Build a sort of updraft tower [link] over a deep sea hydrothermal vent. The water that comes out of these vents is enormously hot -- around 400C. Naturally, this is less dense than the surrounding 2C water. If there were a thermally insulated tower above the vent, the density differential would be
enough to cause the water to flow up through the tower.
If the hot water doesn't cool too much from the pipe walls, then when it get high enough (shallow enough), the pressure will be low enough that the water will boil. To prevent fouling of the the updraft tower with salt, the tower ends a few yards below that depth.
Even though the water isn't boiling *in* the tower, it will nonetheless produce an area of relatively low pressure directly above the top of the tower, which will result in increased water flow up through the tower.
The energy from the upflowing water would of course be harnessed by a turbine, just as in a solar updraft tower or a hydropower station.
The power would then be sent to shore using high voltage DC through superconducting wires.