Investigation of factors controlling the mercury geochemical cycle in Kongsfjorden (Svalbard) under contrasting climatic conditions

In recent decades, Svalbard's climate has undergone significant changes. However, amidst a nearly constant warming trend, 2020 emerged as an anomaly, marked by unusually low temperatures, a strong polar vortex, and extensive sea ice coverage throughout the winter season. Two sampling campaigns were conducted in the Gruvebadet Snow Research Site (GSRS) in Kongsfjorden (Ny-Ålesund, Svalbard): one during the “cold” 2020 (October 2019 to May 2020) and the other during a “warm” year (October 2018 to May 2019). These campaigns aimed to investigate the potential effects of the distinct climatic conditions on the biogeochemical cycle of mercury (Hg). Mercury, a toxic element, has been extensively studied in polar regions yet uncertainties remain to address changes in the Hg biogeochemical cycle under shifting climatic and atmospheric conditions. By comparing data from the “warm” and “cold” years, this study investigates how factors such as temperature and sea ice modulated Hg deposition patterns. We noted an increase in bromine concentrations in snow during the “cold” year, and in particular in the non-sea-salt component of Br ( nss Br and Br enr ), which is likely associated to sea ice emissions. However, we do not observe a systematic impact of high bromine on Hg in snow or atmosphere. In both “warm” and “cold” years, Atmospheric Mercury Depletion Events (AMDEs) not followed by Hg deposition on snow are associated with high solar radiation, suggesting possible photo-reduction of Hg in snow. GEM shows good correlation with temperature during all AMDEs, with no distinction between “warm” and “cold” years, suggesting that AMDEs are not directly controlled by absolute value of temperature.