n-Alkanes as indicators of climate and vegetation variations since the last glacial period recorded in a sediment core from the northeastern South China Sea (SCS)

摘要

Variations in n-alkanes proxies (L/H, C-31/C-27 and ACL), molecular abundances of n-alkanes and stable carbon isotopic compositions of n-alkanes (delta C-13(alk)) from the core STD235 (20 degrees 21.15'N, 118 degrees 22.56'E) have been used to trace characterize the climatic changes that occurred in the northern South China Sea (SCS) during the last glacial period. The ratio of low to high molecular-weight n-alkanes (L/H) and the concentration of n-alkanes indicated that organic matters in the sediments were derived from the mixture of both marine and terrestrial sources, but dominated by marine autochthonous input over the past 20 ka. Total n-alkanes were higher during the last glacial stage relative to the interglacial stage, implying the low sea level and the strengthened East Asian winter monsoon (EAWM) during the glacial time. The delta C-13(alk) data indicated that the terrestrial plants on the adjacent continent of the present study area were dominated by C-3 plants during the Holocene and experienced the expansion of C-4 plants during the last glacial period. This similar result can be proved by the chain length parameter of n-alkanes (C-31/C-27, ACL) and the content of the herb pollen. In addition, n-alkanes distributions and C4 vegetation proportion calculated by delta C-13 of long-chain n-alkanes in the core STD235 recorded a short arid duration paralleled by the Heinrich event 1. Thereby we deduced that the occurrence of the dry event and the variation of regional vegetation community at the adjacent lands of the northern SCS were likely under the influence of the climate change emanated from the boreal high-latitudes.