When Earth’s rotation wobbles with a period of 18.6 years, it moves enormous volumes of water across the globe. This motion creates a global standing wave between the poles and the equator. Due to Earth’s great mass, the tidal response follows the wobble. The standing wave has both a vertical component and a horizontal current, which together create a circular motion in ocean waters. These circulating masses act like a propeller, mixing cold deep water with warm surface water. The tide thus becomes the propeller that powers the nutation-driven climate engine.
George Howard Darwin (son of Charles Darwin) was among the first to understand Earth and Moon as a coupled dynamic system. He demonstrated how tides influence ocean currents and slowly drive the Moon farther from Earth. He discovered how the Moon’s lunar nodal cycle introduces an 18.6-year periodicity into tides, with geological consequences. In his time, such ideas met resistance. Otto Krümmel, in his 1887 oceanography textbook, dismissed the importance of long tidal waves. As a result, the Moon’s role in climate was long considered pseudoscience — a stigma that persisted into modern times. In the 1970s, with the advent of new computers and spectral analysis methods, American and Russian scientists were soon able to detect the 18.6-year Lunar Node Tide (LNT) signal in oceanographic datasets.
Lunar Node Tide Signature
My own studies of the Lunar Node Tide began in the early 2000s, with a broad analysis of available sea-level records from the North Atlantic. These included time series from Stockholm, Aberdeen, and along the Norwegian coast up to Murmansk. The results revealed a lunar-driven spectral signature with periods of [1/2, 1, 4] × 18.6 years — indicating at least three lunar-driven tidal propellers operating in the ocean.
Figure 1: Signature amplitudes for Lunar Nodal Tide periods: 18.6 years (blue) and 74 years (yellow) for the years t = 1900–2000. Values are normalized to the range [-1.0 … +1.0].
Figure 1 shows estimated amplitude variations of the 18.6- and 74-year signature periods for t = 1900–2000. The 18.6-year signal follows the nutation cycle. The 74-year period exhibits a delay of 74.44 / 4 = 18.6 years, suggesting it originates as a current-driven signal from the Arctic Ocean. The 74.44-year nutation period drives cold deep water outward from the Arctic.
This 74-year period declines from 1941 to a deep minimum in 1960, then reverses its trend, rising again from 1979. Maxima occurs around 1988, 1997, and 2006. The year 1941 is associated with a warm climatic phase, while 1960 marks a cold phase.
Nutation-Driven Lunar Node Tide
This study confirms that the LNT signature is driven by the nutation signal. The novel insight is that LNT represents a nutation-forced spectrum, with nutation also modulating deep-water circulation in the Arctic Ocean. The 18.6/2-year period appears to be a current-driven deep-water signal, linked to nutation. The next question is how this LNT signature affects the temperature signal of North Atlantic Water.