南海西部浮游有孔虫含量与水深关系定量研究

Quantitative research on relationship between planktonic foraminifera content and water depth in western South China Sea

南海西部 4°～ 18°N ,10 8 5～ 115°E海域表层沉积物中有孔虫定量分析表明 ,从陆架至深海盆区 ,随着水深增加 ,底栖有孔虫丰度总体呈下降趋势 ;而浮游有孔虫在上陆坡区水深 2 0 0～ 2 0 0 0m处最丰富 ,向浅水和深水方向 ,其丰度均下降 ,浮游有孔虫百分含量 (P)与水深 (D)有明显的相关关系。但在陆架区和陆坡-深海盆区 ,两者关系完全不同 :在陆架区随水深增加浮游有孔虫百分含量明显增大 ,而在陆坡 -深海盆区 ,两者呈负相关关系。经定量拟合水深小于 2 0 0m的陆架区 ,浮游有孔虫含量与水深满足关系式 :lnD =0 0 2 1P +3 2 0 8;而在水深大于 2 0 0m的陆坡 -深海盆区 ,两者满足D =- 5 2 6 3P +5 2 10 5 2。这主要是由于陆架区随水深增加 ,浮游有孔虫增加 ,但水深大于 2 0 0m后 ,碳酸盐的溶解起主要作用 ,浮游有孔虫比底栖有孔虫更易于溶解 ,造成其含量随水深增加而下降。

Water depth is an important index for research on the paleoenvironmental evolution and basin analysis.The authors made research on the quantitative relationship between the planktonic foraminifera content and water depth in modern sediments in the western South China Sea,which provides a reference for paleoenvironmental study.More than 300 samples of surface sediments were collected systematically from the western South China Sea (4°～18°N,108.5°～115°E) for foraminifera identification.The abundance of benthonic foraminifera decreases from the continental shelf to the deep sea basin with increasing water depth,while planktonic foraminifera reach the highest abundance in the upper slope,with water depth between 200 m to 2000 m,and decrease toward both the coast and deep sea basin.There is a distinct relationship between the content of planktonic foraminifera (P) and water depth (D) which is apparently different in the shelf and in the slope to deep sea basin.The content of planktonic foraminifera increases rapidly on the shelf with the increasing of water depth and their relative equation is shown as lnD=0.021P+3.208,but a negative relation from the slope to deep sea basin is shown by D=-526.3P+52105.2.It is mainly because the planktonic foraminifera increase as the water depth increasing in the shelf,however,the dissolution of carbonate becomes the main reason to control the contents of the planktonic foraminfera in the ocean at the depth of more than 200 m.The planktonic foraminifera are easier to dissolve than benthic foraminifera.