Holocene environmental change in Singapore: Insights from sedimentary and foraminifera records

Holocene marine records provide key insights into environmental changes associated with changing relative sea-levels under interglacial conditions. However, most Holocene records are found in the mid to high latitudes, and there is a lack of records in the tropics. Here, we present a multi-proxy record from a sediment core GRBH03 from the Kallang River Basin in Singapore, spanning from 9.1 to 1.2 cal kyr BP. Three sedimentary units and five foraminiferal assemblages were recognised, reflecting the successive environmental change during the early Holocene marine transgression and subsequent coastal progradation. A depositional hiatus of ∼5.8 to 1.2 cal kyr BP and shell layer formed during this period may be associated with falling sea level after the mid-Holocene highstand. Stratigraphic interpretation, anchored by the Marina South Member (MSM), identifies Transgressive and Highstand Systems Tracts in the Kallang River Basin, though evidence for Falling Stage and Lowstand Systems Tracts is limited. From GRBH03, an abrupt increase in sedimentation rate from 8.4 to 8.2 cal kyr BP, with simultaneous increase in Fe/Ca and decrease in δ¹³C_OM values, may reflect drier conditions linked to the 8.2 ka climate anomaly. These findings highlight the combined influence of relative sea-level and climate variability on depositional processes in tropical coastal systems and provide valuable analogues for anticipating coastal responses to future environmental change.