Differences in water temperature in the ocean create movement because– 1. as water heats up, the atoms of water more faster.
2. warm water is pulled more by gravity than cold water.
3. warm and cold water mix and reach the same temperature.
4. bodies of water at different temperatures have different densities.

Warmer water is lighter, so it wants to expand. That's why the ocean water is constantly moving. This means the density of water is always changing. So, the answer is number 4, bodies of water at different tempuratures have different densities.

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