南沙群岛珊瑚礁动力地貌特征

FEATURES OF DYNAMIC GEOMORPHOLOGY OF CORAL REEFS IN NANSHA ISLANDS

南沙群岛受季风、台风和波浪的影响，珊瑚礁体呈ＮＥ－ＳＷ向椭圆形态，西南礁坪宽于东北礁坪。位于不同波能带内的珊瑚礁体发育了与之相适应的动力地貌单元。礁前斜坡高波能带地形陡峭，向风坡礁脊一槽沟系发育。外礁坪消耗大量波能，广泛覆盖生物碎屑，珊瑚生长稀疏。内礁坪宽广平坦，珊瑚生长良好。外礁坪堆积许多大礁块，尤以东北礁坪为甚。在湖低波能带，通常东坡缓于百坡，湖盆一般浪静流缓，为生物碎屑堆积区。

Due to the influence of monsoons, typhoons and waves, coral reefs in Nansha Islands are elliptic extending NE-SW, and the SW reef flat is wider than NE reef flat. Various dynamic geomorphologic units are developed according to wave energy zones. Front slopes of reefs are very steep and spur-groove systems develop best at windward slopes.The outer coral reef flat dissipates wave energy greatly and is covered with bioclasts,while corals are sparse. The inner coral reef flat is wide and plane, and corals grow well.Lots of huge reef blocks pushed by waves form reef ridges, specially in the NE reef flat.The lagoon which is in low wave energy zone with quiet waters is the main area of sediments. In general, the east slope is gentler than the west slope in a Lagoon.