在石墨饱和条件下的俯冲板，从而限制俯冲效率的有机碳，残余的生活，通过时间。我们使用我们的实验数据和板熔体中的CO2溶解的热力学模型来量化有机碳的流动性作为板参数的函数。我们表明，俯冲的石墨化有机碳，和石墨和金刚石形成的碳酸盐还原深度，仍然有效，即使在古老的，较热的俯冲带，氧化碳俯冲可能仍然有限。我们认为，俯冲带中有机碳的固定和地幔中的深部封存促进了古元古代以来大气氧的上升（类似于10（3-5）倍）和维持，并与大氧化事件有因果关系。我们的模型表明，有机碳在大氧化事件之前的循环也可以解释在南极洲偶尔观察到的大气氧气。
The net flux of carbon between the Earth's interior and exterior, which is critical for redox evolution and planetary habitability, relies heavily on the extent of carbon subduction. While the fate of carbonates during subduction has been studied, little is known about how organic carbon is transferred from the Earth's surface to the interior, although organic carbon sequestration is related to sources of oxygen in the surface environment. Here we use high pressure-temperature experiments to determine the capacity of rhyolitic melts to carry carbon under graphite-saturated conditions in a subducting slab, and thus to constrain the subduction efficiency of organic carbon, the remnants of life, through time. We use our experimental data and a thermodynamic model of CO2 dissolution in slab melts to quantify organic carbon mobility as a function of slab parameters. We show that the subduction of graphitized organic carbon, and the graphite and diamond formed by reduction of carbonates with depth, remained efficient even in ancient, hotter subduction zones where oxidized carbon subduction probably remained limited. We suggest that immobilization of organic carbon in subduction zones and deep sequestration in the mantle facilitated the rise (similar to 10(3-5) fold) and maintenance of atmospheric oxygen since the Palaeoproterozoic and is causally linked to the Great Oxidation Event. Our modelling shows that episodic recycling of organic carbon before the Great Oxidation Event may also explain occasional whiffs of atmospheric oxygen observed in the Archaean.