Sulfur Isotope Geochemistry of Ice-Wedges in Yakutia, East Siberia

Sulfur, with its highly varying stable isotope ratio and involvement in numerous biogeochemical processes, is one of the most widely used elements as an isotopic paleoenvironmental proxy, yet the sulfur isotope ratios of ice-wedges and their insoluble fraction remain unexplored. This study first presents the sulfur isotopic compositions of soluble sulfate, particulate organic matter (POM), and lithic particles recovered from East Siberian ice-wedges. Soluble sulfate, primarily representing atmospheric sulfate deposition, shows comparable sulfur isotope ranges in Zyryanka and Batagay, while in Central Yakutia, ice-wedge sulfate is more enriched in 34S, consistent with the orogenic and cratonic terranes in East Siberia. Given the wedge growth during the inland winter, it is likely that sulfate aerosols were derived mainly from erosion and weathering of regional basement rocks rather than from sea salt spray or biogenic emissions. Within individual ice-wedges, however, the sulfur isotopic composition of soluble sulfate varies by as much as 7 parts per thousand, possibly reflecting changes in the relative contributions of sulfur-isotopically distinct source regions. Beyond the origin of sulfate, greater sulfur isotope fractionations between POM and sulfate during the last glaciation suggest that sulfate may have been anaerobically reduced to sulfide and vice versa in the adjacent root zone.