ABSTRACT

High-resolution sea-level data and high-precision dating of corals in the northern South China Sea (SCS) duringthe Holocene provide a reference and historical background for current and future sea-level changes and a basisfor scientific assessment of the evolutionary trend of coral reefs in the SCS. Although sporadic studies have beenperformed around Hainan Island in the northern SCS, the reconstructed sea level presents different values or iscontroversial because the indicative meaning of the sea-level indicators were neither quantified nor uniformcriteria. Here, we determined the quantitative relationship between modern living coral and sea level bymeasuring the top surfaces of 27 live Porites corals from the inner reef flat along the east coast of Hainan Islandand assessed the accuracy of results obtained using coral as sea-level indicators. Additionally, three in situ fossilPorites corals were analyzed based on elevation measurements, digital X-ray radiography, and U-Th dating. Thesurvey results showed that the indicative meanings for the modern live Porites corals is (146.09 ± 8.35) cm belowthe mean tide level (MTL). It suggested that their upward growth limit is constrained by the sea level, and thelowest low water is the highest level of survival for the modern live Porites corals. Based on the newly definedindicative meanings, 6 new sea-level index points (SLIPs) were obtained and 19 published SLIPs wererecalculated. Those SLIPs indicated a relative sea level fluctuation between (227.7 ± 9.8) cm to (154.88 ± 9.8) cmMTL between (5 393 ± 25)cala BP and (3 390 ± 12)cala BP, providing evidences of the Mid-Holocene sea-levelhighstandin the northern SCS. Besides that, our analysis demonstrated that different sea-level histories may beproduced based on different indicative meanings or criteria. The dataset of 276 coral U-Th ages indicates thatcoral reef development in the northern SCS comprised the initial development, boom growth, decline, andflourishing development again. A comparison with regional records indicated that synergistic effects of climaticand environmental factors were involved in the development of coral reefs in the northern SCS. Thus, thecessation of coral reef development during the Holocene in the northern SCS was probably associated with thedry and cold climate in South China, as reflected in the synchronous weakening of the ENSO and East Asiansummer monsoon induced by the reduction of the 65°N summer insolation, which forced the migration of theIntertropical Convergence Zone.