Holocene vegetation evolution, hydrologic variability and sea-level fluctuations on the south coastal plain of Laizhou Bay, Bohai Sea, China: new evidence from pollen, freshwater algae and dinoflagellate cysts

Holocene palynological evidence from the Bohai Sea coastal areas have not been sufficiently discovered. In this study, we carry out analyses using detailed palynological records of pollen, spores, freshwater algae and marine dinoflagellate cysts from Borehole X1 on the south coastal plain of Laizhou Bay, Bohai Sea, northern China. The results based on radiocarbon chronology show vegetation evolution, hydrologic variability and sea-level fluctuations during the Holocene. Abundant non-arboreal pollen (mainly, Artemisia, Chenopodiaceae and grass-type Poaceae) and small amounts of arboreal pollen (mainly Pinus and Quercus-deciduous) and fern spores were identified in this study, suggesting that coastal steppes and coniferous and broadleaved mixed forests flourished in the study area and its adjacent areas, and a cold and dry climate with less precipitation and lower sea-level than the present during the Early Holocene, ca. 9910-7440 cal. yr BP. After that, the steppe areas began to shrink, and coniferous and broadleaved mixed forest areas began to expand, indicating a relatively warm and humid climatic conditions, with more precipitation and marine transgression processes during the Mid-Holocene, ca. 7440-3650 cal. yr BP. Afterwards, relatively cool and dry climatic conditions predominated, with less precipitation. While sea-level continued to rise slowly during the Late Holocene, ca. 3650 cal. yr BP to the present, and the steppe areas shrank, the coniferous and broadleaved mixed forest areas continued to expand.