Applications of mercury stable isotopes for tracing volcanism in the geologic record

Mercury(Hg)enrichments in ancient sediments have been used as a proxy of volcanism,especially large igneous province(LIP)eruptions.However,considering the existence of other potential Hg sources besides volcanoes and the diverse factors(e.g.,organic matters,clay minerals,sulfide minerals and Fe oxides)that can affect Hg sequestration,there are considerable uncertainties to simply regard sedimentary Hg anomalies as signatures of volcanic activities.Mercury stable isotopes,a promising tool for tracing the origins and transformations of Hg,have been increasingly used for determining the causes of Hg spikes and understanding the geochemical behavior of Hg in the geologic record.To date,lots of researches have applied Hg concentrations and Hg isotopes to identify LIP volcanisms linking with significant geological events such as mass extinctions,ocean anoxic events and other environmental perturbations that mainly occurred in the Phanerozoic.However,the results in previous studies clearly show that not all Hg enrichments are derived from volcanic inputs,which emphasize the need for more caution in using Hg as a fingerprint of volcanism.With a better understanding of Hg isotopes in the future,there will be important implications for Hg isotopes to reconstruct volcanic activities in the rock records and their impacts on biological evolution.

Comparison of two pretreatment methods for mercury stable isotope analysis in Antarctic moss

Mercury （Hg） stable isotope analysis can provide new insight for understanding the biogeochemistry and sources of Hg in the polar regions. To completely extract the low contents of Hg in polar samples and to avoid isotopic fractionation during the sample preparation stage, an effective and reliable pretreatment method is needed. In this work, two different pretreatment methods were compared for measuring Hg stable isotopes in Antarctic moss samples. One method was acid digestion （HNO3 ： H2O2=5 ： 3, v/v） and the second was a combustion-trapping treatment with a trapping solution （HNO3：HCl=2：1, v/v）. There were no significant differences in the analytical results obtained with the two methods. The overall mean values and uncertainties of total Hg （THg） and the isotopic compositions of Hg in the referenced materials were all in good agreement with the certified and reported values, indicating that both methods were accurate and applicable. Acid digestion is highly efficient, while the combustion-trapping method can be used to treat samples with low Hg content. The proposed methods were successfully used to determine the Hg isotopic compositions in moss samples collected from the Antarctic.