台风影响下西沙灰沙岛的时空变化特征  

Spatiotemporal changes of lime-sand islands in the Xisha Islands under the impacts of typhoons

作　　者：肖海婷 黄荣永[2,3,4] 刘羿 余克服 XIAO Haiting;HUANG Rongyong;LIU Yi;YU Kefu(School of Earth System Science,Tianjin University,Tianjin 300072,China;Guangxi Laboratory on the Study of Coral Reefs in South China Sea,Guangxi University,Nanning 530004,China;Coral Reef Research Centre of China,Guangxi University,Nanning 530004,China;School of Marine Sciences,Guangxi University,Nanning 530004,China)

机构地区：[1]天津大学地球系统科学学院,天津300072 [2]广西大学广西南海珊瑚礁研究重点实验室,广西南宁530004 [3]广西大学珊瑚礁研究中心,广西南宁530004 [4]广西大学海洋学院,广西南宁530004

出　　处：《热带海洋学报》2025年第2期157-177,共21页Journal of Tropical Oceanography

基　　金：国家自然科学基金项目(4192200195、42030502、42090041)。

摘　　要：文章基于哨兵二号(Sentinel-2)遥感影像,使用梯度向量流–主动轮廓模型(gradient vector flow-snake,GVF-Snake)提取南海西沙北岛、中岛和南岛的海滩基部线(toe of beach,ToB)和植被边界线,获取了灰沙岛及其海滩面积。采用突变检验法,判别出2016—2022年造成研究区岛屿面积发生突变的台风事件。通过统计台风事件中灰沙岛归一化植被指数(normalized difference vegetation index,NDVI)和海滩面积变化,以及ToB线和植被边界线的移动距离,分析了西沙灰沙岛受台风影响后的时空变化特征及其影响因素。结果显示:1)台风导致灰沙岛植被以轻度受损为主,中度及以上受损植被分布在岛屿沿岸,导致了植被边界线的后退,而沉积物随受损植被剥脱,并随风浪冲刷至海滩,导致了ToB线的向海推进。受台风路径方向影响,迎风面沿岸首先遭受冲击,灰沙岛迎风面沿岸植被重度受损,因而导致ToB线和植被边界线在迎风面具有更大的移动距离;2)在台风影响末期,由于灰沙岛沿岸植被受损,植被边界线的后退和ToB线的向海推进,使得海滩面积扩大,而在台风过后,因失去植被的固定,在海滩堆积的松散沉积物在风浪作用下从岛屿运离至礁坪,使得海滩面积缩减。因此,具有固定与缓冲作用的沿岸植被在维持灰沙岛的稳定性方面具有重要作用;3)台风风速增大和台风路径与灰沙岛之间距离的缩短,以及台风期间海洋表层流速的增加,易使得灰沙岛遭受极端波浪和风暴流的影响,将增大灰沙岛严重受损植被的面积,进而造成更大的岸线移动的距离和海滩面积的变化。此外,台风可引起沉积物在灰沙岛及其周围环境中的运移,进而直接改变灰沙岛海滩面积及其形态。台风过后灰沙岛上大量松散沉积物的流失,导致了灰沙岛面积突变减小,加之全球变暖造成生物碳酸盐产率下降,以及来自周围环境的沉积物供应不足,可能是南In this study,we explored the changing characteristics of spatial patterns of lime-sand islands in the Xisha Islands under the impacts of typhoons and their driving factors,which are of great significance to the ecological protection and sustainable development of lime-sand islands in the South China Sea(SCS).First,to determine the area of the BeiDao,ZhongDao and Nandao islands of the Xisha Islands and their beaches,the toe of beach line(ToB) and the boundary of vegetation were extracted using the gradient vector flow-snake(GVF-snake) model based on Sentinel-2 remote sensing images.The monthly average area of the study islands from 2016 to 2022 was examined using the change point detection method,and the typhoon events that had caused significant changes in the size of the study islands were identified.Finally,the spatial and temporal characteristics of the islands affected by typhoons were analyzed based on the changes in lime-sand islands area,vegetation area,beach area and normalized difference vegetation index(NDVI) during typhoon events.The results are shown as follows.1) The vegetation of the islands was mainly slightly stressed by the typhoons,and the severely stressed areas were mainly located along the shorelines.The typhoons caused a significant retreat of the vegetation boundary of the islands,and the sediments were stripped off with the damaged vegetation and washed to the beach with the wind and waves,resulting in the seaward advancement of the ToB line.The windward coasts were the first to be impacted by the direction of the typhoon path,and the vegetation along the windward side of the islands was heavily damaged,resulting in more significant changes in vegetation,vegetation boundary,and the ToB line on the windward side.2) As the vegetation along the lime-sand islands was damaged,the retreat of the vegetation boundary line and the seaward advancement of the ToB line resulted in the expansion of the beach area,whereas after the typhoon,due to the loss of vegetation fixation,the loose sediment accum

关 键 词：灰沙岛 台风 遥感 西沙群岛 

分 类 号：P737.13[天文地球—海洋地质]