Improved understanding of the linkage between Holocene sea-level change and climate variation may provide essential insights into future ice-climate feedbacks and their impacts on coastal lands. Paleoenvironmental records allow us to extend the instrumented record and study coastal environment change in a long-term geological context. 

In this study, we present a coastal sedimentary record from Liaodong Bay in northern Bohai region, China, which has documented coastal environment change since the late-glacial period. We investigate the grain size, total organic carbon (TOC) content, pollen abundances, and phytolith assemblages in sediments to construct the Holocene paleoenvironmental history of Liaodong Bay.

Results suggest that postglacial sedimentary sequence formed during four different stages that marked by lithology and multiple-proxy datasets. (1) Stage I (1730cm-2000cm, 12400-10800 cal. yr BP): tidal flat facies with very low TOC and phytolith concentration but high sedimentation rates. This stage corresponds to the early onset of deglacial sea level rise. Possibly due to the cold and dry climate, fewer phytoliths were transported into the site. (2) Stage II (1030cm-1730cm, 10800-7800 cal. yr BP): nearshore or subtidal facies. At this stage, TOC and phytoliths concentrations were still low but were slightly higher than Stage I. Since the onset of deglaciation, sea-level rose rapidly and provided accommodations for clasts sedimentation. Increases in TOC contents and decrease in mean grain-size indicate that terrestrial inputs are increasing, which might be associated with intensified terrestrial runoff erosion that induced by intensification of monsoon activity. (3) Stage III (270cm-1030cm, 7800-5300 cal. yr BP): subtidal or shallow sea facies. During mid-Holocene, sea level reaches its highest position, providing accommodation for terrestrial clasts. Mean grain-size of the sediments gradually decreased with an increase in TOC contents. Phytolith concentration reaches high values. Later this stage, sedimentation accommodation was gradually filled (consumed) by continuous terrestrial inputs. (4) Stage IV (0-270cm, 5300-4900 cal. yr BP): terrestrial fluvial facies. Since the mid-Holocene, the sea level rising paused (even slightly decreased) partially due to the run out of accommodations. Fluvial sediments deposited on the top of previous marine sediments. In general, our multiple evidence-based reconstructions demonstrated that Holocene sea level change and monsoon climate variations are determining the sedimentary environmental evolution in Liaodong Bay, which is largely consistent with previously-published records. The main driving factors seems to shift at different climate and/or sea-level stages during the Holocene.