Microplastic (MP) pollution is one of the greatest threats to marine ecosystems. Cold seeps are characterized by methane-rich fluid seepage fueling one of the richest ecosystems on the seafloor, and there are approximately more than 900 cold seeps globally. While the long-term evolution of MPs in cold seeps remains unclear. Here, how MPs have been deposited in the Haima cold seep since the invention of plastics is demonstrated. It is found that the burial rates of MPs in the non-seepage areas significantly increased since the massive global use of plastics in the 1930s, nevertheless, the burial rates and abundance of MPs in the methane seepage areas are much lower than the non-seepage area of the cold seep, suggesting the degradation potential of MPs in cold seeps. More MP-degrading microorganism populations and functional genes are discovered in methane seepage areas to support this discovery. It is further investigated that the upwelling fluid seepage facilitated the fragmentation and degradation behaviors of MPs. Risk assessment indicated that long-term transport and transformation of MPs in the deeper sediments can reduce the potential environmental and ecological risks. The findings illuminated the need to determine fundamental strategies for sustainable marine plastic pollution mitigation in the natural deep-sea environments.

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Methane (CH4) is a powerful greenhouse gas with a stronger greenhouse effect than carbon dioxide. The ocean is the largest CH4 reservoir in the world and plays an important role in adjusting climate change. Water column CH4 distribution and sea-to-air in the marine CH4 seeping areas are crucial to finger the ultimate fate of marine CH4. In this research, we investigated the distribution of dissolved CH4 and environmental factors in the water column, and calculated the sea-to-air flux in the "Haima" cold seep area. The results showed that the surface dissolved CH4 concentration ranged from 0.50 to 53.20 nM, and the sea-to-air flux was 38.56 μmol/m 2 /d. Compared with previous studies, it was higher than that on the general ocean surface but lower than that in the estuary area. In addition, the vertical distribution showed that the CH4 concentration in the surface layer was lower than that in the bottom layer, and the maximum value appeared at about 150 m. By PCA analysis, it can be found that SO4 2and TOC were important factors affecting the dissolved CH4 concentration. In conclusion, understanding the CH4 emissions in cold seep areas is of great significance for coping with global warming.