植被是陆地生态系统的主体,其演化对全球气候变化及碳循环有着至关重要的影响。重建过去典型增温过程中植被的变化,是评估全球变暖背景下植被响应的关键之一。末次冰盛期(LGM)是末次冰期中距今最近的气候最冷、冰川规模最大的时段。LGM以来,气候经历了从末次冰盛期到全新世的逐渐增温和后续降温过程。本研究综合公开发表的东北地区的69条孢粉序列,通过生物群区化方法定量重建了LGM以来其植被分布格局变化。结果表明,21~12 ka B.P.,森林仅分布在东部边缘山地,该时期森林类型点位比例最低,仅25%,研究区大面积被草原和荒漠占据;12~9 ka B.P.,森林向西、北方向扩张,草原被迫向内蒙古高原地区迁移,森林-草原分界线逐渐向西移动;9~5 ka B.P.,森林成为主要植被类型,在东北地区广泛分布,森林点位比例在6 ka B.P.达到最大值,约65%以上。温带落叶林分布范围与现代相比,最北界向北扩张大约7°~8°。草原仅分布在松嫩平原东部和内蒙古高原北部。全新世大暖期(6±0.5 ka 14C),森林-草原分界线大致分布在现代300 mm年等降水量线附近;5 ka B.P.以来,草原再次扩张。森林向东部边缘山地迁移。森林-草原分界线向东迁移。此外,温带落叶林出现的海拔变化显示,LGM以来其逐渐上升至全新世早中期开始下降,与全球温度变化类似。进一步分析表明,LGM以来,降水或有效湿度可能是控制东北地区森林整体比例变化的主要驱动因素。此外,5 ka B.P.以来,人类活动对植被分布格局的影响是不可忽视的。
Glaciers in the Yarlung Zangbo Downstream Basin(YZDB) are sensitive to global climate change. The equilibrium-line altitude(ELA) is a key indicator of glacial development.Current models for simulating the meteorological ELA underestimate the extent of glacial advance during the Last Glacial Maximum(LGM) in the YZDB and cannot explain the large-scale glacial extension compared with the Yarlung Zangbo Midstream Basin(YZMB). In this study, the distribution of ELA in the LGM is reconstructed using high-resolution 80-km ECHAM5 simulations and empirical relationships between temperature and precipitation.Changes in ELA between the LGM and pre-industrial era(PI) are compared. Our simulated ELA closely fits the published field data. In the YZDB, simulated LGM ELAs range from ca.3500 m to over 4900 m, representing declines of ca. 300–950 m. The ECHAM5 simulations better reflect the complex topographic features than most coarse-resolution climate models,and the ELA distribution is controlled by the spatial arrangement of river valley systems and mountain ranges and their impact on precipitation. Compared with the PI era, most of the monsoon precipitation in the LGM was concentrated in the YZDB, which is the main driver of glacial extension and the differential response of the downstream and midstream basins.
