摘要
通过对岱海12.08m沉积岩芯210Pb和AMS-14C精确定年及地球化学、物理指标的综合分析,重建了包括8.2ka冷期、中世纪暖期(MWP)和小冰期(LIA)等典型气候事件在内的全新世以来所经历的化学风化及其环境演化过程。全新世早—中期(9.0～3.5ka),岱海流域处于温暖湿润气候环境,主要环境特征表现为流域化学风化显著增强、生物生产力逐步提高、湖泊水位大幅度抬升。在7.90～8.25ka期间存在一次冷气候事件,其发生时间与来自湖沼、海洋、生物组合和极地冰芯等在内的全球环境记录基本一致,具体表现为流域化学风化减弱、湖泊生产力降低以及湖泊水位下降。2.5ka以来,岱海沉积物中环境指标的显著变化,表明进入气候波动更频繁的新冰期。岱海沉积物中的指标变化也展示了本世纪以来的气候增暖过程,但其化学风化强度还没有达到MWP的程度。
A 12.08 m sediment profile from brackish Lake Daihai was dated by AM S 14C and 210Pb activity, and geochemical and physical proxies were analyzed in dependently. Based on the paleoclimatic significance of the Rb/Sr ratio in the l ake sediments, Holocene chemical weathering and hence climate change were recons tructed, including some important climate events such as 8.2 ka cold event, the Medieval Warm Period (MWP) and the Little Ice Age (LIA). During early to mid Ho locene (9.0 to 3.5 ka), a stronger chemical weathering was experienced around th e Daihai watershed under warm and humid climate conditions characterized by a pr ogressive increase of biologic productivity and by highest lake levels, to reach its maximum during about 5.0 ka before the present. However, a globally abrupt cooling climate event occurred in the early to mid Holocene transition indicate d by Rb/Sr ratio increase and by other independent indices such as lake level, b rightness and Corg in sediments, which are contemporaneous with the worldwide ev ent identified in lakes, oceans, land mollusk sequence and polar ice cores at ar ound 7.90～8.25 ka. After ca. 2.5 ka, significant variation of independent proxi es of the sediments indicates the beginning of the neoglaciation with higher fre quent fluctuations. For example, the neoglaciation disturbed by the MWP, though its warm degree was less than that of the Megathermal. The higher Rb/Sr ratios i n the lake sediments indicate a weak chemical weathering during the LIA with two discrete cooling periods, resulting in less Sr into basin. Furthermore, the var iation of Rb/Sr ratios in the sediments also shows an enhancement of chemical we athering under modern warming climate, but its intensity is less than that of th e MWP.
出处
《地球化学》
CAS
CSCD
北大核心
2004年第1期29-36,共8页
Geochimica
基金
国家自然科学基金(40003001)
中国科学院南京地理与湖泊研究所所长特别支持项目(CXNIGLAS-A01-2)
关键词
化学风化
湖泊沉积物
全新世
气候事件
岱海
chemical weathering
lake sediment
Holocene
climate event
Lake D aihai
