南海北部上升流中碳酸钙饱和度及其影响因素研究

Ocean acidification, the result of the oceanic sequestration of the anthropogenic CO2, is a potential significant marine environmental and ecological problem. One consequence of ocean acidification is that it lowers the CaCO3 saturation state and may influence the health of the marine CaCO3 secreting organisms, such as corals. Due to mixing of the upwelled low pH subsurface water, upwelling deteriorates ocean acidification. At the same time, the enhanced photosynthesis in the upwelling consumes protons and relieves ocean acidification. This project will take the Qiong-Dong upwelling system as an example to investigate the relationships of CaCO3 saturation state with upwelling and ocean acidification. The Qiong-Dong coastal upwelling is in the northern South China Sea with extensive coral reef ecosystems. The variability and controls of the CaCO3 saturation state will be investigated. Influences of the anthropogenic CO2 invasion, mixing of the subsurface water, CO2 evasion and the biogeochemical processes on the changes of the CaCO3 saturation state will be revealed. The achievement of this proposed project will provide scientific basis for the comprehensive evaluation of the status and trend of ocean acidification in the coastal ocean system.

海洋酸化是目前备受关注的、由CO2排放引起的潜在的重大生态环境问题。海洋酸化的一个确定的生态效应在于导致碳酸钙饱和度降低，并可能对海洋钙化生物造成危害。由于低pH次表层水的涌升，上升流可能加剧海洋酸化，从而叠加于由人为CO2所导致的酸化效应。而与此同时，上升流所引致的高生产力则可能消耗氢离子，抵消海洋酸化效应。本项目选择珊瑚资源丰富的南海北部琼东上升流为研究区域，探讨上升流与海洋酸化以及碳酸钙饱和度的关系，揭示上升流系统中碳酸钙饱和度的变化范围，阐明碳酸钙饱和度的主要调控过程，定量甄别人为CO2入侵、次表层水混合、海-气CO2交换和生物新陈代谢过程对碳酸钙饱和度的影响。项目成果可望为全面评估近海生态系统海洋酸化的现状及其发展趋势提供科学依据。

调查了珊瑚礁资源丰富的琼东南海域碳酸盐系统的分布，重点研究了上升流及其带来的生态效应对碳酸钙饱和度的影响。通过两个上升流季节的调查发现，琼东南海域表层海水中雯石饱和度指数为2.9-3.6，低值出现在上升流中心，上升流中25米的雯石饱和度指数低至2.3，远低于热带浅水珊瑚生长的适宜范围（>3.5）。雯石饱和度指数与pH、TA/DIC比值和碳酸根离子浓度呈很好的线性关系。调查区域的雯石饱和深度在500米左右，与南海北部接近。通过碳酸钙饱和度指数与pH关系的研究推测，15-20年后琼东南表层海水的雯石饱和度指数可降低至3.0，威胁珊瑚礁生态系统的安全。通过钙离子浓度的测定，在上升流中发现了碳酸钙的溶解过程，表明上升流中快速的海洋酸化过程促进了碳酸钙的溶解。