Response of phytoplankton in European lakes to a change in the North Atlantic Oscillation

The North Atlantic Oscillation (NAO) is a regional weather pattern that can be quantified by differences in sea-level pressure measured at stations close to the centres of the Azores High and the Iceland Low (HURRELL 1995). Recent studies show that, especially in winter, changes in the temperature regime (e.g. PLAUDT et al. 1995), snowfall (BENISTON 1997), west wind stress (ROGERS 1997) and the timing of lake ice break-up (LIVINGSTONE 2000) are related to the NAO in countries surrounding the North Atlantic. In this study, phytoplankton has been chosen to demonstrate the effects of a change in the NAO, and thereby changes in the winter climate, on pelagic ecosystems. The phytoplankton community is an ideal sentinel of changes in climatic conditions because it is dominated by short-lived organisms that respond rapidly to changes in the weather (CATALAN & FEE 1994). It is hypothesised that a change in the NAO has an effect on phytoplankton that is similar in time and magnitude in European lakes.