Silicon isotopes highlight the role of glaciated fjords in modifying coastal waters

Glaciers and ice sheets are experiencing rapid warming under current climatic change and there is increasing evidence that glacial meltwaters provide key dissolved and dissolvable amorphous nutrients to downstream ecosystems. However, large debate exists around the fate of these nutrients within complex and heterogenous fjord environments, where biogeochemical cycling is still often poorly understood. We combine silicon (Si) concentration data with isotopic compositions to better understand silicon cycling and export in two contrasting fjordic environments in south-west Greenland. We show that both fjords have isotopically light dissolved silicon (DSi) within surface waters, despite an apparently rapid biological drawdown of DSi with increasing salinity. We hypothesize that such observations cannot be explained by simple water mass mixing processes, and postulate that an isotopically light source of Si, most likely glacially derived amorphous silica (ASi), is responsible for further modifying these coastal waters within the fjords and beyond. Fjord to coastal exchange is likely a relatively slow process (several months), and thus is less impacted by short-term (