The Distributions of Calcareous Nannofossils and Grain Size in the Surface Sediments of the East China Sea and Their Relationship to the Current Pattern

東海表層沈積物中的鈣質超微化石和顆粒分佈與洋流型態之關係

陳民本(Min-Pen Chen)；黃兆愷(Chao-Kai Huang)

East China Sea ； Surface Sediment ； Nannofossil ； Grain size ； Currcnt path

Terrestrial, Atmospheric and Oceanic Sciences

6卷1期（1995 / 03 / 01）

129 - 150

英文

Nannofossil assemblages, carbonate content and grain size distributions were analyzed in 46 samples of surface sediments collected in the middle and outer shelf of the East China Sea. Thirty three indigenous taxa were identified. Emiliania huxleyi and Gephyrocapsa oceanica were the two dominant calcareous nannoplankton species. The former was derived from both the China Coastal Current and the Kuroshio Current. The latter originated mainly from the Japan longshore current. Sediments containing high carbonate content (＞30%) were deposited along the shelf break of the East China Sea. About 80% of the total carbonate material was composed of shell fragments and foraminiferal tests. Nannofossils were found mainly in the south of the loop current off the Chagjiang River, the western tip of the Japan longshore current and in the western flank of the Okinawa Trough. The grain size distribution pattern can be divided into four types: a unimodal pattern in the fine grain material (about 10μm) which is composed mainly of loess; a unimodal pattern occurrring in the coarse grain size (about 200-300μm) which is composed mainly of foraminifera and shell fragments; a bimodal pattern with a higher concentration of fine sediment, and a bimodal pattern with less fine-grained sediment. The bimodal sediments are distributed between the two single modes. The finer carbonate- free sediment with bimodal size distribution is derived mainly from the Chang, jiang River. The coarse fractions are composed of terrigenous materials derived from either mainland China or from Taiwan. From the factor analysis of ten selected nannofossil species and groups, the sediment transportation path of each current can be deduced from the factor loading contours. In the middle and outer shelf of the East China Sea, seven current tracks, including the main Kuroshio Current, a branch of the Kuroshio Current, the Taiwan Current, the loop current from Changjian, the China Coastal Current, the Tsushima Current and the longshore current from Japan are recognized.