What makes the sea water cold?

cooling of seawater is caused by the evaporation of surface water which takes latent heat from surrounding water molecules, similar to the effect of sweating. Cooling of seawater is also due to brine acceptance, if the water becomes more saline, it will sink as it is heavier than the surrounding water masses and thus cooling as water which becomes more dense has a lower maximum temperature, and pressure causes water to become colder.