The answer is wind because the other options can not be correct. Phytoplankton's are bacteria at the bottom of the ocean which sea life feeds off of. Buoys would not effect the movement of the ocean. Gyres would not effect the surface ocean movement, it is a part of the Coriolis Effect.
Movement of ocean water at the surface is caused by wind.
Horizontal motion refers to the ocean currents and waves whereas vertical motion refers to tides.
Ocean currents can be evolved by wind, density differences in water masses caused by temperature and salinity variations, gravity, and events such as earthquakes or storms.
Wind blows across the oceans, the upper surface waters get mixed starts to move. Direction of movement is not same as the direction of the winds. Coriolis force arises from the rotation of the planet also causes movement of ocean currents.
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