Changes of the plankton spring outburst related to the North Atlantic Oscillation

Changes in the timing, composition, and intensity of freshwater phytoplankton blooms are known to have an impact on water quality and aquatic ecosystem functions. Factors provoking these changes are, therefore, of major importance. In Lake Erken in southeastern Sweden considerable changes in the timing and large variations in the composition of phytoplankton spring peaks have been observed during the past 45 yr. Here we show that long-term changes and variations in Lake Erken are strongly related to a single global parameter-the North Atlantic Oscillation (NAO). Even regional parameters that are known to have most influence on the spring development of phytoplankton such as ice break-up and nutrient concentrations could not provide a more conclusive explanation of the observed changes in spring phytoplankton, making the NAO a very powerful and simple tool in determining the timing and composition of phytoplankton spring peaks in a temperate lake.