海南岛周边海域表层沉积物磁化率 空间分布特征及其物源指示意义

海洋表层沉积物的磁学性质逐渐被证明是分析海洋沉积物物源的有效手段之一。选取海南岛周边海域39个站位的表层沉积物进行了磁学特征研究。结果表明：海南岛周边海域表层沉积物的低频磁化率和频率磁化率具有明显的空间分异特征，表现为高值区主要出现在海南岛以南海域，而海南岛以东和以西海域则呈现从岸向海逐渐降低的趋势。磁化率的影响因素分析表明：研究区海洋表层沉积物的磁化率主要由陆源碎屑物质贡献，因此可以认为沉积物低频磁化率和频率磁化率的空间分布特征能指示陆源输入的变化。利用多个环境磁学参数对采样点进行Q型聚类，并结合低频磁化率和频率磁化率的空间分布特征及采样点的地理位置将研究区划分为4个区域：海南岛以东水深超过100 m的海域（Ⅰ区）沉积物主要来源于其东北面的珠江水系，同时粤西沿岸河流携带来的物质也有一定程度的影响；海南岛以东水深小于100 m和海南岛以南海域（Ⅱ区）沉积物可能主要来自于海南岛沿岸侵蚀搬运以及入海河流输入；北部湾北部海域（Ⅲ区）沉积物受琼州海峡和北部湾沿岸河流输入物质的共同影响；海南岛以西海域（Ⅳ区）沉积物受来自海南岛西南侧河流输入、沿岸侵蚀物和由南向北的洋流所携带的沉积物的共同影响。研究表明：低频磁化率和频率磁化率组合可有效指示近岸表层沉积物的物源变化。

Spatial Distribution of Magnetic Susceptibility and Its Provenance Implication of Surface Sediments in the Sea Areas around the Hainan Island

Study of Magnetic properties of marine surface sediments are gradually proved to be one of the effective means for source analysis of marine sediments. In this paper samples from 39 stations in the sea areas around the Hainan Island were collected to analyze the magnetic characteristics of the surface sediments. It is shown that the low frequency magnetic susceptibility and frequency-dependent susceptibility in the areas have significant spatial differential features. The high values are mainly distributed in the southern sea area of the Hainan Island, while in the eastern and western sea areas the values are gradually decreasing from the coast to sea. The influence factors of magnetic susceptibility analysis shows that the susceptibility of the marine surface sediments in the study area is mainly contributed by terrestrial material, so the spatial distribution characteristics of low frequency magnetic susceptibility and frequency magnetic susceptibility can indicate the diversity of the input of terrestrial material. The studied area can be divided into four parts based on the Q type cluster analysis combined with the geographical location of sampling points. In the sea area to the east of Hainan Island with a water depth over 100 m (Part I) the sediments are mainly from the Pearl River system and to some extent are affected by the terrestrial material carried by the coastal rivers of west Guangdong. In the sea area to the east of Hainan with a water depth less than 100 m and the area to the south of Hainan (Part II) the sediments are mainly from the coastwise eruption and coastwise rivers of the Island; In the northern waters of the Beibu Gulf (Part III) the sediments are from Qiongzhou Strait and coastal rivers around the Gulf; In the sea area to the west of Hainan (Part Ⅳ) the sediments are from the rivers and coastal erosion in southwestern Hainan and from the materials carried by the ocean currents from south to north. The study shows that the combination of low frequency magnetic susceptibility and frequency dependent susceptibility can effectively indicate the source change in the offshore surface sediment.