Early Holocene sea-level changes along the western Bohai Sea coast

Abstract

Meltwater Pulses (MWPs) from the last deglaciation are highly relevant today. Studying their timing and characteristics offers valuable insights into past periods of accelerated sea-level response under intense climate forcing and provides an analog for potential future scenarios. The western Bohai Sea coast (WBSC), located deep within the Asian continent and far from major glaciation centers and subduction zones, exhibits sensitive relative sea level (RSL) responses to any high latitude ice-sheet meltwater influx, offering valuable data to refine the chronology and magnitude of MWPs. This paper presents 25 high-confidence early Holocene sea-level index points (SLIPs) from high marsh vegetation samples, generated through analysis of sediments, microfossil foraminifera, and radiocarbon dating of 14 cores from the WBSC. The altitudes of SLIPs were adjusted for factors such as self-compaction, long-term tectonic subsidence, and ground lowering due to water extraction. The early Holocene RSL history in the WBSC reflects a rapid rise in sea level during ∼9800–6900 cal a BP, occurring within the global context of global sea-level rise. During ∼9800–8100 cal a BP, the RSL rise was faster, averaging 7–8 mm/a, characterized by two distinct stepwise increases. A rapid sea-level rise event before 9500 cal a BP was shown by a sharp RSL rise of at least 5.4 ± 0.63 m, within the narrow timeframe of 9603 ± 288 cal a BP (1σ). The second MWP took place during 8500–8100 cal a BP, adding a total rise of 2.92 ± 0.93 m on the top of background RSL rise, with a two-phase structure where the main phase produced 2.55 ± 0.69 m within a narrow window around 8505 ± 135 cal BP (1σ). Although the rate of RSL rise decreased rapidly to 5.0 mm/a by 7000 cal a BP after ∼8100 cal a BP, sea-level data from the WBSC still show an additional rise of 1.45 ± 0.64 m during 7593 ± 78 cal a BP (1σ). These three distinct sea-level jump events, happened before 9500, ∼8500, and ∼7600 cal a BP, respectively, provide indications of three episodes of enhanced meltwater discharge in the early Holocene, with the latter two closely linked to the decaying history of the Laurentide Ice Sheet.