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.