A rock chronicle where each layer is a page, and spectral analysis reads the rhythm of the lines. In the Realmonte salt mine in Sicily, geologists measured the thickness of 120 three-part cycles: a millimeter-scale clay parting, a thin anhydrite or polyhalite layer, and then a decimeter-scale halite bed. At Pasquasia, they counted 1179 gypsum laminae, each composed of crystals with reverse grading, from fine at the bottom to coarse at the top, indicating deposition from brine over a single evaporation season.
Layer thickness was analyzed using maximum entropy spectral analysis, Lomb periodograms, and Morlet wavelets. In the Realmonte salt record, peaks at periods of 3.2 and 9 years dominate, with less certain peaks at 7.6, 11.5, 15, and 25–27 years. The Pasquasia gypsum record, spanning nearly 1200 years, shows maxima in the ranges of 3.5–5.5, 6, 7.3, 8.6, 11.2, 13, 17.6, 19.6, 51, and 83 years, with the strongest peaks at 4, 20, and 50–100 years.
These periodicities match modern climate oscillations: the quasi-biennial oscillation, El Niño, the Schwabe solar cycle, and lunisolar tidal rhythms. This is the first direct test showing that quasi-biennial, El Niño, and decadal solar-lunar oscillations operated in a warm climate before the onset of Northern Hemisphere glaciation. The result strengthens the position of those who view El Niño not as a product of modern geography but as an ancient, astronomically forced rhythm.
The rock chronicle has been read: even at the height of the salinity crisis, the Mediterranean climate pulsed under astronomical forces independent of geography.
The average thickness of an annual salt layer in Realmonte is 15.1 cm, comparable to the growth rate of salt 'trees' in modern salt ponds (about 10 cm per year). This means that in a single decade, one and a half meters of pure salt accumulated.
In Kim Stanley Robinson's novel 'Forty Signs of Rain', ocean climate oscillations become the key to weather prediction; here, the same rhythms are etched in stone six million years old.