Ancient oysters provide far-field sea-level constraints on ice melt timing and sources during the early–mid Holocene climate transition

Abstract

Holocene relative sea-level (RSL) reconstructions from far-field regions constrain past ice volume and global mean sea-level change, yet records from the South China Sea remain debated, particularly regarding the existence of a mid-Holocene highstand. Here, we present a revised RSL history for the Pearl River Delta based on six new radiocarbon-dated index points from an ancient Saccostrea cuccullata oyster reef, integrated into an updated, quality-controlled database of 292 data points. Ecological, petrographic, and geochronologic analyses confirm that the reef formed in situ within its habitat limits during a sustained RSL highstand. The combined dataset reveals rapid early Holocene RSL rise, reaching + 2.3 ± 0.5 m by 5.4 ka and declining to + 1.6 ± 0.5 m at 3.3 ka before reaching present level. Comparison with glacial isostatic adjustment models suggests delayed early Holocene meltwater input dominated by Northern Hemisphere sources, consistent with far-field records across Asia, Oceania, Africa, and the Americas. Our findings resolve longstanding debates over mid-Holocene RSL evolution in the South China Sea and provide robust constraints for Holocene sea-level budgets.