黑潮溶解有机碳入侵南海北部的交换过程与降解机制研究

Transfer and transformation of dissolved organic carbon (DOC) in marginal sea is a key component of carbon cycling in the ocean. However, we still need in-depth understanding about transformation mechanisms of DOC and its impact in the marginal sea. The exchange between northern South China Sea and West Philippine Sea through Kuroshio intrusion provide a unique set-up to study the exchange and transformation of DOC under different environmental stresses. Basing on the preliminary study this proposal plans to study the biodegradation process of exogenous DOC in the northern South China Sea and the impacts of different stress factors e.g. temperature, nutrients concentrations and compositions (nitrogen to phosphate ratio) through incubation experiments on deck. Solid phase extracted DOC would be analyzed by mass spectrometer. And the molecular composition of DOC would be identified at both northern South China Sea and West Philippine Sea. The molecular information at the two region would be separated to two groups: shared and particular at each site. These two groups of compounds would be studied during the on deck incubation test. Through the experiments we would know better about the biodegradation mechanisms related to both environmental stresses and intrinsic property of DOC. Field observation would be planned to study the exchange of DOC driven by Kuroshio intrusion in different seasons. By applying numeric water mixing model, we could estimate the flux of DOC through Luzon Strait which would allow us to evaluate the impact of degradation of exogenous DOC to the carbon budget in the northern South China Sea.

边缘海溶解有机物碳（DOC）的迁移和转化是海洋碳循环研究中的重要一环，而我们对DOC在其中的转化过程及其影响机制尚缺乏深入了解。受黑潮入侵影响显著的南海北部海域，为研究DOC在边缘海和大洋的之间的交换，以及不同环境因子对DOC降解过程的影响，提供了一个典型的研究区域。本申请项目基于前期研究基础，计划通过现场模拟实验，探讨黑潮入侵的外源DOC在南海北部的降解过程及其环境影响因素，包括温度，营养盐浓度和氮磷比值等；并通过固相萃取结合质谱分析，解析黑潮和南海北部DOC的分子组成异同，定性研究南海与黑潮DOC中相同和相异组分在降解过程中的变化趋势，从环境因素和DOM分子组成两个方面增进对降解机制的理解。通过现场观测，探讨不同季节黑潮DOC入侵南海的交换过程，以及DOC生物可利用性和矿化状态的变化，并构建水团混合模型，初步估算跨吕宋海峡DOC传输通量及其降解过程所贡献的超额碳对南海北部碳收支的影响。

边缘海是大洋与陆源有机物质交汇与转化的重要区域，黑潮与南海的水团交换过程是研究溶解有机物（DOM）循环过程和调控机制的理想研究区域。本项目执行期间，对南海北部和西菲律宾海在不同季节进行了多个航次的现场观测，采集分析了大量DOM的元素组成，分子结构和同位素组成信息，以及相关的物理和生物地球化学参数。研究探明了黑潮DOM相较于南海具有更高的溶解有机碳（DOC）以及微生物可利用性，通过高分辨率质谱对活性和惰性DOM在分子层面上的解析，发现南海北部是DOM微生物转化的热点区域。通过等密面混合模型对南海不同季节DOM的交换和降解进行评估，发现DOC在黑潮与南海混合的锋面区域存在显著的降解（高达10%），同航次的甲板控制培养实验也证明了这一结果。营养盐的供给显著刺激了微生物对DOM的降解作用，同时南海微生物群落结构的差异也促进了DOM的降解过程，这一发现进一步佐证了前人关于DOM惰性机制的环境调控因子假说。结合培养实验和现场观测结果，并利用跨吕宋海峡水体交换量，初步估算黑潮入侵DOM的微生物矿化过程可贡献溶解无机氮约0.46-0.55 毫摩尔每平方米每天, 相较于南海表层海水的初级生产和碳输出是一个不容忽视的营养盐来源。.项目执行期间，本项目共参与现场科考航次12次，取得了大量观测数据，培养硕士研究生两人，博士后一人；在学博士生三人硕士生两人；部分研究成果形成论文发表于国际期刊共四篇，均为JCR二区期刊。