Mercury (Hg) is a globally significant pollutant, which is particularly concerning due to its ability to undergo long-range atmospheric transport and its bioaccumulation and biomagnification in marine ecosystems, even in remote regions like Antarctica. This study explores the biogeochemical cycling of Hg in the marine coastal environment of Terra Nova Bay (Antarctica) by determining the total content of mercury (THg) and its isotopic composition in fish (Trematomus bernacchii), bivalve molluscs (Adamussium colbecki) and sediment samples, collected in 1996-1998 and 2021. Significantly lower THg concentrations are found in the organisms sampled in 2021 compared to those sampled in 1996-1998, with a concurrent shift toward higher δ