浙江景宁县大仰湖沼泽泥炭地形成过程及气候背景

全新世气候演变与湿地泥炭形成、发育具有密切关系。位于中国东南部的浙江省受到东亚季风气候的显著影响,其南部发育着亚高山湿地群,是研究东亚夏季风演变过程及其区域响应的重要区域。本研究以浙江省景宁县大仰湖湿地保护区（27°50'37"~28°00'29 N",119°39'25"~119°47'39"E;613.8~1556.9 m a.s.l.）获得的1.4 m沉积钻孔为研究对象,基于5个AMS ¹⁴C测年结果构建的年代模型,通过对钻孔沉积物140个样品的粒度、有机质含量以及磁化率等指标分析,揭示了大仰湖沼泽泥炭地的形成时间,并结合区域其他山地泥炭记录以及东亚夏季风强度变化,探讨了中全新世区域山地沼泽泥炭地形成的气候环境背景。年代模型结果显示,大仰湖钻孔沉积物始于4800 cal.a B.P.左右。沉积粒度组分、有机质含量以及磁学参数等分析结果表明,钻孔下部沉积物颗粒较粗、磁化率较高且烧失量和含水率较低,表现为沉积速率较快的河流相沉积;而在约4200 cal.a B.P.前后沉积环境发生了显著变化,粒度明显细化,磁化率很低,烧失量和含水率升高,沉积速率显著下降,指示了水体沼泽化的开始。大仰湖沼泽泥炭地形成时间与区域内山地泥炭研究结果基本一致,说明4500~4000 cal.a B.P.是区域山地泥炭或沼泽形成的重要时期。该时期东亚夏季风显著减弱是大仰湖湿地形成的主要原因。夏季风降水减少导致研究区水动力显著减弱,水生植物开始扩张,水体沼泽化,进而导致了大仰湖沼泽泥炭地的发育。

Development and climatic background of Dayanghu marsh peat from Jingning County,Zhejiang Province

Climate change in the Holocene is closely related to the development of mash peat. Study the initiation of peatland and its relative climatic controls will provide a better understanding of the fate of peatland in the future climate scenario. Zhejiang Province (Southeastern China) is strongly influenced by the East Asian Summer Monsoon, and mountain peats have been widely developed in the southern part. In this paper, we aim to study the initiation of Dayanghu marsh peat from Dayanghu Wetland Reserve (27°50'37"~28°00'29 N", 119°39'25"~119°47'39"E; 613.8~1556.9 m a.s.l.), Jingning County, Zhejiang Province, by using the AMS 14C technique and analyzing the sedimentary grain size, organic matter content and magnetic susceptibility of 140 samples from a 1.4-m core. Additionally, we try to reveal the climatic controls of the initiation of Dayanghu marsh peat in the mid-Holocene, based on comparisons with regional peat records and other paleoclimatic records relating to the East Asian Summer Monsoon. The age model shows that the basal age of the Dayanghu sediment is about 4800 cal.a B. P., and the initiation of the marsh peat is around 4200 cal.a B. P. The variations of grain-size components, organic matter content and magnetic susceptibility also reflect a significant change from fluvial to marsh environments right around this time. The initiation of Dayanghu marsh peat is roughly consistent with the formation of regional alpine peat, indicating that 4500~4000 cal.a B. P. is an important period for the initiation of regional mountain peats. Based on paleoclimatic background revealed by previous researches, we suggest that the variabilities of East Asian Summer Monsoon was the main driver for Dayanghu marsh peat formation. The monsoonal precipitation reduced significantly around 4200 cal.a B. P., leading to negative water balance in the study region. The consequential drop in water level and reduced hydrodynamics during this period triggered the expansion of aquatic plants. These processes finally allowed the initiation and accumulation of the marsh peat in the Dayanghu wetland.