炭屑作为植物不完全燃烧的产物,记录了母源植物与古火灾的信息.通过分析大九湖泥炭钻孔中炭屑的形貌特征、浓度及长宽比,并与藿类通量、孢粉等生物源古环境指标进行对比,以揭示炭屑指标的古火灾和古环境意义.结果表明:炭屑的母源信息可由其几何形态、表面纹理及气孔结构来进行识别.炭屑的浓度与长宽比具有明显的阶段性变化,反映了古火灾的强度和主要燃烧生物材质的变化.主要分为两个阶段,全新世中期约8.5～4.3 ka B.P.期间,炭屑浓度普遍较高,与气候干旱相联系,古火灾事件与干旱高峰一致;但7.3～7.0 ka B.P.时段内炭屑浓度呈现低值,频繁降水制约了古火灾的发生.全新世晚期约4.3 ka B.P.以来,古气候由干旱转为湿润,炭屑含量波动性下降;但在3.6 ka B.P.和2.5 ka B.P.左右,波动异常明显,表明湿润背景下的干旱事件与火灾频发密切相关.据此,炭屑可作为与高山泥炭地干旱化相联系的古火灾代用指标.
Charcoal Morphotypes and Potential Paleofire Significance in Middle-Late Holocene in the Dajiuhu Peatland,Hubei Province,Central China
As the product of incomplete combustion of plants,fossil charcoal records the information of parent plants and paleofire events. In this paper,the morphology,concentration and aspect ratio of charcoal in deposits of the Dajiuhu peatland were analyzed and compared with other biogenic paleoenvironmental proxies,such as hopanoids flux and pollen,in order to reveal the paleofire and paleoenvironmental significance. The results show that the parent source information of charcoal can be identified by its geometric shape,surface texture and stomatal structure. The intensity of paleofires and the change of burning fuel types can be revealed by the concentration and aspect ratio of charcoal with obvious changes. These variations can be divided into two stages. During the Mid-Holocene period (approximately 8.5-4.3 ka B.P.),charcoal concentrations were generally high in association with drought climates;which means that paleofire events coincided with obvious drought events. However,during the period from 7.3 to 7.0 ka B.P.,charcoal concentrations were low due to frequent rainfall restriction. In the Late Holocene (Since approximately 4.3 ka B.P.),transitioning from a dry to wet climate has led to decreased fluctuations in charcoal content. However,anomalies occurred around 3.6 ka B.P. and 2.5 ka B.P.,indicating that fire frequency in humid background are closely related to drought events. Therefore,these findings suggest that charcoal can be used as a proxy paleofire associated with aridification in alpine peatland.
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