For some time I’ve been wondering how the longer term cyclicities of the moon might affect the Earth’s climate.
I just came across this very interesting 2008 paper:
Lunar nodal tide effects on variability of sea level, temperature, and salinity in the Faroe-Shetland Channel and the Barents Sea
Yndestad Harald; Turrell, William R and Ozhigin, Vladimir:
Link to full paper (paywalled)
The Faroe-Shetland Channel and the Kola Section hydrographic time-series cover a time period of more than 100 years and represent two of the longest oceanographic time-series in the world. Relationships between the temperature and salinity of Atlantic water from these two areas are examined in this paper, which also presents for the first time comparisons between them and annual mean sea levels in the region. The investigation was based on a wavelet spectrum analysis used to identify the dominant cycle periods and cycle phases in all time-series. The water-property time-series show mean variability correlated to a sub-harmonic cycle of the nodal tide of about 74 years, with an advective delay between the Faroe-Shetland Channel and the Barents Sea of about 2 years. In addition, correlations better than R=0.7 were found between dominant Atlantic water temperature cycles and the 18.6-year lunar nodal tide, and better than R=0.4 for the 18.6/2=9.3-year lunar nodal phase tide. The correlation between the lunar nodal tides and the ocean temperature variability suggests that deterministic lunar nodal tides are important regional climate indicators that should be included when future regional climate variability is considered. The present analysis suggests that Atlantic water temperature and salinity fluctuations in the Nordic Seas are influenced by forced tidal mixing modulated by harmonics of the nodal tide and influencing the water mass characteristics at some point “down stream” from the Faroe-Shetland Channel. The effects of the modulated oceanic mixing are subsequently distributed as complex coupled lunar nodal sub-harmonic spectra in the thermohaline circulation.
Harald has a page on climate here: http://ansatte.hials.no/hy/climate/defaultEng.htm
“ In this analysis we may understand the forced gravitation oscillation between the earth, sun and the moon as a forced coupled oscillation system to the earth. The tide and the earth rotation responds as a non-linear coupled oscillation to the forced gravity periods from the moon and the sun. This is a complex oscillation in periods between hours and thousands of years. The forced gravitation introduces a tidal mixing in the Atlantic Ocean. This tidal mixing introduces temperature and salinity fluctuations that influences climate and the eco system.”
It looks to me like the coincidence of these lunar cycles with the planetary cycles in my previous post may go some way to explaining the peak temperatures Earth experienced recently. These longer term cycles cause tidal mixing and overturning in the ocean which will affect the absorption and release of oceanic heat energy. This will be the subject of my next post.