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Surface Ocean and Lower Atmosphere Study—Air-Sea interactions and their climatic and environmental impacts
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Methane production in the oxygenated water in the marginal seas of China and the potential contribution to the atmosphere
P-C4-13-S
Wang-Wang Ye* , Ocean University of China
Gui-Ling Zhang, Ocean University of China
Xiao-Lei Wang, Ocean University of China
Xiao-Hua Zhang, Ocean University of China
Presenter Email: yezikasuo@126.com |
| Methane (CH4) is an important greenhouse gas and contributes substantially to global warming. Over-saturation of methane with respect to atmospheric equilibrium is ubiquitous in the surface oceans. This is commonly termed Oceanic Methane Paradox because oceanic surface waters are well oxygenated and methanogenic archaea are assumed to be strictly anaerobic. Thus, traditional pathways of methane production are challenged and the basis for this paradox is still controversially discussed. However, the most popular explanation in recent studies is that methane can be formed as the by-product by decomposition of methyl-rich organic matter (such as MPn and DMSP). To better understand the mechanism of surface methane accumulation in the marginal seas of China, we conducted a series of laboratory and onboard experiments to preliminarily explore the paradox. Through DOM-amended incubations, we measured the methane production rates in the coastal waters (Yellow Sea) and open ocean waters (South China Sea). The methane concentration increased 2-3 orders of magnitude when the coastal water was amended with MPn. The results from the 16S rRNA sequencing suggest that vibrionales were the most abundant microbes in the MPn treatments. The vibrionales may play important roles in hydrolyzing phosphonates as a source of phosphorus, but preliminary results show a preference for inorganic phosphorus. In the open ocean, nitrogen-fixing cyanobacteria Trichodesmium is predicted to be capable of cleaving the C-P bond. Our onboard incubations confirmed that methane was significantly released by the degradation of MPn when a Trichodesmium bloom occurred. Taken together, our study in the marginal seas of China demonstrates a mechanism of aerobic methane production, by which it may be directly linked to global methane fluxes, contributing to the surface ocean methane oversaturation. |
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