Geosat had revealed that powerful currents circled in the oceans, forming eddies that measured hundreds of kilometres across. Like coffee being stirred in a mug, the rotating masses of water formed a depression at the centre, while the outer rings rose upwards. It became apparent that these eddies also caused the ocean’s surface to rise and fall, independent of gravitational variations, and that they themselves were part of far larger rings of water - oceanic gyres. From the long-distance perspective of satellite mapping, it became clear that all the world’s oceans were rotating. In the
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