THE discrepancy between Earth-tide theory and Earth-tide observations is mostly the result of the influence of the tides in the oceans1–5, which can easily account for 10%, 20% and 90% of the total Earth tide in gravity, strain and tilt, respectively. These ocean load perturbations can be used to study the upper mantle (in regions where the ocean tide is particularly well known) and the ocean tides themselves. Near large bodies of water it is the region of ocean closest to the observation site that causes most of the Earth-tide perturbation. Models which ignore the rest of the world's oceans reproduce the observed effects well2,3, one reason for this being that the ocean tide circulates around a dozen or so nodal points, or amphidromes, the circularly symmetric nature of an amphidrome causing a first order cancellation in the load at great distances.