海水中CDOM的光学特性及其光降解对主要含碳气体的贡献率

The consumption of CDOM in seawater is mainly caused by photochemical action. The photodegradation of CDOM can alter the transmission depth of ultraviolet and visible light in seawater by affecting the optical properties of seawater, and further affect the biological productivity and ecosystem structure of the sea area. Many carbon-containing gases produced by photodegradation of CDOM can enter the atmosphere through the air-sea interface, which has a certain impact on the atmospheric chemistry and climate. The sea surface microlayer exerts enrichment effect on different substances, thus forming special marine ecosystem. In this project, we will choose China’s shelf seas—the Yellow Sea and East China Sea as main study area and collect different types of CDOM samples to conduct degradation experiments under various radiation conditions. By means of analysis on the main gaseous products including CO and CO2 and dissolved inorganic carbon (DIC) produced by photochemical reactions, we can identify major factors influencing and controlling CDOM photochemical degradation process and gaseous products, and estimate the proportions of contribution of CDOM photo-degradation to CO and CO2 in China's shelf seas. In addition, through in situ investigation, we will analyze the difference of the optical properties of CDOM between the sea-surface microlayer and bulk seawater, and probe into the enrichment situation of CDOM in the sea-surface microlayer. This study has great significance for us to further understand the photochemistry of CDOM and carbonic biogeochemical cycles in China’s shelf seas.

海水中CDOM的消耗主要是光化学作用引起的，CDOM的光降解可通过影响海水的光学性质来改变紫外及可见光在水体中的透射深度，进而影响到海区的生物生产力和生态系统结构。CDOM的光降解产生的许多含碳气体可通过海-气界面进入大气并对大气化学和气候产生一定的影响。海洋微表层对不同类物质具有富集作用，因而形成特殊的海洋生态系统。本项目选取中国典型陆架海区—黄海和东海为主要研究海域，采集不同类型的CDOM样品进行不同光照条件下的降解实验。通过对CDOM光解产生的主要气态产物CO、CO2和溶解无机碳（DIC）进行测定分析，从而识别影响和控制CDOM光降解过程及气态产物的主要因素并估算研究海区CDOM光降解对CO、CO2生成的贡献。另外，通过现场调查，分析CDOM在微表层和本体海水中光学特性的差异，探讨其在微表层的富集情况及影响因素。本研究对进一步认识CDOM的光化学和碳的生物地球化学循环具有重要意义。

海洋中有色溶解有机物（CDOM）是海洋碳库的重要组成部分，独特的光学性质使其受到广泛的关注。本项目选取中国东部陆架海域以及南海和东印度洋作为研究海区，通过现场调查、现场和实验室培养，系统研究了CDOM在海水中的分布特征以及与环境因子之间的关系。对于现场调查，项目组对长江口及其邻近海域、黄海、东海、南海以及东印度洋海域进行了一共8个航次的调查研究，揭示了CDOM的时空分布特征及影响因素。结果表明CDOM的分布具有明显的时空差异。在长江口及其邻近海域，aCDOM(355)和荧光组分与盐度呈现显著的负相关性，说明陆源输入在对长江口CDOM的浓度和分布方面可能发挥重要作用。在东印度洋海域，aCDOM(254)与盐度有显著负相关性，与叶绿素a（Chl a）有显著正相关性，说明东印度洋CDOM的分布可能受浮游植物生产活动和陆源输入的共同影响。微表层对CDOM通常是富集的，其中对海洋自生源有机质的富集效果更好。通过现场和实验室培养实验发现，陆源有机质在光照条件下降解的更多；紫外光对CDOM的降解效果更好；在短波长辐照下，一氧化碳（CO）的生成量高，且陆源有机质降解生成CO的量多。