Magnetic characteristics of Qiangyong Co Lake sediments, southern Tibetan Plateau and its environmental significance during 1899-2011 1899-2011年青藏高原南部枪勇错沉积物磁性矿物的环境意义

Far from major zones of human pollution, the widely developed lakes on the Tibetan Plateau are ideal regions to evaluate global and regional impacts caused by human activities. Based on the reliable dating, they can provide historical records of human pollution. Heavy metal is one of the most harmful pollutants, and is harmful to biological environment and people's health due to its degradation-resistancy. Environmental magnetism characterized by its sensitivity, facility and non-destructiveness, has been applied widely in estimating increased heavy metal pollution in different environmental systems. However, there lacks the relevant research in lake sediments on the Tibetan Plateau. Thus, we conducted a systematic environmental magnetic investigation of lake sediments in the Qiangyong Co Lake, southern Tibetan Plateau to explore the relevance between magnetic minerals and heavy metal (Hg). Results indicate that magnetic mineral species constituted by four different components (C1, C2, C3, C4) remain stable during 1899-2011 AD, but the component C1 (hematite) increased continuously with the corresponding decrease of component C2 (goethite). In contrast, components C3 and C4 (magnetite) have no significant changes. The correlation between SIRM and Hg differs from that between clf and Hg, probably because SIRM and clf are affected by different factors of complex magnetic mineral species (four different components). But the component C1 is correlated well with both Hg content and climate warming of the Tibetan Plateau. This indicates that Qiangyong glacier (the main recharge source of Qiangyong Co Lake) melt faster upon the Tibetan Plateau warming, and the accumulated Hg in glacier and cryoconite were released again. During the processes, C1 (hematite) with large specific surface area absorbs Hg, and is transported to the Qiangyong Co Lake. This research indicates that the magnetic properties of the Qiangyong Co Lake are excellent environmental proxies, which can provide a new method to study the process of Hg deposition in lakes on the southern Tibetan Plateau.