This work sits among studies of ancient climate rhythms: neighboring papers in the archive examine solar tidal cycles, Martian climate swings, the influence of moons on planetary heat, and ice ages driven by orbital parameters. All of them search geological and astronomical records for the same periodicities, from annual to millennial. This paper adds to that picture short-period oscillations of 2 to 100 years recorded in the evaporites of the Messinian salinity crisis.
In the Realmonte mine, the thickness of 120 three-part cycles was measured: a millimeter-scale clay layer, a thin layer of anhydrite or polyhalite, then a decimeter-scale bed of halite. In Pasquasia, 1179 gypsum laminites were counted, each composed of crystals with reverse grading, from fine at the base to coarse at the top, indicating deposition from brine over a single evaporation season. Layer thicknesses were analyzed using the maximum entropy method, Lomb periodograms, and Morlet wavelets. Additionally, the recurrence of clay layers marking wet episodes was assessed.
In the Realmonte salt record, peaks dominate at periods of 3.2 and 9 years, 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 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. Recurrence analysis of flood layers gives probability peaks at 4, 7, 9, 11, 15, 20, 24.5, and 32–35 years, with a maximum in the 7–11 year range. Wavelet spectra reveal beating with a period of about 60 years in Realmonte and persistent 3–7 year variability in Pasquasia, reminiscent of El Niño.
Unlike neighboring studies that rely on orbital cycles of tens of thousands of years or modern instrumental records, this work is the first to reconstruct the spectrum of short-period climate variability for the late Miocene from annual evaporite varves. It provides the first direct test 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 imposed rhythm.
The topic could develop toward searching for similar varve records in other evaporite basins, for example, the Permian formation of Castile or Pliocene lake deposits. Extending the records would allow testing the stability of the 9-year and 60-year cycles over intervals of tens of thousands of years. A separate question is the physical mechanism by which solar-lunar tidal signals are transmitted to the atmosphere and ocean, which remains a hypothesis.
The results are important for paleoclimatology, evaporite sedimentology, and studies of solar-terrestrial connections. They also provide geologists with a tool for refining the age of salt deposits by counting annual layers.
The next step is to search for and analyze longer varve series in evaporites of the same age, as well as to compare with models of tidal effects on ocean circulation under Miocene geography.
For paleoclimatology, the question remains unresolved as to how much climate oscillations like El Niño depend on the configuration of continents and ocean gateways. This work shows that the main frequencies persist even under completely different paleogeography, shifting the emphasis to external astronomical forcing.
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.