Minecraft – Is it possible to play Minecraft with ocean water turned off

Now that it can snow again in snowy biomes, water can indeed freeze to ice after long enough exposure to snowfall. See the 0:15 mark of the linked video for an example.

Try out the Bukkit plugin called Terrain Control. It features the ability to change the water height by modifying the config. However, you will have to run a Bukkit server on your local network to use it.

As of snapshot 14w17a, it is now possible to customize the water level ingame. When creating a new world, this can be achieved by clicking More World Options..., changing the World Type to Customized, and then selecting the Customize button. Here, you can change the sea level by moving the slider that says Sea Level, as well as many more options.