Final answer:
Temperature is the primary control on the density of seawater in most of the surface ocean.
Step-by-step explanation:
In most of the surface ocean, temperature is the primary control on the density of seawater. As water warms, its density decreases, and as it cools, its density increases. This is because colder water is denser than warmer water. While salinity and pressure also play a role in the density of seawater, temperature is the main factor.