Knowledge of the fugacity of CO2 (fCO2) seasonality and variability contributes to our understanding of the drivers of global warming and how the ocean slows down the CO2 increase in the atmosphere. In this thesis, 15 years of surface fCO2 data has been analyzed and the fCO2 seasonality as well as variability within months between western Norwegian coastal waters and the open northern North Sea have been compared. Furthermore, the drivers of the fCO2 change in the surface area were examined by means of a decomposition analysis. fCO2 values were the highest in the autumn and winter months, and the lowest in spring and summer for both areas. The coastal area had much larger fCO2 fluctuations throughout the seasons due to influence of freshwater. Dissolved Inorganic Carbon (DIC) was found to be the main driver for the observed fCO2 seasonality and variability in both areas in spring and summer due to phytoplankton blooms. In autumn, Total Alkalinity (TA) also played a large role, while salinity did not have any significant effect on the variability in any parts of the year. In conclusion, biological processes had a much larger impact on fCO2 variability over seasons than changes in temperature and salinity.
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