涠洲岛珊瑚礁近千年的发育过程及其对气候变化的响应*

高纬度珊瑚栖息地能否成为气候变暖背景下热带珊瑚物种的“避难所”仍不明确, 南海北部的相关研究更是稀少。本文以取自涠洲岛的2根珊瑚礁沉积岩心为研究对象, 通过U-Th定年、沉积组分分析以及珊瑚种属鉴定等方法, 探讨近千年以来珊瑚礁的发育过程及其对气候变化的响应。研究结果发现, Core1(石螺口)岩心沉积的3个快速堆积阶段分别与罗马暖期、中世纪暖期和现代暖期大致对应; 而2个缓慢堆积阶段则分别与黑暗时代冷期和小冰期大致对应, 证实了温暖的气候对珊瑚礁发育有促进作用, 而寒冷的气候则不利于珊瑚礁的发育; 此外, 现代强烈的人为干扰可能也导致了涠洲岛珊瑚礁的迅速退化。Core2(南湾)中陆源沉积含量高, 珊瑚年龄主要集中在800AD—950AD和现代这两个时间段内, 其原因可能与环境变化、风暴作用及湾内现代珊瑚分布特征有关。通过对比这两个站位的珊瑚礁沉积特征, 本文进一步提出“完全避难所”和“非完全避难所”的概念, 揭示涠洲岛珊瑚可能同时具有低纬度热带珊瑚礁和高纬度珊瑚群落这两种发育特征和趋势。

Coral reef growth of Weizhou Island and its response to climate change in the past millennium

Whether high-latitude coral habitat could become “refuge” for tropical coral species under global warming is still unclear, and related research on the northern South China Sea is especially rare. Based on two reef cores drilled from Weizhou Island, the development history of coral reefs surrounding Weizhou Island and its response to climate change in the past millennium are explored with the help of U-Th dating technology, sedimentary component analyses and coral species identification. Three rapid accretion stages of Core1 (collected from Shiluokou) deposition roughly correspond to the Roman Warm Period, Medival Warm Period and Present Warm Period, respectively. And two slow accretion stages roughly correspond to the Dark Age Cold Period and Little Ice Age. They suggested that warm climate promotes reef development, while cold climate has adverse impacts on coral reef development. Strong local disturbances may have caused the rapid degradation of Weizhou Island coral reefs in recent decades. Core2 (collected in Southern Bay) has high terrigenous sediment content. U-Th ages in Core2 are concentrated in a relatively narrow time interval of 800AD—950AD and present, probably referred to environment changes, storms and the distribution of modern corals. By comparing the two sites on the same island, we further suggest the concepts of “Complete Refuge” and “Incomplete Refuge”, and reveal that Weizhou Island corals may have both developmental characteristics and trends of low-latitude tropical coral reefs and high-latitude coral communities.