In 1956, oceanographer Henry Stommel suggested that, because of differences in temperature and salinity between the surface and the deep ocean, if you connect the surface and the deep ocean with a tube and push water through it, it might continue flowing indefinitely. The tube wouldn’t create perpetual motion. The steady flow is possible because the surface and depths of the ocean aren’t quite in equilibrium, thanks to a subtle imbalance in how temperature and salinity equalize between them. Since the water inside the tube can equalize temperature with its surroundings through the wall of the
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