Reconstructing Holocene sea-level change for the Great Barrier Reef using subtidal foraminifera

We assessed the utility of subtidal foraminifera to reconstruct Holocene relative sea levels from the central Great Barrier Reef shelf, Australia. We collected contemporary foraminiferal samples from Cleveland Bay and Bowling Green Bay, with water depths from −4.2 m to −48.0 m Australian Height Datum (AHD). The subtidal foraminiferal assemblages were divided into two distinct foraminiferal zones: an inner shelf zone occupied by Elphidium hispidulum, Pararotalia venusta, Planispirinella exigua, Quinqueloculina venusta and Triloculina oblonga; and a middle shelf zone dominated by Amphistegina lessonii, Dendritina striata and Operculina complanata. The zonations of the study areas and relative abundances of individual species indicate that the distributions of subtidal foraminifera are related to water depth.

We used the subtidal data to develop a transfer function capable of inferring past water depths of sediment samples from their foraminiferal content. The results indicated a robust performance of the transfer function (r2jack = 0.90). We produced ten sea-level index points, which revealed an upward trend of Holocene relative sea level from −8.86 ± 4.5 m AHD at 9.3–8.6 cal kyr BP to a mid-Holocene high stand of +1.72 ± 3.9 m AHD at 6.9–6.4 cal kyr BP. Sea level subsequently fell from the highstand to the present-day. The sea-level reconstructions are consistent with geophysical models and previous published data.