No, an object will only float if the water it displaces weighs more than the weight of the object itself. read more
I think it would float rather than sinking to the bottom as it is the Ocean we are throwing a water bottle in it. As the ocean is filled with water which is much denser and weighs alot than a plastic bottle, it will float on the surface of ocean. This only happens if the cap of the bottle is closed I guess. But this can be tested by an experiment. read more