南海北部表层沉积物碳酸盐含量和δ^(18)O及δ^(13)C的空间与粒径分布特征及其控制因素

Spatial and grain size distribution of carbonates contentδ^(18)O and δ^(13)C in surface sediments from the northern South China Sea and their controlling factors

为深入研究南海北部表层沉积物中碳酸盐的来源及其控制因素,采用湿筛法,对南海北部珠江口、陆架、陆坡及海盆表层沉积物中碳酸盐的含量、δ18 O和δ13C及其粒度分布特征进行了研究。结果表明,南海北部表层沉积物中的碳酸盐可能主要以海洋自生碳酸盐为主,其含量在空间上以陆坡显著高于海盆、陆架及珠江口为特征。粒度上,陆架(水深80m)和浅陆坡(水深550m)处碳酸盐的粒度分布相对平均,但在珠江口及730m以深,76.9%～84.5%的碳酸盐分布于小于32μm的粒级中。另外,珠江口和陆架与陆坡和海盆碳酸盐δ18 O和δ13 C的空间及粒度分布特征显著不同。珠江口陆架区,在空间上从珠江口向陆架,全样碳酸盐的δ18 O和δ13 C由轻变重。粒度上,碳酸盐的δ18 O和δ13 C随着粒径的增大而变重,并且δ18 O和δ13C之间正相关,主要受珠江淡水的δ18 O及其δ13CDIC控制。陆坡海盆区,空间上,从陆坡向海盆,δ18 O略有变轻,δ13C基本不变。粒度上,碳酸盐的δ18 O和δ13C随着粒度的增大没有明显的变化趋势,并且δ18 O与δ13 C之间不相关或负相关。其δ18 O可能主要受表层海水的温度控制,其δ13C可能主要受海水δ13CDIC控制。

Bulk and grain size content,δ18 O andδ13 C values of carbonates in the surface sediments collected from the Zhujiang Estuary,shelf,slope and basin of the northern South China Sea were analyzed in order to determine the source of carbonates and the controlling factors ofδ18 O andδ13C of carbonates.The results show that the carbonates in the surface sediments of the northern South China Sea are mainly authigenic.The carbonate contents of the slope are obviously larger than those of the Zhujiang Estuary,shelf and basin.In the Zhujiang Estuary with water depth of 34mand the basin with water depth of more than 730m,76.9%～84.5%of carbonates are distributed in the particles which grain diameter is less than 32μm.Correspondingly,in the shelf with water depth of 80mand the slope with water depth of 550m,the carbonates are evenly distributed amongall grain sizes.In addition,the spatial and grain size distribution ofδ18 O andδ13C of the carbonates in the Zhujiang Estuary and the shelf are obviously different from those in the slope and the basin.In the Zhujiang Estuary and the shelf,the bulkδ18 O andδ13C values of carbonates become heavy from the Zhujiang Estuary to the shelf;the grain size distribution of δ18 O andδ13C values of carbonates are that theδ18 O andδ13C values of carbonates become heavy with the increasing of grain size and theδ18 O values are positively related toδ13C values;indicating that theδ18 O andδ13C of carbonates in the Zhujiang Estuary and the shelf are mainly controlled byδ18 O andδ13CDICof the water from the Zhujiang River.In the slope and the basin,the bulkδ18 O values of carbonates become light from the slope to the basin and the bulkδ13C values of carbonates do not have an obviously variation from the slope to the basin;the grain size distribution ofδ18 O andδ13C values of carbonates are that theδ18 O andδ13C values of carbonates do not have a clear trend with the increasing of grain size and theδ18 O values are not or negatively related toδ13 C values;indicating that theδ18 O of carbonates are mainly controlled by surface seawater temperature and theδ13 C of carbonates are mainly controlled by theδ13CDICof surrounding seawater in the slope and the basin.