Stabilization of the coupled oxygen and phosphorus cycles by the evolution of bioturbation
Stabilization of the coupled oxygen and phosphorus cycles by the evolution of bioturbation
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DOI：
10.1038/ngeo2213
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发表时间：
2014-09-01
影响因子：
18.3
通讯作者：
Lenton, T. M.
中科院分区：
文献类型：
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作者：
Boyle, R. A.;Dahl, T. W.;Lenton, T. M.
在埃迪卡拉纪/寒武纪边界（1-3）的运行过程中，动物的穴居和沉积物混合（生物扰动）开始了，在一个可变的（8，9）全球氧气储层的背景下，在分层的前寒武纪（6）和混合更好的中生代（7）沉积记录之间开始了一个过渡（4，5），其大小可能比现在小（10，11）。磷是通过有机碳的埋藏（13）产生氧气的长期（12）限制性营养素，生物扰动（14-18）增强了磷在海洋沉积物有机物质中的保留（相对于碳）。在这里，我们探讨了生物扰动引起的有机磷汇在一个简单的模型中的地球化学意义。我们发现，增加生物扰动强烈触发全球氧平衡的大小净减少，其幅度取决于生物扰动和层状沉积物之间的碳磷比的规定差异。生物扰动也降低了稳态海洋磷酸盐水平，但这种影响被铁吸附磷酸盐埋藏的下降所抵消，这是由于氧浓度的降低。将氧敏感生物扰动引入动力学模型运行足以触发负反馈循环：生物扰动的强度受到其最初引起的氧减少的限制。这种反馈的发生与早寒武世生物扰动的兴起期间观察到的氧化还原变化是一致的，这使我们认为生物扰动有助于调节早期的氧和磷循环。
Animal burrowing and sediment-mixing (bioturbation) began during the run up to the Ediacaran/Cambrian boundary(1-3), initiating a transition(4,5) between the stratified Precambrian(6) and more well-mixed Phanerozoic(7) sedimentary records, against the backdrop of a variable(8,9) global oxygen reservoir probably smaller in size than present(10,11). Phosphorus is the long-term(12) limiting nutrient for oxygen production via burial of organic carbon(13), and its retention (relative to carbon) within organic matter in marine sediments is enhanced by bioturbation(14-18). Here we explore the biogeochemical implications of a bioturbation-induced organic phosphorus sink in a simple model. We show that increased bioturbation robustly triggers a net decrease in the size of the global oxygen reservoir-the magnitude of which is contingent upon the prescribed difference in carbon to phosphorus ratios between bioturbated and laminated sediments. Bioturbation also reduces steady-state marine phosphate levels, but this effect is offset by the decline in iron-adsorbed phosphate burial that results from a decrease in oxygen concentrations. The introduction of oxygen-sensitive bioturbation to dynamical model runs is suffcient to trigger a negative feedback loop: the intensity of bioturbation is limited by the oxygen decrease it initially causes. The onset of this feedback is consistent with redox variations observed during the early Cambrian rise of bioturbation, leading us to suggest that bioturbation helped to regulate early oxygen and phosphorus cycles.