深海是海洋的主体，是海洋有机碳矿化和长期储存的主要场所，在地球系统物质能量循环中起着重要的作用。然而，迄今对深海系统的研究相当缺乏，对深海生物圈能量来源、代谢策略、碳氮硫生源要素的循环过程知之甚少。本项目所要解决的关键科学问题即是：深海生物圈碳需求和能量供给的不平衡。项目以南海及邻近西太平洋为研究海域，链接微生物活性参数和生物地球化学过程分析，估算深海微生物碳需求量及主要生地化过程的碳贡献量。验证工作假说：深海生物圈碳需求与生物泵沉降颗粒物通量之间巨大的不平衡（缺口）主要由①悬浮和②侧向传输颗粒物，以及③颗粒物再矿化释放的或颗粒物微环境携带的高浓度还原性无机化合物所支撑的黑暗固碳填补。并揭示深海微生物群落从根本上不同于表层群落的代谢运作机制，及其应对深海长期饥饿环境的能量代谢策略。项目将有效链接微生物定性研究与元素循环定量估算，为国际上海洋学深海系统研究提供新的参数和创新理论。

The dark ocean consists of the mesopelagic (below the euphotic layer to 1000 m depth) and bathypelagic (1000 to 4000 m depth) and abyssal zones (> 4000 m), accounting for ~70% of the global ocean’s volume and representing one of the largest biomes on Earth. This realm is characterized by low temperature, high hydrostatic pressure, and most of the dissolved organic carbon present in the form of recalcitrant dissolved organic carbon. All these conditions seem to inhibit the metabolic capacity of living organisms in the dark ocean, but growing data indicate that the dark ocean contains diverse and active microbial communities. However, deep-ocean energy supply, without solar energy, meeting the microbial metabolic demand remains an enigma. The key scientific problem to be solved in this project is the imbalance between carbon demand and energy supply in the deep-sea biosphere. The research area is the South China Sea and the adjacent Western Pacific Ocean. We would perform a comprehensive analysis of the organic carbon supply and microbial demand in the deep ocean, combining a series of microbial activity parameters and functional metagenomics with multiple biogeochemical processes. Finally, we would quantitatively estimate the contributions of sinking particulate organic carbon (POC), suspended or slowly-sinking POC, laterally transported POC, and dark carbon fixation to the deep-sea microbial carbon demand and verify the scientific hypothesis. This project would also reveal the metabolic mechanism of the deep-sea microbial community fundamentally different from the surface community and their energy metabolic strategies for dealing with long-term carbon deprived deep ocean. The project will establish the stoichiometric relations between carbon and nitrogen processes and between matter and energy conversion. Overall, this project will provide new data sets and make breakthroughs in theory for the deep ocean system research.