Seasonal total and methylmercury surface and groundwater data from Simpson Lagoon, Alaska, 2021-2023

Supra-permafrost submarine groundwater discharge (SGD) is an understudied source of chemical species to the Arctic Ocean. Given the high concentrations of mercury (Hg) in Arctic soils, SGD has the potential to mobilize large quantities of previously sequestered Hg to the Arctic Ocean as warming drives deeper coastal sediment thaw depths each year. To investigate the potential of SGD to transport Hg to the Arctic Ocean, this study looked at seasonal differences in total mercury (THg) and methylmercury (MeHg) concentrations in supra-permafrost groundwater, coastal surface water, and rivers adjacent to Simpson Lagoon, Alaska. Within this dataset are dissolved THg, dissolved MeHg, salinity, and dissolved organic carbon concentrations from five sampling campaigns: spring (June 2022), summer (August 2021, July 2022, and July 2023), and autumn (September/October 2022). Hg samples were taken using trace metal clean techniques and preserved using acid until analysis at the University of Connecticut.