No. Although the amount of salt in the ocean is relatively constant on time scales of years to decades, sea surface salinity (SSS) varies because freshwater input & output - part of the global hydrologic or water cycle - varies from place-to-place. The large scale pattern of evaporation and precipitation is established by Earth's atmospheric convection cells. In the simplest case - for example, if Earth were covered by oceans and not spinning - the atmosphere would move heat between the hot tropics and cold poles in a very simple way. Hot air would rise along the equator, creating a band of low atmospheric pressure. Cold air would sink at the poles, creating regions of high atmospheric pressure.

The presence of continents and Earth's rotation complicates the idealized "two cell" system. A fairly realistic model of Earth's atmospheric circulation consists of six cells: three on each side of the equator. This pattern has atmospheric pressure highs at the poles, 30°N and 30°S. It also has atmospheric lows along the equator, 60°N and 60°S. Away from the poles, cloudiness and precipitation (P) dominate bands of low pressure: these latitudes host the world's rainforests. Dryness and evaporation (E) dominate bands of high pressure: these latitudes are home to deserts.

In terms of SSS, lower salinity generally occurs where precipitation is greater than evaporation (P>E). Higher SSS generally occurs where evaporation is greater than precipitation (E>P). Compare the "six cell" model with the map of global average SSS (image upper right). How well do SSS patterns mirror bands of high and low atmospheric pressure? In places where they do not match, what other types of freshwater inputs & outputs might be occurring?