多元统计及物源分析支持的北部湾东部海域沉积物输运趋势

Sediment transport patterns in the eastern Beibu Gulf based on grain-size multivariate statistics and provenance analysis

通过对北部湾东部海域表层底质样的粒度和重矿物分析,获得了粒度和矿物组成特征。对粒度进行因子分析获得了4个主控因子,其中因子2和3分别代表细颗粒的悬移质组分和陆源粗颗粒推移质组分,指示来自琼州海峡和北部湾西岸、西北岸的物源贡献,而且因子2的高得分区与弱环流背景相吻合;因子4反映了粤西和海南岛东岸沿岸流的物源贡献。采用重矿物组合,将研究区沉积物的物质来源划为4个分区。分别对4个物源分区使用粒径趋势分析模型,把它们合并后获得了整个研究区的趋势矢量,其中海湾北部沉积物输运汇聚中心的位置与余环流的中心位置基本一致,海南岛西部海域沉积物显示为向北输运的特征,与地貌、水动力特征基本吻合,在一定程度上可消除物源混合造成的影响。在使用粒径趋势分析模型获取沉积物净输运方向时,需要综合考虑物源差异和空间尺度对沉积物粒径趋势的影响。

Sediment samples collected from the eastern Beibu Gulf were analyzed in the laboratory to obtain grain-size distributions and mineral components.Four main control factors are obtained using a factor analysis.Factor 1 is contributed by 2.5Φ-3.75Φ and 5.75Φ-7.75Φ.Factor 2 respects fine suspended load component,indicating that the provenance contribution from the Qiongzhou Strait and the high score area is consistent with the weak circulation.Factor 3 is a indicator of terrigenous coarse bedload component from the west and northwest coast of the Beibu Gulf.Factor 4 can reflect the transportation by the coastal current along the east coast off Hainan Island and the west of Guangdong Province.The study area can be separated into four subareas of the sediment sources on the basis of heavy mineral analysis.A grain-size trend analysis model is separately used for the four subareas to estimate the net sediment transport pathways,which can remove the affects induced by the sediment mixing from different sources.A converge center of grain-size trend vectors in the area of the west of Hainan Island might result from the mixing of different sources of sediments,instead of sediment transport.Actually,the northward transport dominates this area of the west of Hainan Island.Another converge center in the northern area is well agreement with the local geomorphology and large-scale ocean circulation pattern.Thus,the application of grain-size trend should consider the effect of sediment sources and spatial scales in order to derive the reasonable net sediment transport pathways.