北部湾现代沉积速率

MODERN SEDIMENTATION RATES IN THE BEIBU GULF

运用210Pb法测定了北部湾16根柱样的现代沉积速率,结果显示北部湾柱样210 Pb剖面分布呈现三段式正常型、二段式正常型和倒置型3种类型,主要受沉积物组成、沉积物供应和水动力条件控制。北部湾东侧现代沉积速率相对较高的区域分布在钦州湾附近20m水深以浅的地区和涠洲岛至海南岛西岸一线外水深20～50m的内陆架。而在海南岛西岸水下岸坡带、琼州海峡西口附近和北部湾顶东北角这3处强潮区,现代沉积强度可能较弱或无现代细粒沉积。在北部湾中部50m水深以深,由于物质供应匮乏,现代沉积速率也极低。北部湾东侧存在由环流驱动的沉积物"传送带",自南向北运动,其西边界在琼州海峡一线以南是在50m等深线附近,以北是在109°E附近,冬季可能略向西拓展。

Modern sedimentation rates for 16 cores recovered from the Beibu Gulf were measured with the 210Pb method.The results show that there are 3 types of 210Pb vertical distribution patterns,say,normal 3-segment,normal 2-segment and inversion types,depending upon the composition and sediment supply as well as sediment dynamics.In the eastern part of the gulf,relatively high sedimentation rates appeared in the area near the Qinzhou Bay at a water depth less than 20 m and the inner continental shelf south to Weizhou Island,west Hainan Island at a water depth between 20 m and 50 m.The modern sedimentation rates,however,are low on the west subaqueous slop of Hainan Island,the west mouth of Qiongzhou Strait and the northeastern corner of the gulf due to strong tide.The area in a water depth more than 50 m in the central part of the gulf has low modern sedimentation rates due to poor sediment supply.It seems that there is a sediment conveyor belt driven by the anti-clock circumfluence on the east side of Beibu Gulf,which transports fine sediment from south to north.The circumfluence is bordered to the west by the south of Qiongzhou Strait along the 50 m isobaths and to the north by the Qiongzhou Strait near 109°E.The border may move westward a little in winter time.