Influence of coastal upwelling on the air–sea gas exchange of CO2 in a Baltic Sea Basin

Abstract

During coastal upwelling cold water from the ocean interior with high CO2 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 CO2 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 CO2. For each event, the observed pCO2 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 pCO2. A bulk formula was then used to estimate the air–sea CO2 flux during the upwelling events. The results show that the CO2 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 CO2. Upwelling may also influence the CO2 fluxes on larger scales. A rough estimate indicates that it may also be of significant importance for the average annual CO2 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