While preparing to drain an "above ground" pool with a regular garden hose, I was thinking about how the hose actually generated a "suction" force. Place one end at the bottom of the pool, connect the other end to a water flow (water spigot), disconnect from spigot, and then place that end at an equal or slightly lower elevation to generate suction.
At this point, the hose is draining the pool of all its water until air stops the suction force at the submerged end. In this scenario, the hose is acting as an extension (increases the volume) of the source of water and the suction force should be just a partial vacuum (relative negative pressure).
Scaling this idea up, use the setup except now the ocean is the source of water. The atmosphere of the earth is pushing down on the entire 2-dimensional surface of the ocean. The water itself has mass that is pushing on all sides of the submerged hose opening. Once the flow has been reversed from adding to the ocean to removing, would it be possible to generate electricity with only the "negative flow"?