Which property most determines water’s vertical position in the ocean?

Density

Explanation: Density is a property that helps in determining the ocean water's vertical position. This density is controlled by the two factors, such as-

Temperature is inversely proportional to density, but salinity is directly proportional to density. This means that higher temperature waters are less denser than lower temperature water. And high salinity waters are more denser.

The denser water are found in the Antarctic region, as the temperature is low there and salinity is high. And normally near the surface the waters are relatively warm than at deep sea, due to the receiving of maximum sunlight. As we go down into the ocean, the water temperature decreases.