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The food source of hadal endemic fauna provides an insight into the carbon cycle in trenches and a biological adaptation to the impoverished and harsh trench environment. Here, we present the first Delta C-14 results of hadal amphipods from three trenches in the Pacific to define the organic matter source in these remote ecosystems. Amphipod muscle tissues contain a bomb C-14 signature (Delta C-14 from 10 +/- 2 parts per thousand to 65 +/- 2 parts per thousand), thereby revealing a dietary preference for labile and fresh organic matter derived from the surface water. Thus, the carbon cycle in the deepest ocean trench has a tight linkage with the surface ocean via the food chain. The bomb C-14 dating result suggests that hadal amphipods have a low tissue turnover rate and an unexpectedly long lifetime (>10 years), at more than 4 times higher than the common longevity (similar to 2 years) of amphipods in shallow waters.

Plain Language Summary Hadal trenches (depth > 6,000 m) are the remotest and the least explored places on our planet, with characteristics of low temperatures, high pressure, limited food, and frequent geological activity. Knowing the source of organic matter for hadal life is key in understanding the ocean carbon cycle and the biological adaptation in trenches. We report the first C-14 results of hadal amphipods from three trenches in the West Pacific, including the deepest ocean trench, Mariana, which indicates that the organic matter for amphipods is mostly from the surface water. This tight linkage between the organic matter within the hadal fauna and in surface water points out that the anthropogenic pollution can reach the deepest ocean trench rapidly via the food chain. Moreover, the bomb C-14 dating method can be applied to hadal amphipods, thereby suggesting a low tissue turnover rate and an unexpectedly long lifetime, which might be a result of an adaptation to the impoverished and harsh environment.