Application and uncertainty analysis of beachrock to Mid-late Holocene sea-level reconstruction in the northern South China Sea

The characteristics of the past sea-level change have important scientific and practical significance for understanding the process of the modern sea-level change, and predicting future scenarios. Beachrock, as a unique sedimentary rock in coastal intertidal zones in tropical and subtropical regions, is an important indicator of coastal change and the past sea-level elevation. However, due to the change of dynamic conditions after the formation of beachrock, the different dating methods, the estimation of indicative range represented by beachrock and error analysis, the results of past sea-level reconstruction based on beachrock are still controversial and uncertain. Therefore, we analyze and summarize the progress of sea-level reconstruction of Mid-late Holocene based on beachrocks in the northern South China Sea, as well as the existing problems and potential opportunities in sea-level research. The uncertainty of sea-level reconstruction based on beachrock is further quantitatively studied from the aspects of the formation age of beachrock and the elevation change after the formation of beachrock . At the same time, the high-precision elevation measurement and U-Th dating of three in-situ coral reefs (one large massive Porites and two Porites microatolls) along the east coast of Hainan Island in the northern South China Sea were conducted, and six new sea-level data are obtained. In conjunction with Glacial Isostatic Adjustment (GIA) and ICE-5G model results, they were applied to the reliability analysis and comparison of the reconstructed Mid-late Holocene sea level in the north of the South China Sea based on beachrocks. The uncertainty analysis and results indicate that the accuracy of sea-level reconstruction result is further improved after the correction of age and elevation, which can provide reference for the uncertainty and reliability analysis of the reconstructed sea-level based on other sea-level indicators.