No aridity in Sunda Land during the Last Glaciation: Evidence from molecular-isotopic stratigraphy of long-chain n-alkanes

Molecular distribution and stable carbon-isotopic composition (δ13C) of n-alkanes determined in a sediment core (17962) from the southern South China Sea (SCS) show that no obvious change has taken place in vegetation on Sunda Land from the last glacial period to the beginning of the Holocene. A shift in the accumulation rate of long-chain n-alkanes (C27 to C33) was recorded at a depth of about 620 cm, probably indicative of precipitation enhancement related to winter monsoon. The δ13C values are within the range of −33.7 to −27.1‰ for C29 n-alkanes and −33.9 to −28.4 for C31 n-alkanes in the whole core sequence. Such an isotopic composition is characteristic of n-alkanes biosynthesized mainly by plants utilizing the C3 photosynthetic pathway. Continuous development of C3 plants on Sunda Land and its surroundings evidences that the climate during the last glacial period in the southern SCS was not drier than what it is today.