The effect of widespread early aerobic marine ecosystems on methane cycling and the Great Oxidation
The effect of widespread early aerobic marine ecosystems on methane cycling and the Great Oxidation
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DOI：
10.1016/j.epsl.2015.11.021
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发表时间：
2016-01-15
影响因子：
5.3
通讯作者：
Lenton, Timothy M.
中科院分区：
文献类型：
--
作者：
Daines, Stuart J.;Lenton, Timothy M.
证据的平衡表明，氧气光合作用在3.0-2.7 Ga进化，比大约2.4 Ga的大氧化期早几亿年。先前的研究表明，如果在大氧化之前，含氧光合作用在全球范围内传播，这可能会支持海洋表面广泛的需氧生态系统，而不会氧化大气。在这里，我们使用一套模型来探索碳循环和大氧化的含义。我们发现，在早期需氧海洋生态系统中，氧和碳的循环将限制甲烷和氧气从海洋中逸出的平衡通量，从而降低大氧化转变及其后续的大气甲烷浓度。这反过来又会削弱氢气逃逸到太空中对氧气的稳定反馈，从而使大气中氧气的高稳定性降到最低。结果将是一个更可逆的，可能是在大氧化转变期间间歇性的氧气上升，与现有的地球化学证据一致。由此导致的甲烷含量下降到大约10ppm，这与当时的气候变冷是一致的，但也增加了是什么让元古代的其他部分保持温暖的谜团。大氧化前氧绿洲丰富甲烷化情景的关键测试是其对有机碳同位素（δ C-13(org)）记录的预测影响。我们的开放海洋环流模型预测三角洲C-13（org）接近于-30至-45千分之一，与2.65至2.45 Ga的大多数数据一致。然而，δ C-13（org）值接近- 50ppm需要一种极端的情况，例如在陆架斜坡上涌的富甲烷水与含氧陆架水相遇的情况下，高浓度的甲烷化产物产生。(C) 2015年作者。Elsevier B.V.出版
The balance of evidence suggests that oxygenic photosynthesis had evolved by 3.0-2.7 Ga, several hundred million years prior to the Great Oxidation approximate to 2.4 Ga. Previous work has shown that if oxygenic photosynthesis spread globally prior to the Great Oxidation, this could have supported widespread aerobic ecosystems in the surface ocean, without oxidising the atmosphere. Here we use a suite of models to explore the implications for carbon cycling and the Great Oxidation. We find that recycling of oxygen and carbon within early aerobic marine ecosystems would have restricted the balanced fluxes of methane and oxygen escaping from the ocean, lowering the atmospheric concentration of methane in the Great Oxidation transition and its aftermath. This in turn would have minimised any hi-stability of atmospheric oxygen, by weakening a stabilising feedback on oxygen from hydrogen escape to space. The result would have been a more reversible and probably episodic rise of oxygen at the Great Oxidation transition, consistent with existing geochemical evidence. The resulting drop in methane levels to approximate to 10 ppm is consistent with climate cooling at the time but adds to the puzzle of what kept the rest of the Proterozoic warm. A key test of the scenario of abundant methanotrophy in oxygen oases before the Great Oxidation is its predicted effects on the organic carbon isotope (delta C-13(org)) record. Our open ocean general circulation model predicts delta C-13(org) approximate to -30 to -45 parts per thousand consistent with most data from 2.65 to 2.45 Ga. However, values of delta C-13(org) approximate to -50 parts per thousand require an extreme scenario such as concentrated methanotroph production where shelf-slope upwelling of methane-rich water met oxic shelf water. (C) 2015 The Authors. Published by Elsevier B.V.