Glacial meltwater and primary production are drivers of strong CO2 uptake in fjord and coastal waters adjacent to the Greenland Ice Sheet

[摘要] The Greenland Ice Sheet releases large amounts of freshwater, whichstrongly influences the physical and chemical properties of theadjacent fjord systems and continental shelves. Glacial meltwaterinput is predicted to strongly increase in the future, but theimpact of meltwater on the carbonate dynamics of these productivecoastal systems remains largely unquantified. Here we presentseasonal observations of the carbonate system over the year 2013 in the surface waters of awest Greenland fjord (Godthåbsfjord) influenced by tidewater outlet glaciers. Our data reveal thatthe surface layer of the entire fjord and adjacent continental shelfare undersaturated in CO₂ throughout the year. The average annual CO₂uptake within the fjord is estimated to be 65 g C m⁻² yr⁻¹, indicating that the fjord system isa strong sink for CO₂. The largest CO₂ uptake occurs in the inner fjord nearto the Greenland Ice Sheet and high glacial meltwater input during the summermonths correlates strongly with low pCO₂ values.This strong CO₂ uptake can be explained by the thermodynamic effecton the surface water pCO₂ resulting from the mixing of fresh glacial meltwater and ambient saline fjord water,which results in a CO₂ uptake of 1.8 mg C kg⁻¹ of glacial ice melted.We estimated that 28% of the CO₂ uptake can be attributed to the inputof glacial meltwater, while the remaining part is due to high primary production.Our findings imply that glacial melt\-water is an important driver for undersaturation inCO₂in fjord and coastal waters adjacent to large ice sheets.

[学科分类] 地球化学与岩石