Models of ocean acidification are required at scales relevant to the prediction of regional biogeochemical and ecosystem responses to carbon dioxide increase.Significant advances have been made in modelling the meridional ocean pH response (Caldeira and Wicket,2003; Orr et al.,2005) and spatial scales of aragonite saturation (Orr et al,2005).Here,we discuss regional modelling of centennial ocean pH decrease and aragonite and calcite saturation for the North Atlantic and Nordic Seas and sites of important cold water coral reefs on the Norwegian shelf slope.Bergen Climate Model (ARPEGE/IFS coupled to MICOM) output forced with IPCC scenarios is fed to a CO2 model utilising regional,empirical relationships between the CO2 system and hydrography (Olsen et al.,2003; Bellerby et al.,2005).Further,the model has been refined to include recent advances in our understanding of the North Atlantic CO2 response to anthropogenic forcing (Olsen et al.,2006; Omar and Olsen,2006).There are significant regional differences in centennial the oceanic CO2 system response with the Arctic dominated waters exhibiting the greatest surface acidification.The Atlantic inflow will be a return source of excess CO2 to the atmosphere.The mixed layer anthropogenic signal has already surpassed the natural variability of the system. CaCO3 levels show regional,depth dependant variability which should be accounted for when assessing future calcification and ecosystem response of coral reef and planktonic calcifiers.Importantly,coral reefs and pteropods (due to their diurnal and seasonal migrations to depth) will encounter saturation levels approaching aragonite equilibrium by the middle of this century.Calcitic organisms residing in the euphotic zone will encounter saturation values equivalent to those of the Bergen mesocosm experiments (DeLille et al.,2005) by the end of this century.