联合应用210Po-210Pb和黑碳示踪南海中层水体颗粒有机碳沉降动力学

中层海洋碳循环决定了年代际-百年时间尺度上海洋吸收CO2的能力，但现有研究表明中层海洋碳收支不平衡，对颗粒有机碳（POC）沉降过程理解的局限性是问题的关键之一。课题立足现有研究基础，以中层水体POC沉降动力学为切入点，选择南海为目标区域，以甄别不同途径输入的POC为突破口，联合运用放射性同位素（210Po和210Pb）和地球化学指标（黑碳）定量陆架沉积物水平输送和当地生源颗粒沉降对中层水体POC的贡献，从宏观角度揭示南海中层水体POC沉降通量的时空特征及衰减动力学规律，从微观角度阐释颗粒物沉降速率、化学组成和水文条件对POC沉降动力学的影响，获取中层水体POC循环的关键动力学参数，探明南海上层-中层水体POC之间的耦合关系，综合评价南海在年代际-百年时间尺度上的储碳能力。项目将在陆架-海盆相互作用复杂的边缘海中层水体POC沉降动力学方面取得突破。

Carbon cycling in the mesopelagic ocean largely determines the ability of global oceans to sequestrate carbon dioxide over decadal to centurial timescales. Available datasets reveal a noticeable carbon imbalance between particulate organic carbon (POC) supply and carbon demanding in the mesopelagic water, partially due to the limitation on the understanding of POC sinking within this dark and crucial oceanic regime. This project will focus on the kinetics of POC sinking in the mesopelagic water of the South China Sea. By using radionuclides (210Po and 210Pb) and a geochemical tracer (soot black carbon), shelf sediment derived POC (via resuspension and lateral transport) would be discriminated from locally settling POC (biogenic in the local euphotic zone). This separation of locally sinking POC would be used to illustrate the spatiotemporal pattern of POC sinking flux in the mesopelagic zone and to characterize its downward attenuation through mathematical approaches. In addition, particle sinking velocity will be constrained via simulating the distributions of 210Po below the euphotic zone. Together with particulate component analysis, the influence of both sinking velocity and particle composition on POC sinking flux would be investigated in depth. A cluster of crucial parameters, including remineralization depth, carbon sequestration ratio etc., could be finally calculated to synthetically examine the coupling of POC between the euphotic zone export and mesopelagic attenuation and to evaluate the ability of mesopelagic water to sequestrate carbon dioxide in the South China Sea. This project will make progress in the understanding of the POC cycling in marginal seas where there exist complicated shelf-basin interaction and material exchange.