Hadal trenches (>6000 m) act as depocenters for organic carbon (OC) and host intensified benthic microbial activities as compared to adjacent abyssal sites zone (~6000 m). However, microbial activities in the hadalpelagic ocean (>6000 m) and its dependence on OC sources have rarely been studied. Here we presented the first study of dark carbon fixation rate (DCF) and size-fractionated microbial community respiration (MCR) proxy, along with particulate organic carbon (POC) over the full ocean depth at the Atacama Trench. The results demonstrate that the POC, DCF, and MCR proxy attenuated rapidly from the surface until a depth of 1000m where they remained relatively stable throughout bathypelagic and abyssopelagic zones (1000-6000m). The hadalpelagic zone showed no apparent patterns. On average, 71% of the total MCR proxy was attributable to the particle-associated communities. The volume-specific DCF below the surface layers was low but the average depth-integrated DCF accounted for a significant source of organic material for the pelagic communities corresponding to ~25% of the surface NPP as estimated from remote sensing.