The ocean is the largest sink of CO2 and regulates the global climate. Marine primary production is a key process for CO2 removal and is limited by iron availability in large parts of the ocean. Marine iron concentrations are directly controlled by their sources to the ocean. Meltwaters from glaciers are considered as significant iron sources. To reach the ocean this glacial meltwater transits through fjords. When iron encounters oxygenated seawater, it is rapidly oxidized and settles as particulate iron to the seafloor. The recycling of particulate to dissolved iron in the seafloor and back to the overlying water regulates ice-to-ocean iron transport and is promoted by sediment reworking by benthic fauna. However, the mechanistic link between benthic fauna community composition, faunal activity and iron recycling is poorly understood. This knowledge gap prevents a reliable assessment of the future efficiency of this ice-to-ocean iron transport and thus changes in marine primary productivity, the global carbon cycle and the projected climate. This PhD project will advance our understanding of the mechanistic links between macrobenthic functional traits and activity, environmental conditions and seafloor iron cycling, through a combination of field studies, experimental microcosm incubations and the development of novel mechanistic modelling tools that will allow us to predict and evaluate future changes in macrobenthic activity and iron recycling from Arctic fjords.