The pelagic mineralization rates will be more efficient and the phytoplankton uptake more than doubles (Meier et al., 2012a). As a result the oxygen levels are drastically reduced in large parts of the Baltic Sea (Fig. 5a). In the BSAP scenario the total load of nutrients from land and atmosphere was decreased by about one third. However, the reductions of external nutrient loads are not reflected in the internal dynamics, and the oxygen levels in large parts of the Baltic Sea do not improve significantly compared to present state. In the areas where the deep-water oxygen levels are critically low today the improvements are only slight or not evident

at all (Fig. 5b). This is an indication that climate-change NVP-LDE225 purchase impacts will reduce the effectiveness of the present abatement strategies during the simulation period. Worsened oxygen conditions in weakly stratified Selleck NVP-BGJ398 shallow areas are due to the temperature effect on oxygen solubility.

Both the BAU and the BSAP scenario indicate improvements in the Bothnian Bay and the Gulf of Finland. This is a response to increased mixing due to decreased stratification from the increased freshwater input from the northern rivers and Neva and slight increases in wind speed (Meier et al., 2011). Global modeling simulations show that if we reach a concentration of 850 ppm of CO2 in the atmosphere (equivalent with the IPCC SRES scenario A2, Fig. 6), we are facing an average pH decrease in oceanic surface CYTH4 waters of 0.4–0.5 pH units (Orr et al., 2005). This will result in a 100–150% increase in H+ concentration and a 50% reduction in CO32− concentration. The average surface pH of the ocean would be lower than it has been for more

than 20 million years (Feely et al., 2004). Baltic Sea model simulations (Edman and Omstedt, 2013 and Omstedt et al., 2009) indicate a change from stable conditions before industrialization and the beginning of acidification as CO2 concentrations in the atmosphere increases, with a likely dampened effect on the rate of acidification due to eutrophication (see discussion in the next section). However, results from Omstedt et al. (2012) illustrates that increased nutrient loads will not inhibit future Baltic Sea acidification. Regardless of the scenarios used the results implies that acidification will occur in the entire Baltic Sea. The impact of eutrophication on pH in the simulations was mainly by amplifying the seasonal pH cycle due to increased biological production and mineralization and reducing acidification in the anoxic deep layer. The projection of the surface water pH in the Eastern Gotland Basin (daily resolution) is illustrated in Fig. 7. Here the “business-as-usual” scenario (BAU-A2) is based on the IPCC SRES A2 scenario, together with increasing nutrient loads. In the simulations the seasonal pH cycle is amplified due to the increased nutrient loads which cause increased biological uptake of CO2 in surface waters.