Significant Sea-Level Fluctuations and Transgression During the Holocene in the Bohai Sea, Northern China

Holocene relative sea-level (RSL) fluctuations and recurrent transgressions have been critical drivers of global coastal evolution. Sedimentary records in the Bohai Sea preserve abundant information on climatic fluctuations and sea-level variations, making this region an ideal natural laboratory for reconstructing past sea-level dynamics. However, disagreement persists regarding the spatiotemporal patterns of Mid-Holocene sea-level heights in the Bohai Sea, particularly concerning the issue of whether RSL was higher than present. Furthermore, no consensus has been reached on the onset of the Holocene transgression. To address these issues, this study investigates the Holocene RSL history of the Bohai Sea, characterizes distinct phases of transgression, and explores their responses to climatic-environmental system evolution. Our findings confirm that the Mid-Holocene RSL in the Bohai Sea was 2.2–3.49 m higher than the modern sea level. Notably, we identify the initial phase of transgression in the Bohai Sea occurring between 7.7 and 7.3 cal kyr BP. A subsequent expansion of transgression is observed during 7.0–6.6 cal kyr BP. A 2300-year phase of RSL persistently higher than modern sea level initiated at 6.2 cal kyr BP, resulting in complete inundation of the Bohai Sea's coastal regions. Crucially, the Holocene RSL in the Bohai Sea is closely linked to global patterns, particularly reflecting the influence of Mid-Holocene far-field Glacio-hydro Isostatic Adjustment. Furthermore, Early Holocene RSL changes in the Bohai Sea provide new evidence for the 8.2 ka event. These findings advance our mechanistic understanding of sea-level variability while providing essential scientific insights for coastal zone planning and management.