报告题目：青海湖碳库效应与古气候重建
主讲人： 2019级博士生 曹振平
报告时间：3月17日（周四）中午12:00
报告地点：16教学楼221会议室
报告摘要：青海湖位于青藏高原东北部，为探索亚洲夏季风和西风带控制的气候环境变化提供了理想的全新世古气候沉积记录。放射性同位素14C常用于研究沉积物年代学信息，但其碳库效应仍存在争议。本研究对青海湖3.5m长的岩芯进行了多种样品的14C分析（植物残体、碳酸盐、有机质）并结合矿物学、常量元素、TOC、TN、TIC、δ13Corg、δ13Cinorg和δ18Oinorg等，来研究青海湖14C碳库效应和古气候变化。研究结果表明，青海湖东南部近6000年以来的平均沉积速率为0.562 ± 0.007 mm yr-1。根据常规14C年龄-深度线性回归模型，自生碳酸盐的表层碳库效应年龄高于植物残体和有机质。恒定沉积速率假设模型表明，碳库效应在~6到~4 ka之间呈现波动变化。自全新世中期以来千年时间尺度暖湿期分别发生在~6.0、~4.9、~4.1、~1.9、~0.6和~0.1 cal ka BP，干旱期发生在~5.4、~4.7、4.0-2.0、~0.9和~0.3 cal ka BP。这些特征可能受控于与全球气候变化密切相关的夏季风的变化。
Title: The 14C reservoir effects and paleoclimatic reconstructions in Lake Qinghai, northeastern Tibet
Abstract: Lake Qinghai located in the northeastern Tibetan Plateau provides ideal Holocene paleoclimatic records to explore the climatic and environmental changes controlled by the Asian summer monsoon and the westerlies. Radiocarbon (14C) is commonly used to constrain the sediment chronology, however, the temporal variations of 14C reservoir effects in Lake Qinghai are still under debate. Here, we carry out multiple 14C dating and multi-proxy analyses (mineralogy, major elements, TOC, TN, TIC, δ13Corg, δ13Cinorg, and δ18Oinorg) on a 3.5 m-long core (QH1) in Lake Qinghai to illustrate the 14C reservoir effects and paleoclimate changes during the last 6000 years. The average sedimentation rate of the southeastern Lake Qinghai is 0.562 ± 0.007 mm yr-1 during the last 6000 years. For the conventional 14C age-depth linear regression, the authigenic carbonate has higher surface reservoir age than plant remains and organic matter. The constant sediment accumulation rate model shows that reservoir effects fluctuate between ~6 to ~4 ka. Since the Mid-Holocene millennial-timescale warm and humid periods occurred at ~6.0, ~4.9, ~4.1, ~1.9, ~0.6, and ~0.1 cal ka BP and relative droughts occurred at ~5.4, ~4.7, 4.0-2.0, ~0.9, and ~0.3 cal ka BP. These features can be attributed to the rapid strengthening and weakening of the summer monsoon circulation, which are closely connected with global changes.
