Abstract. The Greenland Ice Sheet releases large amounts of freshwater, which strongly influences the physical and chemical properties of the adjacent fjord systems and continental shelves. Glacial meltwater input is predicted to strongly increase in the future, but the impact of meltwater on the carbonate dynamics of these productive coastal systems remains largely unquantified. Here we present seasonal observations of the carbonate system over the year 2013 in the surface waters of a west Greenland fjord (Godthåbsfjord) influenced by tidewater outlet glaciers. Our data reveal that the surface layer of the entire fjord and adjacent continental shelf are undersaturated in CO 2 throughout the year. The average annual CO 2 uptake within the fjord is estimated to be 65 g C m −2 yr −1 , indicating that the fjord system is a strong sink for CO 2 . The largest CO 2 uptake occurs in the inner fjord near to the Greenland Ice Sheet and high glacial meltwater input during the summer months correlates strongly with low pCO 2 values. This strong CO 2 uptake can be explained by the thermodynamic effect on the surface water pCO 2 resulting from the mixing of fresh glacial meltwater and ambient saline fjord water, which results in a CO 2 uptake of 1.8 mg C kg −1 of glacial ice melted. We estimated that 28 % of the CO 2 uptake can be attributed to the input of glacial meltwater, while the remaining part is due to high primary production. Our findings imply that glacial meltwater is an important driver for undersaturation in CO 2 in fjord and coastal waters adjacent to large ice sheets.

Abstract. The Greenland Ice Sheet releases large amounts of freshwater, which strongly influences the physical and chemical properties of the adjacent fjord systems and continental shelves. Glacial meltwater input is predicted to increase strongly in the future, but the impact of meltwater on the carbonate dynamics of these productive coastal systems remains largely unquantified. Here we present seasonal observations of the carbonate system in the surface waters of a west Greenland tidewater outlet glacier fjord. Our data reveal a permanent undersaturation of CO2 in the surface layer of the entire fjord and adjacent shelf. The average annual CO2 uptake for the fjord is estimated to 65 g C m−2 yr−1 indicating that the fjord system is a strong sink for CO2. Primary production and the high input of glacial meltwater strongly affect the carbonate system in the Godthåbsfjord system. The largest CO2 uptake occurs near to the ice sheet. High glacial meltwater input during the summer months correlates strongly with high levels of CO2 undersaturation, which can be explained by the non-linear effect of salinity on surface water pCO2 resulting from the mixing of glacial meltwater and ambient fjord water. Our findings hence imply that glacial meltwater may form a major driver for CO2 undersaturation in fjord and coastal waters adjacent to an Ice Sheet.