Development of coral reefs around Weizhou Island and its bearing on climate

The Weizhou Island, located in the northern border of the tropics, is relatively too high in latitude to coral growth. Low temperature in winter time is the key factor which limits the coral growth and reef development. Reconstructing the development of coral reefs on the Weizhou Island is of great scientific significance for understanding the response of corals to past climate and predicting the development trend of coral reefs in the future. This study is devoted to the drilling cores extracted from the Well GS-3 on the Weizhou Island. The cores were dated with high-precision uranium series dating, upon which the chronological framework of the coral reefs is established. Particle size, biological composition and mineral composition are analyzed for revealing the composition of the coral deposits. The age of the coral reefs at 5.57 m in depth of the core GS-3 is dated 3737 ± 17 aBP. The average vertical accretion rate of the coral reefs is 1.49 m/ ka calculated based on this age. The growth of coral reefs on the Weizhou Island were accelerated during the periods of 3737～2476 aBP, 2288～1191 aBP and 325 years ago to present with vertical accretion rates of 2.21 m/ka, 1.13 m/ka and 1.85 m/ka respectively, and decelerated during the periods of 2476～2288 aBP and 1191～325 aBP and the correspondent vertical accretion rates were 0.64 m/ ka and 0.48 m/ka respectively. The biological components of sediments are mainly composed of corals, coralline algae and mollusks, while the mineral compositions dominated by aragonite and quartz. The correlation between coral reef vertical accretion rate and its climate background suggests that the rapid development stage of coral reefs on the Weizhou Island could roughly correlated to the Late Megathermal Period, Roman Warm Period and Current Warm Period, and the slowing down stages of development of reefs roughly corresponded to the cold periods, namely the Late Dark Ages Cold Period, the Medieval Climate Anomaly and the early Little Ice Age. In general, the development of coral reefs on the Weizhou Island at relatively high latitudes is depending on climate changes. The warm periods are conducive to coral growth and otherwise, coral reefs growth would slow down as cold periods came.