The ocean currently takes up a large fraction of the anthropogenic emissions of carbon dioxide and thus mitigates global warming. To predict the future oceanic carbon uptake and its spatial distribution it is important to understand the mechanisms behind this uptake. In this talk I will illustrate how changes in the buffering capacity that are related to nonlinearity of seawater carbonate chemistry affect the pattern and temporal evolution of anthropogenic carbon uptake. I will show that changes in the buffer capacity will lead to a peak-and-decline behaviour of anthropogenic carbon uptake in the North Atlantic and to an increase of the biologically driven uptake in the Southern Ocean. I will illustrate the theoretical arguments with ouput from scenario runs until the end of this century.