南海西部表层沉积物碳酸盐分布特征及其溶解作用

Distribution and its dissolution of carbonate in seafloor surface sediment in the western South China Sea

碳酸盐是海洋沉积物的重要组成部分,在南海表层沉积物中含量最高可超过70%,因此深入研究现代碳酸盐的分布特征具有十分重要的意义。对南海西部底质的大量取样分析表明,该区CaCO3含量在上陆坡最高,其中在北部和中南部含量较高,中部和东南部含量较低,其分布特征主要受陆源物质供给量的控制,与陆架的宽度和陆坡的坡度密切相关。CaCO3最富集区出现在水深400～600m的上陆坡区,其中水深500～600m内的平均含量最高,达44.37%,水深超过1300m时含量开始明显下降,表明溶解作用增强。对CaCO3含量与水深关系进行多项式拟合,结果表明,本区没有出现碳酸盐溶解作用突然增强的溶跃面;但在水深3500m附近,拟合曲线出现转折点,CaCO3含量由随水深迅速下降变为相对稳定,因此该水深应为碳酸盐临界补偿深度。

As an important composition of marine sediment, carbonate makes up more than 70% in sea floor sediment in the South China Sea. It would be muchvaluable to research for the distribution of carbonate in recent marine. Base on large numbers of sampling at sea floor in the western South China Sea, the contents of carbonate are highest in the upper continental slope in total, especially higher in northern and mid southern, but lower in middle part and southeastern. It is suggested that the contents of carbonate in the shelf and the slopeare controlled by the terrigenous material supply and are close relationship with the extent of shelf and the gradient of slope. They are lower in the steeper upper slope outside the narrow continental shelf, with abundant supply of terrigenous material, while they are higher in the flatter upper slope outside the wide continental shelf, with less supply of terrigenous material. The contents of carbonate are highest in the area of water depth between 400 m to 600 m. The average content in the area with water depth of 500 m to 600 m is as high as 44.37%. The dissolution of carbonate intensified after water depth of 1 300 m, as thecontents decreased distinctly. It is suggested by polynomial fits between the contents and water depths that no distinguished carbonate lysocline depth (CLD) in the western South China in which the dissolution increased abruptly. But it issuggested that 3 500 m should be a CCrD of the sea area, but not CCD, for an inflexion appears at 3 500 m in which the contents of carbonate are about 8% in average and changed from decreasing to steadily as the water depth increasing.