کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6427724 | 1634722 | 2016 | 10 صفحه PDF | دانلود رایگان |
- Aerobic ecosystems could have been widespread prior to the Great Oxidation.
- Aerobic methanotrophy suppressed methane and oxygen fluxes to the atmosphere.
- We predict a reversible and probably episodic rise of oxygen at the Great Oxidation.
- We predict a low Proterozoic atmospheric methane concentration â10 ppm.
- We simulate δCorg13ââ30 to â45â° consistent with most data from 2.65-2.45 Ga.
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 â2.4 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 bi-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 â10 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 (δ13Corg) record. Our open ocean general circulation model predicts δCorg13ââ30 to â45â° consistent with most data from 2.65 to 2.45 Ga. However, values of δCorg13ââ50â° require an extreme scenario such as concentrated methanotroph production where shelf-slope upwelling of methane-rich water met oxic shelf water.
Journal: Earth and Planetary Science Letters - Volume 434, 15 January 2016, Pages 42-51