Influence of coastal upwelling on the air–sea gas exchange of CO 2 in a Baltic Sea Basin

Abstract

During coastal upwelling cold water from the ocean interior with high CO 2 concentration is brought up to the surface, allowing this water to interact with the atmosphere. This sets the stage for events with potentially altered sea–air CO 2 fluxes. Four upwelling events off the east coast of Gotland in the Baltic Sea were analyzed to assess the impact of upwelling on the air–sea exchange of CO 2 . For each event, the observed pCO 2 were found to be a function of sea-surface temperature (SST) in the upwelling area, which allowed satellite observations of SST to form a proxy for surface water pCO 2 . A bulk formula was then used to estimate the air–sea CO 2 flux during the upwelling events. The results show that the CO 2 fluxes in the study area are highly influenced by the upwelling. Comparing with idealized cases without upwelling yields relatively large differences, ranging between 19 and 250% in reduced uptake/increased emission of CO 2 . Upwelling may also influence the CO 2 fluxes on larger scales. A rough estimate indicates that it may also be of significant importance for the average annual CO 2 flux from the Baltic Sea. Including upwelling possibly decreases the Baltic Sea annual average uptake by up to 25%. Keywords: coastal upwelling, carbon dioxide, air–sea exchange, Baltic Sea measurements, remote sensing (Published: 11 December 2013) Citation: Tellus B 2013, 65 , 21831, http://dx.doi.org/10.3402/tellusb.v65i0.21831