边缘海碳循环是地球系统碳循环的重要环节，但至今我们依然不能回答为什么有些陆架边缘海是大气CO2的汇，有些是源，这主要缘于我们对控制边缘海碳循环的主要过程和关键机理尚有诸多不明之处。基于申请团队扎实的研究基础，项目拟验证假设为：南海盆地的CO2源汇格局与深部过程密切相关，南海存在源自相邻大洋深部的外源溶解无机碳，当外源无机碳被输送至其上层时，如果不被同时上涌的营养盐所支持的有机碳生产完全消耗，其过剩部分即会逸出至大气。故项目拟解决如下关键科学问题：(1) 输入南海深部的外源无机碳、营养盐的通量有多大？(2)南海深部及至南海上层的过程中调控无机碳、营养盐输运的关键生物地球化学和物理过程是什么？(3) 南海上层新陈代谢过程如何控制海-气界面CO2通量？项目直面南海的碳循环过程与机理研究，揭示深部过程与上层海-气界面交换的关联，这是解决现代南海碳循环问题的核心，对认识南海碳循环演变也具重要意义。

The contemporary coastal ocean, characterized by abundant nutrients and high.primary productivity, is generally seen as a significant CO2 sink at the global.scale. However, mechanistic understanding of the coastal ocean carbon cycle .remains limited,leading to the unanswered question of why some coastal systems .are sources while others are sinks to atmospheric CO2. Recently, we proposed .a new hypothesis:in addition to the processes identical to those in the open .ocean such as thermodynamic and biological pump controls, both land input .and exchange with the open ocean are significant determinants of the CO2 fluxes .in the coastal ocean. .There are at least two distinct settings: River-dominated Ocean Margins (RiOMar) .and Ocean-dominated Margins (OceMar). In a simplified scheme, RiOMar, as .recognized previously, is featured by concurrent inputs of autotrophic (nutrients) .and heterotrophic (organic matter) loadings, while OceMar is characterized by .concurrent off-site inputs, typically from depth, of nutrients and dissolved .inorganic carbon (DIC). This proposal is to test if the hypothesis stands using.the basin area of thelargest marginal sea of the Pacific, the South China Sea as.a case. We are to answer the following critical questions: (1) what are the.fluxes of the non-local sourced DIC and nutrients transported into the deep .South China Sea basin through the Luzon overflow? (2) how do the major.biogeochemical and physical processes modulate the transport of DIC and.nutrients from the depth to the upper South China Sea? (3) how the upper.metablic processes control the air-sea CO2 fluxes in the upper South China Sea..We contend that OceMar, in contrast to the previously recognized .River-dominated Ocean Margins, is a significant concept to improve our .mechanistic understanding of the coastal ocean carbon cycle. .Moreover, the approach this proposed research is going to adopt shall be.applicable to many other systems with similar physical settings, thereby.to enhance the impact of the South China Sea Deep program.