Herbaceous vegetation expansion on the north equatorial Sundaland during the last glacial maximum

Vegetation types on the exposed Sunda Shelf are important to understand the evolution of regional biodiversity and to assess the global terrestrial carbon storage during glacial periods. There are two conflicting opinions on glacial vegetation distribution over the exposed Sundaland, one considers that savannah occupied most of the exposed shelves while rainforest contracted into a ‘refugia’ condition; and the other believes that tropical rainforest prevailed over the most glacial Sundaland. So far well-dated paleo-vegetation reconstructions from the northern Sundaland are still lacking, which impedes the unveiling of this mystery. In this study, changes in the distribution of plant wax-derived n-alkanes of a marine sediment core from the southern South China Sea, close to the northern Sundaland paleo-river mouths, are used to reconstruct the vegetation changes over the northern Sundaland since LGM. The Average Chain Length（ACL）of n-alkanes is as high as 30.0 between 22 and 14.5 kaBP, indicating that herbaceous vegetation expanded on the northern Sundaland during the LGM compared to the Holocene. Previous modelling results suggest that a fell down of sea-level during the LGM can induce a weakened Walker circulation and the prevailing of El Niño-like conditions. This may further result in overall drought and increased dry-season water stress conditions on the glacial Sundaland, which may have contributed to the flourish of herbaceous vegetation.