Methane released from the subseafloor is significantly attenuated during upward migration, yet the preservation of methane-derived organic carbon (OC) in global deep-sea sediments remains poorly understood. Here, we measured carbon isotopes coupled with temperature-ramped analyses on various methane seepage sediments. Our results reveal a correlation between the radiocarbon (14C) content in deep-sea surface sediments and sulfate-methane transition depth. Notably, our findings suggest that a substantial amount of 14C-depleted OC may originate from deep-seated methane and is efficiently preserved in surface seapage sediments. We propose that efficient OC preservation is related to microbial-mediated aggregate formation at the seawater sediment interface, where physical occlusion within coarse-grained matrices reduces oxygen availability and enhances OC stability. We estimate that at least 6 TgC of methane-derived OC are preserved annually in surface sediments of the global continental slopes. This process may play a non-negligible role in OC preservation in sediments, reducing methane emission from seafloor.

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