Paleoenvironmental change base on a pollen record from deep sea core MD05-2904 from the northern South China Sea during the past 20000 years

Abstract

This paper presents the palynological record of deep sea core MD05-2904 (top 749 cm of the sequence, 80-19189 cal a BP) from the South China Sea (SCS). Base on pollen data from the core, the vegetation type and climate history were reconstructed for the last 20000 years. During the Last Glacial Maximum (zone P1, 749-479 cm, 19.2-15.1 cal a BP), vegetation assemblages were dominated by a large number of herbs, some tropical-subtropical arboreal taxa and some cyperaceous plants, which grew in local wetlands in some exposed areas of the SCS shelf. The northern hills were covered with a large number of conifers. Dark coniferous forests dominated by the hemlock were found on the top of mountains, which indicate that the climate was relatively cold and dry. During the last deglacial period from 15.1-11.4 cal ka BP (zone P2, 479-309 cm), the sea level rose continuously and the SCS shelf was gradually submerged. In addition, the herbaceous spectrum gradually decreased, suggesting a rise of temperature and humidity. During the Holocene (zone P3, 309-1 cm, 11.4-0.1 cal ka BP), vegetation assemblages were dominated by broad-leaved evergreen forests. Tropical montane coniferous forests were distributed in the surrounding hills. Under the forest canopy, pteridophytes grew as a response to a southern subtropical climate. However, during of the time when the 309-263 cm interval was deposited (bottom of zone P3, 11.4-10.1 cal ka BP), the percentage of herbaceous and aquatic plant pollen increased, particularly that of Artemisia and Cyperaceae. This implies that there was a substantial drop in temperature, and an increase in moisture. From comparing deep sea oxygen isotopes data, the deglacial warming seems to have been earlier in low-latitude regions than in high-latitude regions of the Northern Hemisphere.