Mid Holocene relative sea-level changes from coral microatolls of Pulau Biola, Singapore

Coral microatolls are precise proxies of relative sea-level (RSL) change in low-latitude coastal regions. These coral colonies live in the intertidal zone where partial mortality due to low-water events produces a characteristic planform ring structure. Since ring elevations reflect changes in local RSL during a coral’s lifetime, we can use the surface profiles of microatolls to quantify short-term (decadal) rates of RSL change. Therefore, Holocene fossil microatolls can produce sea-level index points (SLIPs) with relatively high spatial and temporal resolution. In this study, we present preliminary sea-level reconstructions from Pulau Biola (Violin Island), Singapore, based upon several Porites sp. and Diploastrea heliopora fossil microatolls. We calculated the difference in elevation between the fossils and local living microatolls of the same genus to quantify the magnitude of past water level. We also combined U-Th ages, structure-from-motion photogrammetry and LiDAR 3D models, and survey data to generate a RSL history spanning more than two centuries in the mid Holocene. The highest-elevation fossil microatolls at Pulau Biola are consistent with an overall rise in sea level, from 0.2 to 0.7 m above present, between 7.7 and 7.4 kyr BP. In addition, decimetre-scale sea-level fluctuations during this period are inferred from decreasing and increasing ring elevations within corals. These fluctuations indicate a more complex sea-level history than resolved by other proxies or glacial isostatic adjustment models, and ongoing work aims to reconcile conflicting Holocene sea-level models and datasets in the Singapore region.