Salinity is lower near the equator because precipitation is higher. Salinity is low near the mouths of major rivers because of input of fresh water. The temperature of surface seawater varies with latitude, from near 0 o C near the poles to 29 o C near the equator. But restricted areas can have temperatures up to 37 o C. Properties of seawater also vary with depth. The density and salinity of seawater increase with depth.
Temperature decreases with depth.
Ocean Circulation Surface Ocean currents are result of drift of the upper 50 to 100 m of the ocean due to drag by wind. Thus, surface ocean currents generally follow the same patterns as atmospheric circulation with the exception that atmospheric currents continue over the land surface while ocean currents are deflected by the land. In each hemisphere cooler waters from higher latitudes circulate toward the equator where they are warmed and circulate back toward the poles. Such circulation, because it controlled by both temperature differences and differences in salinity of the water, is called thermohaline circulation . Ocean Tides Tides are due to the gravitational attraction of moon and to a lesser extent, the sun on the Earth.