Holocene Relative Sea-Level Change from Coral Microatolls at Sentosa, Singapore

Located away from the deformation zone of former Late Pleistocene ice sheets and on the relatively stable Sunda Shelf, Singapore is in a strategic location to understand global mean sea-level changes over the Holocene. There have been notable attempts to reconstruct Holocene relative sea-level change in the region. However, temporal data gaps and large vertical spread in existing sea-level reconstructions make discerning the timing and amplitude of the mid-Holocene highstand and nature of late Holocene relative sea-level fall challenging. Here, we present new data from in-situ fossil Diploastrea heliopora coral microatolls in Sentosa, Singapore, to complement other proxy records in the region. Coral microatolls are precise sea-level indicators that grow within a narrow vertical range in the lower intertidal zone, their upward growth limited by subaerial exposure during the lowest of tides. Determining relative sea-level change from fossil microatolls requires an understanding of the indicative meaning (or vertical range) of this upper limit of growth (i.e. highest level of survival; HLS) on modern counterparts the variability of which constitutes uncertainties in our relative sea-level reconstructions. We explore a novel approach to quantify HLS across different microatolls by combining photogrammetry with surveying, which enables a more complete sampling of HLS compared to point estimates obtained by more traditional levelling methods. Comparison of the indicative meaning of HLS across different sites may shed light on some of the processes controlling this upper limit of growth. While this abstract focuses on reconstructing relative sea level in Sentosa and on quantifying the uncertainty in the indicative meaning of microatolls, other related contributions to this session explore the possible drivers of HLS variability and infer relative sea-level change from coral microatolls at other sites in Singapore.