近40年来对南海化学海洋学研究的新认知

New understanding about Chemical Oceanography in the South China Sea since 1980

作为西太平洋最大的边缘海,南海在全球海洋和海洋学研究中占有重要地位。近40年来,南海的化学海洋学研究取得了大量系统的新发现、新认识,提出了不少新的理论观点,对全球海洋学的发展进步做出了重要贡献。研究发现了南海次表层存在以海水亚硝酸盐为代表的生态环境参数极值现象,不同参数水层深度范围不同,由此形成的跃层生态系统有着与其他生态系统显著不同的特点。从系统研究获知,南海碳循环过程十分复杂,生物作用下的生物泵过程以及碳源汇区域和季节变化巨大,南海碳源汇在不同的区域不同的时间的性质和强度迥异,全年尺度上总体表现为大气二氧化碳的弱源。南海北部的珠江口邻近海域和深海盆的生态环境特征与化学物质循环和陆架边缘海、珊瑚礁等密切相关,但又与陆架边缘海、珊瑚礁等显著不同,表现为珠江口底层存在缺氧现象,珠江口海域是一个以缺氧为特征的生态脆弱区。在系统认识南沙珊瑚礁生态系统物质循环快速、生物过程控制着化学物质的垂直转移的基础上,提出了维持珊瑚礁生态系统高生产力的新机制——"拟流网理论"。对南海沉积物化学的系统研究认识到,沉积物-水体化学物质循环有密切的耦合关系,南海珊瑚礁或沉积岩心化学物质分布变化可反演其历史变化,如南海冰期表层海水古生产力为间冰期的1.6倍;晚中新世南海南部发生了一次"生物勃发事件",其生产力主要受季风和陆源营养物质输入量影响;东北季风与西南季风在不同区域其影响程度不同等。40年来南海化学海洋学研究的这些新发现和新认识对系统揭示南海的海洋学过程奠定了强有力的基础,未来南海化学海洋学研究也必将为南海资源环境的可持续利用提供科学支撑。

As the largest marginal sea in the western Pacific,the South China Sea(SCS)plays an important role in the global ocean and the global oceanographic research.In the past 40 years,chemical oceanographic research in the SCS achieved systematic new discoveries and new understandings;researchers put forward many new theoretical viewpoints,making important contributions to the development of oceanography.A subsurface layer was revealed in the SCS,maximum values of ecological environmental parameters represented by nitrite are present;and the depth ranges of water layers for different parameters are different,forming a thermocline ecosystem that has significantly different characteristics from the other ecosystems.The carbon cycle process in the SCS is very complex,and changes of the biological pump controlled by biological activities,and the regional and seasonal changes of carbon sources and sinks,are all great.The characteristics and intensity of carbon sources and sinks in the SCS are unique in different regions at different times.Annually,the SCS is a weak source of atmospheric carbon dioxide.The characteristics of ecological environment and the cycling process of chemical material in the Pearl River Estuary and deepsea basins were found not only closely related to but also significantly different from that in shelf marginal seas and coral reefs,as the dissolved oxygen concentration is low in the bottom,and the Pearl River Estuary is basically an ecologically fragile area characterized by hypoxia.Based on the systematic understanding of the rapid material circulation and vertical transfer of chemical substances controlled by biological processes in the Nansha coral reef ecosystem,a new mechanism-"resembling driftnet theory"was proposed to explain how the coral reef ecosystem could maintain high productivity.Systematic studies on the sedimentary chemistry of the SCS show that there is a close coupling between the sediments and chemical cycling of water bodies.The distribution of chemical substances in coral reefs or in sediment cores of the SCS can be used to retrieve historical environment changes.The paleo productivity of surface seawater in the SCS during the glacial period was 1.6 times higher than that of the interglacial period.A"biological explosion event"occurred in the southern SCS in the late Miocene.The productivity in that period was mainly affected by the monsoon and terrigenous nutrients input,while the influences of northeast monsoon and southwest monsoon differed in different regions.These new discoveries and new understandings in chemical oceanography of the SCS in the past 40 years have laid a strong foundation for further systematic and indepth understanding of the oceanographic processes in the region.In the future,chemical oceanographic research will definitely provide scientific support for the sustainable utilization of resources and environment in the SCS.