High air–sea CO2 uptake rates in nearshore and shelf areas of Southern Greenland: Temporal and spatial variability

The present study is based on hourly samplings of wind speed, monthly sampling sessions of temperature, salinity, dissolved inorganic carbon, alkalinity, nutrients, primary productivity and vertical export in the outer sill region (station GF3) of a sub-arctic SW Greenland fjord (Godthåbsfjord) through 2005–2010. Air–sea CO2 fluxes varied at GF3 from c. − 20 g C m− 2 month− 1 (uptake from the atmosphere) to 25 g C m− 2 month− 1 (release to the atmosphere) during 2005–10. The average annual air–sea CO2 flux of − 83 to − 108 g C m− 2 yr− 1 was within the range of the local gross annual primary productivity of 76–106 g C m− 2 yr− 1. Furthermore, the estimated vertical export of phytoplankton carbon to depths below 60 m of 38–89 g C m− 2 suggests that a large fraction of the mineralization (release of CO2) occurs in deeper waters in the outer sill region of the fjord. However, there was no statistically significant correlation between average annual gross primary production and annual air–sea flux during 2005–2010, which suggests that regulation of pCO2 in the fjord is more complex. Despite three confined periods with supersaturated pCO2 conditions in surface waters during 2005–2010, Godthåbsfjord can be considered as a strong sink (7.2 tons C month− 1 km− 2) for atmospheric CO2. In addition, measurements from Godthåbsfjord during the summer season showed that mixing between glacial meltwater and coastal water could explain a large part of the low pCO2-values observed in the innermost part of the fjord. Finally, a larger survey confirmed the existence of very low pCO2 conditions in nearshore and shelf waters around Southern Greenland.