Pollen distribution in hemipelagic surface sediments of the South China Sea and its relation to modern vegetation distribution

Abstract

This paper analyses the distribution of pollen in the surface sediments of the South China Sea as recorded in 28 samples from the area 6°09′–20°07′N and 112°05′–119°45′E, at water depths of 329–4307 m. Pollen concentrations range from 444 kgrains/g (dry wt) on the lower part of the continental slope in the northeast to zero in the central basin below 4000 m water depth. Pollen distribution patterns in the concentration and percentage isopolls (incorporating data from the literature) reflect the routes and mechanisms of pollen transport, pollen source areas and considerable systematic differences between north and south. The northern SCS is distinguished by very high concentrations due to the high production and effective long-distance transport of pine pollen and fern spores. The maximum of their concentration occurs in the north, adjacent to the convergence of the Bashi and Taiwan Straits, rather than near the estuaries of big rivers, and stretches as a saddle from NE to SW, consistent with the direction of the NE winter monsoon and sea current. This pattern implies that pine pollen and fern spores, adapted to wind transport and water flotation, come from the northeast through the straits borne on the winter monsoon and sea current forced by it. Their source areas should cover large regions, probably including south and southeast China. Most pollen of tropical and subtropical broad-leaved trees found in the northern part of the SCS occur in low concentrations, however, these concentrations decrease uniformly offshore, implying a fluvial discharge from nearby lowlands in South China. In the southern part of the SCS, pollen of tropical and subtropical broad-leaved trees predominate. Total pollen concentrations, however, are much lower, only 1/10 of those of the northern part. The greatest concentrations occur offshore north Borneo and decrease toward deep water, suggesting fluvial input from relatively local sources on the adjacent islands (e.g. Borneo).