The co-evolution of the nitrogen, carbon and oxygen cycles in the Proterozoic ocean
The co-evolution of the nitrogen, carbon and oxygen cycles in the Proterozoic ocean
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DOI：
10.2475/ajs.305.6-8.526
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发表时间：
2005-01-01
影响因子：
2.9
通讯作者：
Falkowski, PG
中科院分区：
文献类型：
--
作者：
Fennel, K;Follows, M;Falkowski, PG
地球化学证据表明，在光合作用的进化和地球大气中氧气的积累之间有数亿年的延迟。深海似乎在大气层含氧后保持了几亿年的纯氧状态。在本文中，我们研究的可能性，在大气和海洋的氧化的非凡延迟是由碳埋藏，净氧生产和氮循环在元古宙海洋的演变之间的代谢反馈所造成的地球化学的“瓶颈”。在缺氧条件下，海洋中的铵相对稳定，但随着氧浓度的上升，硝化作用和随后的反硝化作用会迅速从海洋中去除固定的无机氮。反硝化作用通过剥夺产氧光合自养生物的一种必需营养物（即固定无机氮），对游离氧的进一步上升施加了强有力的限制。为了研究氧和氮循环之间的动态相互作用，我们开发了一个五箱模型，该模型结合了氧，氮和碳循环，海洋环流和海洋-大气气体交换的显着特征。在大气或海洋中没有游离氧的厌氧条件下启动的模型模拟，其特征在于最初减少的深海具有丰富的铵，随后是一个延长的时期，当两种形式的固定氮是稳定的，和一个充分氧化的阶段与丰富的硝酸盐。我们推断，在早元古代海洋氧化的过程中，该系统必须经历一个氮限制的阶段，在此期间，输出生产严重衰减。我们的研究表明，存在增加有机物埋藏的浅海是决定海洋和大气中氧气浓度的关键因素，而磷酸盐浓度在决定深海氧化率方面发挥了关键作用。
Geochemical evidence suggests that there was a delay of several hundred million years between the evolution of oxygenic photosynthesis and the accumulation of oxygen in Earth's atmosphere. The deep ocean appears to have remained euxenic for several hundred million years after the atmosphere became oxygenated. In this paper we examine the possibility that the extraordinary delay in the oxidation of the atmosphere and oceans was caused by a biogeochemical "bottleneck" imposed by metabolic feedbacks between carbon burial, net oxygen production, and the evolution of the nitrogen cycle in the Proterozoic oceans. Whereas under anoxic conditions oceanic ammonium would have been relatively stable, as oxygen concentrations rose, nitrification and subsequent denitrification would have rapidly removed fixed inorganic nitrogen from the oceans. Denitrification would have imposed a strong constraint on the further rise of free oxygen by depriving oxygenic photoautotrophs of an essential nutrient (that is, fixed inorganic nitrogen). To examine the dynamic interactions between oxygen and nitrogen cycling, we developed a five box model that incorporates the salient features of the oxygen, nitrogen and carbon cycles, ocean circulation, and ocean-atmosphere gas-exchange. Model simulations, initiated under anaerobic conditions with no free oxygen in the atmosphere or ocean, are characterized by an initially reduced deep ocean with abundant ammonium, followed by an extended period when neither form of fixed nitrogen is stable, and a fully oxidized phase with abundant nitrate. We infer that, in the process of oxidizing the early Proterozoic ocean, the system had to go through a nitrogen-limited phase during which time export production was severely attenuated. Our studies suggest that the presence of shallow seas with increased organic matter burial was a critical factor determining the concentration of oxygen in the ocean and atmosphere, while the phosphate concentration played a key role in determining the rate of oxygenation of the deep ocean.