Tracing the century-long evolution of microplastics deposited in cold seep

Abstract Microplastic (MP) pollution is one of the greatest threats to marine ecosystems. The deep sea is regarded as a hotspot for MP accumulation, but how do deposited MPs evolve from a long-term perspective? In particular, the occurrence features of MPs in cold seeps, which are characterized by methane-rich fluid seepage fueling one of the richest ecosystems on the seafloor, are unclear. Here, we demonstrated how MPs have been deposited in the Haima cold seep since the invention of plastics. We found that the burial rate of MPs exponentially increased since the massive global use of plastics in the 1930s, and this cold seep accommodates more MPs than do coastal areas. Upwelling fluid seepage facilitated the fragmentation and degradation behaviors of MPs. More MP-degrading microorganism populations and functional genes were discovered in methane seepage areas. Our findings illuminated the need to determine fundamental strategies for sustainable marine plastic pollution mitigation in the natural deep-sea environment.