南海中北部表层沉积硅藻的高分辨空间分布及其与现代环境因子的关系

本文通过对南海中北部1 266个站位19种硅藻的生物地理分布格局及其对环境因子偏好的研究,查清了南海中北部沉积硅藻高分辨的空间展布特征,并探讨了硅藻分布与海洋环境因子的关系。南海北部陆架和西部陆架表层沉积硅藻以广温的半咸水潮间带种或沿岸种和咸水-半咸水浅海种为主,珠江口以东的粤东北部陆架Paralia sulcata呈集中分布,粤西北部陆架多样性最佳,Cyclotella stylorum相对富集,西部陆架则以Cyclotella striata占显著优势。北部陆坡和西部陆坡以热带浮游远洋种为主,其中Azpeitia nodulifera和Nitzschia marina分别在琼东南陆坡、西部陆坡和东北部陆坡占优势地位,Chaetoceros messanensis、Fragilariopsis doliolus集中分布于北部陆坡。深海盆以热带浮游远洋种为主,A.nodulifera最具优势,其次为N.marina,Thalassionema nitzschioides和Thalassiosira eccentrica在吕宋海峡入口、深海盆东部和东南部礼乐岛坡集中分布。硅藻种和环境因子的Pearson相关性分析和冗余分析表明,热带远洋种与表层海水温度显著正相关,广温广布种与温度和盐度呈一定正相关,多数沿岸种和浅海种与盐度显著负相关。硅藻组合与海洋流系控制下的环境因子关系密切。可分为6个硅藻组合,其中陆架区3个组合主要受到盐度和营养盐(NO₃,PO₄,SiO₄)浓度的影响,陆坡区2个组合主要受表层海水温度、盐度和营养盐(PO₄)浓度的影响,而深海盆硅藻组合主要受温度的影响。对比前人研究,本文提高了对南海沉积硅藻空间分布认识的分辨率,充实了研究相对薄弱的西部陆架和深海盆的最新资料,佐证并修正了前人基于少量数据而得出的硅藻组合分区认识,消弭了前人观点的分歧。生物因素和沉积过程会使沉积硅藻对环境因子变化的响应关系更为复杂。

High-resolution spatial distributions of diatoms in surface sediments and their correlations with environmental factors in the central and northern South China Sea

To map the present distribution of sedimentary diatoms, a new data set on the relative abundance of diatom species preserved in 1266 surface sediment samples is generated, which covers the environmental factor characteristic of the central and northern parts of South China Sea (SCS) between 12° and 24°N. The biogeographic distribution patterns of as well as the preferences for environmental variables for 19 diatom species are documented. The relative abundance patterns of the major diatom species were statistically compared with six environmental variables, namely the annual sea surface temperature and salinity, dissolved oxygen, and concentrations of three surface nutrients (nitrate, phosphate, silicate). Pearson correlation and redundancy analyses indicated that species correlated so strongly with the environmental factors that six diatom assemblages could be established. Among which, the Paralia sulcata-Actinoptychus undulatus and Cyclotella stylorum-Cyclotella striata-Actinoptychus splendens-Coscinodiscus decrescens assemblages, located on the east and west sides of the Pearl River Estuary on the northern continental shelf of the SCS, respectively, are related to freshwater inputs from the Pearl River and Guangdong coastal current and Kuroshio intrusion. The Cyclotella striata-Paralia sulcate assemblage off the coast of Vietnam is related to the western boundary current of the SCS. The Nitzschia marina-Rhizosolenia bergonii-Azpeitia africana-Chaetoceros messanensis-Fragilariopsis doliolus assemblage in the northeastern SCS is significantly influenced by the Kuroshio intrusion and the SCS warm current and northern slope current. The Azpeitia nodulifera-Nitzschia marina-Hemidiscus cuneiformis and Azpeitia nodulifera-Nitzschia marina-Thalassionema nitzschioides-Cyclotella striata assemblages located on the Xisha Islands and in the SCS deep-water basin, respectively, correlate strongly with the sea surface temperature pattern. Some biological and sedimentological factors may cause stronger effects on diatom distribution, and may mask the influences of environmental variables.