Anthropogenic activity and millennial climate variability affect Holocene mercury deposition of an alpine wetland near the largest mercury mine in China

Abstract

Mercury (Hg) is a volatile heavy metal that can be transported globally through the atmosphere and has a significant harmful impact on terrestrial and aquatic ecosystems. Mining is one of the most important anthropogenic Hg contaminant sources worldwide, which has been shown to cause adverse ecological effects in Hg-mined areas. However, the dynamics in Hg deposition in the largest Hg mine in China and their driving forces remain poorly explored. Here we reconstruct the atmospheric Hg depositional fluxes (named here Hg influx (Hg_influx)) during the Holocene in the Fanjingshan Mountain, which is only 65 km to the Wanshan Mercury Min, using a ~0.5 m alpine wetland sediment core. Our record showed an abrupt, rapid increase in Hg concentration since 2500 cal yr BP, suggesting that Hg mining in southwest China may have started before the establishment of the Qin dynasty. Estimated Hg_influxwas highly variable before the Neolithic period. Two major Hg_influx peaks were found during the periods 10,000 - 6,000 and 6,000 - 3,800 cal yr BP, with an increase in Hg deposition by a factor of 4-8. We speculate that critical millennial-scale climate changes, i.e., the Holocene Climatic Optimum (HCO) and the Mid-Holocene Transition (MHT), were the potential triggers of these two Hg_influx peaks. This study highlights the importance of climatic variability and local Hg mining in controlling atmospheric Hg deposition during the Holocene.