Friction from the tides drains about 3.7 terawatts out of the Earth-Moon system, which is roughly a fifth of all the power humanity uses, dissipated as heat in shallow seas.

That energy comes out of Earth's rotation, which is why the day is lengthening and the Moon is retreating. Most of it goes in a handful of shallow shelf seas where the water has to scrape along the bottom — the Bering Sea, the Patagonian shelf, the seas around Britain — rather than in the deep ocean.