资源环境科技发展态势分析平台

Sand cays are valuable paleo-archives that can significantly increase our understanding of Holocene tropical cyclone variability. Here we conducted detailed sedimentological and chronological analyses from a 195-cm-depth pit excavated on Guangjin Island (northern South China Sea), a cay influenced by frequent tropical cyclones. Radiometric dating of multiple deposits revealed that foraminifera, soft coral spicules, and gastropod shells yielded variable age distributions, while U/Th ages of pristine Acropora branches provided a clear record of deposition and cay formation. Based on this robust chronostratigraphy, the proportions of >2-mm grain size fraction within the deposits corresponded with the frequency of paleotyphoons recorded by historical records in recent centuries. U/Th ages (CE 1687 +/- 12, CE 1735 +/- 6, and CE 1813 +/- 5) of Acropora branches from the deposits matched with three known historical typhoon events. Our results highlight the potential of cyclone-deposited sand cays as new archives for recording paleocyclones.

Plain Language Summary Determining accurate chronologies of sand cay formation is key to understanding their temporal dynamics and stability and their potential as paleo-archives. We reconstruct the growth of a sand cay strongly influenced by frequent tropical cyclones in the South China Sea. Accelerator mass spectrometry C-14 and U/Th dating of coral, soft coral spicules, mollusk, and benthic foraminifera revealed substantially different ages among calcareous components within layers. Relatively small benthic foraminifera, including Amphistegina sp., Rotalia calcarinoides, and Calcarina hispida, yielded abnormally old ages, suggesting a disparity of centuries to millennia between the organism's death and final deposition. U/Th ages derived from Acropora branches with eroded surfaces exhibited variable but older ages, while accelerator mass spectrometry C-14 ages from gastropod and large benthic foraminifera exhibited younger ages within the same layers. Taphonomically pristine Acropora branches commonly recorded in "cyclone deposit" layers were consistently the youngest component of all radiometric ages and align with paleotyphoon records throughout the Little Ice Age. The age distribution pattern of the dated coral fragments also provides a detailed record of the island formation history.