The model simulations reveal a net outgassing of CO2 from the ocean to the atmosphere when the dissolved organic carbon and the partial pressure of carbon dioxide in river runoff are doubled. However, an increase in the ocean's ability to take up carbon dioxide occurs if concentration of nutrients in the runoff increases, which is a result of increased primary productivity. The ocean also acts as a stronger sink for atmospheric carbon dioxide when increasing the air temperature, wind speed or the atmospheric partial pressure of carbon dioxide. To reflect the conditions at the end of this century a simulation with changes of several forcing parameters was performed, i.e. with doubled atmospheric partial pressure of carbon dioxide, 4 ¡ãC temperature increase in the air, doubling the runoff dissolved organic carbon concentration, increasing the river discharge by 25 % and increasing the wind speed by 10 % . This simulation increased the uptake of the ocean by more than five times, from ? 0.9 (¡À 0.3) to ? 4.6 (¡À 1.3) mol C m? 2 y? 1. The main effect is due to the doubling of partial pressure of carbon dioxide. In a model simulation without the increased atmospheric partial pressure of carbon dioxide, the CO2 uptake decreased by 0.2 mol C m? 2 y? 1 to ? 0.7 (¡À 0.6) mol C m? 2 y? 1.