Last Glacial Maximum, early Holocene and modern environments of the northern South China Sea region: Insight from SEM analysis of Oak (Quercus) pollen.

Oak (Quercus) pollen was identified at the infra-generic (i.e. sub-genus to species) utilizing Scanning Electron Microscope (SEM) images of modern (i.e. 18 species from southern China) and fossil pollen grains from northern South China Sea (SCS) marine and terrestrial sediments. Key morphological characteristics of Quercus exine sculpture were used to separate the pollen into evergreen and deciduous groups, with this distinction applied to the fossil oak pollen from the Last Glacial Maximum (LGM) and early Holocene periods. The presence of Quercus pollen from the modern Pearl River and northern SCS suggests long distance transport from inland temperate to tropical regions surrounding the SCS. Fossil oak pollen from terrestrial and marine sediments from the northern SCS region suggests different pollen representation between these two sedimentary environments, with the terrestrial site dominated by evergreen Quercus types and the marine location showing greater representation of deciduous oak species. The presence of both evergreen and deciduous oak pollen in the LGM age marine sediments suggests only moderate cooling during this time period, while the dramatic increase of deciduous Quercus pollen in the marine core, as well as generally higher pollen influx values, reflects greater fluvial discharge, which in turn is linked to increased precipitation in the region during the early Holocene period.

Morphological diversity of Quercus fossil pollen in the northern South China Sea during the last glacial maximum and its paleoclimatic implication.

We aimed to obtain high resolution vegetation data and climate information about the LGM in the inland of the northern SCS based on key pollen types. Dominant Quercus fossil pollen grains in the core from the continental shelf of the northern SCS have been identified at the infrageneric level by using scanning electron microscopy. Based on tectum ornamentation, we recognized five sculpture types of Quercus pollen, namely, rodlike, rodlike masked, rodlike vertical, verrucate and micro-verrucate. Such a high diversity of Quercus fossil pollen types indicated that broadleaved forests were widely distributed in the inland along the northern SCS and included species of the subgenera Cyclobalanopsis and Quercus, of which subgenus Cyclobalanopsis populations were highly dominant. Low abundance of deciduous Quercus pollen probably derived from temperate-subtropical forests, while abundant evergreen pollen types of subgenura Quercus and Cyclobalanopsis, as well as other pollen of broadleaved taxa in the pollen assemblages, strongly suggest that the inland has been covered by dense subtropical forests. Consequently, the warm and humid subtropical climate prevailed during the LGM in the inland along the northern SCS. Our results shed new light on regional climatic conditions during the LGM in eastern Asia based on high diversity of Quercus fossil pollen in marine deposits from northern SCS.