Drivers of Late Holocene relative sea-level change in the Sunda Shelf: new insights from coral microatolls in Singapore

Existing Late Holocene relative sea-level (RSL) records from the Sunda Shelf suffer from spatial and temporal discontinuities and/or a lack of precision, hindering an understanding of the drivers of RSL change. Here, we present the first RSL record from fossil coral microatolls in Singapore, which has high vertical (<± 0.20 m, 2𝜎) and temporal (<± 26 yrs, 95% highest density region) precision.We applied a novel approach to produce sea-level index points and infer sea-level tendencies by combining (1) the use of photogrammetry with traditional levelling techniques; (2) 230Th dating; and (3) surface morphologies of the fossil coral microatolls. The fossil corals reveal a gradual, 0.31 ± 0.18 m (2𝜎) fall in RSL between 2.8 kyrs BP and 0.6 kyrs BP, with rates averaging 0.15 ± 0.10 mm/yr (2𝜎). Our coral record lies within uncertainty of some of the published RSL records from the region but disagrees with others, suggesting that local to regional processes may be driving spatial variability in RSL in the region. Misfits of the data with glacial isostatic adjustment (GIA) models may be explained by the influence of non-GIA processes, such as vertical land motion, and/or the need to fine-tune GIA model parameters. Work is ongoing to decompose the drivers of relative sea-level change within the region.