MODERN SEDIMENTATION RATES IN THE BEIBU GULF

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.