The discussion about a possible link between long tidal waves and climate variability has taken place over a period of more than 100 years. George H Darwin discovered the tidal wave of 18.6 years when he analyzed the data series for water level outside London, and believed that this would affect the climate. At the beginning of the 1900s the Swedish oceanographer identified a relation between long tidal waves and herring periods in Gullmarfjord. This research from Pettersson was later continued by Russian scientists, well into the 1960s.
The international marine research organization ICES started in 1900 measurements of North Atlantic water inflow to the Norwegian Sea and the Barents Sea. Now these data series represents the longest continuous oceanographic data series in the world. Yndestad has undertaken a wavelet spectrum analysis of these data series in partnership with Scottish and Russian oceanographers. The result shows that temperature and salinity fluctuations in the data series are related to the lunar nodal tidal of 18.6 years, and to harmonic periods of 9.3 and 74.4 years. The explanation is a tide driven mixing process in the Gulf Stream, before the water reaches the Norwegian Sea and Barents Sea.
Yndestad has identified the same periodic fluctuations in time series of Norwegian rainfall, in the NAO winter index, in extent of Arctic ice, the winter temperature in Greenland, and in the Barents Sea ecosystem. The observations are explained by the theory of coupled oscillators. The relationship between earth, sun and moon can be seen as a 3-body problem, which produces a spectrum of forced oscillations. The observed fluctuations in climate and ecosystems can be seen as coupled oscillations with temporary stable behavior.