Evolution of the nitrogen cycle and its influence on the biological sequestration of CO2 in the ocean
Evolution of the nitrogen cycle and its influence on the biological sequestration of CO2 in the ocean
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DOI：
10.1038/387272a0
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发表时间：
1997-05-15
期刊：
影响因子：
64.8
通讯作者：
Falkowski, PG
中科院分区：
文献类型：
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作者：
Falkowski, PG
随着地质时间的推移，海洋中的光合碳固定已经超过了有机碳的呼吸氧化。这两个过程之间的不平衡导致了氧气在地球大气中的同时积累和二氧化碳的吸收，以及有机碳在海洋沉积物中的埋藏(1-3)。通常认为，这些过程受到磷(4，5)有效性的限制，磷(4，5)由大陆风化和河流排泄(5-7)提供。在过去两百万年中，冰川时期大气二氧化碳浓度的下降与从地表水向海洋沉积物出口有机碳的增加相关(8-11)，但磷通量的变化似乎太小，不能解释这些变化(12，13)。因此，人们假定海洋初级生产力总量在冰期向间冰期过渡期间保持相对不变，尽管在冰期期间输出到沉积物中的生产力比例有所增加(12，14)。在这里，我对生物地球化学循环的演变进行了分析，认为固定的氮，而不是磷，在地质时间尺度上限制了初级生产力。固氮和反硝化比率的微小变化可以显著改变从冰期到间冰期时间尺度上的大气二氧化碳浓度。这两个过程的比例似乎是由海洋的氧化状态和微量元素，特别是铁的供应决定的。
Over geological time, photosynthetic carbon fixation in the oceans has exceeded respiratory oxidation of organic carbon. The imbalance between the two processes has resulted in the simultaneous accumulation of oxygen in, and drawdown of carbon dioxide from, the Earth's atmosphere, and the burial of organic carbon in marine sediments(1-3). It is generally assumed that these processes are limited by the availability of phosphorus(4,5), which is supplied by continental weathering and fluvial discharge(5-7). Over the past two million years,decreases in atmospheric carbon dioxide concentrations during glacial periods correlate with increases in the export of organic carbon from surface waters to the marine sediments(8-11), but variations in phosphorus fluxes appear to have been too small to account for these changes(12,13). Consequently, it has been assumed that total oceanic primary productivity remained relatively constant during glacial-to-interglacial transitions, although the fraction of this productivity exported to the sediments somehow increased during glacial periods(12,14). Here I present an analysis of the evolution of biogeochemical cycles which suggests that fixed nitrogen, not phosphorus, limits primary productivity on geological timescales. Small variations in the ratio of nitrogen fixation to denitrification can significantly change atmospheric carbon dioxide concentrations on glacial-to-interglacial timescales. The ratio of these two processes appears to be determined by the oxidation state of the ocean and the supply of trace elements, especially iron.