Reconstructing Late-Holocene relative sea level using mangrove sediments in Singapore

Abstract

Mangrove sediments have served as valuable archives of Late-Holocene relative sea-level (RSL) change. However, challenges such as age uncertainties due to root penetration and bioturbation, as well as elevation uncertainties from surveying, indicative meaning, and sediment compaction remain. Here, we reconstructed Late-Holocene RSL from Singapore using a multi-proxy approach combining litho- (grain size and loss on ignition), bio- (pollen), and chrono-stratigraphical (Accelerator Mass Spectrometry radiocarbon dating) techniques to produce a series of sea-level index points (SLIPs). We surveyed the SLIPs to mean tide level, quantified the indicative meaning from the contemporary mangrove environment and minimised compaction by producing mostly basal SLIPs. We developed nine SLIPs and assessed RSL change using the Error-In-Variables Integrated Gaussian Process (EIV-IGP) model. We compared the RSL reconstructions with Glacial Isostatic Adjustment (GIA) models and a database of SLIPs from the East Coast of the Malay–Thai Peninsula. Our results show that RSL gradually decreased from 0.33 ± 0.75 m to −0.07 ± 0.17 m between ~4000 cal. yrs. BP and ~500 cal. yrs. BP. The EIV-IGP model suggests RSL likely (66% probability) went below present-day levels between ~900 cal. yrs. BP and ~500 cal. yrs. BP, aligning with regional RSL reconstructions but differing from GIA model predictions. Potential drivers of the Late-Holocene RSL fall and subsequent rise to present include global ice-sheet expansion, regional ocean-atmosphere interactions and the subsidence of Sundaland. Future research should refine far-field RSL reconstructions to determine the extent and drivers of Late-Holocene RSL lowstands.