Pollen–spore distribution in the surface sediments of the western Bohai Sea, China

Abstract

Eighty-six seafloor surface sediment samples from the western Bohai Sea were analyzed palynologically to understand the distribution pattern and transport paths of pollen and spores. The results reveal that the pollen assemblages are dominated by arboreal pollen, which accounts for an average of 52% and mainly includes Pinus, deciduous Quercus, Carpinus, Betula, Nitraria, Castanea, and Ulmus. The pollen percentages of herbaceous taxa reach an average of 25%, mostly represented by Chenopodiaceae, Artemisia, Gramineae, Liliaceae, Polygonum, Typha, and Cyperaceae. The fern spores are mostly Selaginella, Osmunda, Triletes, and Monoletes. The distribution characteristic of pollen and spores implies that the pollen assemblages correspond well with the watershed vegetation. Variation in the pollen assemblages in different parts of the marine area could reflect differences in local vegetation, especially the vegetation along the inflowing rivers. The spatial distribution of pollen assemblages further suggests that the discharge from the Yellow River and Luanhe River has a great contribution to the pollen inputs into the western Bohai Sea. Pollen concentrations are lower in the nearshore sea area (water depth < 20m) due to the combined effects of dynamic sedimentary environment and inflowing rivers. By contrast, pollen concentrations show higher values in the deeper waters of fine sediments near estuaries of Yellow River and Luanhe River and the sea area north of 39.5°N, reaching a maximum concentration of 7000 grains/g. Based on the distribution characteristics of pollen and spores, the PCA analysis results of the distribution of the dominant pollen taxa confirm that pollen grains and spores deposition into the western Bohai Sea was primarily affected by the hydrodynamic condition or water sorted effect (including river flows and ocean currents), and secondarily through aeolian transportation. Non-arboreal pollen were mainly carried by fluvial input and deposited in the nearshore shallow water area. Arboreal pollen dominated by Pinus were mainly transported by winds and ocean currents, and fern spores mainly by river flows and ocean currents. The latter two types were mostly concentrated in relatively deeper water area.