Comparison of the impact of regional and North Atlantic atmospheric circulation on an aquatic ecosystem

Atmospheric circulation is important in affecting surface climate and ecosystems. In this study, we compared the impact of North Atlantic and regional atmospheric circulation, as represented by the North Atlantic Oscillation (NAO) index and a set of regional circulation indices on local air and water temperature, ice phenology and the phytoplankton spring bloom in a Swedish lake. All these variables were significantly correlated to both circulation indices, except for the water temperature due to the insulation effects of ice and snow cover. These relationships were more powerful using the regional circulation indices, implying that the regional indices explained the variability of the lake variables with a higher power compared with the NAO index. Additionally, the application of regional indices allowed the determination of underlying processes. For example, the timing of the ice break-up could be explained with 73 % by the regional index associated with total wind speed from January to March. This example suggests that regional circulation indices are very useful tools, in addition to global circulation, to improve the understanding of the interaction between ecosystem processes and climate.