A 47.0-kyr record of mercury deposition in lake sediments from Dahu swamp in the East Nanling Mountains, southern China: Implications for paleoclimatic and environmental changes

Abstract

In this study, we provide an ~47.0-kyr mercury (Hg) deposition record derived from a lacustrine sedimentary sequence in Dahu swamp in the eastern Nanling Mountains, China. The results indicate that organic matter (OM) input played a role in Hg accumulation, whereas the contribution of inorganic weathering detritus had a negligible impact. On the other hand, evolution of the plant community and wildfire events were also important factors affecting Hg accumulation. Compared to arboreal plants, lower (herbs and ferns) plants had stronger absorption and enrichment ability for Hg thus favoring enhanced Hg accumulation in the sediments. We therefore infer that Hg deposition in Dahu sediments was greatly controlled by changes in climatic conditions. Relatively dry and cold climatic conditions, which resulted in reduced arboreal plant communities and increased lower plants, would favor an increased Hg accumulation rate; furthermore, dry conditions may cause more wildfire events thus leading to enhanced release of Hg into the environment and increased contribution of Hg to the sediments, whereas relatively wet and warm conditions would result in the opposite situation. The record of Hg deposition demonstrates a synchronous orbital-scale variation trend with the intensity of the East Asian summer monsoon. Period analysis reveals several millennial- and centennial-scale cycles similar to solar insolation, together with several millennial events of increased Hg concentration and accumulation rate, which coincided with the corresponding Heinrich events, suggesting joint impacts of solar irradiation and the action of melting water as well as changes in zonal atmospheric circulation on Hg accumulation in Dahu sediments.