Mercury stocks and vulnerability in permafrost soils and lake sediments

Abstract:

Mercury (Hg), an environmental neurotoxin, has accumulated in permafrost soils and sediments over millennia following deposition from natural and human sources of Hg. Permafrost thaw due to amplified high-latitude warming may result in the mobilization of previously sequestered Hg, potentially countering global efforts to reduce anthropogenic atmospheric Hg pollution. Understanding the distribution of Hg stocks and vulnerability to thaw is important for public health. Recent efforts to quantify Hg in pan-Arctic permafrost soils used the ratio of mercury to soil carbon (RHgC) from sites in Alaska and Siberia, producing estimates of soil Hg stocks ranging from 597 - 1656 Gg Hg in the top 3 m. These global estimates, while useful, are derived from samples with limited spatial representation. To refine estimates of permafrost mercury stocks, our study synthesized RHgC from soils and lake sediments in permafrost regions of North America and Eurasia. Our statistical methods used a curve-fitting approach to model the empirical relationship between Hg and carbon with separate models for soils and lake sediments. We then assessed Hg distribution within thermokarst landscapes (subject to thaw-initiated land subsidence), one mechanism for Hg release. These results will provide better constrained estimates of Hg stocks in permafrost soils and sediments and identify regions vulnerable to Hg mobilization through thermokarst. This study will help to lay the foundation for future work examining mechanisms and quantity of Hg release through permafrost thaw.