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4. What is the Source of the Salt?

To this and other questions of the sea, scientists seek answers with full awareness much about the oceans is not fully understood.

• Sea water is a weak, but complex solution made up of many things including mineral salts and decayed biologic matter from marine organisms.
• Most of the ocean's salts are derived from gradual processes, such as weathering and erosion of the earth's crust and mountains by the  dissolving action of rains and streams.

Some of the ocean's salts have been dissolved from rocks and sediments below the sea floor, while others have escaped from the Earth's crust through volcanic vents as solid and gaseous materials.

Salts become concentrated in the sea because the Sun's heat evaporates almost pure water from the surface of the ocean,  leaving the salts behind. This process is part of the continual exchange of water between the Earth and the atmosphere, called the hydrologic cycle, which, along with the sources of salt, is illustrated in the following diagram.

Water vapor rises from the ocean surface through evaporation and is carried landward by the winds in the form of clouds and humidity.

When the vapor in the clouds collides with a colder mass of air, the moisture condenses (changes from a gas to a liquid) and falls to Earth as rain.

The rain runs off into streams, or underground as groundwater, both of which transport water back to the sea.

Evaporation from both the land and the ocean again causes water to return to the atmosphere as vapor and the cycle starts anew.

Natural products like dissolved salts are not the only chemicals that are transported by rivers to the sea.... Listen to Seaweb's Ocean Report for a short discussion on non-point source pollution of our coastal regions.

Send to Don Reed
Department of Geology
San Jose State University

#2 Why does the concentration of dissolved salts increase in the sea (as opposed to the low level of dissolved salts in river water)?

a) Because there is more salt than water in the sea.
b) Because there is more water than salt in the sea.
c) Because solar energy evaporates nearly pure water from the sea, leaving the salts behind as a residue.
d) All of the above.
e) None of the above.