Characteristics of pollen in surface sediments from the southern South China Sea and its paleoclimatic significance

• Pollen in seas near Nansha Islands mainly is from the local trilete spores.
• Similar pollen characteristic is found when global warming occurs since 12 Ma.
• Pollen on the coast of Kalimantan Island is from plants on the edge of the island.
• Nansha Trough facilitates the entry and storage of pollen from outside area.
• Pollen grains from below and above 200 m water depth are transported by rivers.

We investigated pollen distributions in surface sediments of the southern South China Sea (SCS) and their relation to seabed topography and the environment of the terrigenous sources. In this study, we analyzed 62 surface sediment samples collected from the SCS through modern pollen analysis methods. The results of our study can be summarized as follows. (1) trilete spores dominate the pollen and spore spectrum, which reflects the dominance of ferns in the Nansha Island vegetation. Similar pollen characteristics were found for different periods of high sea level and global warming after 12 Ma in ODP site 1143 and site 18287 in the southern South China Sea. Most pollen and spores on the Kalimantan Island coast are produced by herbaceous plants and trees, while few trilete spores produced by ferns are present. Furthermore, similar pollen characteristics were found for different periods of low sea level and global cooling in ODP site 1143 and site 18287. (2) Through an analysis of pollen samples from a transect line extending from the northwest to the southeast, the complex terrain of the Nansha Islands was observed to be unsuitable for pollen migration through ocean currents. Pollen counts in samples collected near the southern Nansha Islands decreased gradually from the east and west continental shelf areas to the central basin area. However, the same analysis confirmed that the Nansha Trough facilitates the entry, dispersal, and storage of pollen from external sources. (3) Principal component analysis (PCA) of samples collected from two different water depths in the southern SCS demonstrates that trilete spores and monolete spores in 4 samples near the Mekong River with water depths of < 200 m are transported primarily by river flow. Conversely, pollen and spores mainly transported by rivers near Kalimantan Island were found at water depths of > 200 m. However, analysis of samples from the northern SCS in a previous study obtained different results.