1.5 Gyr of tides: how inaccurate are deep-time tidal model simulations?

The ocean tides are a key driver of a range of Earth system processes. Tidal energy drives vertical mixing with consequences for ocean circulation, climate, and biological production, and the tidal stream transport sediments, pollutants, and other matter through the ocean. On long time-scales tidal drag acts to slow down Earth’s spin, which means the Moon must move away from Earth to conserve angular momentum. The problem here is that the age of the moon doesn’t fit today’s recessions rate and it has been suggested that the tides must have been much weaker for prolonged periods of Earth’s history. Numerical modelling efforts over the past decade have shown that the tides today are very large and a poor representation of past tides, and that for the past 1.5 Gyr, tidal dissipation rates have been around 45% of present-day values. Here, we present a new series of high-resolution simulations of Phanerozoic tides and discuss sensitivity to topography, forcing, and ocean stratification. The results confirm previous results about dissipation rates obtained at lower resolution. Furthermore, we apply proxies for tides collated from the geological literature for three selected periods (the Devonian, Jurassic, and Cretaceous) and show that our simulations mostly conform well with the proposed tidal characteristics from the proxies. The simulations also show that the most important controller of tides on long scales is tectonics: the locations of the continents set the size of ocean basins, and basins of the right size can host very large tides due to tidal resonance. Consequently, the supercontinent cycle generates a corresponding supertidal cycle with weak tides during supercontinent stages and a series of tidal maxima during the dispersion and assembly of the supercontinent.