末次盛冰期巽他大陆北部草本植被扩张

末次盛冰期(Last Glacial Maximum,LGM)全球低海平面时,巽他陆架大面积暴露,其上的植被类型对于生物多样性演化和全球陆地碳储库有重要影响。但目前植被重建结果仍存在很大争议:一种观点认为LGM时巽他陆架主要分布稀树草原植被,雨林只零星存在于少数区域;而一些数值模拟结果和沉积记录显示巽他陆架上不存在大面积跨赤道的稀树草原,雨林植被仍占主导。LGM时巽他大陆北部可靠的植被记录十分有限。本研究依据靠近巽他陆架北部古河流入海口的沉积物岩芯,利用叶蜡烷烃含量和正构烷烃平均链长指标重建LGM时北巽他大陆的植被信息,结果显示平均链长在22~14.5 kaBP期间出现最大值,推测相对于全新世,冰期时巽他大陆北部草本成分增加。海平面降低使得冰期太平洋沃克环流减弱,呈现类厄尔尼诺状态,导致巽他大陆地区干旱加重,特别是赤道外围区域(南北纬7°以外)降水季节性增强,这种气候状态可能是草本植被成分增多的主要因素。

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.