The deep ocean, where water depth exceeds 1,000 m (hydrostatic pressure greater than 10 MPa), covers 90% of the ocean’s area and harbors the largest biosphere on Earth. It also serves as a significant reservoir of heat and greenhouse gases, absorbing over 90% of thermal surplus and 40% of anthropogenic CO₂, thereby mitigating the effect of global warming. High hydrostatic pressure (HHP) is a universal parameter shared by all the deep-ocean ecosystems, while its influence on biogeochemical cycling remains insufficiently investigated due to technical challenges. To address the research needs, we developed a platform of oceanic environment simulation and in-situ experimental equipment including Deep Ocean Experimental Simulator (DOES) with real-time optical and electrochemical monitors, In-Situ Fixation Sampler (ISFS), Ocean Automatic Series Incubation System (OASIS). With these technologies, we are able to reveal that HHP induces oxidative stress and alters intracellular oxidation level. It results in incomplete oxidation of organic carbon by microorganisms, thus regulating the carbon cycle in the deep ocean and reducing the release of greenhouse gases such as CH₄ and CO₂. Additionally, HHP stimulates microbial denitrification that reduces NO₃^- to N₂O and N₂ in oxic environments, making deep ocean a hotspot of nitrogen loss and enhancing the release of greenhouse gas N₂O. These findings challenge certain traditional perspectives and suggest a reassessment of the marine carbon and nitrogen cycling.
 

hydrostatic pressure, piezophile, carbon cycling, environmental adaptation