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南沙群岛珊瑚礁砾洲地貌特征
周胜男, 施祺, 杨红强, 严宏强
中国科学院南海海洋研究所
摘要:
南海珊瑚岛礁广泛分布,具有重要的战略地位和意义。灰沙岛堆积出露于珊瑚礁之上,经历着不同的发育阶段,改变着南海珊瑚岛礁的数量、分布以及地貌特征。珊瑚礁砾洲是灰沙岛发育早期阶段的一类地貌类型。通过对南沙群岛永暑礁、西门礁和安达礁三个砾洲的现场调查,并基于理论最低潮面和平均海面分别计算了砾洲的可能分布范围和平均出露范围,获得了砾洲的地形地貌特征。三个砾洲均为向西北凸出的弧形,呈北东-南西向展布。永暑礁和西门礁砾洲周边地势较高,中部相对低洼,分布有多条砾脊,边缘向海侧主砾脊高度最大,内部多条较低的次砾脊相交于主砾脊并汇聚于砾洲东部;安达礁砾洲则中部凸起地势较高,周边较低,无多重砾脊分布。推断砾洲的发育由最初珊瑚枝块堆积于中部形成凸起,逐渐向北东和南西两侧以砾脊形式扩展,最终形成砾洲由内向外的洼地-砾脊-砾滩的地貌分带模式。砾洲的地形地貌特征表明,南沙群岛砾洲的发育主要受北东-南西向水动力条件季节性交替的控制,反映了南海海区盛行季风的影响。南沙群岛珊瑚礁砾洲的地貌特征为深入研究南海珊瑚礁灰沙岛地貌发育演化及动力机制提供了基础数据。
关键词:  南沙群岛 灰沙岛 砾洲 地貌特征 水动力环境
DOI:10.11759/hykx20180822001
分类号:
基金项目:中国科学院战略性先导科技专项(A类)(XDA13010103),国家自然科学基金项目(41506061,41776128)
Geomorphic Features of Coral Shingle Cays in the Nansha Islands
zhoushengnan, shiqi, yanghongqiang, yanhongqiang
South China Sea Institute of Oceanology, Chinese Academy of Sciences
Abstract:
Coral reefs and islands are widely distributed in the South China Sea and play an import role on the national maritime strategy. Coral islands are accumulated and emerged on reefs with different development stages, which changed the numbers, distribution and geomorphic features of coral reefs in the South China Sea. Coral shingle cay is one of geomorphic types in the early development stages of coral islands. Three coral shingle cays locating respectively on the Yongshu Reef, Ximen Reef and Anda Reef in the Nansha Islands were investigated. Based on the theoretical lowest tide (TLT) and mean sea level (MSL), we calculated the areas of possible distribution and average outcrop of the cays and obtained the topographic and geomorphic features of the cays. The three cays are northwest-facing arc-shaped and spread with northeastern-southwestern direction. In the cays on the Yongshu Reef and Ximen Reef, the surrounding areas are relatively high and the central parts are relatively low. Shingle ridges are found in the two cays, where a high main ridge is located at the seaward edge and multiple low sub-ridges distribute in the interior intersecting the main ridge and gathering in the eastern part. Differently, the cay on the Anda Reef is bulging on the central part and is low-lying on the edge area without shingle ridge. It’s speculated that coral branches and gravels accumulated and bulged initially at the central part and extended towards northeast and southwest respectively as shingle ridges, formed a shingle cay finally with geomorphic zones composed inside-outside of depression-shingle ridge-shingle beach. The topography and geomorphology of these cays indicate the seasonal northeastern-southwestern hydrodynamic condition controlled the development of shingle cays in the Nansha Islands reflecting the influence of the prevailing monsoon in the South China Sea. The geomorphic features of coral shingle cays in the Nansha Islands provide basic data for the deep study on the geomorphic development and dynamic mechanism of the coral islands in the South China Sea.
Key words:  Nansha Islands  coral island  coral shingle cay  geomorphic feature  hydrodynamic condition
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