论文部分内容阅读
Better understanding the long-term historical trends of atmospheric mercury(Hg)deposition is critical to assess the regional and global impact of anthropogenic Hg emissions.An ice core(Mt.Geladaindong in inland Tibetan Plateau)and four sediment cores(Gokyo,Phewa,Qiangyong,Nam Co)were collected across the Tibet-Himalaya,which contain high-resolution records of atmospheric Hg deposition during the past 500 years.Variations of Hg concentrations were positively correlated with micro-particles since 1477 AD as retrieved by the ice core,indicating Hg deposition was mainly dependent on particulate matters.However,there was no correlation between ice core Hg and particulate matters after 1940s and 3-fold increase of Hg concentration was observed since 1940s compared with the preindustrial times(before 1840s),suggesting that the increase of ice core Hg was mainly contributed by anthropogenic emissions.This is supported by historical trends of Hg concentrations reconstructed from four lake sediment records during the last 150 years,which showed a clear and dramatic increase of Hg concentrations since 1950s,and Hg reached a maximum value during 1980s-1990s which is 2-4 times higher than those in the 19th century.Generally,the 500-year history of Hg variations indicated atmospheric Hg pollution worldwide since 1800,especially an intensive pollution happening in Asia since 1950s,which was synchronous with enhanced Hg emission in Asia during the last decades.Moreover,by using a binary mixing model,we demonstrated the major sources of Hg recorded in lake sediments since 1950s was largely influenced by anthropogenic activities(Gokyo with 64.6%; Nam Co with 46.8%),indicating that isotopes of Hg ratios and their variations are helpful in determining the possible transport route of atmospheric Hg to the hinterland of Tibetan Plateau across the Himalayas.